1991 johnson vro

[lil re-speck]

question guys, my Johnson motor runs rough, it shakes quite a bit .once it warms up it runs good. I've had it tuned up and checked. I was told I needed a total rebuild about 4 years ago. but ive been running it since then. the only problem is the rough idling. any suggestions.

[Barnacle Bill]

Start by doing a compression test.

[Scrapper]

and a leakdown test if they can do it.

Anyone can say it needs rebuilt. Compression test and leakdown test will tell the health of the motor.

I would say 85-90 psi minimum. Thats getting pretty tired. Would like to see them all in the 100's. The biggest thing is difference though. No more than a 10% difference. Lets say you have a 3 cylinder engine....125psi, 128psi, 105psi. The 105 is more than 10% out from the other two. This may not seem like much...but you get way less "push" or psi on that particular cylinder. This will cause the roughness you speak of. When it warms up...the engine seals better because of expansion of metal, hence the possibility of the smoothing out. I would rather have less compression and close compression than a low hole and higher numbers. IMHO There are LOTS of other causes of a rough running engine. Get the compression numbers. Then go from there. If you can watch them do it and ask for the particular numbers. I never like the "they are all in range"....or "they are within spec"...answer. I like numbers.

Let us know what you find out.