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Discussion Starter #1
I have a 1980 pantera 5000 (500cc) twin with single carb, 34MM. Last year (ever since I got it) it would foul out the fan side cylinder plug. climbing a mountain I siezed one engine because the fan side plug would foul immediatly and I had to get home and overheated the pto side. I thought it was the engine, (internal crankcase air leak) but when I got it rebuilt and put back together, it did the same thing. Have a friend with the same sled, tried all the ignition stuff but same results, fouls out fan side. I tried a carb off an old Yamaha 330, jets where smaller, don't know bore size, the machine ran great but was way to lean. so here is the jet size of my current 34MM: main240, primary30, needle jet p8 and needle 6dh7.  I went leaner about one step on all of the above, it quite fouling fan side plug, seems like it lacks power for a 500, needs to go leaner, but the pto side cylinder looks like it would run to lean. does anyone know if a 34MM is to small for this engine? I was thinking of going to a 38, thinking that this 34 is not getting enough air and fouling it out with fuel. I can get one used carb for under a 100 bucks. Or I get another 34MM, get new manifolds, throttle cable, air cleaner, etc. getting 2 carbs is going to be a lot more exspensive, and this machine is probably worth only $500 at twenty feet away. any sugestions? thanks in advance
 

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i am not trying to be a #####!!!!! imho get your sled a new home far away from you (sell it). and get a newer one, leave it alone, and ride for fun. maybe i am not understanding you correctly but if you are fouling or cooking one piston with a single carb, the carb isn't the problem, if both fouled or cooked that would be different. i would look at crank seals.
 

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Discussion Starter #3
I got F=%*ed on this thing. I have got so much money into it I can't get rid of it. The engine only has 300 miles on it. I got a brand new 700, this is for friends or family to ride. I got to get it running right. Its not the crank seals, its a new engine. I am into engine performance, and right now its good practice on getting a basket case to run right. I have borrowed different carbs with good results. I am thinking of buying a new one,but how do you replace it! there are so many different types of vm34. Don't ask me why this carb fouls it out!!! I decided to stick to one carb, 2 is just not cost effective. the biggest problem I have now is trying to find out what type of 34 I have, Its a nightmare, no one I have found has a code book, there is like so many different types. the bell horn (air cleaner installs at) are all different, chokes, non-chokes. it sucks. anyone know? On one side of the throttle slide is a pad with the number letter combo: PO62, where the choke cable goes into the housing there is a number 34 then underneath it is 264. let me know if you do, Paul
 

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Paul,

First off, you say its an '80 pantera, but i dont think AC had a pantera for the '80 model year.  I know there were '79 and '81 models, but im not so sure about '80.  This is vital b/c from these two years used a different model carb. from the factory.  For '79 it was the VM34-175, and '81 was the one you mention, VM34-264.  Now, im not sure how different these particular carbs are, but im pretty sure about those #'s...hope this helps just a little.  Also, stock main jet for this was a 300, but your other internal parts (needle jet p-8 166 and needle 6dh7) are right...im not sure about the primary.  if youre only running a 240 on the main, that could be a big source of problem!
 

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BTW,

That main jet size and other info was for the VM34-264 ...for the 175, the main would be a 280 in case you were wondering.
 

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little more for ya...

primary for the 264 is supposed to be a 25.

Sorry this info is coming in pieces, but im finding it as i go.
 

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little more for ya...

pilot for the 264 is supposed to be a 25.

Sorry this info is coming in pieces, but im finding it as i go.
 

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Discussion Starter #8
ok, the needle is the same, so is the needle jet, as for primary, it had when I got it a 30, and a 240 main, I ride from 4000 ft to 8000 feet. It would foul out the fan side with that set-up. I went to a PO needle jet and a 6dh4 needle I robbed out of another carb, and changed the main to a 230 and kept the same primary, flat out its a little dead, but at least it don't foul the fan side anymore. There must be a crack or something in the carb. whatever set-up I do, If I go to rich, the fan side fouls, if I go to lean, the pto side looks to hot, it might be a cooling issue. In my Mountain Maxx triple, I know the outside or middle carb is jetted leaner than the other two. I think I am going to try another 34, anyone got a decent one for sale? I need one for a cable choke, Idle speed don't matter what side. Thanks for the info wizzells
 

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I am still trying to figure out how a single carb fan cooled sled can have 2 major different burning temps in the cylinders.  Although, my 75 ski doo tnt seems to do something similar and I can't figure out why, I threw away the original tillotson carb (which gave me a richer side than the other) and put a mikuni 34mm on, same result, although I have not eliminated a bad crank seal as the source of the problem.
 

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this might sound stupid, but what plugs are you useing and are they both the same type?also, are their twin pipes on it for some reason?one more thing, are you running a stock iar box or a k&N type filter?
 

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Discussion Starter #11
Tell me about it, stock air box. no K&N,  I own a smog shop, and sponsor/and work on  a alcohol sprint car, mixtures are my specialty (on cars) There is something wrong with that carb. Tonight I went and bought 2 Mikuni 34's for 80 bucks, one of them I used to test ride this cat when I first installed the rebuilt  engine. It ran great but was a little too lean, tomorrow I will tear one of them down and see what jets, and needle jets are in it. It also ran good with an old ski-doo carb.
The only thing I can figure out is that one cylinder is running a lot cooler than the other due to the fan being right next to  it and possible that the carb is cracked somewhere or something.  If I lean it out, pto is too lean, if I richen it up, fan side fouls, I think the magic is going to be in the needle jet, whatever needle jet is in that borrowed carb is what I am going to stick with, it ran great, I will just try a bigger main, the real solution is to stick 2 carbs on it, then I could jet each cylinder accordingly, but thats too much money. on my 2001 700 Yamaha triple, pto side main jet is richer than center or altenator side. And thats water cooled. When the snow flie's I will let you know, Thanks for the help.
 

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Paul,

You hit on the head in your last post the Mag(fan) side will always run cooler on a fan sled.  Try to run a 1 step hotter plug in that cyl.  This probbaly will solve the problem.  This was common practice to get better performance out of a fan cooled sled.

If you still think it is the carb that is causing you your woes, then a through cleaning is in order.  

This is an old sled, and sat for a long time not used.  

The carb probbaly has a plugged air passage.  Take a good look that the pilot circut.  If it's air intake is plugged it will draw a lot more fuel than it should, causing your fouling problem, and is not uncommon.  Take the carb apart all the way and soak it in parts cleaner.  If that does not help, then you may need to manualy clean out the air passages with a small drill bit.
 
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