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Author Topic:   Thoughts on carbureted FourStrokes

pcrussell50 posted 02-13-2012 04:35 AM ET (US)
[Mercury four-cycle outboard engines with carburetors are] much-maligned for their complexity and unreliability, caused by tiny orifices in the carburetors getting plugged up. They were short-lived in the market before EFI took over. And I have one: A c.2000 Mercury 90hp carbureted FourStroke. I also finally found the time and gumption to dig into the factory repair manual and I'm pleased to observe that checking and tuning the induction setup is really not all that bad... IF you RTFM, and I mean, really read it. The removal, checking, and reassembly of the four carburetors, the way it's presented in the manual, is quite straightforward, and makes eminent sense. No freeze plugs like the carbs on my old beloved carbureted two-strokes, and it has modern-style O-ring gaskets instead of old school paper gaskets. Yay!
As someone who tunes my own EFI automotive race motors with a laptop, there was not much that scared me more than the prospect of [repairing] those carbs and getting them set up to run right again. That concern is drastically reduced, now.
Comment from the manual on ethanol blended into gasoline:

quote:
IMPORTANT: Gasoline containing alcohol (ethanol or methanol) can cause a formation of acid during storage and can damage the fuel system--blah
No mention of -any- acceptable percentage of ethanol in the gas. Seems odd for a my 2000 motor.
Anyway, I've pretty much lost all my trepidation over doing a carburetor job on this thing if it turns out I have to. Pretty stoked and for some reason, actually happy it's not EFI--for now.
-Peter
weekendwarrior posted 02-13-2012 02:48 PM ET (US)
Having owned my 1999 Honda carbed motor since new, I have so far not had a reason to dismantle the carbs. It gets year round use and when it isn't used I do my best to run it a few minutes every other week or so, and I do use Stabil in the gas. There is the minor inconvenience of having to choke it when cold, but reliability wise I can't complain so far. In theory you need to resync the carbs at tune up time, but I haven't found the need.
That said, my brother in law bought essentially the same motor used, and it had been sitting for a long time and the carbs were horribly clogged and needed some work to get back to working condition. But I think the root of the problem was abuse by improper storage.
EFI would be nice, especially for the increased mileage and better cold starting behavior, but I don't personally find it enough of a reason to justify changing the motor.
Tohsgib posted 02-13-2012 09:47 PM ET (US)
EFI rules but when it breaks(if it does)costs much more. 12 years without doing a carb job is probably 5-7 years too long with todays fuel.
sosmerc posted 02-14-2012 11:55 AM ET (US)
pcrussell50.......if your engine is running fine I would recommend that you do not disturb the linkage. If you really do need to service the carbs it can be challenging, but you are very wise to have the factory manual. I have had to do several 4 strokes recently and the older (1996 vintage F50) was pretty time consuming. Having gone to the trouble to remove everything, and having found quite alot of scum at the bottom of the float bowls, I elected to put in complete carb kits. They were pretty expensive, but they did include new floats and needles as well as new pilot needles and all o-rings. If you tear your carbs down and find that they are dirty, you should probably invest in an ultrasonic cleaning tank. You can get one fairly cheap through outfits like Harbor Freight. I think I paid less than $200 for mine and it has already given me a couple of years of service and has proven to be invaluable for cleaning 4 stroke carbs. I bought a small one so I can only do one carb at a time. Wish I had bought a larger model with room to accommodate multiple carbs or larger parts.
When all is well, the carb 4 strokes run just fine. But it is extremely critical to keep your fuel clean and fresh and run the engine as often as you can. Your engine is equipped with Yamaha's Prime Start system so it sure be "turn-key" starting without fuss. Be sure to let the engine fully warm up before trying to "take off".
pcrussell50 posted 02-14-2012 01:46 PM ET (US)
Sos, thanks for the insight... especially valuable coming from a pro. Having studied the manual pretty carefully, it doesn't look to be that challenging... at least to me.... With the balancing tool, and EPA plugs removed, what do you find to be the most challenging part of the carb job on these Merc'ahas? I love the hot-wax-based cold-start-enrichment system, btw... it works AMAZINGLY well.
'Nother question, what experience have you had, if any, with the built-file lines degrading in the prescence of ethanol?
-Peter
pcrussell50 posted 02-14-2012 03:20 PM ET (US)
That was meant to be:
"What experience have you had, if any, with the built-in fuel lines degrading in the prescence of ethanol?"
