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This isn't a request for help but it is an important warning and I wanted as many folks as possible to see it!!

I have 88k fantastically fun miles on my C50C although the last 30k had been plagued by a nearly random but vicious when it hits sputtering that would leave me running rough until I turned off the key, turned it back on, waited for the buzzing to stop, then restarted. Most often it would happen as I was engine breaking to a stop then I'd have to rev to keep her running to get through an intersection and I'd pull over, do the key off trick, then she'd run great again for another random 20 minutes. I'd gotten good enough on a straight run to turn the key, wait the few seconds, then drop the clutch again and get her happy without stopping or using the starter.

Searching through these forums you'll find plenty of folks who have similar problems. They trouble shoot it to a bad primary or secondary throttle position sensor, clogged fuel injectors, etc etc. What was going on with mine was self induced, completely avoidable, and may be the culprit in plenty other folks problems if they made the tragic mistake of PLAYING WITH THE FLAPPER VALVES!!

After finally deciding that it was getting ridiculous that I could be on a great sweeping turn that I just engine braked into only to find myself sputtering to a stop when I needed to be rolling on the power I finally decided to sort it all out. Digging through the forums had me prepping my ohm meter to check sensors and rigging a maintenance mode switch to recalibrate the throttle position if it was bad. All the reading led me to the warning that PLAYING WITH THE VALVES can damage the tiny gears that actuate the upper set in tune with what the ECM wants to do with the fuel/air mix. I'd never seen that warning in the Clymer manual but I'm sure it's there and I grew up with carb butterflies you could mess with all day when you wanted to spray cleaner around. I completely understand know why you should never mess with a fuel injection throttle body and won't on any vehicle ever again... just spray cleaner where you can and leave anything that can move alone.

My problems started when I noticed some gunk build up at 50k miles during a valve adjustment and started playing with everything while spraying it clean. Got the valves happy but it ran like crap so I opened it up again, double checked the valves, fussed with the throttle flapper again, put it back together and it ran great. I assumed I'd left the valves too tight and was getting bad blowback blah blah blah. Turns out I just got lucky improving whatever I threw off or broke in the throttle intake actuator gear monkeybusiness. Each valve adjustment was like a box of chocolates where whatever I was doing to the throttle body would make things immediately better or worse which also kept making me think it had something to do with a tight valve blowing back fussing with the fuel injecting sensing somehow (far fetched but all I could sort given the timeline).

For this last trouble shooting effort I went out and listened much more closely to the buzzing when you turn the key on and there was a grinding at the end. Whether that was busted or bent teeth or the fact that I'd spun things to where the full open or closed was no longer calibrated I'll never know but I definitively fixed it and it's been running fantastically for a week making me confident I can post this WARNING and my solution.

Rather than sort out whether any particular sensor was out of calibration or if the teeth in the actuator or a sensor were truly unhappy I simply got another perfect throttle body with 2.8k miles on it with injectors, hoses, etc for a remarkable $319 on Ebay from a 99.9% Positive Feedback used parts vendor. I went this route because most of the parts that could be contributing were $100-$200 new, the body itself where the actuator that was probably broken is $1000 by itself at most parts shops and new injectors are $150 per. So, for a mere $319 and an hour of strip and swap I dodged all the troubleshooting and brought an 88k mile bike back to running like an essentially new dream.

I'm only posting this to make sure nobody TOUCHES ANYTHING IN THE THROTTLE BODY and creates their own weird intermittent problems. You can probably spin the lower set and spray where you can't reach from above but my new rule is simply LEAVE FUEL INJECTION THROTTLE BODIES ALONE.

BONUS- if you have a high mile bike that's running marginally getting a low mileage used throttle body with injectors and all the fixins' for $300 on Ebay may save you a dozen hours of trouble shooting and lots of dollars if all you really want to do is get happily back on the road.

Looking forward to hitting 100,000 miles this year unless something obscenely hard to fix and pricey goes...

Hopefully after reading this nobody ever touches their throttle body butterfly valves unless they know exactly what they're doing and why!

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