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Author Topic:   4-stroke Motors: More plumbing
jimh posted 03-13-2002 11:23 PM ET (US)   Profile for jimh   Send Email to jimh  
I had the cowling off a 2002 Mercury 25-HP 4-stroke engine recently for the purpose of just giving it a look to see what was under there. I found several interesting things you are probably not accustomed to finding on a classic 2-stroke engine.

Fuel cooling: the fuel line led to a filter then to a pump which also seemed to integrate a fuel cooler. Lake water was routed by hoses through the pump/cooler, apparently for the purpose of cooling the fuel before delivery to the engine.

Crankcase ventilation: another hose appeared to be some form of crankcase ventilation, returning crankcase blow-by gases back to the induction manifold.

Oil filter: a small spin-on oil filter was another new article under the cowling.

Oil dipstick: another artifact of the 4-stroke engine was an oil sump level dipstick.

Oil sump drain plug: you have to have some way to drain and change the oil, a new concept on an outboard.

Now the engine didn't come close to equalling the number of hoses, lines, and multiple carburetors that used to fill the engine compartment on my wife's old HONDA Prelude,
but it was noticeably more complicated than that 1960's Johnson outboard we used to have when I was a kid.


Whaletosh posted 03-14-2002 09:21 AM ET (US)     Profile for Whaletosh    

As have owned a 60 Hp carbed 4-stoke Mercury and a a 60 HP 4-stoke EFI 4-stroke Mercury I can state that this is another reason for liking EFI. All of the hoses that you state are on my EFI but because there aren't the carbs on the right side of the motor it is a lot cleaner in the layout.

the left side of the motor is a different story. It is a about the same as the carbed motor except for some large aluminum casting that has something to do with the fuel. I need to look at the service manual to find out what it is.

The motor is deinately more complex. On the other hand there isn't anymore maintenance that I can see. I never need to adjust the timing or carbs. I do need to change the oil every once a season (for my usage rate) and the oil filter. My plugs should last a lot longer. rplacing the belt for the camshaft should be a breeze. The only real pain is the valve adjustment. It would be fairly quick except that there is a lot of stuff to take off. Good thing it doesn't need to be done all that often.

whalerron posted 03-14-2002 09:57 AM ET (US)     Profile for whalerron  Send Email to whalerron     
jimh, is that really a fuel cooler? Automobile manufacturers always routed heat up under the carbs on car engines to help heat the fuel. This was done to help the fuel atomize better as it was sent to the cylinders. I am trying to think of a good reason to cool the fuel. When you cool fuel, you get a large amount of contraction and so you would get more fuel in the same volume. Maybe it has something to do with smaller "squirts" into the cylinders but each "squirt" contains more btu's in its volume because of the cooling?
Bigshot posted 03-14-2002 10:52 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Never heard of heating it. The cooler the gas(and air) the better the burn. Too hot of gas will give you vaporlock. This is basically when the gas boils and you suck in air or vapor instead of gas. The concept of intercoolers should also come to mind which does the same thing...cools the gas.
SteveC posted 03-14-2002 11:25 AM ET (US)     Profile for SteveC    
I'm not sure about what is done in this particular case, but for cars the concept is to cool the liquid fuel to prevent it from boiling (vapor lock) and to heat the air fuel mixture to help vaporization.
Salmon Tub posted 03-14-2002 12:02 PM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Whalerron, on carburated cars, coolant was routed under the carb (coolant that was warm or hot) in order to operate the choke. I.E. when then engine cooled overnight, the choke system would re-set somewhat like a thermostat. Then when you started the engine in the morning, the carb was choked and the throttle was advanced while the engine warmed up. As the whole system warmed up, the increasing temperature would warm the carb, and the system would slowly "open up" once fully opened, the engine was at normal temp., normal idle,and ready to go. If you ever had one of these systems, you would notice it when you fire up the engine, it would idle fast 1500-2000 prm, then slowly drop rpm's until warm. Most people though probably didn't have time to do this, and just got up and went. I had an old Mitsubishi p/u that had this system, most little Jap. p/u's that were carbed had similar. EFI does this with computers and doesn't use coolant system (mechanical as opposed to electronic.)
whalerron posted 03-14-2002 01:43 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Salmon Tub, now I remember. That exhaust gas crossover in the intake manifold of V8 engines was indeed for cold start. Once the engine is warmed, there is enough residual heat around the carb that the exhaust gas crossover has little effect on fuel atomization.

