Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
pcrussell50
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Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Sun Aug 07, 2016 7:44 pm

Back on the old forum, I started a running thread on my life with this motor that has given some folks in the past, trouble. It's a 2000 Mercury 90-HP FourStroke (Yamaha powerhead), carburetor engine powering my 1998 Alert 17 (special services classic Montauk).

Due to some things that come up in life, (fortunately none of them, bad), I haven't turned a prop in anger with that boat since summer 2013, which I wrote about back on the old forum in a thread of the same title. Fast forward 9 months to June 2014, after sitting unused the whole 9 months with nothing but Sta-Bil, I hadn't even drained the carburetors. And it fired right up just like a car you drive every day. BUT, I didn't use it that day, or the rest of the summer because the grease in the tilt tube had turned to epoxy, and even the full pressure of the hydraulic steering couldn't budge it. So I put it away for the summer of 2014. In 2015, I ended up having to cut the steering rod off the tilt tube because most of it was frozen inside it. And Teleflex changed the design of their Baystar system and obsoleted any repair parts I needed, so I got a new cylinder and hoses which I am now ready to install.

1) So January 2016, with no steering, on nearly three year old fuel, I tried to fire it up on the muffs and it barely ran. I pulled the carbs on the spot and cleaned them and reinstalled them (about a three hour job, hurrying). Did not try to start it.

2) Just a few days ago, I put fresh gas in the tank, and? WOOT! It fired right up into a smooth idle like it had been doing it all along. YAY!

3) Yesterday, I used a $99 SyncPro motorcycle manometer to balance the carbs (fun and easy), enjoying every minute of listening to it's purr get better and better. Best advice I ever got on this forum to buy that, instead of the $1200 electronic factory balancing tool.

So that's where I am now. Going to hook up the new steering hoses and have fun Whalering with my 17 again. My trusty 13 Sport has been running like a champ the whole time, so it's not like I've done completely without.

More to come later


-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby Wweez » Thu Aug 11, 2016 7:50 pm

Great to hear from you and your good experiences with the 90. I traded mine. It had a burned piston, in my opinion, from fuel starvation due to some blockage. I am sure, had I used it a lot more, It would have been a better engine. Had it been able to use real gasoline, not gubernment garbage, I would still have it. Thank you for all your good ideas and for sharing your experience. Good Luck, keep up the fun!

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Thu Aug 11, 2016 11:46 pm

Likewise, good to hear from you. Sorry to hear you had an expensive failure. And sorry to lose one of my stalwarts on the carburetor "Mercaha" team. What did you replace with? E-TEC 90's seem like the lightest option for a classic Whaler that was never designed for the weight of a four-stroke-cycle outboard.

A carb jet blockage of course could result in a burned piston, which you would think occurs while on the main jets at high rpm or load. Whereupon you might think that if a main was clogged, the smaller mids and idles would clog first, telegraphing pending trouble. Of course, nothing says it couldn't have been a random piece of debris, rather than a progressive accumulation of residue.

We spent the month of July this year in San Carlos, Mexico. I had my 13 Sport with oil injected Yamaha 40hp, two-stroke-cycle. And we made friends with a local boat mechanic, who had extra storage space in his boat yard, where we kept our trailers. In his yard was a carbureted Mercury FourStroke 75, like our 90's, on the back of a panga. I asked him what he thought of them. He said, "Yamaha powerhead, with carburetors. Good. Very very good.". He was both enthusiastic and certain. I suspect, that in his mind, they were pretty straightforward to tune and maintain in a third world country where they get used almost daily, by fishermen. Also, Mexico has good gas unadulterated by alcohol.

Jim put forth an idea about how to avoid residue-related clogging:. Keep the bowls full. Full bowls = no dried up evaporated fuel residue. As an added step, I might even pump the bulb firm every so often just to make sure, and maybe even loosen the drain plugs when I do, to circulate some fresh fuel into the bowls, before re-tightening the drains... Just an added thought.

