# Carb slide diaphragms question



## msmith56 (Dec 4, 2014)

Hello, 


I have two older brute force ATV's, I got the 650 running great now but my 750 never seemed to run right as long as I've had it. I bought it used knowing that it backfired and didn't want to run smoothly. Anyway, I have cleaned and rebuilt the carbs for the 750. It starts quicker and idles fine now but if I rev it to WOT it doesn't seem to have any high end. So after reinstalling the carbs I noticed that the slide diaphragms are not moving under throttle. They will move by hand easily though. When I push them into the carb, they come back out rather quickly, not very slow by any means. From what I understand, they should come back out slowly right? 

The tiny brass fittings in the tab have been cleaned and reinstalled and I can run a small wire through them so I don't think they are the problem. Also when I took the caps off, the edge of the slide diaphragms was seated very nicely in the grooves. I can't seem to get them to stay in those grooves when I go to screwing down the caps. Is there some type of trick to get them to stay in the grooves? I don't want to use adhesive as I may not be able to get them out again in the future. I'm thinking that since they are not seated correctly that is what is causing my problem or is there something else causing it?


----------



## dman66 (Feb 20, 2011)

Sounds like the diaphragms are leaking. You could try a tacky adhesive on the carb surface, the press in the diaphragms so it holds in place. Then try it. If it works, then look into buying new diaphragms. My diaphragms sit in the groove on the carb every time.


----------



## NMKawierider (Apr 11, 2009)

Old diaphragms shrink some so it hard to get them to stay. Drop them into a bucket with gas and a little oil for a while and that will soften and re-hydrate them back up..some..but it sounds like it's time for some new ones so I wouldn't bother with the old one.


----------



## FABMAN (Dec 18, 2008)

yep the diaphragms have to be in the grooves I've had the glue mine in place. I only glued mine in a couple spots just to hold them in place not the whole thing


----------



## msmith56 (Dec 4, 2014)

Thanks to all of you for the information and feedback, I was finally successful after following NMKawierider's advice. That allowed me to get them to stay in the grooves. I found a method that may be helpful on the internet to find out how to check if they are working properly. If you use compressed air across the one rectangular vent on each of the carbs, the slides should move as a result of the air being blown across each vent. I tried that immediately after putting the caps on and the slides moved so I was convinced I got it right this time.

I reinstalled the carbs, tightened down the clamps, connected fuel, heaters, and throttle and fired it just to confirm. Sure enough, they were moving in and out like I thought they were supposed to. Installed the air box, hit the choke, and it cranked a little and then fired right up, turned choke off, revved to WOT and rpm's and engine sounds are now where I thought they should be. No backfiring or hesitation at all. Thanks again for this great forum!


----------



## DaveMK1 (Nov 8, 2009)

One thing you could of done while you had them out was polish them up. A lot of the guys on here with carb'd brutes will do that. Take some mothers metal polish and a dremel with the polishing attachment and go to town on them. After I did mine I noticed that they moved alot smoother with less binding.


----------