For a gasoline engine, you want warm fuel and cold intake air. Cold air gives you more molecules of air in the cylinder and warm fuel atomizes better. This is the reason that race-heads dump ice on top of their v8s before making a 1/4 mile run. The ice cools the intake so that incoming air is cooler. They pack the ice on top of the engine but not against the carb.

As for intercoolers, they are used to cool intake air and intercoolers do a better job than dumping ice on an intake manifold.

Bigshot posted 03-14-2002 02:43 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
By the way kids....that gas cooler (just like on Optimax's) has to be winterized as well or else she will crack. Hope I am not too late being it is March.
whalerron posted 03-14-2002 05:30 PM ET (US)     Profile for whalerron  Send Email to whalerron     
All, I stand corrected. I always was told that warm fuel atomized better and resulted in a better burn. Check out this link:
Along with cooling the intake air on their outboards, Suzuki also uses a fuel cooler: "The fuel delivery system incorporates a cooling system. Cooler fuel enhances power output."

Hmm. I wonder how much better my old Johnson would run if I packed the cowling with ice?

whalerron posted 03-14-2002 11:44 PM ET (US)     Profile for whalerron  Send Email to whalerron     
Ok, that danged forward slash somehow got in there. Try this...

Bigshot posted 03-15-2002 09:59 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
You only need to run the fuel line through an ice chest. Might make a difference.
Salmon Tub posted 03-15-2002 10:35 AM ET (US)     Profile for Salmon Tub  Send Email to Salmon Tub     
Whalerron, actually, warm fuel is less dense, and gives you what is called a more "efficient" burn, do not mistake this with a more "powerful" burn, remember, this stuff was installed into cars for fuel economy, during the mid to late 70's, not for power. You won't find this stuff on the vehicles from the 50's and 60's. Once the Green Giant is done with the 2 Strokers, he will most likely go after the 4 stroke carbed, and DFI systems. Besides, I am not familiar enough with EFI, but would imagine that since the fuel delivery is computer controlled, they probably need to keep the fuel at some nominal "normal" temperature, without haveing its temp. vary too much depending on ambient conditions. That is probably why they have a cooler there, only my guess though.
SuburbanBoy posted 03-15-2002 10:37 AM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
Pack em' with dry ice, for that "just started" feel! Sheesh, you would think we had to race our BW's this weekend.

Speaking of plumbing, I remember my old Black Max, it seemed to have miles of small diameter black tubing routing from "God knows were" going to "I have no idea". A tiny plastic tee broke within the mass of tubing once. I feared major fires or seizure, but after replacing the broken "tee" I noticed no change.


whalerron posted 03-15-2002 11:59 AM ET (US)     Profile for whalerron  Send Email to whalerron     
I have a wort cooler that I use when making beer. It looks like a spring thats about 10 inches tall and has a diameter of about 9 inches. It is made of 1/2 inch soft copper tubing. I could sink that cooler in a chest full of ice and then route my fuel through it. I bet I could get the fuel temp down to about 40 degrees at the engine. Man, I bet that Johnson would hop!
jimh posted 03-16-2002 09:56 AM ET (US)     Profile for jimh  Send Email to jimh     
Also noted on the MERCURY 4-Stroke:

The spark plugs were NHK-brand and included rather cool plug wire attachments with the letters NHK stamped on them. Perhaps more of the electrical are Japanese than I thought!

Is Mercury using NHK plugs in engines of their own design?

Whaletosh posted 03-18-2002 08:29 AM ET (US)     Profile for Whaletosh    
Seeing that Federal-Mogul has filed for bankruptcy, champion plugs may become a thing of the past.
lhg posted 03-18-2002 04:35 PM ET (US)     Profile for lhg    
JimH: Mercury has been using NGK Spark plugs as factory equipment for a long time. My 1985 in-line 6's came with them, as have both sets of my 200's. That's all I buy when I change plugs.
vdbgroup posted 03-21-2002 10:55 PM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
Could it be that the fuel cooling system is used to minimize pre-detonation?
fireball posted 03-21-2002 11:12 PM ET (US)     Profile for fireball  Send Email to fireball     
In perspective-hot water freezes at a much faster RATE, not speed, than cold water-the same applies to the fuel cooling thoughts. Does anyone know if it works ? fb flkeys

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