What issues can cause surging?

[majorramifications]

I have ’63 Gale 15 HP 15D15B outboard that is surging at 3/4 throttle to WOT. It is a VERY rythmic, smooth surge that starts somewhere above 1/2 throttle and becomes more pronounced as I go to WOT. Thinking it was a fuel supply issue, I gently squeezed the primer bulb (which was firm) in the fuel line, no change. Then I FIRMLY squeezed the primer bulb and the motor conked out as though it had way too much fuel, as expected.
It starts easily, idles smoothly, and runs great at full throttle for a minute when it is cool, but then it starts surging and keeps surging until I take it down to half throttle.

The fuel pump has been rebuilt by me but I don’t think this is the issue due to no change when gently squeezing the bulb.
I suspected the fuel tank/line, but again, gently squeezing the bulb (which was already firm) made no difference.
The carburetor has been rebuilt by me. I would suspect it, but I can adjust the high speed mixture from too lean to too rich, and it the motor reacts as expected except that the surging continues throughout.
The ignition system has been gone through by me but it surges very smoothly, not abruptly like it did when I was losing spark on one cylinder.
I was having an issue with rough surging because of a bad lower crank seal, but I changed both crank seals and it runs great for a minute and then starts smoothly surging.

Could this possibly be a temperature issue? The water pump was done by me and it has plenty of flow out the back. The flow is hot, but I figured that is because there’s exhaust mixed in with it. I’m pretty sure this motor did not come with a thermostat, but could plugged water passages cause surging like this?

I am perfectly willing to re-do anything that I already did, I will not be insulted in the least if you say I must have done something incorrectly, but I just don’t know what it could be. Any help is certainly appreciated.

Greg

[Anonymous]

What number spark plug are you using?

[frankr]

You make it very clear that it is a smooth surging. If it were not for that, I would suspect a worn clutch dog is causing it to jump in and out of gear. But that would be a definite “clunk” feeling, not a smooth surge. OK, just for laughs, rest your hand on the shifter lever and see if you feel a wiggle each time it happens.

[fisherman6]

I have had crankcase leaks cause surging. I worked on a 4hp Evinrude that had a rhythmic surge at WOT and sometimes at lower speeds too. That one had a casting flaw in the crankcase. Once that was fixed the surge went away. Just thinking of possibilities. Look for any places under the cowl around the powerhead that may be getting dampened by fuel mix.
-Ben

OldJohnnyRude on YouTube

[fleetwin]

Well, first I would like to know when the last time the engine ran normally, or has it behaved like this ever since you have owned it… Next, I’m wondering how it idles….It would seem like any sort of crankcase leak/seal issue would show up more at idle/low speeds than at higher speeds. After re-reading your post, you mention the engine starts and idles just fine. You also mention changing both crankcase seals, how did it idle before the seals were changed?
Next, I am wondering if this is one of the Gales with the combination of remote and integral fuel tank. If so, I would be suspect of the fuel lines/plumbing on the engine. Pumping the fuel bulb won’t necessarily overcome some sort of obstruction in the fuel lines/connector or carb…You must have a heck of a grip, I surely have never been able to overcome the carb/float with the primer bulb… Do you have the float level set correctly? I have heard of floats being installed upside down, but don’t know if that is actually possible. What type of filter does the fuel system have? Does it have one of those “sintered filters” in the glass bowl under the carb? If so, remove it and retest. Have you tried a different fuel tank/line? What about the choke linkage? Some of these engines have funky linkages, perhaps the choke valve is fluttering slightly at WOT.
Your symptoms surely seem like some sort of fuel restriction issue, but anything is possible. A sloppy mag plate could cause WOT timing to vary just a bit. Does this engine have a stop switch? If so, unplug the leads and retest. I am assuming that you have checked compression and it is OK. A water leak into the crankcase/cylinder(s) could cause an issue like this, but this is a very remote possibility. Try running the engine at WOT and let it misbehave for awhile, then shut it right down and pull the plugs to see if they both look the same…
Feel free to post some pictures as well…D

[chris-p]

I too believe it is a fuel restriction. Is the vent open on the tank?? Try taking the cap right off, does it go away?

[fleetwin]

chris-p wrote:

I too believe it is a fuel restriction. Is the vent open on the tank?? Try taking the cap right off, does it go away?

Excellent suggestion indeed….Never overlook the simple stuff…

[majorramifications]

I forgot to mention, that yes, the vent was open, and yes, I did remove the fuel fill cap, and also I removed the engine shroud, thinking it may be breathing it’s own fumes, but none of that made any difference. The fuel lines under the hood are all new.

As far as how it ran before, this motor has NEVER run correctly for me. When I first got it, it didn’t run at all, and I went through it and did all the usual stuff. I had a problem where it would only run on one cylinder, and then the other one would kick in and nearly toss me out of the boat. That was because I had installed one of the new plug wires a little crooked into the coil. Then, it would either have a rough surge or run only one one cylinder until I changed the crankshaft seals. It finally starts easily and runs smoothly until it has run about a minute.
The choke butterfly is normal, not able to close when the choke lever is pushed in.
The plugs are Champion J4C and I was planning to replace them as all that running on one cylinder fouled the lower one.

• This reply was modified 5 years, 5 months ago by majorramifications.

[fleetwin]

Well, it wouldn’t be the first time a bad plug has caused a strange problem…Does this engine have a thermostat? If not, you may want to use the champion J6C instead. OK, you loosened the fuel cap and ran without the engine cover, good simple things to do for sure. And, the choke linkage is not causing any issues….
Have you tried a different fuel tank/hose? Where is the fuel filter(s) on this engine? OK, was afraid you were going to report that the engine has never run correctly for you since you purchased it…There must be some hidden ghost here, hopefully a simple one…
Try running the engine at WOT for a few minutes, then shut it down and inspect the plugs….
Does this engine have an integral tank as well as the separate tank? Post some pictures if you can….

• This reply was modified 5 years, 5 months ago by fleetwin.
• This reply was modified 5 years, 5 months ago by fleetwin.

[bobw]

As Ben noted, surging can be caused by crankcase leaks or some other source of air leaks, perhaps in the fuel line or a bad carburetor or reed plate gasket.

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[Author]

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