1978 115 Johnson stalls near full throttle

[skifreak]

I just bought this boat and it has been my biggest boat expense yet. When i get it all warmed up and idle around or even go about 10mph there isn't any problems. But as I throttle up I hear an ocassional bang type of noise and then she stalls. I am able to get her started but unable to run at higher speeds. I am thinking i need to rebuild both carbs. Thoughts???

Thanks in advance,
Mark

 

[Daviet]

Re: 1978 115 Johnson stalls near full throttle

Since you just bought it and don't know the history of the engine, I would start with a couple of simple tests.
Check the compression and make sure all cylinders are within 10% of each other.
Check the spark with an air gap tester, spark should jump a 7/16" gap and be bright blue. Make sure plugs are the proper ones and gapped properly.
You might also check the filter in the fuel pump, check the fuel pump flow to make sure it is getting fuel to the carbs.
If all the above checks out, then move on to the carbs.

 

[skifreak]

Re: 1978 115 Johnson stalls near full throttle

Compression is good, new plugs put in fuel pump was just replaced (had a crack). so basically you are confirming what I thought. Carbs need redone. I've done them on past boats so I shouldnt have any issue. I also need to replace the gas tank as the inline filter has gunk in it and I just put it on a few rides ago. Not to mention it is probably close to the original. Thanks for your advice!


Mark

 

[skifreak]

Re: 1978 115 Johnson stalls near full throttle

I just rebuilt both carbs and new gas tank, primer bulb line, fuel pump and it still knocks and will try to stall. I throttle back and i am able to keep her running. She will run at 1/4 - 1/2 throttle with no problem.

Any suggestions? I am guessing now it is power head related.. boy I hope not.

 

[skifreak]

Re: 1978 115 Johnson stalls near full throttle

Does anyone have any suggestions at all?

 

[emdsapmgr]

Re: 1978 115 Johnson stalls near full throttle

Sometimes you'll get backfiring from incorrect ignition firing. A couple of thing to check: 1. I'd double check the link arm from the spark advance lever to the timer base to insure that the timer base is moving properly. If the link arm becomes disconnected, you can get timing that is off. 2. Possible one of the spark plug leads is on the incorrect plug. Double check the color-coded orange wires to from the packs to the coils-then to each plug. [You can double check plug firing by indexing the flywheel for plugs 3,4 (1,2 are already done on that flywheel) and then check the timing for all 4 spark plugs with an inductive timing light.]