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Discussion Starter #1
I have a stock 929 motor I've put into a single seat sand rail. It has an intermitent bad stutter around 7000 rpm under load. its so bad when it happens that it acts like a really crappy rev limiter and wont let the motor rev past it, but its intermitent and only under load. I never ran the donor bike and dont know anything about its history.

Any ideas?
 

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Are you running the stock exhaust system, airbox and filter?
Do you have a Power Commander on it?
 

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Discussion Starter #3
I'm running the stock air box, k&n filter, no power comander, I made my own header with primaries within about an inch of stock, they go to the stock htev ? valve then to an aftermarket canister. Just to reiterate this is a major stutter when it happens the car doesnt ever get through it, it just sits there stuttering and cutting out.

I dont know a lot about that valve in the middle of the exhaust but perhaps it is malfunctioning? is 6-7k rpm the range that the valve opperates in?
 

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You said it's intermittent, only under load and _when_ it happens it's bad - so I read it as not being all the time :)
Is there good airflow to the air intakes?
Is there any backfiring when it does it?
Are you running a tach to confirm it's not hitting the limiter?
Are you running a dash to see if it's throwing any codes?
Is the HTEV working?
Is the flapper still in the airbox?
If it is, is it opening at 8000rpm?
Can you try a stock exhaust system on it to rule that out?
 

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When my HTEV broke before I locked it open there was a TERRIBLE stutter like you are talking about between 5.5k-6.5k and it was flat as Kansas from 5k-6k when it didn't stutter. Id say its prolly an issue with exhaust flow somewhere. Valve works at 3k and 8k btw
 

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Discussion Starter #6
You said it's intermittent, only under load and _when_ it happens it's bad - so I read it as not being all the time :)
Correct it is not all of the time
Is there good airflow to the air intakes?
yes stock airbox nothing restricting it
Is there any backfiring when it does it?
no back firing
Are you running a tach to confirm it's not hitting the limiter?
Yes I'm using the stock dash
Are you running a dash to see if it's throwing any codes?
I'll check for codes
Is the HTEV working?
I've been reading the forums and think I need to check this, it rotates one way at 3k and then the other way at 8k right?
Is the flapper still in the airbox?
yes
If it is, is it opening at 8000rpm?
I dont know I should check
Can you try a stock exhaust system on it to rule that out?
no its gone

Should I disconnect the htev then lock it so each primary goes strait through and see if that fixes the stutter problem?


Thanks for all the info!
 

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I would give it a try for sure.
The flapper in the airbox probably won't help the topend if it's staying closed at 8,000rpm.
If it's not happening all the time though I can't imagine it being either of these.
Does it suddenly occur when it's been running okay for a while or is it a problem that only occurs from start up?
 
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