-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby jimh » Sat Aug 13, 2016 10:20 am

When I had a six-carburetor V6 c.1992 Evinrude engine, I always tried to keep the engine in a normal operating position, as vertical as possible, when in storage. I would pump the primer bulb to keep the bowls full of gasoline. There was enough clearance on the trailer for the engine to sit in an operating position, but you could not move the trailer much. Any little slope or dip would result in the skeg hitting. But for sitting all winter, or for extended periods, keeping the engine vertical and the carburetor bowls filled worked well. The engine would typically start right up.

I see some fun in keeping an older carburetor engine running these days, and particularly so now that gasoline prices are back to the $2-per-gallon range. I only get about 50-hours of operation a year, and you cannot really consume a lot of fuel in that amount of time, even with a thirsty six-carburetor V6.

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby pcrussell50 » Sun Jun 18, 2017 1:47 pm

When we last left off, it was late summer 2016. [See earlier posting for details.] The boat sat since then with the carburetors and fuel tank drained.

Recently, I finally broke out our classic Montauk-Alert 17. I put in fresh gasoline, pumped the primer bulb firm--I had to pump a lot because the carbs were empty. I clamped on the muff adaptor and turned the key. Two or three rotations of the crank and the Mercury 90-HP four-stroke-power-cycle engine [with Yamaha powerhead with carburetors] fired into a steady, smokeless idle--as if it were EFI. Back in business.

Even though I also have a nice classic 13 and another brand of speed boat (essentially a bass boat hull, with seats instead of casting decks and livewells), I had been missing my Montauk-Alert. I took out my wife and two little girls, age three and seven, to enjoy the warm water on Lake Mead. I had to pry them away when it was time to go--as it should be:

Image

Still not missing electronic fuel injection as long as this engine keeps running like this with simple maintenance.

-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby FISHNFF » Tue Jun 20, 2017 1:52 am

Hey Peter!
Glad that motor still purrs and you are still loving that hull! I still believe that particular 17 is the best riding Classic 17 around!

It still looks great. Even the Merc stickers look good.

That boat has gone all over and done a lot. Glad it's still making people happy!

Remember you gotta call me if you ever sell!!!


FISHNFF

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby swist » Thu Jul 13, 2017 7:39 am

I believe I was one of the original contributors to that thread [from the old forum]. I've been away for a while. But to summarize, I basically kept that thing going until 2015 with a cocktail of additives, completely draining the fuel out of the carbs in the off season and other care by a really good Mercury tech.

However in the Summer of 2015 it died a horrible death with a cracked block. I would guess about 400 hrs on the engine. I repowered with a 2016 EFI 90 hp command thrust Merc. I got a good deal and thought I'd save money by not having to rerig.

The new engine bears little resemblance to the old. Just looking under the cowl, it has so many fewer moving parts and fewer "things" apparently stuck on everywhere and actually looks quite elegant.

Some of us kept our Yamamercs running, but there was no getting around the fact that they were engineering "kludges" as we used to say at work.

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby jimh » Thu Jul 13, 2017 7:50 am

Mentioned several times, the discussion on the old forum that preceded this current discussion is still archived and available at

http://continuouswave.com/ubb/Forum3/HTML/020236.html

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby pcrussell50 » Thu Jul 13, 2017 10:54 am

swist wrote:I believe I was one of the original contributors to that thread [from the old forum]. I've been away for a while. But to summarize, I basically kept that thing going until 2015 with a cocktail of additives, completely draining the fuel out of the carbs in the off season and other care by a really good Mercury tech.

However in the Summer of 2015 it died a horrible death with a cracked block. I would guess about 400 hrs on the engine. I repowered with a 2016 EFI 90 hp command thrust Merc. I got a good deal and thought I'd save money by not having to rerig.

The new engine bears little resemblance to the old. Just looking under the cowl, it has so many fewer moving parts and fewer "things" apparently stuck on everywhere and actually looks quite elegant.

Some of us kept our Yamamercs running, but there was no getting around the fact that they were engineering "kludges" as we used to say at work.


