spark plug gap???? Are these compression readings good???

[tiftonk9]

What is the gap measurement for spark plugs on a 1988 johnson 120?

Also, My compression readings were 120,115,120, and 110. Is this good?

 

[ezeke]

Re: spark plug gap???? Are these compression readings good???

They are OK numbers. You might get them closer together and improved somewhat by a decarb as described in the engine FAQ forum.

http://www.iboats.com/bbboard/bbBoard.cgi?a=viewthread;fid=36;gtid=1035555

Chart Gap is .03. Most use .04 if they troll a lot.

http://www.boatsetup.com/SparkPlugChart.pdf

 

[WillyBWright]

Re: spark plug gap???? Are these compression readings good???

probably .040

 

[tiftonk9]

Re: spark plug gap???? Are these compression readings good???

thanks for the help. I am going to clean my carbs in the very near future. Will I still need to decarb after that? I'm new at this so any help would be appreciated.

 

[rickdb1boat]

Re: spark plug gap???? Are these compression readings good???

Yes, do the decarb also....

 

[ezeke]

Re: spark plug gap???? Are these compression readings good???

If it were me, I would decarb first. The purpose is to get any carbon build up out of the combustion chambers and pistons, rings etc.

After that, you will want to check the recirculation valves to make sure that they are clear and functioning properly.

 

[tashasdaddy]

Re: spark plug gap???? Are these compression readings good???

decarb. plugs are Champion QL77JC4 or L77JC4 gapped at .040 if use mostly for high speed they recommend the non gap plug QUL77V or UL77V.

 

[Vic.S]

Re: spark plug gap???? Are these compression readings good???

If it runs ok why do a decarb (or even a carb overhaul for that matter.)

If it aint broke dont fix it!

 

[OBJ]

Re: spark plug gap???? Are these compression readings good???

A decarb is just good preventive maint Vic. Keep the carbon down and your less likely to have sticky/stuck rings. As far as the carb overhaul....maybe he just don't know the last time it was done. Sure can't hurt....d

 

[tiftonk9]

Re: spark plug gap???? Are these compression readings good???

I posted a thread about my motor running at wot at around 3000 rpms at around 5 mph it eventually fixed itself and got up to 5500 to 6000 rpms at 50 mph. I just bought this 18.6 ft cajun bass boat and as earlier stated the compression readings were close so i didn't believe this to be the problem. someone answered a previous thread and told me that it sounded like the carbs needed cleaning. I thought it might be the feul pump but he stated that the rpms wouldn't fluctuate the way they do.