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Discussion Starter · #1 ·
HI.
I have a problem with my z440 engine , dual carbs vm34 280main jets. The left cylinder is fouling plugs like mad , I have tried cleaning carbs changing them, synchronising them, changing wires on coil but the result is always the same. Right cylinder perfect spark plug insulator (brown) and the left one is getting black till it's fouled that bad so it's backfires bogs and after that dying. What can cause that? Can it be a crankshaft seal? And could you recommend me a shop that send parts to Europe , like gaskets pistons ect ? Thanks
 

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Could be spark related. Check your stator ohms. Check the spark and see if it is bright blue when the motor is cold and then warm it up a bit and check the spark again to see if it is still bright blue. You said you changed the carbs...did you switch them? Just want to make sure the issue did/didn't follow the carb. Check compression yet?
 

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Discussion Starter · #3 · (Edited)
I have done a compression test and I got 7bars , more than 1 bar under minimum acceptable pressure. Engine is disassembled , and I need a new piston, rings , gaskets , and a crank rebuild it look's like previous owner rode it till it's end. Could you recommend me a shop in USA or Europe that sell parts to Arcitc cat z440 engine?
 

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Discussion Starter · #4 ·
Guys does anyone know what is the dimension of new piston? My cylinder wall is 65.02mm no taper or other failures , used piston was 64.80, and I don't know should I buy new piston or look for new cylinders...
 

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If the cylinder is not gouged you should just order a new set of pistons and rings. Try forward power sports. www.forwardpowersports.com They should have the parts you need. I just am not sure if they ship overseas or not. I would replace both at once and hone them for a 60 degree cross hatch with a 400 grit stone set or a ball hone. For about 105 U.S. dollars you will get both pistons, rings, wrist pins, and clips.
 

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The EXACT same thing happened to me last weekend with my 97 Z440.

Turns out my pilot jet had come loose and fallen down inside the fuel bowl. SO she was sucking so much fuel it wouldn't even try to fire.

Check all your jets over and reset the pilot air screws and you'll be ok. Remember on the screws, turning them in richens the mixture. 1 turn out is the stock spec for them.
 

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Discussion Starter · #8 ·
I have dissasebled the engine and it was badly worn out , bearings seals and it had leak in crankcase.... I have problem with pulling clutch of the crank it does not want to get out.
 

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Discussion Starter · #9 · (Edited)
Here I come again, Brand new Wiseco forged pistons , new outside seals and bearings,. Now the problem if the engine is cold it will start then bog in low rpm (wait a 1 - 2s ) then works good but when he gets the temperature and I shut him off , there is no chance of starting him again , I have to wait till engine is cold. I will post a video of it later. Carbs were cleaned and set up, fuel pump is working good ( I think cause it pump the fuel to carbs, how should I check her?) And I need to use choke every time, when it's hot using choke cause backfire.
 

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Check the carbs again. Make sure the chokes are seating and then check the pilot jets. Also try turning out the idle air screw a 1/4 turn at a time.
 

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Discussion Starter · #11 · (Edited)
After few hours of trying tuning it , I think that there are way too rich jetting. When I tried to run it without air filter , lean setting on needle and turned out idle jet screw plugs were black and with a lot of carbon build up also engine misfires into exhaust. Right now I have 280 main jet and according to table that I found I should have 260 (correct altitude and temp), but the low speed jet doesn't have a number stomped, so my question is What kind of size it should be stock?I think I need to go 5 sizes less one. Sled is from 1996, dual mikuni vm34 european. I checked chokes and they don't leak or hangs up.
 

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Pilot should be a 30 on that sled. If it is backfiring still I would start to suspect crank phase. It would be best to have a dial indicator to check that, but you can see if they are close with two rods. one in each cylinder. Get the stator side to top dead center and make sure the pto side starts to rise at the same time the mag side starts to go down. If it recommends 260's you may be able to drop a size or two without issues. When you do this I would not get out in deep snow and work it hard or you could heat up and burn down.
 

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Discussion Starter · #13 · (Edited)
I have put the 260 mains and sled didn't backfired even once, 27,5 pilots and there is still problem with something like 3000-4000 rpm bog just after the clutch engages. Sled is going like 15-20km/h and have problem to get higher rpm, when driving from little hill it comes on on the higher rpm but there is not violent burst of power(I have also Phazer II and it rips comparing to Z440). Left side is little richer (wet white and black isolator) than the right side (brown chocolate) when checking the plugs. The only thing that is old in engine is a center crankshaft seal, but shouldn't both cylinder work bad when seal is bad? Tomorrow I will try 25 pilot on left side if this doesn't help, I will disassemble the engine again and get the center crank seal replaced.
 

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Discussion Starter · #14 · (Edited)
OK sled is working right now. Crank was twisted by 30 degrees... I put new bearings on crank and new middle seal and the man who was replacing it told me that it's not ok..
 
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