intermittent miss, 1975 70 hp

[Paddy60]

Last year I replaced Power pack, Coils and Rectifier on a non running motor I bought. That did the trick and she started with ease.

I re-conditioned the carbs at the same time though they looked clean. Fuel pump rebuilt as well along with all new fuel lines, fuel tank and supply primer hose.

I did not use it much last year but at some point I noticed it randomly miss fire. Hard to describe but smooth running for 5 sec and then the short duration miss fire. No back fire just a RMP/power issue. It appears to do this at all RPMs but you hardly notice it until WOT, then you feel it. The 'toon never has moved so fast, so plenty of power for what I need.

As I was getting the 'toon ready for the first use of the season, I noticed a small spark jumping from the rectifier. Then I noticed it was loose. I tightened it down and no more sparking. I thought that was it but it was still missing here and there as before. Gas tank cap was loose to insure vented.

Any suggestions?

Patrick T

 

[Bosunsmate]

Re: intermittent miss, 1975 70 hp

Sounds more like electrical to me since at all rpms.
Can be hard to track these down.
Try cleaning all grounds
RUn at night and look for a short from HT leads etc

 

[F_R]

Re: intermittent miss, 1975 70 hp

Make sure water isn't getting into the cylinders. Leaking exhaust cover gaskets causes it. Worse than just a misfire, it will destroy the powerhead.

 

[Paddy60]

Re: intermittent miss, 1975 70 hp

Thanks gents

I'll check out both potential issues. Good reason to run the boat at night with living on the lake. I take it the water in cylinder issue would show as a really really clean plug?

Patrick T