78 115 johnson low #1 compression

[kylake254]

motor will run great at wot,slow down it starts to miss put in netural it dies.have to choke some to start,put in gear it dies.if i put it gear fast to keep it running it misses,open up all the way it runs great.also did compression test #1 cyclinder is at 10,rest are around 92-95.someone told me i could have a stuck valve or broken spring.just can not figure out why it misses in netural bad.but running at wot it runs good.

 

[ezeke]

Re: 78 115 johnson netural it dies wot runs fine

Re: 78 115 johnson netural it dies wot runs fine

It misses because you are trying to run on three cylinders; keep doing that and you will need to find a scrap metal dealer.

You need to remove the cylinder head on the bank that has the low compression and see what the situation is. It is very possible that you only need a new head gasket, but it could be more severe.

BTW, advise your consultant that two stroke engines don't have valves.

 

[kylake254]

Re: 78 115 johnson netural it dies wot runs fine

Re: 78 115 johnson netural it dies wot runs fine

ok pulled head off #1 cyclinder is all black & so is piston.#3 looks good nice and clean.#1 piston has some dings and a small like rounded or bump on the top side.also is there supose to be a little play in piston inside cyclinder walls?also took the part on top of head off it looks like water jackets on top of head.the gasket was torn also a bunch of like gray milky stuff inside the groves.tried to download pictures but did not work.

 

[kylake254]

Re: 78 115 johnson low #1 compression

about to give up should i just look for a rebuilt motor on rebuilt head?

 

[tx1961whaler]

Re: 78 115 johnson low #1 compression

I'd try putting a new head gasket on first, if the cylinder wall looks OK.

 

[kylake254]

Re: 78 115 johnson low #1 compression

had new head gaskets put on a year ago.could it be that the cover i pulled off the head with bad gasket, and gray milky stuff not letting enough water go threw it to cool head and make head gasket blow?the cover i am talking about is on top of head and has like channels in it to let water go threw it.i think that is what it does.

 

[tx1961whaler]

Re: 78 115 johnson low #1 compression

If you suspect that it has overheated, the head may be warped a bit. You can true it by taping a sheet of fine sandpaper on a sheet of glass and sanding the head until the whole surface is shiny.
The water jacket cover gasket needs to be replaced after all of the passages are confirmed to be open..

 

[ezeke]

Re: 78 115 johnson low #1 compression

The water cover has a chalky material between it and the water cover gasket; the water flows between the gasket and the cylinder head, so it likely has nothing to do with your current problem.

The excess carbon is probably the result of long-term lack of de-carbon treatment or lugging, but needs to be dealt with in any event.

You should remove the bypass cover beside the bad cylinder and see if you still have rings on the piston.

If the rings are OK, , replace the cylinder head gasket and de-carb the engine. Then you can do another compression test.

 

[wilde1j]

Re: 78 115 johnson low #1 compression

Are you talking about grooves in the cylinder wall? If so, rebuilding or a rebuilt PH is in order.

 

[tx1961whaler]

Re: 78 115 johnson low #1 compression

Are you talking about grooves in the cylinder wall? If so, rebuilding or a rebuilt PH is in order.

He's talking about the water cover.

 

[wilde1j]

Re: 78 115 johnson low #1 compression

In that case, he needs to pull the head and examine the head and the cylinder carefully for damage.