~3500rpm stutter
 

Hello all! I did read some similar threads but wanted to post because I couldn’t find anything conclusive.

Replaced engines over winter, using my existing carbs, exhaust, and airbox. Installed MCCT’s and removed PAIR on the new
(to me) engine before it went into the frame. On old engine my setup worked very well.

bike started beautifully. Idles perfectly and revs well when parked (albeit some very quiet clatter from front cylinder, might need to tighten front cct). First actual test ride, lots of stutter at 2500rpm, and lots of afterfire off throttle. Came back, opened airbox and the two ‘blocks’ that fit inside the airbox were off. Placed them correctly, buttoned up and now lots of stutter at 3500rpm. Also odd - revs all the way well in 1st, but stutters from 2nd gear up.

Checked carbs for sync and they’re perfect. Checked voltage at TPS connector (harness side) and got 4.9V. Replaced plugs - did notice that previous owner had DPR7’s in the engine. I’ve replaced with DPR9.

where would you guys start diagnosing this? Should I tear all the way down and start with timing?

Are you sure you have the cams timed correctly? Vacuum leak? How clean are the carbs? Torn carb diaphragm?

Hey Xeris,
I’m 99% sure timing is correct - I used the zip tie method when I swapped CCT’s and am positive the chains didn’t jump any teeth. However... that 1% of doubt makes me want to just tear down and make sure before I run it again. The only confusion I have is that it revs through 1st, and idles so well.

The cam timing can be 180 out and run pretty good up to, iirc, 6000 or so rpm then no more. Someone will correct me on this if I’m wrong. Your description doesn’t match, so probably not.
Explain “stutter”.

Bike accelerates normally (as far as I can feel haha) up to about 3500, and if I roll on gently at that point it coughs, doesn’t want to accelerate and I can hear and feel massive carb farts. If I go WOT it will [over a couple of seconds] get past 4K or so and then continue to accelerate normally.

I’ve got some brand new vacuum hose leftover from a recent car project and am planning on replacing as much as I can. I will also most likely confirm timing (following the MCCT install guide) and confirm front CCT slack while I’m in there. If I also do the tps check/mod, I suppose the only culprits left are petcock diaphragm and carb boots?

Vacuum line to the petcock on correctly?

out of sheer paranoia I took carbs off, covers off and confirmed timing is set correctly. Front was slightly loose, now set to ~6mm play.

funny you ask about the vacuum line - it was correct on petcock: but super loose at engine end. Retainer had slid off, the line popped off with the gentlest touch.

checked tps - it’s at 897ohms so will mod tomorrow!