Engine prob, carbs?

[Rapson]

I have a 1987 Yamaha 140Hp 2 Stroke with a intermitent engine prob.

Starting out from the ramp go to full throttle with no probs. Get to fishing grounds and shut down for about an hour. Start the engine and get to about 1500rpm when engine starts to struggle, if i continue to push throttle it dies. Does sound like one cylinder isnt firing. Continue along for a couple of minutes and missing cylinder comes good and can push to full throttle no probs. drop to idle and then to full throttle no probs.

Bit of history. Bought boat about 4 months ago. Fuel filter was full of crap so replaced fuel filter, fittings, filter on engine and removed and drained fuel tank. There was probs with electrics so engine had to be stopped by flicking on the choke, probs have been fixed now. New spark pligs installed.

Any tips on where to start trouble shooting would be appreciated.

 

[rodbolt]

Re: Engine prob, carbs?

the 140 was an international model and I have only delt with a few.
its very similar to the US market 130.
test spark, test compression then fix the fuel system.
that crap is most likly residing in the fuel pump and carbs now.

 

[Rapson]

Re: Engine prob, carbs?

Cheers rodbolt, thats what I was thinking, I will give the carbys and pump a good clean this arvo and see how it goes.

 

[Rapson]

Re: Engine prob, carbs?

Pulled the fuel pump, filter and carbies apart this arvo and gave them all a good clean with a carbie cleaner and some compressed air. Once reinstalled the engine started first go every time, which was not the case before. Wont know for sure until I do a test run in the water but it is looking good to have fixed my problem.
Thanks for the input guys.

 

[Rapson]

Re: Engine prob, carbs?

Headed out today and not much difference. The engine was running a lot better so cleaning the carbs and fuel pump did do something but didnt fix the problem. Gave the plugs a bit of a scrub before to so I might replace them as well.

To top it off conditions and fishing were rubbish!

Oh well, still beats work!

 

[Rapson]

Re: Engine prob, carbs?

Update. I have dismantled the carbys and cleaned, new spark plugs and a new inline filter. Took her for a test run with a seperate fuel tank and line and there is still no change.

Gets to about 1500rpm and if I push the throttle any further she dies. Let her go for about a minute and then slowly push the throttle it sounds like a cylinder isnt firing and then kicks in and she runs fine. Slow down to idle and then can push the throttle flat out with out any dramas.

Should I now be looking at electrical?

 

[rodbolt]

Re: Engine prob, carbs?

electrical is simple to test.
even without a DVA.
would rather have a DVA but.
simply use your DVM, compare each ign primary output and see if one is very different from the rest.
then go fix the fuel issue .
its possible you have ign issues and its quick and easy to test.