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Discussion Starter #1
2000 arctic cat z440 fan SINGLE CARB
Pulling my snowmobile out of storage and noticed that the sled wouldn't stay idleing, so I cleaned the carb, I did find a blockage. Put the carb back in and now it is doing this:
Fire the sled up and it slowly idles down, once it gets to a low enough rpm one cylinder cuts out. If I don't let it idle down and get on it, it runs fine, no bogs or anything, and both cylinders are fireing, but once I let it idle all the way down it it goes to one cylinder. If I try hitting the throttle when it is on one cylinder it bogs and I can't get the rpms up, BUT if I choke it while it is on one cylinder I can get the rpms up and go again. I swapped the plug wires and the problem stayed with the cylinder (i.e. the same cylinder is cutting out). The cylinder that keeps cutting out is the mag side cylinder. It has new plugs, I even swapped the plugs to no help. Compression is 130psi on both cylinders.

So being that it is a single carb twin cylinder, is there any chance this is a carb issue? "If" there is a clogged or partially clogged pilot circuit can 1 cylinder hog all the air and fuel and make the other cut out? Not sure if this is relevant but the fuel pump pulse line is hooked up to the cylinder that cuts out.

Sled ran fine when I parked it last year.


update:
did more work on the sled, still didn't fix the problem. Here is what I did. Took the carb apart for the 4th time, soaked the carb and jets in an ultrasonic parts cleaner for 2 hours at 130 deg f. Didn't fix it. Took the fuel pump apart and cleaned it, didn't fix the problem. Took the fuel filter out of the equation, didn't fix it. Replaced the fuel pump pulse hose, didn't fix it. Took the y pipe off to look at the pistons, I didn't see anything out of the normal, everything looked good. I sprayed wd 40 around as much of the case halves as I could while it was running, the rpms didn't change. I took the recoil off while the sled was running and sprayed wd-40 as best I could behind the flywheel, the rpms didn't change. The head nuts were tight. I sprayed wd-40 around the head, rpms didn't change. Only one thing I haven't done, I haven't checked all the gaskets on the intake for that cylinder. I sprayed wd40 on the outside 2 gaskets of the intake and the rpms didn't change but I can't get to the 2 inside gaskets without taking the shrouds off.

Question, I took the fuel pump pulse hose off of the fuel pump and I blew into it, I didn't get very much resistance, I was able to keep pushing air. This seem right? Where is that air going? I made sure the piston was all the way down when doing it.

any more suggestions?
 

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A fuel pump runs on a push-pull theroy or a pulse. You should NOT be able to blow through the pulse hose. You should be able to blow through the inlet on the pump tward the carb. You should not be able to blow throught the carb side of the pump back to the tank....there's a check valve there.

I'd try and get it started where it runs on both cyclinders and take it arounf the yard a few time's....going easy. Check your plugs and see if the mag side is running lean. With every thing you have checked sounds like there might be a crank seal issue. Singel carb setups are simpel, this dosn't sound like a card issue.

The only other thing that comes to mind it a broken piston skirt(or damaged). With the intake off(if you can) out your hand over the intake port(blocking with hand, not in side) and pull it over, should have suction on both side's....if you don't see a problem with the piston skirts.

Have you tryed your WD-40 in teh carb running to see what it will do to the RPM's, rev up of dye out.
 

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one carb means that if you having problems on only one side I would look more towards fire than fuel. If your getting fuel on one side, you should be getting it on both.

What does the spark plugs look like?? Can the plug wires be swapped?? I know on my zrt, they all fire the same time and I can swap them over. If you can swap them, do it and see if your non firing cylinder switches sides also,,, if it does, your problem is fire not fuel. If it doesnt, then its either fuel or compression.
 

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Discussion Starter #4
one carb means that if you having problems on only one side I would look more towards fire than fuel. If your getting fuel on one side, you should be getting it on both.

What does the spark plugs look like?? Can the plug wires be swapped?? I know on my zrt, they all fire the same time and I can swap them over. If you can swap them, do it and see if your non firing cylinder switches sides also,,, if it does, your problem is fire not fuel. If it doesnt, then its either fuel or compression.[/b]
I tried swapping plug wires, problem stayed, same cylinder is not firing. Old plugs did not show any signs of white, I put new plugs in so there is no real color indicator yet. But both have a normal wet look to them.

I'm really stumped..... :confused:
 

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Discussion Starter #5
swapped out the carb with a good carb from a running z440 fan, same results, mag cylinder cuts out at idle. With the good carb in place I also swapped out external coils, again no change. you think it is time to open up the motor?
 
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