1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

[Spariduck]

engine worked good for a few weeks then lost all power, did a compression check and only had 10psi on one cylinder. broken rings, rebuilt engine 1 new piston and new rings for all. did some honing as well. got approx 120 psi on all. got it to run but not sure if i put the coils in the right spots on the right side. i have manuals but they don't mention where the coils go. the engine will run ether way.. they are getting spark (ouch! almost went off the back of the boat) so i need to know which cylinder is which 1.2.3.4 and what coil goes where (from back side of engine) A (orange/blue) B (orange) left side ( A is on top cylinder B on bottom ) on right side not sure.

Timing may also play a big roll in my issue.

in current state its happy to let air and fuel to leak/blow out of the side panel and give me good power (approx 4500 rpm and top speed of about 35mph with a 13.25/17 prop, 16' heavy fiberglass ski boat(86 Larson sezna)).

can give lots of other information.

 

[daselbee]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

Cyls are as shown:

2 --- 1

4 --- 3

Port Stbd

Orange/blue goes to top coil, orange goes to bottom coil. It will backfire and run real rough if they are swapped.

 

[daselbee]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

You know, I keep reading this..and I wonder...are you really blowing bypass cover gaskets or not?

First thing, you cannot, or make that, should not, run it with a blown bypass cover gasket. It will cause the cyl to run lean, and possibly do exactly what you are describing happened....broken rings...etc.

Secondly, those bypass covers come very, very close to the crankcase seam. I wonder if the crankcase seam is leaking and you are thinking it is the bypass cover? The crankcase half flange seam at that point is very thin, maybe 1/4" wide, and if the gelseal has failed there....well...there could be your leak. Check it out very carefully. Soapy water, etc.

 

[Spariduck]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

Alright, thank you, That was how I am set just followed a wire wrong last time. I will reinstall the gasket on the bypass cover and see how it goes, most likely a bad seal on the bottom crank.

 

[Spariduck]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

You know, I keep reading this..and I wonder...are you really blowing bypass cover gaskets or not?

First thing, you cannot, or make that, should not, run it with a blown bypass cover gasket. It will cause the cyl to run lean, and possibly do exactly what you are describing happened....broken rings...etc.

Secondly, those bypass covers come very, very close to the crankcase seam. I wonder if the crankcase seam is leaking and you are thinking it is the bypass cover? The crankcase half flange seam at that point is very thin, maybe 1/4" wide, and if the gelseal has failed there....well...there could be your leak. Check it out very carefully. Soapy water, etc.

I fixed the gasket 3 times, when it goes i can feel air and fuel spatter from it. then i fix it and no air/ gas, till it blows again. may have fixed the issue since the last repair of the gasket, not sure.

 

[ddiggerr]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

I'm having the exact same issue. Num 1 bypass cover gasket keeps blowing gas/air. I fix it and it runs great for less than a minute , then puff puff....stall.

Is there any reason why it would be doing this? I can't figure out why.

 

[Spariduck]

Re: 1981 140hp johnson 2stroke, Keeps blowing bypass cover on right side.

I'm think it has to do with timing but unsure. during high rev approx 3400+ no problems and no leak on gaskets but during idle approx 650 - 1500 sooner or later the gasket will go. this is before I re-timed the engine a week or so ago. since I'm doing a camp job right now and will be home in 2 more days I will see if my issue is fixed or not. Also will be rebuilding the whole engine even if it works without blowing a cover gasket as found a leak in the bottom crank seal.

Ran great after last rebuild, then a puff and seal gone again.. could be on the crank houseing it is hard to tell.