I got a Honda 90 thats about 2 yrs. old. The last couple of times my boy tried to ride it he had problems getting it started. We tried pull starting it, and it finally started after a long time, but seems to run crappy, no power. I pulled the plug and put my finger over the hole and it seems low on compression. I'm not sure what a small motor like that has but it seemed pretty low. I tried to use my compression tester on it but I didn't have the right fitting for that size of hole. So my question is, does that motor have a decompression device on it that might be malfunctioning or am I just sol. I was just wanting to make sure that before I go tearing the motor apart that I didn't miss something simple. Does anyone know for sure how many lbs. of compression it should carry. I'll check that for sure before anything else. Thanks DennisC

 

It does not have a decompression device to malfunction. Not sure what normal compression should be. Have you checked the carb? I think I'd be tempted to look for a crudded up carb or a stuck float before tearing the engine apart.

Jaybee

 

Try adjusting the valves.

Simple and easy.

Just a thought.

SB.

 

honda online spec manual says 178 psi compression. make sure you hold the throttle wide open when checking. if you don't have a compression gauge, you should not be able to keep your finger over the spark plug hole while cranking. it should blow your finger off pretty easily. if it seeems low, do what smb05 said, adjust the valves. spec is .05mm or .002" for both intake and exhaust. its easier to adjust the exhaust valve w/ the machine standing up on the rear grab bar.

 

Where can I find a online manual thats explains how to adjust the valves? I've rebuilt several 2 stroke motors but this will be my first 4 stroke. What would the carb have to do with it? If it was a carb issue wouldn't it run rough? It doesn't backfire at all. I'm sure its a compression issue, when you hold your finger over the hole it doesn't even have enough compression to blow your finger off the hole. I was wandering if the exhaust valve could be stuck open. Thanks Dennisc

 

I agree with the suggestion of adjusting the valves. A valve not seating will cause low compression.
Try that first and then go from there.

Unless that 90 was well....and I mean well....abused....there should be no problems with that engine.

 

The first thing I would do is replace the spark plug with a new one. The only time my trx90 failed to start was when it was three years old so I replaced the original plug with a new one and it ran fine after that.

 

And also make sure you have the spark plug connected to the spark plug wire and grounded could burn the coil CDI out and make sure your not the ground [img]i/expressions/face-icon-small-blush.gif[/img]

goodluck