Welcome to the new board! Yes, you were a contributor to this thread and others concerning this motor. Thanks for your input over the years. 400 hours seems an early and untimely death. Mine is close to 900 these days. Yamamerc or Mercaha? Either way. There was a lot of confusion early on about the powerhead and how it differs from Yamaha, but in the end, it was much adieu about nothing. I don't think these motors are kuldgey, (we use that term too, in sports car racing), because the powerheads themselves are pure Yamaha. In fact, even though Mercury calls them a 90hp, these powerheads are actually complete Yamaha F100's. So much so, that when I take the motor for service that I don't perform myself, I take it to the Yamaha dealer, who uses his Yamaha service manual for the F100. Also, when I order powerhead parts, I order them from Yamaha, where they are actually cheaper than getting them from Mercury. Anyhow, I just wanted to clear the air on the hybrid brand nature of this motor. The powerhead is pure Yamaha through and through, not a mix. I'm less sure about the mid and lower. They may be actual Mercury. In fact, I suspect they are. But they are pretty straightforward, too.

Enjoy you new motor like I know you are :)

-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby jimh » Thu Jul 13, 2017 1:25 pm

When Mercury bought thousands of power heads from Yamaha to use in their four-stroke-power-cycle outboard engines under the model descriptor of "FOURSTROKE", they typically mated the power head to a Mercury midsection, Mercury transom mount and power trim-tilt, and Mercury lower unit or gearcase. They also generally changed the electrical wiring harness so it had Mercury-style connectors and could mate to a Mercury rigging harness, ignition key switch, and gauges.

I have collected some information over the years about the Mercury-branded Yamaha-powerhead four-stroke-power-cycle 90-HP engines sold under the Mercury brand as 90 FOURSTROKE models. See

A Brief History of the Mercury 90-HP FOURSTROKE
http://continuouswave.com/forum/viewtopic.php?f=4&t=2405

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby Wweez » Wed Jul 19, 2017 10:25 pm

Peter,
It has been too long since I checked on these posts. Great news of your experiences with the carb 90. You always did your homework and kept up with maintenance.
As I said last year, I am sure m experience could have been better with more work on my part. Once the bad gs fromone marina had tainted the situation, I never got on top of the game again. So very many of the subjects posted here and other sites are really maintenance related as I experienced.
I put an E-Tech 90, on the 170 and it has been fine. It starts! And for what they cost, it should.
Have not put it to enough use, but all is well.
Keep up the good work and enjoy the good life. Thank You for your continued help.

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby pcrussell50 » Fri Aug 09, 2019 12:33 am

After another two year hiatus, stored with the fuel tank and carburetors drained and the drain screws loose, I filled the tank with fresh gas, (and my additive cocktail), closed the carburetor drain screws, pumped the bulb firm and she started almost as if she had been used yesterday. Then I took her out on the lake today and went several miles, beached, swam, fished, picnicked, and drove several miles back... without a hiccup.

Still, this motor retains my opinion that it has many of the benefits of EFI, but with user serviceability. If there is a way this differs from the refinement EFI in daily operation, I have yet to see it. Amazing. Loving it.

-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby jimh » Fri Aug 09, 2019 9:43 am

PETER--thanks for the further update. Simplicity and ease of repair has benefits.

ASIDE: I was thinking about buying a somewhat fancier than usual car, perhaps an Audi or something. I came across this motto: "Never own a German automobile that is out of warranty." I think there is some truth in that. Modern outboard engines are now rather complex and unrepairable.

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby biggiefl » Tue Aug 13, 2019 9:52 am

I have three German cars that are out of warranty and have been so for years and decades. Jim—I must disagree.

Dave Neal has the Yamaha 100-HP version wit carburetors, and I think it has over 4,000-hours run time.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby pcrussell50 » Wed May 27, 2020 11:39 pm

Just put the drain screws back in, filled with fresh gas, and the engine fired right up again. I didn't take her out today, but got her pretty close to ready for use.

This time, I decided to take the lower clamshell off of the midsection. The "tray" comes off with it. And this action makes a HUGE difference when working on anything below the rim of the cowl. It turns minor things from an unnecessary frustration, into joy. It may not save any time in the long run, but it makes things that should be easy become easy.

