70hp idle problems

[Forgotten]

I have a 77 70 hp Evinrude. When it is running low rpms (2000 or less) it "shudders" quite a bit. At first it sounded like it was picking up a cylinder, but it loves to foul the plugs now. I got new plugs and gapped em to .030 and it seemed to run fine for a little while. I noticed if I take the plugs out and spray em with carb cleaner or take the motor cover off and rev it up a little it will clear the fouling off the plugs and be okay for a little while longer. Any ideas as to what could be the cause of this?

 

[Forgotten]

Re: 77 70hp low rpm problems

Re: 77 70hp low rpm problems

Oh and I did a compression check and it has about 135 on all cylinders and the spark seems good on all too

 

[Forgotten]

Re: 77 70hp low rpm problems

Re: 77 70hp low rpm problems

any suggestions?

 

[Forgotten]

Re: 77 70hp low rpm problems

Re: 77 70hp low rpm problems

took the fuel pump off and one of the little flat pieces of spring steel wasnt sitting tight on the housing. I turned it over and its sitting tight now. The large diaphram seemed a little stiff, but the little diaphram was nice and rubbery. The thing was pretty clean inside. The little plastic discs that fit against the diaphrams had that old plastic look to em but other than that seemed fine.

Think this will solve my problem?

 

[Daviet]

Re: 70hp idle problems

You mentioned that if take cover off and rev it up it seems to clear up. What happens if you run the engine with out the cover off for a long period of time. If you have a blown base gasket it will fill the cover with exhaust. The engine needs fresh air to run properly.

 

[Forgotten]

Re: 70hp idle problems

Havent tried that yet

 

[Forgotten]

Re: 70hp idle problems

That wouldn't explain the jump in rpm and the frequent plug fouling though would it?

 

[bowman316]

Re: 70hp idle problems

maybe you have too much oil in your fuel. try putting no more than 2.56 ounces of oil per gallon of gas.

is any oil leaking down the side of the lower unit, from the power head? may be A bad head gasket

 

[Daviet]

Re: 70hp idle problems

Just thinking, if you have a blown base gasket, it fills the engine cover with exhaust, and replaces fresh air with exhaust. If the engine does not get the proper air/fuel ratio it will not run properly, Sometimes this is worse at lower speeds because of air flow into the cowling. Also it is very easy to try.

 

[bowman316]

Re: 70hp idle problems

is a base gasket the one that goes on the cover to the carbs? never heard of that before

 

[Daviet]

Re: 70hp idle problems

The base gasket is between the power head and the exhaust housing. If blown the engine cover will fill with exhaust.

 

[Forgotten]

Re: 70hp idle problems

Ok, tried taking the motor cover off and no difference. I dont have any oil leaking from anywhere either, so I guess the gaskets are in good shape. I have been mixing my oil at a 50:1 ratio like the manual told me to do and was using Citgo 2 stroke oil

 

[Forgotten]

Re: 70hp idle problems

Oh, and I ran the battery down to almost dead with the trolling motor and had to pull start it and it seems like this problem started shortly after that, and I think the battery I have may be on the verge of becoming junk

 

[Forgotten]

Re: 70hp idle problems

Does Chemtool mix with 2 stroke oil? This would be an easy way for me to give the carbs a cleaning, but I don't want the motor to seize up because the chemtool removed the oil from the crank

 

[Forgotten]

Re: 70hp idle problems

Anybody know?

 

[Forgotten]

Re: 70hp idle problems

Any chem tool 2 stroke oil experts out there?

 

[oldsub86]

Re: 70hp idle problems

We have a 78 Johnson 70HP. The fuel pump started to leak and we had to replace it. The bonus was that it now idles much smoother. No stalls when shifting gears etc.You might want to look further at the fuel pump. If it has been replaced with the newer version you can get a kit to rebuild it for about $20. If it is original, you will likely have to replace it with the newer style like we did. Cost was about $100.

Randy