Vibration, even with prop off?

[seaox20]

Hey guys, I own a 89' 200 yamaha outboard ran it the other day and ran fine on the way out. Cut the motor off and just relaxed for about half hour. Started it back up to run back in and as a started to get on plane i noticed a vibration in my feet as well as a very low bass kind of sound. I pulled back and tried again, still there. I notice that i cant go full throttle and my rpms are only at 4300 wide open instead of 4700-4800 wide open. I trimmed up and the vibration lessend, but was still there holding me back. The motor is not overheating and runs good. I got home and took the prop off, hooked my ears up, and started the motor. As i increase rpms the vibration gets worse so i know its not the prop and the shaft looks fine to the eye. Anyone had this problem? Ive read alot about similar problems but it came back to the prop. Any pointers would be great. thanks all SeaOx20 out

 

[99yam40]

Re: Vibration, even with prop off?

Probably is a cylinder not firing properly.
I would check compression and spark on all cylinders.If they are good then you have a fuel problem.
While you have the plugs out look at the plugs to see what they look like as that may at least indicate what cylinder has the problem

 

[seaox20]

Re: Vibration, even with prop off?

I checked the the spark plugs, they were oily and nasty so i went and bought new ones to maybe get lucky. I also checked the fuel water seperator and after emptying it into a see-threw container, i noticed a bunch of crud in the bottom of the container. I put it back on and still have the vibration. Could it perhaps be time to re-clean my carbs? Note that the vibration is not there until i get about 23-2500 rpm's then the vibration starts. I dont have any compression testers except the ol' finger and all appear to be doing their job. Anymore Tips?

SeaOx20 Standing by

 

[99yam40]

Re: Vibration, even with prop off?

If it is running fine at low RPMs then compression and spark seems to be good.
Unless that motor has a high speed charge coil that is not providing the proper spark, but it would effect more than one cylinder. But then you said all plugs look bad.

I would be looking at carbs and change filter, if it had trash in it then it could be starting to plug. Is this the on board filter of transom mount unit? Transom one may not be cleanable like the one on motor.
Testing equipment is good to have on hand if you plan on troubleshoot things yourself.