Pumper carb question

Joined
Jun 18, 2000
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#1
The following is for my 2001 KTM 520sx.

Does anybody know which is the correct way the accelerator pump diaphragm goes in? I had a local dealer look at my carb awhile back for the early throttle hesitation. Last night I took the cover off for cleaning and I think they put it in wrong. First off, they had the spring sitting on top of the diaphragm (it was nested between the carb body and the diaphragm instead of under the diaphragm). That seems wrong, as the spring would always keep the chamber under the diaphragm closed. Since I’m looking at this again, I just want to make sure. I noticed the diaphragm center has a small contact rod in the middle for the plunger arm. One side of the contact rod is a little longer than the other. Which side faces up toward the body of the carb? Any help would be appreciated as I think I’ve wasted the last two months of adjustment on a carb that was not properly assembled. Ack! It is really hard to tell from the picture in the manual.

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Joined
Jan 24, 2001
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#2
With the carb upside down place the membrane with the labeling faceing upwards. Next the spring then pump housing. Here is a trick that works most of the time. Grind 3/32 of an inch off of the tit on the labled side. This will increase the pump stroke. On my two 520s I have two run two turns out on the air screw with #50 jetting.

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Joined
Jun 18, 2000
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#3
Thanks. It appears that they had the diaphragm in upside down as well.

I'm going to just re-assemble correctly to get a feel for it, then maybe try the tip you mentioned.

This really explains alot of the problems I've had.

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ochster

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#4
Oh No! say it isn't so, Not one of those "factory trained service technicians", with all the plaques hanging on the wall.

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