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Discussion Starter · #1 ·
Okay, here's the deal. I am working on a '72 ski doo olympic 335. I just got done putting it all back together with a carb rebuild which I just did. It is an old tillotson HR series carb. All I really did was clean it up and put a new set of diaphragms in and I was going to put in a new needle and seat but the old one looked fine. Well, actually, the needle and seat didn't really look like a needle and seat... it was more like a glass eye that lets fuel by. Its really hard to explain. I didn't replace that because it looked like it was in working order.

Now the problem... My friend and I managed to get it going twice but only for a few seconds. What is happening is gas is spitting and dripping out of the air intake. It seems to be getting too much gas, so we turned the gas down... Well, we closed the gas screw down to about one turn. It still sprays a mist of gas out of the intake. I'm not sure what is going on! I am stumped. Has anyone ever come across a needle and seat that had an "eye" type thing in it? Gas also is going right through the engine and dripping out the exhaust. I just cant figure it out, and yes it has a spark!

If you would like to see some pictures of the carb I would be more then happy to post them. I don't know if I want to take the carb apart again to get a picture of weird needle and seat. I think though, I might replace it. It could be letting too much gas though.

Any suggestions or input is greatly appreciated!

Thanks!
Rob
 

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KHE What you have come across is a grossjet valve. It is an aftermarket needle valve supposed to prevent vapor locking. I haven't seen one in about 15 years but then again it's been a long time since I worked on a Tillotson. It sounds like you are definatly getting too much fuel. Theres a good chance the ball isn't seating good.
 

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Yeah, I agree. It sounds like the needle n seat, or grossjet valve (the fuel inlet valve) is the suspect. They're cheap, so I'd replace it and go from there. I bet this would solve your problem though.
 

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Discussion Starter · #4 ·
Thanks for the input. I just have one more question... Will I have a problem of vapor locking with just a regular needle and seat? Is it common? Should I be concerned?

Thanks!
Rob
 

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I can't tell you for certain, because well.......what is. But I can tell you from my own experience, and that of anyone I've ridden with, that I've never seen it happen.

One other thing to think about is that every carbed sled I know of, comes with the standard needle n seat. If you do decide to switch to one of these, just be sure that it is speced to you carb and sleds needs.
 

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i actually had a sled vapor lock on me once. 77 ski doo tnt 400 with the tilleson carbs i was haulin @$$ down a snow covered road all of a sudden BLAM! it blew the clutch up it stopped so quick and the clutch slapped together too fast. piston shattered needless to say i junked the sled and opted for my John Deere Sprintfire 340 l/c and oil injected.

anyways are you trying to restore that sled?? or just make it ridable? if you do go back to the needle and do just like Tfin says make sure it is spec'd for that carb. do you have the carb model number by chance?? i could possibly help ya out with those part numbers are
 

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Discussion Starter · #8 ·
Okay... I believe it is where your engine gets so hot that the gas in the carb, which is also hot, evaporates, so the engine is just running on fumes.

Bobinwi - well, I believe I have the right needle and seat, pretty sure anyway. I got the HR needle and seat for the HR series carb which is what the carb on the snowmobile says. I got it at central snowmobile in green bay, which you might know of.

As for the snowmobile, it is really my friends snowmobile and I am helping him fix it. Its his first snowmobile, and I am familiar with old ski doo's...
He has painted it and the hood is perfect, it looks pretty nice. I think all he wants to do with it now is get it running and do some riding. It has a lot of potential to be a show sled, and we might drag it to a show here or there...

I will post pictures soon!

-Rob
 

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yes vapor locking is when the gas coming into the cylinders is actually a vapor not a raw fuel and the vapor gets between the piston and cylinder and puts so much pressure on the piston that it basically freezes it that was the onlytime me or anyone i know that that has ever happened quite wierd


yes i know central snowmobile well. they are kinda a bunch of jerks tho IMHO but do you have the part number handy for the needle and seat? cuz it has 2 different part numbers for it. Tillotson# 233-672 and 233-660 just trying to help out as much as possible

bobby
 

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no offence guys and thanks for the replies but those explanations dont really help me to understand. Any one else? The part I dont get is how the vapours dont get expelled during the exhaust cycle.
 

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well the reason being is that it creates a pressure on the intake side that doesnt allow the amount of fresh fuel to enter the cylinder so what does that do??? lean it out BIG time then what happens??? you got it kaboom
 

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Those old Olympics always spit gas at ya when your trying to get them going. I had 2 of my Dad's around for just anybody to ride but I spent so much time fix'n them it wasn't even fun anymore. I'd rather be dragged by a new sled than ride one of those things for a day. But if you have a paper clip and some duct tape you can fix anlmost anything on them.
BTW how is the compession, kinda sounds like weak rings.
 

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Discussion Starter · #13 ·
Bobinwi- Well, I have the central snowmobile
catalogue and I got the needle and seat for the HR Carb. Now in the catalogue it says that the needle and seat that I got from them fits HL/HR models, #233-660, and #233-672, so I believe I have the right part. Does this sound right?

Its supposed to snow tomorrow night and Saturday, for a total of 10 or more inches! according to the weather channel...

Rob
 

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Discussion Starter · #15 ·
Thanks for the input! I will let you know when we get it fixed, and running!

Rob
 
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