Taking off the fiberglass lower cowl also revealed some nuts and bolts that were harboring some corrosion from it's previous life as an ocean boat.

-Peter

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby pcrussell50 » Fri Aug 14, 2020 12:20 am

As summer draws to a close, another 15 hours or so on the carburetor 2000 Mercury 90 FourStroke. It continues to behave as if it were fuel injected. Starts quickly and easily without a choke. Runs smoothly and smoke free or so little it's hard to notice, sips fuel in comparison to my two stroke-cycle engines. Just turn the key and go. Amazing. Other than being HUGE and HEAVY for my Alert 17 (Special Service classic Montauk), it's a delight.

Look how big this motor is:
gray whale at willow 2020.jpg
gray whale at willow 2020.jpg (127.99 KiB) Viewed 15032 times


Now, I do drain the carburetors after the main boating season at the end of the summer, and keep the battery on a trickle charger. But that's about it. Yes, this is a Yamaha powerhead.

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Re: Life with my carbureted Mercury/Yamaha FourStroke (continued)

Postby floater » Fri Aug 14, 2020 8:14 am

I have a Mercury 200 hp 1991. Not sure if it is a Mercury or Yamaha Power head. I would like to balance my carbs as well. Where do you plug in your lines for your tester? I've tried to look it up but can't find any info. Thanks and glad it worked out for you.

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Tue Jun 15, 2021 11:22 am

I hate to sound like a broken record, but yet again, de-winterized (such as the winters are in the South West), and she fired right up. Had a nice day motoring around the lake, stop, start, run smooth, repeat. Again, this carbureted Mercury 90hp FourStroke might as well be the fuel injected version as far as my usage is concerned. Other than being heavier* than a two-stroke-cycle 150hp motor, I love this motor. I also like that it's a Yamaha. I shop for powerhead parts as a Yamaha F100, and they are cheaper because they don't get the extra markup that Mercury takes, over and above the Yamaha prices.

My "winterizing" routine: take out the carburetor drain screws and let the carburetors drain
My "summerizing" routing: install the carburetor drain screws

*It's also dimensionally big. I was at the gas station last summer with it and some thirty-something woman asked me how fast it was and if it was a race boat. When I told her it only goes about 35mph, she couldn't believe it. She thought that with that "big" motor, it was some kind of hot rod. :-)

-Peter

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Sun Jul 02, 2023 12:33 am

And the boring saga of continued reliable operation continues. Started right up after nine months of non-use, and settled into a nice purring idle. I tested out a carburetor balancing tool called the Carbtune Pro. It worked a treat even though the carburetors were pretty well in balance as it was. I'll upload and post a short clip of it. I had been using a Motion Pro, SyncPro which uses a proprietary blue fluid. But it is too intolerant of the large suction from 1700cc's and much better suited to four cylinder motorcycles up to 750cc, and so the fluid is susceptible to getting sucked into the engine. This causes no harm, but it ruins your attempt at balancing the carburetors. The CarbTune Pro on the other hand, uses steel rods that are sucked up in their tubes. It has the look of liquid mercury but it isn't.

Anyway, this motor just goes and goes.

-Peter

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby jimh » Sun Jul 02, 2023 2:13 pm

Perhaps you could explain exactly what element or elements of the carburetor are adjusted to achieve the “balance” that is to be indicated on the test gizmo. I think the test gizmo measures vacuum or negative pressure in the region of the carburetor venturi areas.

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Sun Jul 02, 2023 3:45 pm

jimh wrote:Perhaps you could explain exactly what element or elements of the carburetor are adjusted to achieve the “balance” that is to be indicated on the test gizmo. I think the test gizmo measure vacuum or negative pressure in the region of the carburetor venturi areas.
Here is a youTube short of my engine idling, with the carburetor balancing tool (CarbTune Pro), attached. The tool is receiving a signal from after each carburetor at the elbow before the air-fuel-mixture enters the engine.

https://www.youtube.com/shorts/JPbupt7ZHvE

You can see on the tool, that the levels are already pretty close, since I had already started making adjustments. Some small adjustments on the butterfly micro-adjusters will bring them even closer. You would be surprised how far off they can be if they have never been balanced before and how much smoother the idle is, after balancing. Note fuel injection butterflies can benefit from balancing if they are mechanically actuated.

