Top Cylinder Carb Fuel Spitback

[WernerF]

Hi everyone,
1989 60hp J60TLCEA. The #1 cylinder spits small drops of fuel out of the carb. After 2min idle there is a puddle in the carb throat. The other two carbs stay almost dry. Here's what I tried to fix it, but it didn't help.
1. Replaced float and seat valve. Adjusted float.
2. Applied a drop of loctite to the brass idle tube (as shown in the OMC manual)
3. Swapped #1 and #2 carb for a test without throttle linkage. #1 cylinder kept on spitting; #1 carb on #2 cylinder stayed dry.
4. Replaced #1 cylinder leaf valves. Two of them stood open a tiny bit, but could be closed with minimal force. The manual says this is acceptable. Replaced them anyway (have a spare set of reeds).

Looking closer at the intake I found an additional hole creating a passage from #1 crankcase to the intake. What's the purpose for this?
This passage is much wider compared to the passage in the bottom cylinder and additionally ends close to the carb's butterfly gap and idle circuit. I compared top and bottom passage by attaching a small hose and blowing through.

I think this is the reason for spitting and I'm chasing a phantom. What do you think?

 

[Daviet]

Re: Top Cylinder Carb Fuel Spitback

Have you run the engine since you replaced the reeds?
Normally if you have spitting OUT of a carb the reeds are the problem.
Not sure what the passage is for, can't help you there.

 

[WernerF]

Re: Top Cylinder Carb Fuel Spitback

Yes, the engine runs the same with the new reeds.
I think, I know now what the passage is for. The passage helps lubricating the upper main bearing. Not enough oil would flow upwards behind the crankweb to the bearing.

 

[Faztbullet]

Re: Top Cylinder Carb Fuel Spitback

Pull the cylinder head, most likely your going to find piston scuffed on exhaust side...

 

[emdsapmgr]

Re: Top Cylinder Carb Fuel Spitback

My 92 does the same thing. It's "normal," according to an old OMC master tech. The factory-enginered crankcase lube system internal to the block lubes the crank/rotating assembly every rotation of the crank. Any leftover fuel/oil exhausts out the intake manifold on the top cylinder carb throat. The crankcase compression forces a small amount of fuel/oil out that tiny port each stroke. It winds up as a type of mist-coming out of the top carb. If you remove the top carb, you will see the hole in the intake manifold. I think it's odd, but with the airbox cover on, any excess fuel/oil will get recircuated back into either the top carb, or the bottom cyl through the airbox drain hose. As "normal" as it may be, it seems to be an odd situation to me. My engine has run great the way it is for many years.

 

[WernerF]

Re: Top Cylinder Carb Fuel Spitback

Wow, thanks a lot for your replies. Probably you both are right.

Compression is 100/95/100, but this doesn't necessarily mean that there is no little blow-by of combustion gases increasing the crankcase pressure pulse. Maybe even the cooling system's air trap problem has something to do with it and there might had been an overlooked top cylinder overheat situtation in the past.
On the other hand the 3-cylinder engine seems to be sensitive: There's the internal lube system blowing into the intake and one carb feeds a single cylinder only making the carb's air flow highly pulsating. So the air can reverse easily between two suction phases. The lube passage should better have been directed to the carb's bottom.

I'm not sure whether I can see or feel anything on the cylinder wall at 100psi compression. Can the upper piston be removed in a looper without separating the crankcase?

So I'm going to run the engine as it is. Hopefully, it will work for a couple of seasons and gracefully degrade. If it eventually fails, I'm going to replace it with a fuel saving E-TEC.

 

[boobie]

Re: Top Cylinder Carb Fuel Spitback

The spit back on that mtr is perfectly normal.