1977 70HP dies on acceleration

[rude70]

Previously my Evinrude 1977 70HP started fine and after about 20 minutes of running, it would die when shifting from idle. I would have to up the revs with the warm up lever and shift very quickly into forward to half or more throttle. This happended on the past few outings. Yesterday it was running well and lost power at 3/4 throttle. Eventually it started ran a bit rough and idled. Every time I shifted into gear it died. Got it home, ran it on the muffs and it sounded rough. Pulled the plugs and no1 was black, 2 & 3 were ok. Could this be a coil or power pack problem or something else?
Thanks

 

[HighTrim]

Re: 1977 70HP dies on acceleration

What plugs are you running?

What is the compression of the top cylinder?(Sorry but Im guessing it is going to be low)

When was the carb last rebuilt/cleaned?

 

[tashasdaddy]

Re: 1977 70HP dies on acceleration

compression all cylinders?

 

[rude70]

Re: 1977 70HP dies on acceleration

The plugs are champion QL77JC4. I bought the motor second hand about a year ago and I only know that it had a new stator fitted. Don't know when cards were rebuilt if at all. I will get a compression tester today and test
Thanks
Rich

 

[rude70]

Re: 1977 70HP dies on acceleration

The compression test was not good, 25-110-105, one pretty sick engine, although it still fired! Is it worth re-building an engine of this age? I was intending to pull the head off and inspect the cylinder. If I re-build will all pistons have to be renewed along with the big end and main bearings? Not a good start to our Aussie summer!

Thanks

Rich

 

[HighTrim]

Re: 1977 70HP dies on acceleration

I wish that it would have been something different for your sake.

Open her up and lets see what is going on before proceeding. Post pics if you can.

 

[rude70]

Re: 1977 70HP dies on acceleration

Hi Chris (High Trim), I took the head off to reveal a badly pitted no.1 piston. Pics of piston and pitted head are attached. The cylinder has some of the piston fragments attached. No2 sylinder looks fine, no.3 has a minor mark that is visible and can be felt with your finger nail. Any ideas what could have caused the piston pitting/destruction? All of the other parts on the engine (gearbox carbs etc) appear to be fine. I will continue to strip the engine and take it to a shop to be re-bored. I notice that you can get 030" pistons, I guess the head can be polished to remove the pitting! What is the standard bore size? What is your opinion on fixing this babe? Any help/advice would be appreciated

Thanks

Rich

 

[HighTrim]

Re: 1977 70HP dies on acceleration

There are guys on here that are extremely experienced on rebuilding these, so I will leave it in their able hands. They will be able to guide you better than I could.

 

[rude70]

Re: 1977 70HP dies on acceleration

Ok, thanks.

 

[tashasdaddy]

Re: 1977 70HP dies on acceleration

you have a PM.

 

[rude70]

Re: 1977 70HP dies on acceleration

What is a PM please?

Thanks

 

[HighTrim]

Re: 1977 70HP dies on acceleration

What is a PM please?

Thanks

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