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Misfire at WOT

Old 06-21-2017, 08:58 PM
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Misfire at WOT

Hi Superhawk forum,

Recently my superhawk has shown a weird symptom. Sometimes it will jerk or stutter with WOT especially in the higher RPMs. Any ideas to what this can be?

I would appreciate any opinions that any of you have to offer.

Nathan
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Old 06-23-2017, 07:08 AM
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Welcome to the forum.
Give us more information: total miles, service/or not history, has the bike been unused for a length of time before this problem, etc.
You have a bit of checking to do. Start with a simple pulling the plugs and inspect. This might lead you to the answer first. Checking coil winding and plug lead resistance would be another simple check.
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Old 06-23-2017, 02:13 PM
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not that this would be your issue... perhaps a fuel delivery issue? i just went through this with my ktm 500. fuel filters were bad. they would allow enough fuel through at small throttle openings and the bike ran smooth. then i'd open the throttle up for jollies and the filters couldn't flow enough fuel and it would cut out. new filters and the good times are back
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Old 06-23-2017, 05:44 PM
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I just checked yesterday and I found a nasty vacuum leak in the front carb boot. Ordered a new boot and I'll replace it when it gets here on monday. I also ordered new spark plugs because the current ones are on the way out. Hopefully those two things will fix the issue.

Vacuum Leak:

Thanks for the help so far. I'll post an update come monday.

Some info: Bike is at 24k miles, just did the valves, changed oil, and changed air filter from BMC to HIFLO. The carbs have a jet kit (dynojet). 45 pilot (both), Keihin mains 195 rear and 190 front. The needles are at the highest setting (was surging at second to highest setting). Exhaust is Two Brothers
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Old 06-23-2017, 06:00 PM
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i hope you get it sorted out
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Old 06-26-2017, 09:36 PM
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Update

Hi again,

I tried changing the front carb boot, but the vacuum leak is still there. Seems to be worse when i spray up towards the top of the front carb near the throttle area.

Could the throttle shaft possibly have a vacuum leak? If so, how can I fix it?

Also, where else should I check for leaks?

Also, I figured out the WOT issue. I think the bike is running too rich. Firstly, it only happens when the bike gets hot. Also, I recently switched from a BMC race filter to a HIFLO, which I hear is more restrictive. I never had any issues with the BMC and WOT.

However, the vacuum leaks persist and I definitely need to get that figured out. My superhawk as always run quite rough down low, and I think that fixing the vacuum leak might fix that.

Nathan
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Old 06-27-2017, 06:51 PM
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Another Update

I cut off the plastic restrictor from the hiflo filter and removed the restrictor bar from the airbox. The bike stopped stuttering for the most part and now it pulls hard again. Thanks for the help. Safe riding!
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Old 06-30-2017, 03:33 AM
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I have done the same to my air filter every time I replace it.

I use hi flow as well.

This mod is referred to as the Bernie Morgan mod !

Made my bike smoother. Now get on it and ride.
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