I have a Magnum 425, having carb issues. My slide isn't raising as it should,I've been through the carb, can't find the problem. Usually it's that the diaphram is ripped or not sealing, but best I can tell it's sealing, no visible rips, so that doesn't appear to be the problem. Is there anything else that could affect the operation? I am getting ready to get a carb kit for it just to make sure, but hate to spend the money if there is some other issue than the diaphram that the kit won't fix.

Any ideas/information would be appreciated.

 

What, nobody knows anything about the constant velocity carbs? I admit I don't deal with them often, I avoid 4 strokes as much as I can, but need to get this thing running. Any ideas?

 

I don;t know what you mean by diaphram.

I have a 34 CV on my scrambler 400 from what I have seen many of polaris's quads have used this carb.

 

How are you determining the slide isn't raising?

 

The Mikuni CV is a constant velocity carb, used on 4 strokes to eliminate the need for an accelerator pump, something the 2 strokes don't need, I don't think any 2 strokes use them. The 400's I've seen had a Mikuni round slide, the CV is a butterfly throttle type carb with a vaccum actuated slide.

As far as how I know, basically, it runs like crud, spits, backfires, fouls plugs...pull the airbox boot, and you can see the slide not raising. If I manually raise the slide while running in neutral, engine revs out fine.

 

I guess it could be a number of things. Jets pluged or air filter dirty also a diaphram bad. Have you completly disassembled the carb and cleaned it? The slide will not open correctly with the air box boot off. It takes vaccum to open the slide and when you take the boot off it don't have the right amount of vaccum to open it correctly.

 

I know it won't work right with the airbox boot off, but it doesn't move. Last night I pulled the carb apart, big port on the airbox side is fine, jet on engine side is clean, hole in slide is clear, tried a little light grease around the outer edge of the diaphram to make sure it seals, no difference. Slide doesn't even attempt to move, just sits at the bottom. Are there any other passages?

 

The slide is controlled by pressure differential and spring pressure, on the lower side of the diaphram is atmospheric pressure. This chamber is vented to outside air, make sure this port is open and there isn't a plugged filter. On the top of the diaphram low pressure is created when the throttle is opened. You should be able to blow into the outside air port and raise the slide, don't use compressed air as it may damage the diaphram. If that works you may have mechanical issues with the engine causing low vacuum...
Another thought, make sure the intake boot isn't split/leaking

 

I agree with Powerslider to check the rubber intake boot for a split. Almost sounds like it's sucking air from somewhere......

 

Check your intake to the carb sounds like it is plugged and not getting vacum.
does your slide move freely by hand no binding ?
did this happen all at once ? did you roll your bike onto its side ?