As to why to do it, this is an excerpt from the manual:

Carb balance will affect the response,smoothness, mileage, performance and running temperature of your engine.

Carb synchronisation consists of adjusting eachthrottle valve for carburettors or fuel injection throats so that theypass as much fuel-air mixture as all the others. This balances the loadcarried by each piston.

If one carb is opened further than the othersthat cylinder will run hotter than the others. The other carbs willalso supply a richer mixture and mileage will suffer.


Note... You might be able to tell from the spelling of certain words, that the CarbTune Pro is a product made by "pommie bastards" ;-)

-Peter

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby jimh » Mon Jul 03, 2023 9:14 am

The vacuum measurement device input tubes seem to attach to fittings just downstream of the carburetors on the intake manifold.

Q1: were the tapped holes for connecting those tubes already there?

Q2: if the tapped holes were already there, do all older carburetor outboard engines have such measuring ports?

Q3: is the only adjustment done to the mechanical linkage connecting each carburetor’s throttle plate to the common throttle movement lever?

Q4: do all multi-carburetor engines have these linkage adjustments?

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Mon Jul 03, 2023 1:42 pm

Good morning Jim.

jimh wrote:Q1: were the tapped holes for connecting those tubes already there?
Affirmative. The tapped holes were already there. In fact, both Yamaha and Mercury include the discussion on balancing in their respective factory manuals. Of course as usual, the factory tool they refer to is expensive: $750 these days, marked up to well over $1000 if you buy the same thing with Yamaha or Mercury branding, last I looked.

jimh wrote: Q2: if the tapped holes were already there, do all older carburetor outboard engines have such measuring ports?
Based on what I gather from the Carb Tune Pro web site, it’s not only outboards, but sporty motorcycles too. Pretty much anything in the class of four-cylinder, dual overhead camshaft motors. Also to include the fuel injection versions of those motors, if the the individual throttle butterflies are mechanically linked to one another and not actuated individually by separate fly-by-wire stepper motors for each butterfly.

jimh wrote: Q3: is the only adjustment done to the mechanical linkage connecting each carburetor’s throttle plate to the common throttle movement lever?
There is a link bar connecting all four butterflies to one another. But three of them have what I call, micro-adjusters that allow you to adjust the respective butterfly enough to achieve balance, without moving the link bar.

jimh wrote: Q4: do all multi-carburetor engines have these linkage adjustments?
For some reason, [linkage adjustments] only seems to be a player when it comes to four-stroke-power-cycle engines, both fuel injection and carbureted. Though the CarbTune manual discusses the odd occasion where you might also do it with a two-stroke.

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby jimh » Tue Jul 04, 2023 9:30 am

I think the carburetors on the Yamaha powerhead are made by Mikuni.

Cf.: https://mikuni.com/

Also see mention of Mikuni in

Mercury 90 FOURSTROKE Carburetor Problems
https://continuouswave.com/ubb/Forum3/HTML/009936.html

ASIDE: I assume that in normal operation those test ports are closed by a threaded plug. If so, then Step One of the test procedure must be: “Remove test port threaded plugs and set aside; do not lose them…”

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby pcrussell50 » Tue Jul 04, 2023 1:17 pm

jimh wrote:I think the carburetors on the Yamaha powerhead are made by Mikuni.
That would be a reasonable guess. But they are not. They are made by Keihin. Both on the Mercury 90 FourStroke and its twin, the Yamaha F100.

Other interesting bits:
  • I buy parts for this motor from Yamaha sources because they are cheaper before Mercury adds its markup.
  • The Mercury parts sources often have parts listed as “no longer available” while the identical part is listed and available from Yamaha sources
  • Mercury lists it as a 90-Hp while Yamaha lists the identical motor as 100-HP. My guess is it’s a “strong” 90 (probably closer to 100). But that’s pure conjecture.
  • I mentioned in a previous post that a boat mechanic down in Mexico had high praise for these carbureted FourStrokes because of their ease of repair and maintenance. More recently I had a USA based mechanic say the same thing. He did say that you have to take pains to keep the carburetors small passages and orifices clean. I use a 10 micron Racor water separating fuel filter. In the handful of times I have had the carburetors apart they have always been clean.

