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Discussion Starter · #1 ·
Few months ago I had THIS problem (engine rockets to 4000rpm while giving NO throttle).

And it was solved after changing both spark plugs for new ones. The engine ran perfect then.

Now, after 2 months standing still I started the engine again, and guess what.... the problem has returned


Now I'm about to buy and change the spark plugs again, but it is making me wonder: can ignition coils (or some other electrical part) ruin spark plugs, even while the engine has run only 15 minutes since the first spark plug-change???
 

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I would suspect some kind of carburetion issue rather than the spark plugs. Like a binding throttle cable when the handle bars are turned a certain way. Another thing that can make the engine race is a vacuum leak.
 

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Discussion Starter · #3 ·
That's what I thought too. So I cleaned the carbs with no result. Then I changed the entire carbs for new ones. No luck. The vacuum leak I'm still not sure about. I could recheck the L+R insulators. I wonder: can a vacuum leak also be on the inside of the engine?
 

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Discussion Starter · #5 ·
Thanks Ronster. I ckecked the butterflies, they're fine.

What I did NOT do yet, is firmly tighten both throttle cables on the carb's side. But I don't know if that can be the cause of the problem. If that ís the cause then I suppose I should see the whole throttle mechanism on the carbs turn quite a few degrees when the engine rockets to 4000rpm. But I'm almost sure that that's not happening.



Another thing that crossed my mind:

I am wondering if it is possible that both axes (shafts) on which the cam chain runs are perhaps 1 or 2 teeth out of sync. Could that cause a similar behaviour?
 

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Loose or binding throttle cables could definitely cause your problem. Under no load the engine can rev pretty high with only a small change in throttle position. 3 or 4 degrees at the carbs would really rev it. I don't think cam timing would cause uncontrolled reving of the engine. it would cause a loss of power on the road or engine damage if very far off.
 

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Discussion Starter · #8 ·
Thanks for this. I'm gonna get some help next Saturday. The guy's bringing in a couple of coils and a cdi. Hopefully we're gonna be able to find out what's wrong.



To be continued.



Thanks again.
 

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It seems extremely unlikely that erratic or unexpected acceleration could be electrically related on these machines. Racing engines sometimes is indicative of fuel starvation, I'd check the fuel flow from the petcock and the fuel hoe too. Clearly, changing the spark plugs the first time did not actually have any substantial effect on this problem. Also, look at or replace the o-rings on the insulkators (intake manifolds) to head connection. If these are original, they are likely brittle and cracked, and will lean out the mixture.
 

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Discussion Starter · #10 ·
Thanks RichNCR. I might try that tonight. I don't have the o-rings in stock yet but perhaps I could try it by wrapping some duct tape around the intake manifolds and see what happens.
 

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I hate to disagree but it would be rare that an ignition coil could in any way affect a spark plug unless it was putting out way too high of a voltage that was causing the insulators to break down. Even this would be unlikely as once a properly gapped spark is started across the gap it really can't go any higher than what the gap will allow.



Using the wrong plugs or gaps can be a major problem though, as can using plugs other than the manufacturer's recomendations.



I can't argue with the iridium plugs in the least, being able to hold a more consistent gap in an engine that puts a decent strain on the plugs (10:1 compression and lean burn) is a definite plus. I sure wish AC-Delco would make a 41-9xx series for ths bike, I'd love to try them out as those double platimum plugs would far outdo the iridiums in our modified GTPs with the superchargers. Some say the tiny amount of platinum which comes blasting out with the spark tends to serve as a catalyst that helps the fuel/air mixture ignite more evenly but there's absolutely no scientific proof to this and nobody ran any true tests to explore the matter. Oddly enough NGK made most of the AC-Delco 41-9xx series but they only come in certain sizes, and unlike NGK's numbering system there's little revealed by AC-Delco's numbering so figuring out if there was a cross might tend to be an impossibility.



About as far as I've got the NGK plugs our bikes use are a lot colder heat range than most AC-Delco plugs produced. We use an 8 on NGK's heat range whereas the stock plugs for most cars that use the AC-Delcos would be equivalent to the far hotter 4, 5 or 6 level.
 
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