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Old 05-10-2013, 06:20 PM   #1
MKJ OP
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Nuke it

MKJ screwed with this post 05-14-2013 at 06:18 PM
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Old 05-10-2013, 09:03 PM   #2
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Is it possible that while the motor was apart someone went thought the carb? It sounds like a bike with its slide in backward. I would also look for an air leak and double check valve clearance.
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Old 05-10-2013, 09:09 PM   #3
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Originally Posted by cross-country View Post
Is it possible that while the motor was apart someone went thought the carb? It sounds like a bike with its slide in backward. I would also look for an air leak and double check valve clearance.
The carb was rebuilt by Dave Hopkins. I have two of these bikes. I placed the stock carb from my other bike on it while I was waiting for Dave to rebuild the carb from this bike, and it behaved the exact same. Rechecking valve clearance was next on my trouble shooting list.
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Old 05-10-2013, 09:23 PM   #4
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Id make sure it wasn't off a tooth while checking the valves, also it's easy to be out 180 degrees while setting up the valves.
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Old 05-10-2013, 09:40 PM   #5
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Thumbs down

one of the stupidest things ive ever seen is KTM's TDC setup..... freaking morons...

make sure, then make sure you are in the slot, then make sure again..... i work at a all brands shop and we do a bit of KTM stuff.. even the boss whos very well informed about KTMs has a hell of a time getting that stupid TDC bolt/slot setup right the first time....

oh and did i say freaking morons...
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Old 05-11-2013, 07:42 AM   #6
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I don't get it, I've done a lot of top ends on RFS motors. The TDC procedure always seemed fairly simple to me.

OP; you checked the timing with the chain adjuster engaged? The chain adjuster is functioning correctly? I've seen a couple of adjusters that had worn out the teeth on the pawl.

While you are in the head (and if you have not already) inspect the rocker arm bearings, tappet feet, follower bearings, and the cam surface.

If you can't find anything else, check that the flywheel hasn't sheered it's pin and spun on the crank, this could change the timing.
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Old 05-11-2013, 09:37 AM   #7
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And, make sure the adjuster nuts are tight! There's been a few disasters from them backing out.
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Old 05-11-2013, 11:17 AM   #8
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Exhaust leak?
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Old 05-11-2013, 02:31 PM   #9
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Quote:
Originally Posted by cross-country View Post
I don't get it, I've done a lot of top ends on RFS motors. The TDC procedure always seemed fairly simple to me.

OP; you checked the timing with the chain adjuster engaged? The chain adjuster is functioning correctly? I've seen a couple of adjusters that had worn out the teeth on the pawl.

While you are in the head (and if you have not already) inspect the rocker arm bearings, tappet feet, follower bearings, and the cam surface.

If you can't find anything else, check that the flywheel hasn't sheered it's pin and spun on the crank, this could change the timing.
Are my symptoms indicative of timing off? Cam has new bearings and was checked for wear. Timing chain tensioner is something I have not considered. The bike ran great before the work was done. It feels strong on acceleration, just stumbles when backing off throttle. I will continue trouble shooting,
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Old 05-12-2013, 02:13 PM   #10
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It feels strong on acceleration, just stumbles when backing off throttle. I will continue trouble shooting,
lol ok i guess i mis-read your post..... if its just popping on decel then look for an air leak (carb intake/airbox,exhaust-all joints)
sounds like an air leak to me if its popping on decel....

does it run well once warmed up ? if so then its lean at startup (cold)
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Old 05-12-2013, 02:16 PM   #11
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Originally Posted by cross-country View Post
I don't get it, I've done a lot of top ends on RFS motors. The TDC procedure always seemed fairly simple to me.
its easy if ya lock it down while cylinder/head off.

you must have a really skinny neck and really good eyes...
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Old 05-12-2013, 05:37 PM   #12
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Quote:
Originally Posted by qkenf4u View Post
lol ok i guess i mis-read your post..... if its just popping on decel then look for an air leak (carb intake/airbox,exhaust-all joints)
sounds like an air leak to me if its popping on decel....

does it run well once warmed up ? if so then its lean at startup (cold)
Not it. Thanks though. It's the stumbling and flat power after backing off the throttle that is the real symptom. Not concerned with a a little backfiring. That should be corrected with a mixture adjustment.
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Old 05-13-2013, 06:35 AM   #13
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Crank Seal

Check the clutch side crank seal. I've road raced these bikes for years and when the crank seal pops the bike will run great on the bottom but will lose the top end. Not exactly what you're talking about but if everything else checks out (carb clean, etc), it sound like it could be a possibility.
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Old 05-14-2013, 09:47 PM   #14
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Spark plug gap was the culprit.
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Old 05-15-2013, 05:59 PM   #15
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Spark plugs can look perfect - and not work properly
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