-Peter

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued

Postby jimh » Wed Jul 05, 2023 8:50 am

Another element of the often-cited carburetor problem on these four-cylinder four-stroke-power-cycle engine is the fuel flow rate at idle and low speed was probably much less than would be occurring with an old two-stroke-power-cycle engine, particularly a 90-HP engine. Typically a 90-HP Mercury engine would be a three-cylinder. At idle speeds the fuel flow rate in the two-stroke-power-cycle engine would be much higher, and the carburetor metering jets would not be as likely to be clogged by deposits or evaporated fuel residue because they were larger diameter.

In my experience with classic carburetor two-stroke engines, their fuel economy was awful at low engine speeds. Really, the reason four-stroke engines seemed to have such better fuel economy was mostly because of their much better fuel economy at low speeds.

Boaters were not accustomed to having carburetor problems to the degree they appeared in these four-cylinder 90-HP engines.

Here is an anecdote: a fellow bought a new 170 MONTAUK with the Mercury-Yamaha 90-HP carburetor engine in c.2006. That particular engine was just awful. It was always in the dealer’s shop for carburetor work, and being done under warranty because the engine was not reliable and ran so poorly. After more than a year, the guy got a new engine, which by then was the very new all-Mercury FOURSTROKE 90-HP EFI, which used electronically controlled fuel injection instead of four carburetors in what I recall was an attractive deal on the engine swap.

In retrospect, looking back at this in the context of this discussion about carburetor balancing, maybe the carburetor engine was never properly set up. And maybe the service techs were not familiar with carburetor balance tuning, because they were all old two-stroke guys. Or maybe the gasoline that was available was awful quality. Or, possibly the engine vibrations caused the settings on the carburetor linkage to loosen and wander from the factory settings.

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby jimh » Wed Jul 05, 2023 9:08 am

pcrussell50 wrote:[the carburetors] were made by Keihin. Both on the Mercury 90 FourStroke and its twin, the Yamaha F100.
ROGER. This was noted in another discussion about these carburetors:

2005 Mercury 90-HP FOURSTROKE
https://continuouswave.com/ubb/Forum3/HTML/017925.html

The name Mikuni was stuck in my head; I couldn’t recall the name Keihin when I went searching for the manufacturer.

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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby GuardianRC » Fri Aug 18, 2023 5:33 am

Nice to find a thread on the Mercaha 90 - i've recently acquired one on the back of a 2005 Montauk 170 i've purchased in the UK. I bought the boat with the engine untested, perhaps unwisely with the hours I have/will spend on it.

I'm familiar with the Yamaha 100hp after owning one a few years ago which shared the powerhead so with this ones poor running the carbs came straight off. I found blocked idle jets, unsurprisingly due to their minuscule holes and a serious amount of gummed fuel and fuel hose innards due to the grey fuel hose delamination. After changing the fuel hose and filter I got somewhere but had to do another carb clean to fully clean out the system.
I use a cheap amazon balancing gauge kit (linked below), purchased when I owned the Yamaha, and while it does the job, one of the gauges has failed and caused me a bit of a headache thinking i'd got air leaks while balancing. If I ever replace it I will buy something higher quality, which will also allow a smoother reading.

My first run out was disappointing due to fairly poor running, certainly due to fuelling, so off came the carbs again. I found the air intake with enough fuel to pour out of it and a wet carb 4 venturi. Stripping down there were no obvious problems, apart from a tiny amount of gum again, but upon rebuilding I made sure to check the floats for proper operation once they were built again. She fired up and no more pouring fuel at the moment.

I also had some problems with the cooling system - I had read that the Mercaha engine was a bit of a pig with this too. I had to replace the water pump base due to very heavy corrosion. Upon removing the lower unit I discovered a large mangled bush on the drive shaft which i could not locate on the engine schematic drawings - it's now happily (I hope) running without it. The engine still struggled to pump water but after my first run at sea she appears to have cleared this problem which i now put down to partially blocked passages.