-Peter
sosmerc posted 02-14-2012 03:48 PM ET (US)
The linkage is VERY touchy. When you have a carb balancing tool hooked up you can see changes occur even by just touching the adjustment screws. And, in some cases, the links that connect multiple carbs can expand and contract with temperature changes and this can alter the carb balance.
Most newer engines now have EFI and often there is only one throttle butterfly so.......no more balancing issues.
Regarding fuel line, yes, I have seen alot of issues with fuel line (and the inside of primer bulbs) starting to flake apart and cause problems. Maybe the answer will one day be all metal lines under the cowl?
pcrussell50 posted 02-14-2012 04:09 PM ET (US)
Sos, what solvent do you use in your ultrasonic cleaner?
Aha. The hypersensitivity of the adjustment screws is one of those things I couldn't tell about from reading the manual. Good to know. My motor no longer runs perfectly... a little misfire every now and then, and sometimes resists going into WOT, (FISHNFF/Brian, the previous owner had a similar problem that was fixed by rebalancing the carbs). It's not so bad that it's killing me, because the Pacific Ocean is usually too rough to use WOT anyway, and I can usually get it to go to WOT if I nurse it... most outings I never even have occasion to try WOT. So doing a carb job has been pretty far down my list of round-tuits, but because I actually _like_ doing stuff like that, I've been thinking of doing it, and reading the manual made me even more confident.
-Peter
sosmerc posted 02-14-2012 04:48 PM ET (US)
I use just water and joy dish soap. My tank does heat the water to 80 degree centigrade and sometimes I run the carb for 2 hours. If the float bowls are extremely bad, I may poor a little OMC/BRP engine tuner directly in the carb bowl and let it sit for an hour before then putting the carb in the tank. The reason I use just water and soap is that I have heard that overuse of strong de-carbonizers like engine tuner can cause a carb to become porous. That would not be good!!
I strip the carb down some, but do not always remove the o-rings (if I am trying to avoid buying carb kits)..some of the more complex o-rings can be almost impossible to re-install if you remove them. I DO NOT run the inlet needle in the tank or in solvent. I don't want the tip to swell.
It's not a bad idea when you are done to verify that all the passages are open by running some fuel through the passages using a syringe. (if you have ever had a tooth pulled, your doctor probably gave you a syringe to clean out the hole where your tooth was......these work great for forcing fluid through small holes and passages) Be sure to immediately soak the rubber part of the syringe in water or it will be useless the next time you try and use it!

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Author	Topic: Thoughts on carbureted FourStrokes
pcrussell50	posted 02-13-2012 04:35 AM ET (US) [Mercury four-cycle outboard engines with carburetors are] much-maligned for their complexity and unreliability, caused by tiny orifices in the carburetors getting plugged up. They were short-lived in the market before EFI took over. And I have one: A c.2000 Mercury 90hp carbureted FourStroke. I also finally found the time and gumption to dig into the factory repair manual and I'm pleased to observe that checking and tuning the induction setup is really not all that bad... IF you RTFM, and I mean, really read it. The removal, checking, and reassembly of the four carburetors, the way it's presented in the manual, is quite straightforward, and makes eminent sense. No freeze plugs like the carbs on my old beloved carbureted two-strokes, and it has modern-style O-ring gaskets instead of old school paper gaskets. Yay! As someone who tunes my own EFI automotive race motors with a laptop, there was not much that scared me more than the prospect of [repairing] those carbs and getting them set up to run right again. That concern is drastically reduced, now. Comment from the manual on ethanol blended into gasoline: quote: IMPORTANT: Gasoline containing alcohol (ethanol or methanol) can cause a formation of acid during storage and can damage the fuel system--blah No mention of -any- acceptable percentage of ethanol in the gas. Seems odd for a my 2000 motor. Anyway, I've pretty much lost all my trepidation over doing a carburetor job on this thing if it turns out I have to. Pretty stoked and for some reason, actually happy it's not EFI--for now. -Peter
weekendwarrior	posted 02-13-2012 02:48 PM ET (US) Having owned my 1999 Honda carbed motor since new, I have so far not had a reason to dismantle the carbs. It gets year round use and when it isn't used I do my best to run it a few minutes every other week or so, and I do use Stabil in the gas. There is the minor inconvenience of having to choke it when cold, but reliability wise I can't complain so far. In theory you need to resync the carbs at tune up time, but I haven't found the need. That said, my brother in law bought essentially the same motor used, and it had been sitting for a long time and the carbs were horribly clogged and needed some work to get back to working condition. But I think the root of the problem was abuse by improper storage. EFI would be nice, especially for the increased mileage and better cold starting behavior, but I don't personally find it enough of a reason to justify changing the motor.
