Accelerator Pump Diaphragm ripped....AGAIN!

Hi guys,

I posted a thread on here a while back trying to troubleshoot why my bike would die when any throttle was applied. Well, I finally had had enough of it and sent it into the shop, and by sheer luck they found the accelerator pump diaphragm was torn when they were tearing down the carb to clean it. It ran fine for approximately an hour and a half, and then the same thing happened again! Right as I was about to get out of a short corner and into some whoops, I gave it about 3/4 throttle and it died, and wouldn't start up. Now, its back to square one.

Now for my question. Why would two Accel Pump diaphragms tear? The mechanic talked to me over the phone and said that one tearing was rare, but two tearing was unheard of. If you have any ideas, please feel free to chime in, because I'm really getting frustrated with this one. :smirk::smirk:



Wrong diaphragm

Excessive travel of the AP - Is you linkage wired together?

Bad fuel, solvent on the diaphragm

What year/model? Diaphragm came from Yamaha?

Have you torn down the carb and looked at the diaphragm and confirmed it's torn or are you assuming it's torn because it's doing the same thing? If you haven't verified then it might not be the diaphragm again. You may have some stuff lodged up in the AP squirter

Excessive travel of the AP - Is you linkage wired together?

Does this stress it?

Just asking because i wired mine and someone told me not to.

Ift is wired and you do not check to see if it binds, that can damage the AP.

The reason it has a spring at the black cam is to remove slop at the same time, allow the system not to bind. The problem with the stock spring on all bikes except for Hondas (07 forward) is it is too weak. So the oring mod came along to add a 'stiffer spring'. Then Merge Racing made a stiffer spring (the best solution). But many did not want to spend the $16 for one and if the AP does not bind, having it locked together is fine. Except when you have to tweak the timing adjustment, then you have to reso the wire, though not a biggie.

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