The carb has been this way since I bought the ATV. Got it cheap, worth working on.

I pulled the carb completely apart, cleaned all passages, still no change. Thinking that I may as well spend the money on the diaphram, although it looks good, that is the only thing left I can think of. Should the needle valve have a seal where it passes through the slide? The vacum to pull the slide up comes from the hole in the bottom of the slide, correct?

I can blow into the inlet and the slide will move a touch, but won't run up to the top. Must have a leak someplace. I've made sure the lid seals the diaphram, so that's checked. New air filter, no split boots. I have a good dealer nearby, but hate to take it in to them to let them troubleshoot at $75 per hour...

 

You should be able to blow in the Inlet and the slide show goo all the way to the top and stay thier if you keep pressure on the inlet. It sounds like you Diaphram is bad, but your SLIDE could also be split cause this problem aswell. You are right about the vacuum being generated from the port on the bottom of the carb, but if thier is a split or small hole in the slide anywhere else it wont work properly. What sive CV carb does your Magnum take? You can pick up a good used CV carb for peanuts off of alot of the sportquad owners.



Bigger.

 

I hadn't thought of a problem with the slide, but checked and that's not it. Wondering if I just have too much drag on the slide, maybe a burr on the delrin insert or something...should it be greased at all? I can't come up with any good ways to check and see if anything is leaking...

Also, I am assuming I have good vacum, how much should a 425 pull? I have 160 psi compression, so assume the motor is in good shape, but I don't deal with 4 strokes (too many little contraptions to go wrong as this carb is proving to me).

Anybody out there have a carb they pulled off they would want to sell? I will measure mine, see what size it is and start looking around to see if that could fix it.

 

When you have the slide out, is the vacuum port on the bottom clear.
That is, when you hold it up to a light their is no obstruction - open thru.

Also check for a missing o-ring that the cover holds inplace.
Sometimes when you take the metal top off the o-ring sticks to it and then falls off.
Some cv carbs, the o-ring is part of the bladder. On most it is a separate o-ring.
If there is a side passage with a recessed hole and there is no o-ring, that is probably your problem.

 

If it's always done this, the diaphram spring could be streched and providing too much tension on the slide to move upward as it normally would.

 

What is it with people the ask for help and post for days and weeks, asking questions of people and then never posting the fix!!!