Tohsgib	posted 02-13-2012 09:47 PM ET (US) EFI rules but when it breaks(if it does)costs much more. 12 years without doing a carb job is probably 5-7 years too long with todays fuel.
sosmerc	posted 02-14-2012 11:55 AM ET (US) pcrussell50.......if your engine is running fine I would recommend that you do not disturb the linkage. If you really do need to service the carbs it can be challenging, but you are very wise to have the factory manual. I have had to do several 4 strokes recently and the older (1996 vintage F50) was pretty time consuming. Having gone to the trouble to remove everything, and having found quite alot of scum at the bottom of the float bowls, I elected to put in complete carb kits. They were pretty expensive, but they did include new floats and needles as well as new pilot needles and all o-rings. If you tear your carbs down and find that they are dirty, you should probably invest in an ultrasonic cleaning tank. You can get one fairly cheap through outfits like Harbor Freight. I think I paid less than $200 for mine and it has already given me a couple of years of service and has proven to be invaluable for cleaning 4 stroke carbs. I bought a small one so I can only do one carb at a time. Wish I had bought a larger model with room to accommodate multiple carbs or larger parts. When all is well, the carb 4 strokes run just fine. But it is extremely critical to keep your fuel clean and fresh and run the engine as often as you can. Your engine is equipped with Yamaha's Prime Start system so it sure be "turn-key" starting without fuss. Be sure to let the engine fully warm up before trying to "take off".
pcrussell50	posted 02-14-2012 01:46 PM ET (US) Sos, thanks for the insight... especially valuable coming from a pro. Having studied the manual pretty carefully, it doesn't look to be that challenging... at least to me.... With the balancing tool, and EPA plugs removed, what do you find to be the most challenging part of the carb job on these Merc'ahas? I love the hot-wax-based cold-start-enrichment system, btw... it works AMAZINGLY well. 'Nother question, what experience have you had, if any, with the built-file lines degrading in the prescence of ethanol? -Peter
pcrussell50	posted 02-14-2012 03:20 PM ET (US) That was meant to be: "What experience have you had, if any, with the built-in fuel lines degrading in the prescence of ethanol?" -Peter
sosmerc	posted 02-14-2012 03:48 PM ET (US) The linkage is VERY touchy. When you have a carb balancing tool hooked up you can see changes occur even by just touching the adjustment screws. And, in some cases, the links that connect multiple carbs can expand and contract with temperature changes and this can alter the carb balance. Most newer engines now have EFI and often there is only one throttle butterfly so.......no more balancing issues. Regarding fuel line, yes, I have seen alot of issues with fuel line (and the inside of primer bulbs) starting to flake apart and cause problems. Maybe the answer will one day be all metal lines under the cowl?
pcrussell50	posted 02-14-2012 04:09 PM ET (US) Sos, what solvent do you use in your ultrasonic cleaner? Aha. The hypersensitivity of the adjustment screws is one of those things I couldn't tell about from reading the manual. Good to know. My motor no longer runs perfectly... a little misfire every now and then, and sometimes resists going into WOT, (FISHNFF/Brian, the previous owner had a similar problem that was fixed by rebalancing the carbs). It's not so bad that it's killing me, because the Pacific Ocean is usually too rough to use WOT anyway, and I can usually get it to go to WOT if I nurse it... most outings I never even have occasion to try WOT. So doing a carb job has been pretty far down my list of round-tuits, but because I actually _like_ doing stuff like that, I've been thinking of doing it, and reading the manual made me even more confident. -Peter
sosmerc	posted 02-14-2012 04:48 PM ET (US) I use just water and joy dish soap. My tank does heat the water to 80 degree centigrade and sometimes I run the carb for 2 hours. If the float bowls are extremely bad, I may poor a little OMC/BRP engine tuner directly in the carb bowl and let it sit for an hour before then putting the carb in the tank. The reason I use just water and soap is that I have heard that overuse of strong de-carbonizers like engine tuner can cause a carb to become porous. That would not be good!! I strip the carb down some, but do not always remove the o-rings (if I am trying to avoid buying carb kits)..some of the more complex o-rings can be almost impossible to re-install if you remove them. I DO NOT run the inlet needle in the tank or in solvent. I don't want the tip to swell. It's not a bad idea when you are done to verify that all the passages are open by running some fuel through the passages using a syringe. (if you have ever had a tooth pulled, your doctor probably gave you a syringe to clean out the hole where your tooth was......these work great for forcing fluid through small holes and passages) Be sure to immediately soak the rubber part of the syringe in water or it will be useless the next time you try and use it!