Can you foul plugs at WOT?

[Watty]

Hi guys,

Running around the buoys last night at WOT. The ski was absolutely flying (just like they do when they are about to pop!) when the engine just died. I figured I had run it lean so I waited for a few minutes, started it and limped into the beach.

On the way in, I was blipping the throttle, and there was plenty of response there, just like normal.

I took the ski out for another run, as the plugs looked ok, and found that it ran fine with the exception of symptoms similar to that of a fouled plug. I didn't have any spares or anything to clean these ones with, so I just packed up and went home.

After pulling the head, there are some marks on the bore (I'm pretty sure from previous water injestion) but they are not all the way around, and nothing major at all, well what you would expect from a surf boat.

Can you foul plugs from running too rich in the top end causing a stall? I'm running 135 mains with Novi MF 46's on a highly ported cylinder with about 165psi comp (well, 35cc ADA's)

Cheers.

 

[Matt_E]

I am no expert by a long shot....but I think if you're running rich enough to foul plugs, the boat wouldn't be screaming like you describe.
Plug fouling rich is usually performance killer rich, is it not?

 

[Watty]

Yeah, thats what I'm thinking too. I would have thought the performance would drop off, or slowly build up and I've never heard of a WOT run for about 30 seconds foul a plug or 2.

Strange, really strange. I may have to start looking elsewhere?

 

[Matt_E]

If the plugs looked okay, I don't think they were fouled.

 

[hangtime]

If you ran it lean enough to stall it out than you would most likely need a new top end especially at WOT .
I had a 550 that was running so strong the best it ever ran until it seized from being to lean .

Just clean the plugs off you don't need new ones .I change my plugs once a year if that .Actually I replace them when they start to rust from salt .Of course Paul tuned my carbs :biggthumpup:

 

[steve802cc]

Did you do a compression test afterwards?
Any drop?
Steve

 

[jetskiking]

another thing to look at would be the fuel selector. They go bad and make the ski starve for fuel. I can have my selector in the on position and it will give the same symptoms but when I run it on reserve there is no problem. Just a thought.

 

[ANT]

its just a little too lean on the top. If you run at wot for too long and its lean it'll run out of gas. turn out your high speed adjusters a 1/4 at a time on each carb.

 

[SurfCrazed]

another thing to look at would be the fuel selector. They go bad and make the ski starve for fuel. I can have my selector in the on position and it will give the same symptoms but when I run it on reserve there is no problem. Just a thought.

i had the same problem on my ski but it wasnt the selector... ended up being a clogged gas like to the selector. ski at WOT would cut power in and out and then die out of nowhere new gas line fixed it right away!

 

[#ZERO]

It sounds like you may have had a slight lean seizure.

What do the marks on the bore look like and do you have any pictures?

 

[Watty]

I don't but it just looks liek water has been in there and the skirt of the piston has scuffed the bore. I'm going to run it as it anyway, but when I look closely, it looks as though it is only in the rear cylinder.

I've got the carbs off and have cleaned them, so it may fix up the problem. I've raced with this config and never had a problem, and with a stock CDI and 135 mains, I thought this would be more than ok. Thanks god I didn't have the Advent in there!

As for the fuel selector, yes, I've had that one before, but I don't think I've run one of those on my ski's for at least 5 years!!

Cheers

Leigh

 

[jetskiking]

Gotcha. Mines just in there to block up the hole. Just throwing it out there didnt know if you were running one or not.

 

[waxhead]

i would think its was more than likely a overheat

 

[jetskiking]

Yep I agree sounds like a slight overheat to me also. Its not unusual for it to be just in the rear cylinder. Do to the crank flexing and the mechanical timing being slightly retarded on the pto side it can cause the rear cylinder to start showing symptoms first.

 

[sjetrider]

check your fuel filter bro.