Hard to start when warm

[jerryswiss]

1977 Johnson 9.9. Compression about 82 psi each cylinder. Starts great when cold, warm it up on a boat and does not want to start again. Is the compression too low?

[billw]

They usually start in about half a pull when warm. I want to say that I remember seeing over 100 psi compression on them? I don’t own any, anymore, that I could test to compare. Anyway, this may go back to the infamous water tube grommet under the power head, that restricts water flow and cooks power heads, blows head gaskets, etc. This is especially true of salt water motors.

You could check for a flooding carb or a leaking fuel pump diaphragm, which would cause a rich condition.

Ironically, sometimes they used to exhibit hard start only when COLD. That’s usually because somebody put the choke knob in upside down and the choke didn’t quite close all the way. Obviously not YOUR problem; just interesting.

Long live American manufacturing!

• This reply was modified 4 years, 11 months ago by billw.

[fleetwin]

Well, your 1977 model does not have one of the redesigned grommets that causes all the issues, so I wouldn’t replace it unless there is an issue.
These engines have a linkage that limits how fast the engine can be run/started in neutral. It is very easy to adjust, there are two screws on the shift linkage that position the limiting bar.
Like Bill says, the choke linkage is often positioned upside down which will cause the choke not to close completely, but you are not having an issue starting the engine cold, so this seems unlikely.
That being said, don’t be afraid to use the choke to restart a warm engine if it doesn’t start after a few yanks with the choke off.
Once restarted, the engine idles and runs OK? If so, seems like the compression is OK, though the readings seem a bit low.
Try testing the compression on your engine when it is cold, before using it, then rechecking after using it to see if there is a difference.
Post some pictures of your engine and carb/shift linkage if you have further questions…

[Buccaneer]

Check the spark plugs after shut off. Perhaps the head gasket is allowing water
into the cylinder(s)?

Prepare to be boarded!

[jerryswiss]

Thanks for the info. I should have stated my elevation is 4800 feet, so comparative compression at sea level is probably about 87 psi. I know that seems low, but it runs good on the boat. I have other motors with between 90-110 psi. I will check the linkage in neutral, float and fuel pump.

[Author]

Posts