Motor "surges"...any suggestions?

[ToonGuy]

It's a 1983 Johnson 140. Compression is good and even, starts well, idles well, revs fine. Runs great almost up to 4000rpm, then it "surges". The best way I can describe it is if I hammer down & leave the throttle pegged, the motor will rev/accelerate up to 3500-4000. Then it looses all power, drops at least 1K for a second, and starts reving again. Repeat. It seems to my novice knowledge of outboards to be starving for fuel. Could this be a carb issue? Could it actually be a spark issue? Some sort of timing issue? Or is it a fuel delivery problem? NOTE: I did have a heck of a time priming this thing when I got it together. The tank is mounted approx. 14' from the motor, and the check valve in it seems awfully tight. I did find an old 12V fuel pump laying around and tried that in line but it made no difference (to be honest I don't know if the thing is any good or not, I just know it came on when I powered it up). PS the fuel pump on the motor is new.

[STEVEBRENDA]

I would try a new bulb for your fuel line and check the condition of the hoses for cracks or leaks.

[pontchartraintoon]

Along with the last suggestion, try running it from another fuel source. That's what got me on track to finding my long term issue.

[scfishnman]

Both of my jet skis suddenly started acting the same way. Redline is 10000 RPM. They would only run up to 7000 - 8000 then would surge to 10000 for a few seconds and drop back down to 7000-8000. They also would not idle smoothly and were difficult to start. It turned out to be spark plugs. The old plugs looked good (clean, proper gap, no noticeable wear) but were apparently not producing the necessary spark. It started about 15 minutes of run time later on one ski than on the other.

A previous Yamaha 115hp 4-stroke did the same thing. That is why I suspected spark plugs when the problem appeared with the jet skis. My dealer said the plugs fail internally before they look bad.

Just another thing to check out. Good luck finding a quick and inexpensive solution.

[ToonGuy]

I would try a new bulb for your fuel line and check the condition of the hoses for cracks or leaks.

All brand new....

[ToonGuy]

Good idea with the fuel source...didn't even think about that Perhaps I'll throw a set of plugs in while I'm at it.

[GregF]

Surging screams fuel. Ignition problems will usually be a "miss" thing.

[ToonGuy]

That's what I was thinking. I'm hoping to head to the lake tomorrow after work with a test tank and check that out.

[ToonGuy]

Well, new plugs and running it off a portable tank did not change any thing. I'm done...any one need a brand new tri-toon with an older motor I've got too many irons in the fire I think I'm just gonna sell this one and move on.

[badmoonrising]

At this point, a carb rebuild...

[curtiscapk]

At this point, a carb rebuild...

I agree!

[ToonGuy]

I know, not a big deal especially after I've come this far but seriously I have sooooo many projects going so I'm going to give some one a deal on this one and move on. I already listed it on ebay...