One low cylinder? How bad is it?

[Cucaracho]

Johnson 110hp 1989.
I have been having problems since I got it about 6 months ago. The boat had a full tank of fuel for maybe 10 years so the first thing I did was to clean everything from the tank to the carbs. The fuel lines kept clogging with fuel gunk and I cleaned the tank again, and changed everything again, right now I think everything is gunk free.
The motor at first it runs fine and after a while it boggs down and then it revs up again. Changed fuel lines, filters, used sparate fuel container, cleaned the carb, new fuel pump...........and the same results.
Did a compression test, on a cold engine, yesterday and the results are:
1.- 100, 2.-100, 3.-100, 4.-85........could the low compression on the fourth cylinder be the cause for bogging down? Today I am going to decarb the engine and do the same test again and hope for better results.

Any advice? would really help because I am out of options.

 

[tashasdaddy]

Re: One low cylinder? How bad is it?

decarb may help. # 4 is 15 % down rule of thumb is 10%. if you have new fuel lines, i would do the decarb, and reclean the carbs, especially the jets and float needle and seat. then do a link n sinc. http://forums.iboats.com/showthread.php?t=244013

 

[Cucaracho]

Re: One low cylinder? How bad is it?

Thanks for your advice, I sill decarb and service the carbs this weekend.
Sorry but I am new to this terms, what is "link n sinc"...........timing?

 

[Silvertip]

Re: One low cylinder? How bad is it?

I would be real concerned about continuing to run this engine until you get the surging taken care of. Anytime an engine does this it is a symptom of lack of fuel. Lack of fuel means the engine is running lean. Two strokes don't like that because lack of fuel also means lack of lubrication which may very well be the cause of one cylinder being down on compression as that cylinder may be damaged (as in scored). If you didn't pull the fuel pickup in the tank, I suggest you do so and check for obstruction. If you haven't removed the anti-siphon valve and replaced it with a barb fitting for test purposes I suggest you do that. I also suggest you rebuild the carbs. Cleaning the float bowl is does not constitute a rebuild. Carbs need to be totally disassembled, soaked, blown out and every passage and jet inspected for debris. If that much trash has been sucked up by the engine, there is a good chance the carbs are trashed as well. Continuing to run a lean running engine will have you looking for a rebuild or a new engine. Link & Sync is the very precise process of synchronizing carburetor opening with ignition timing. You must start this process at the beginning and run through it to the end. If you start in the middle and adjust one thing you muck up everthing ahead of that and the results you are looking for on that particular adjustment may not be correct. You need a factory service manual for this. It is far too long and detailed to go into here.

 

[Cucaracho]

Re: One low cylinder? How bad is it?

I just ordered the carb kits.......next week I will get into the carb rebuilding.
Wont run the engine until I rebuild the carbs, don't want more damage.
Thank you.