87 force 125hp high speed studder

[puffitu]

Hey fellas
My 1987 force 125hp has developed a slight high speed studder or miss. Any ideas as to what it may be? It only does it while wot. If I back off the throttle it seems to clear-

 

[racerone]

Run with a timing light to look for a spark issue.----Drain gear oil to look for metal bits.

 

[Bat32]

I just had a similar issue. I just replaced the spark plugs and must have got a bad one from the factory. Swapped them out again with 4 new ones and problem fixed.

 

[jerryjerry05]

Could be a plug or a loose trigger wire?
Do a spark test while underway?

 

[puffitu]

Thanks to you all-I’ll be playing with it today so I’ll post what I find

 

[puffitu]

Could be a plug or a loose trigger wire?
Do a spark test while underway?

Kinda hard to do by myself, but checked for spark at my shop and all checked out fine…swapped with new plugs under load and no change, still doing it. May have to dive deeper into this issue I recon

 

[puffitu]

I just had a similar issue. I just replaced the spark plugs and must have got a bad one from the factory. Swapped them out again with 4 new ones and problem fixed.

I swapped out with new and problem persists. Not overly too concerned just kinda annoying actually. I generally don’t go wot but if needed I’d like for it to be there without issues. I just hope it’s not something major. It’s got even ok comp although been a while since I cleaned the carbs

 

[topgun3690]

Just throwing this out there....was having similar WOT issues.....did the starting fluid test and found an air leak around the transfer port covers. Replaced the gaskets on all 3 and fixed my problem. Then 2 weeks ago was out and blew the powerhead....bottom cylinder is toast, but that is another story......Since the bottom cylinder port cover was the one showing signs of leaking air am thinking this caused that cylinder to run lean and possibly caused the damage eventually.

 

[puffitu]

Just throwing this out there....was having similar WOT issues.....did the starting fluid test and found an air leak around the transfer port covers. Replaced the gaskets on all 3 and fixed my problem. Then 2 weeks ago was out and blew the powerhead....bottom cylinder is toast, but that is another story......Since the bottom cylinder port cover was the one showing signs of leaking air am thinking this caused that cylinder to run lean and possibly caused the damage eventually.

Thanks Top
I’m not discounting your suggestion as my feeling tells me that there may be an issue with the port covers and maybe even head gasket. I’m planning on diving into it deeper over the next couple of weeks; my work just got crazy so there’s not enough time in the day right now. Will post back however, as this should be a relatively easy fix-just gotta find it lol

 

[puffitu]

Update to this issue as of today. Ended up buying a new head gasket as I never actually checked it on this powerhead. The transfer port gaskets were replaced two years ago so I had a feeling those were not the issue. Took it out today and the high speed hickup seems to disappear and I actually first try starts where as before it took a couple two three times-didn’t see anything wrong with old gasket but it did seem much less flexible than the new

 

[jerryjerry05]

The port cover gaskets, even brand new can go bad with one backfire or studder.
Do the starting fluid test?
Glad its running good.

 

[puffitu]

The port cover gaskets, even brand new can go bad with one backfire or studder.
Do the starting fluid test?
Glad its running good.

I hear ya but for right now I’m not wrenching on it as it’s pretty close to as new running condition probably in 20 years lol. And yes I did the starting fluid test several times

 

[jerryjerry05]

Run it.