The steering is also very stiff, I have ruled out the cable steering system, so that is my next job. Yesterday I heated the engine steering bracket tube before pumping in grease to try and flush out old stuff. There is only one grease nipple, at the top, so I'm not sure how successful this is. There was a very slight improvement but I would like to make it better than this to avoid a snapped steering cable while running.

A couple of observations/questions...

- Yamaha later de-rated the 100hp to a 90hp, so maybe the real figure for this powerhead lies in the middle somewhere.

- Is there a way to get any data from the engine? Mine is rigged with just a rev counter and a non-working water pressure gauge. I wouldn't mind getting this working or knowing the engine hours.

- Does anyone have any further techniques of releasing the steering somehow? I'm considering drilling/tapping for more greasing/flushing points.

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Phil T
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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby Phil T » Fri Aug 18, 2023 1:32 pm

There is no grease nipple for the steering cable in the tilt tube only for the tilting feature of the engine.

In the States the recommendation is to change the port side nut on the tilt tube with a nut that has a grease fitting.
https://www.wholesalemarine.com/steersman-boat-steering-guard-1.html

Frozen Steering:

The steering cable has two parts, an outer sleeve and an inner cable/rod. The sleeve bolts on to the starboard side of the engine and rod slides thru the tilt tube of the motor. The rod is connected to the motor by the steering arm. The tilt tube needs lubrication. Lack of lubrication and water can cause corrosion. This results in the rod sticking.

Warning: if your steering is stuck, do NOT try forcing the wheel to turn. There are small teeth in the helm (behind the wheel) that can break. If several teeth break, you will need to replace your helm.

Verify the steering cable is stuck by removing the steering arm from the rod. With your hands, grasp the motor and move it. If it moves, the steering cable is the source of the problem.

The easiest method that can free a slightly frozen rod is using the engine tilt motor to try to break the rod free. When the motor moves the rod does rotates slightly. Repeated tilting full up/down can break free a rod.

Steering Linkage

If still stuck, with the steering arm still disconnected, remove the port side nut from the engine bracket. Spray heavy amounts of penetrant like PB Blaster into the tilt tube. Keep some rags or towels handy. Let this soak for a few hours. Repeated spraying and letting it sit helps reduce the effort to break it free.

Wrap the flat end of the steering rod with a towel and use a wrench or adjustable and gently rotate up and down while having a helper put light pressure on the wheel.

If not successful, unbolt the starboard side nut that attaches the cable to the engine. With a block of wood and a hammer, drive the port side end of cable. A combination of force and spraying penetrant will break it free in 90% of the cases.

If the cable will still not budge, the last resort is to use heat. With a propane torch (not MAP or other high temperature fuels) apply heat to the tube. After a few minutes, whack the cable. Repeat the soaking and apply more heat and hitting the cable.

Unfrozen and Prevention:

Now that your cable is unstuck, you should take the time to make sure it doesn't happen again. If the boat is new to you or has not been serviced recently, removing the steering rod, cleaning the tube and reinstalling with fresh marine grease is recommended.

If your rod does not have a nut with a grease fitting on the port side,it is highly recommended you install one like the one shown in the photo above. One brand is Steersman Nut
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

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Phil T
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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby Phil T » Fri Aug 18, 2023 1:37 pm

One of the proven preventive measures when running a Mercaha motor is to add Mercury Quickleen to every gallon of gas. This seems to stop the carburetors from getting the perpetual gummed up condition
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003

GuardianRC
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Re: Life with my Carburetor Mercury-Yamaha FourStroke (continued)

Postby GuardianRC » Fri Aug 18, 2023 2:40 pm

Thanks Phil, my wording was a bit rubbish. The cable steering system Is free and working smoothly. The concern I have is with then engine's own swivel bracket.

I add quicksilver fuel treatment to each tank of fuel, and I hope this keeps the engine running well.

Fortunately I have carburetor tear-down to a fine art at this stage if the engine is not running well.