Author Topic: Reduced Top Speed  (Read 2135 times)

pimpdaddydog123

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Reduced Top Speed
« on: June 12, 2014, 12:47:14 PM »
Hi! My SYM has started performing badly (engine sounds healthy, no misfire).
I pulled the air filter connection and notice that even when throttle is fully open the throttle slide is not rising up.
I have checked the butterfly valve is opening and that the diagphram is in good condition.
The slide moves freely and if I push it up with my finger the engine revs much higher than when I don't.
No obvious air leak.
What could be causing the throttle slide to remain closed?

tortoise

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Re: Reduced Top Speed
« Reply #1 on: June 12, 2014, 02:00:55 PM »
the diagphram is in good condition

Will be interesting to see how this issue is NOT diaphragm related.

Checking carburetor slide diaphragms for problems

ootscoot

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Re: Reduced Top Speed
« Reply #2 on: June 12, 2014, 07:54:21 PM »
Sounds like the carb diaphragm is leaking - try sealing the rim with Teflon sealer and check for any pinholes
Ooty's Scooters - Santa Barbara, CA.
SYM Dealer, SYM rider, SYM owner - got them all!

pimpdaddydog123

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Re: Reduced Top Speed
« Reply #3 on: June 13, 2014, 02:40:53 AM »
 :) Fixed!!

It definitely was diaphragm related.

With the carb removed I attached a vacuum cleaner to the carb outlet and opened the butterfly manually, no throttle slide movement.

I removed the diaphragm again and inspected it thoroughly, there were no tears, holes etc but I noticed that it appeared to have "shrunk" around it's sealing edge so I re-fitted it and bedded the edge into a small bead of sealant as suggested.

Re connected the vacuum cleaner and bingo, it works perfectly.

The carb is now back on the bike and all is well in the world again.

Thanks for the help guys!