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Discussion Starter #1
I have a 79 jag that is not getting fuel to the carb. It died while my son was riding it. I replaced all the lines, rebuilt the pump, new plugs. Checked spark--it's excellent. Will not get fuel thru the lines. Spray it with ether it fires right up but still won't pull fuel thru lines. I checked all the lines and can easily suck fuel from the tank--so their not plugged.
Is it the carb or could it be the vacuum line from the motor is not creating enough vacuum to open the pump? If it's the carb--what would be the cause?
 

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Clogged jet in the carb is my guess. Being a 79 model, I assume it's been a while (if ever) that the carb was rebuilt. Is it a Walbro, Tillotson or Mikuni? I had the same problem, had the carb rebuilt, and now have the opposite problem...too much fuel (see Walbro WF carb posting). Vintage snowmobiling will surely test a person's patience! Seeing that you're also from south central WI like I am, we're both trying to take advantage of the snow we finally have! I feel your pain brother.
 

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I think your problem may still be the fuel pump. I've rebuilt fuel pumps before and they never worked the same afterwards. I now always buy a new fuel pump when one goes. You can usually get a new one for about $20.00. You may want to check there are no holes or cuts in the impulse line. Also make sure the gas cap is venting properly. I don't think the 76-81 jags had a vent tube from the tank but if it does, make sure it's clear. The carb should have nothing to do with the fuel flowing.
 

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Discussion Starter #4
It's a mikuni slide carb. I've had the sled for 2 years and never had a reason to tear the carb apart. It's always started and ran like a dream.

Mehalco-it's not the pump. I actually rebuilt that pump for another 79 Jag I have the other day because the impulse line was filling up with fuel on that one. After I rebuilt that sled runs great and no problems with the impulse line filling w/ fuel. Anyway I suspected the pump on the 79 in the field and removed the rebuilt pump from the other one and put it on--still not getting gas thru the lines. I replaced all 3 lines w/ new fuel line. Stuck my finger over one end and vacuum tested all 3 as I replaced them--no leaks=no holes. If I put a vacuum pump on the impulse line I get fuel from tank to the fuel line for the carb (if I remove the line from the carb and lower it to the level of the pump).
That's why I was wondering about the motor not creating enough vacuum at the impulse line to the pump. I am going to have to pull that line to the pump and install a vacuum gauge and turn the motor over to check for vaccum.
My thoughts were the same about the carb not having anything to do with fuel flowing but consider this--- you go to start your sled after replacing fuel lines, and the the impulse line gets vacuum to the pump and opens it so fuel can flow. The fuel will flow as far as gravity allows it (below the fuel tank) you will see that the fuel makes it to the pump and just a little ways past the pump in the line to the carb. I believe the pump is just a one way vacuum operated valve to hold fuel at the carb once it gets there. The carb creates vacuum that pulls the fuel up the line from the pump and continues to suck fuel into the carb. I do not believe the fuel pump as we call it is actually a pump at all but rather a fuel valve that stops fuel from flowing back into the tank. If I pull the line off my carb and pull my engine over it does not pump gas all over the place, it just sits in the line. I've done it to all my sleds when checking to see if they are getting gas--none of them pump gas out the fuel line if it is disconnected from the carb as I pull the engine over. Now I replaced all my fuel line with clear line so I can see what's going on with fuel delivery.
 

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Hi there,

the fuel pump should push the fuel up to the carb. I have electric start and when I pull the fuel line of the carb and crank the engine, fuel spurts out the fuel line. I was actually caught out in a blizzard several years ago and I burned a sled buy doing this. I coated the engine with fuel from the fuel line and pulled the plugs to start the fire. You may want to check the impulse fitting at the crank. Like you said there may not be enough pressure. Another thing you may want to try is to take the gas cap off and pull the engine over. Maybe there too much pressure in the tank for fuel to flow. When you replaced the lines, did you check the line in the tank? Some sleds have a filter with a check valve in the tank and they sometimes clog or get stuck.
 

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Hey buddy, I think I hear a crank seal[:0] Thats what brought the end to my jag, crank seal was shot, which mean low compression, which means feul pump is not working properly, and when it works, sled runs ****ty, cause loss of compression in gas, if i woulda fixed that crank seal, that sled would run like a champ, but no, i let it go, and melted the piston[V] So yea my bet is the crank seal, or maybe a dif seal, run a compression test, or start the sled, ur going to need to have sopme one else hold another gas can above the carb and let the gas drain down a homemade gas line you made into the carb, and while the sleds running at idle, spray carb cleaner or strater fluid in between the clutch and motor, if it revs a little higher, your cranks eals bad, they go very easily in old cats[:p]
 

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pulse line?
 

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Discussion Starter #8
Impulse line-- runs from the base of the engine to the fuel pump and supplies a pulsed vacuum to the pump.

Chevy-I'll do a compression check on it later today, I also have a carb that I just rebuilt for the other 79 jag--I'll try and swap it over just to make sure it isn't the carb-- and post results later.
 

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Discussion Starter #9
It was the carb!!!!!

Compression was over 120 each cylinder. Replaced the carb-choked it- 3 pulls and it fired right up. I'm rebuilding the one I took off tonight.
Thanks guys!
 
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