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Joseph Pagan
01-04-2003, 07:29 PM
I"ve got a kitted SR50 with a 20mm Mikuni that hasn't been running that great. Symptoms led me to believe that it was a fuel feed problem: Starts fine, take of fine, but as soon as I give it throttle it starts cutting out, and stuttering. I was told by an Aprilia mech. that it wasn't likely that it was the fuel filter, but a dirty jet.

Took the carb off. (Damn, these things are a pain to work on with all those body panels) Cleaned the main jet and the choke with carb cleaner. Reinstalled everything. Had trouble getting the clip/barrel/spring assembly back on the choke. Cut one of the choke adjustment tubesdown by 2-3mm so that the end of the cable would extend beyond the spring. So now, the choke should have to be cranked even more to be engaged. Right?

Well, now it will barely starts. Seems like the choke is on, but I can't see that it is. Won't rev at all. Any suggestions are most welcome. Thanks!

Sketch hs
01-04-2003, 09:29 PM
you probably already tried this but....


Take it apart and put it back together (correctly, make sure nothing can come loose) check all your connections.

Check all jets and needle.

Check for choke and throttle operation.

that's all I can think of for now.

Don't worry my scooter problems are worse than yours! I have a 172cc beast that refuses to run, might tear down the engine and check for damage if it passes the spark/cdi check :(

good luck! (at least better than mine has been!)

-Sketch

buckeroo bob
01-04-2003, 10:02 PM
The first carb I ever had to clean took three tries. Just soaked it the first time. No good. On the second effort, I soaked longer and used compressed air to blow out the jets. There are little holes and passages everywhere. Still no good. The third time was the charm after I used a tiny wire to probe clean all jets and then blew them out with compressed air. Then I just set the screws to the manual specs and the engine ran perfectly. Good luck.

tiba karotsu
01-05-2003, 07:30 PM
when you clean carb parts and dip them in solvent always stick something in the carb jets to make sure no dirt or foreign matter doesn't block it when you assemble it again, also check your fuel lines from the tank to the carb it maybe fuel or the lack of it that's causing your woes.

Dutch Royal T
01-05-2003, 08:30 PM
Also make sure the vaccuum line / pump is working properly. Otherwise it might not suck enough fuel out of the tank to fill the bigger cilinder.

Joseph Pagan
01-06-2003, 03:18 PM
Thanks for all the tips! Took the carb off again. When I did, there was a rattling sound that shouldn't have been there. Opened up the bowl, and the main jet was rolling around unattached. I *know* that I screwed it in, but apparently not tight enough. Still scratching my head on that one.<img src=http://www.ezboard.com/intl/aenglish/images/emoticons/embarassed.gif ALT=":o"> Oh well. Cleaned the carb some more, put it back together and it's running great. Now to install that Delta Clutch, yellow rear pulley spring, and gear up kit. And once I sell my Kymco, I'm getting a Leovinci ZX Handmade exhaust. Thanks for the tip on that, Stan.

Joseph Pagan
01-08-2003, 08:22 PM
Today was the first day I've ridden the scooter beyond the neighborhood since getting it running again. Turns out the scooter seemed to bog in the midrange: turn the throttle higher and it slows down. If I opened the throttle gradually, then it didn't bog as bad. Take offs were, for the most part okay. Well, I get home, pull the spark plug expecting it to be on the dark, wet side because A. the way it's running and B. it was running a little on the rich side before it started running poorly, and after the carb cleaning, it should be getting even more fuel. WRONG! The plug bass was white. EEEK!:( I didn't change anything on the carb. Just cleaned it out. How can it be running so lean now? Color me confused. How do I proceed from here?

tiba karotsu
01-09-2003, 10:29 AM
go up 1 or 2 sizes bigger, be glad you didn't "holed" the piston, it's always smart to be on the rich side of things especially on an air cooled motor. just keep adding bigger jets till you feel the scooter doesn't bog down when you open the throttle fully.

Joseph Pagan
01-09-2003, 07:54 PM
Tiba,

I think I had an air leak. It shouldn't have been a jetting issue since the scooter had been running fine for months. Preliminary spark plug check seems to be good. Keeping my fingers crossed.......

thanks

tiba karotsu
01-10-2003, 09:37 AM
seems like a leaking manifold to me, check if it has cracks or the mounting flange could also be leaking so try putting elastomer sealant like Three Bond liquid gasket.

if manifold has cracks replace it with aftermarket rubber manifold like Malossi. i seized me Dio pretty bad 'coz of an air leak, it turns out the inlet rubber of the manifold has cracks already so it cost me the whole race, i went home disappointed.:(