Engine Surge at WOT

levinmark wrote: To answer a couple questions, the plugs are sooty and not oily, I guess that means running pretty rich. I replaced the plugs last fall during winter layup and have only put about 30 hours on it this year, and no, I do not burn any oil. I check it before every outing and after and looks like just changed it. Is replacing the valve seals a fairly simple process. I know I can handle it with a little guidance if I do have to. Plan is to get out this weekend to see how she goes, I plan on changing plugs and testing each on to test spark. Thanks guys for all the input with this.

Mark, like a few have said I think you have multiple problems. If you aren't burning any oil the valve seals are probably OK, or at least OK enough to ignore for now. So you likely have a combination of ignition and fuel delivery issues.

Since timing is straightforward and can be easily measured, tackle that first. You need to get your total timing into range, 22 degrees just isn't in the ballpark of what you should have. The advance mechanism isn't working correctly.

Once you get the timing solved, you can run it and see where you are, read the plugs again after cleaning them or installing new. It's possible that will do it, that your lack of advance isn't allowing a complete fuel burn since it doesn't ignite early enough in the stroke. If not you can then turn to the carb, but at least at that point you'll know your ignition is working properly.

You won't be able to run it with 16-20 degrees initial, that's way too advanced for idle.

Echobravoecho in a post above recommended really getting into the advance mechanism. It's not hard to get at, and simple enough to see if it's working smoothly. Maybe someone prior to you messed with it, changed out the springs?

Thanks guys, Ill mess around with it and see how it goes Saturday. Ill keep you guys posted

The advance in this application works strictly on RPMS. So, load doesn't matter as far as the dizzy is concerned.

I'll let other's weigh in on whether or not you want to rev it over 3.5k rpms in neutral though. I wouldn't go over 3, but that's just opinion.

Lack of full timing advance won't cause a surge. It will just make it doggy all around.

Inaccurate advance IE. jumping around would cause a surge as it made more and less power but that's unlikely.

Just rev it through the rpm range until it doesn't advance anymore. 3500 rpms in neutral won't hurt a thing. Make sure the timing reading you see advances in a linear motion and it's not "sticky" or "jumpy".

I hear ya Peter, plan on getting out Saturday morning, will update on how things ran

Ha, not a chance! Skiing and footn only. We've had our Ski for almost 4 years now and not once hooked a tube to it and dont plan on ever doing so!

Brian, to answer your questions.
1. When I bought the boat it was sitting in a garage for 3 years without any use. The carb was pretty fouled up and the secondaries were stuck shut/hard to move by hand. At time I didn't know to much (still don't) about these boats. So of course I took it to the nearest dealer where they tried to rebuild it but decided to replace with a new one. After replacement didn't have an issue till next season. So pretty much I have been fighting this since we've had the boat.

2. As far as arching goes, I have not noticed it but will definetly check for that again now that you mention it.

3. Now for the secondaries, I'm not sure but will find out Saturday. Plan on taking doghouse and flame arrestor off, having wife drive while I check things out. Oh yeah, you can add new fuel pump to the list also, replaced that last year.

Any other things I should check, was planning on advancing timing to 32-34 degrees, replace plugs, replace fuel filter, maybe check secondary float (see if its parallel upside down), clean needle and seat again in secondary bowl?

Take the actuator diaphram off - I bet it has a hole in it.

Well i took of the top of the diaghram actuator and the rubber looked ok, didnt see any visible holes. How do I go about testing the diaghram to see if thats the issue? How do I do the suction tube process and what am I looking for?
Thanks guys

I can do that Chris, but I could use a little guidance on this. What should the process be for tracing the vacuum path? How do I test to see if there is a leak? and how do I test the diaghram to see if there is a pin hole in it? Sorry for so many questions, but I have never really dug into any carbs before besides checking float adjustments, so I am definetly a newbie to this process. I'm more than capable of doing so, just need my hand held along the way. Thanks

Well, never had this particular problem either. I usually just take things apart & considering the theory of operation, look for something that has changed.

What have you got to lose?

Mark, you could be chasing a leak or a blockage. Todd W's boat had a similar issue a few years ago and he found the vacuum path to the secondary diaphram was blocked. The circled area on the diagram below.



edit, exactly what Brian above is referring to, either as leak or a blockage there could cause your issue.

Ok, so Ill take the secondary diaghram off and apart, Im assuming I should take some carb cleaner and blow out with compressor?

backfoot100 wrote: You shouldn't have to take the diaphragm housing apart. You should be able to take it off the carb body intact. Get a cheap vacuum pump at AZ or anyplace else. Put a vacuum on the vacuum port and if everything is good, you'll see the secondary rod move like it's supposed to as you pump it up. Hold the vacuum and make sure it doesn't leak. If that's all good don't mess with it. Everything is good as a unit and the problem has to be in the carb body itself.

Vacuum Pump, I guess that would work, I just put the thing to my mouth and use the lungs, seriously you should be able to suck on it and pull in the rod, block it off with your tongue and it should stay in. Then if it passes as Eddie mentions you should move onto the carb body.