Advice on compression & other problems 90hp vro

[rhcotton]

I just checked the compression on my 1985 90hp vro. It was 120, 120, 115, & 90. Am I in trouble with the one reading 90? My motor has cut off suddenly twice as if the switch was turned off while running at full throttle. It has not cut off on me again but I can only get about 70% power out of it now and it runs smooth. I have checked out fuel tank vent,fuel filter, gas line, changed plugs and they are all firing. Please give me any suggestions or help.

 

[OBJ]

Re: Advice on compression & other problems 90hp vro

rh....was the lower compression readings on the same abank of cylinders? 90psi on the one is getting low compared to the other. Try a decarb and recheck. You may be seeing the early symptoms of a cylinder running lean. Catch it now before it really goes south.

 

[rhcotton]

Re: Advice on compression & other problems 90hp vro

Yes the lower readings are on the same side. The right side standing at the back of the motor. Could you tell me what a "decarb" is? Thank you.

 

[OBJ]

Re: Advice on compression & other problems 90hp vro

Decarb is short for decarbon. This is a process which helps clean out the carbon built up in the cylinders and around ring. Bomby "Engine Tuner", SeaFoam, are examples of products you can use. The process simply involes running the engine on muffs untill at operating temp, then shooting the decarb agent into the carbs. After standing for a while, restart the engine and finish blowing out the decarb. Directions vary with decarb agents so be sure and read the directions.

 

[ob]

Re: Advice on compression & other problems 90hp vro

Another test you can perform is to shoot a little two cycle oil in each of the lower compression cylinders,distributing it around so that it coats the entire circumference of the cylinder and recheck compression.If it improves momentarily it is likely due to sticky rings that are carboned up or scored cylinder walls in which case a decarbonization may help with the sticky rings .If it has no effect ,you may have a leaking head cover gasket.