1989 xp100 Evinrude miss at high speed

[yam350yfm]

I just looked at a boat that has a 1989 Evinrude xp100. Overall the motor looks and sounds good but there was a slight miss at high rpm, starts are roughly 3800 and up. The gas is fresh and when the plugs are pulled they all look the same. The current owner has had it for a couple of years. All he has done is change plugs and lower unit oil. It starts fine, idles smoothly, no abnormal amount of smoke. I have not done a compression test yet and I am not sure what the compression should be for this motor. The prop needs to be replaced as it is pretty banged up, otherwise seems solid. I plan to go this weekend and perform a compression test, provided it has not been sold before then.

Any advise on what to look for or what might cause the miss at high RPM. I want to understand what I could be getting into and factor that in before I make an offer.

The boat is a 17' fiberglass fishing boat, and it appears to be the original combination. The current owner used it on the river, the boat has always been fresh water.

Thanks.

 

[omcboats]

Re: 1989 xp100 Evinrude miss at high speed

Could you describe the "miss" more?...How frequent is the miss and how abrupt. Many times what sounds like an ignition miss, especially if it only happends at higher rpm is actually the clutch dog in the lower unit skipping because the dog and forward gear lugs are overly worn. Basically the unit is jumping out of gear for a split second and then pops right back in. It happens so fast that it sounds like an engine miss.

Easy way to check for ignition miss....have someone drive the boat while you use a timing light to check each coil (plug) wire. Light will skip on that cylinder if problem exists.

And yes, do a compression check before doing anything else. That motor should have around 120-130 per cylinder. Main thing is that the compression reading is even (within 15) between cylinders.