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Leaking transfer port gaskets 1990 90 hp

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yellowbird

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Hi I have a pair of 1990 90hp Johnsons on my boat and the Port engine has started to leak fuel from the two Starboard side transfer port covers, can anyone tell me whether this is just a gasket problem or if there is something more sinister developing. The compressions are all between 138 to 140. I have tried to reseal the joint with gasket cement but it keeps blowing through so I have ordered new gaskets and plan to replace the old one's when they arrive. The engine is hard to start and wont idle in gear anymore and seems slow to build up to top revs compared to the Starboard engine, I'm assuming these are problems associated with the leak believing if fuel can get out air can get in, any help would be great, thanks.
 
It is a straight forward job to change those gaskets.-----------------------Nothing is going to jump at you.----------------------Have a good look at the pistons and rings while the covers are off.----------------I do not believe that these leaks will drastically change engine performance. But you never know , depends on how bad the leak is and I can not see it here at my desk..--------------------Check for spark on each cylinder that will jump a gap of 7/16" or more.
 
Thanks for the reply racerone I've had the covers off a few times now, the pistons and rings look fine. The engine was getting harder and harder to start and get to idle and I noticed 2 stroke oil running down the mid section from under the bottom of the cowl, so I thought I had some sort of fuel leak coming from the vro or carby's. When I couldn't find any leak there I had a good look around the block and noticed fuel dripping from the block to the cowl, when I followed that back I found it leaking from the lower transfer port cover and bubbles coming out of the top cover. I took them off expecting loose bolts but they were tight that's what made me think something else might have caused enough of pressure build up to blow past the gasket, hopefully new gaskets will sort it out. I've put them back together with gasket cement and the motor starts and runs fine for around a minute and then the bubbles start to reappear as the fuel gets past the gasket again and the motor cuts out and is hard to start again.
 
Make sure the tranfer port cover's are not warped, then make sure the sync and link is spot on, if all that is ok sounds like it has to much crankcase compression. The only things that can cause that would be: blocked VRO pump pulse fitting in the crankcase or crankshaft seal rings. :confused::confused::confused:
 
Blocked VRO pulse limiter or leaking crankcase seal rings will not cause high crankcase compression.----------------------NOT A CHANCE AT ALL.-------------------------Warped covers ( rare ) are the likely cause of leakage.------------------------------Poor starting / poor idle ----Look for poor cylinder compression / spark must jump a gap of 7/16" on all 4 cylinders / flywheel key must not be sheared / carburetors must be absolutely clean / reed valves must not be broken or held open by debris.
 
When the port covers are sealed it's not hard to start or get to idle, it's only when they start keaking that it stalls and becomes hard to start and hard to get to idle, the only thing I'm not sure of is whether the leaking port covers are to blame for it being slow to come up to full revs. Do you think I should put some sort of gasket sealer or cement on the new gaskets or just put them on clean.
 
The gaskets should be put on dry and torqued to 60-84 INCH POUNDS but with the trouble you have been having there is another problem
 
racerone said:
Blocked VRO pulse limiter or leaking crankcase seal rings will not cause high crankcase compression.----------------------NOT A CHANCE AT ALL.-------------------------Warped covers ( rare ) are the likely cause of leakage.------------------------------Poor starting / poor idle ----Look for poor cylinder compression / spark must jump a gap of 7/16" on all 4 cylinders / flywheel key must not be sheared / carburetors must be absolutely clean / reed valves must not be broken or held open by debris.
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Well racerone---------------------- I didnt say the seal rings maybe leaking, i said there maybe a problem with them, and if you had read the thread CORRECTLY the compressions are between 138 and 140 which is well within specs----------------------- and leaking transfer port covers WILL change engine performance--and no spark WILL NOT cause leaking transfer port covers, AND a sheared flywheel key WILL NOT cause transfer port covers to leak--
 
BUT!!!! Leaking transfer port gaskets will cause a lean condition in the cylinder, though. The fuel that is leaking out is SUPPOSED to get into the cylinder, remember? And it is not.
Get those fixed properly ASAP, don't pookie them up with silicone. Covers must be non-warped, and gasket surfaces must be properly cleaned and prepped.
Also, you will see that there is a very narrow edge on the side closest to the block for proper sealing. Pay attention there.

I also agree that a blocked VRO pulse limiter will not affect the crankcase pressure. All that will do is make the fuel pump not work. That doesn't sound like his problem.
 
One other thing...the last crossflow I did with leaking transfer port gaskets...wasn't it at all. It was leaking between the crankcase halves, coming out right at the transfer port cover area. The owner mis-diagnosed it, put silicone all over it, and then brought it to me with #1 and #3 burned up, broken rings, etc.
 
Thanks for the tip "dasalbee", the problem is definately with the crankcase and not the transfer port covers. I've got the powerhead off for repair today.
 
Joe Reeves holds the all time LEGACY TRIBUTE of these boards....he has the "Joe Reeves WOT Timing Procedure". Classic!!!

The Reeves method... I love it!

Joe Reeves and JWBmarine and Haffiman have really taught me alot. Invaluable.
 
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