So yes I know this is a yamaha forum but I thought that someone on here may be able to help me diagnose my 1978 Arctic Cat JAG 2000 problem. Carb has been cleaned and timing is good but the sled dies immediately after priming. An air bubble is stuck in the fuel line from the pump to the carb. It doesn't seem like it has enough flow. Would longer fuel lines cause this? Any ideas would be greatly appreciated. Thanks.
78 JAG fuel problems
- Thread starter SXviperER
- Start date
if you pull off the fuel line at the carb and pull the sled over (with the kill switch to'off'), does the fuel pump push gas out of the line?
If it DOES push out gas:
1.) check the float in the carb, it may be stuck or the needle and seat is stuck and wont allow fuel to enter the carb, try and remove the carb without turning it upside down and see how much gas is in the float bowl.
2.) once the float bowl is off and you check the movement of the float and needle/seat, check the float level. You want the arm of the float to be about paralel to the top of the carb body where the float bowl bolts on when you hold the carb upside down.
If it DOESNT push gas out:
1.) check the pulse hose coming from engine to fuel pump, can have a break,slit in it and it wont pump fuel
2.) if the pulse line is good take apart the pump and see if the diaphram is good or the pump is full of silt/dirt.
1.) check the float in the carb, it may be stuck or the needle and seat is stuck and wont allow fuel to enter the carb, try and remove the carb without turning it upside down and see how much gas is in the float bowl.
2.) once the float bowl is off and you check the movement of the float and needle/seat, check the float level. You want the arm of the float to be about paralel to the top of the carb body where the float bowl bolts on when you hold the carb upside down.
If it DOESNT push gas out:
1.) check the pulse hose coming from engine to fuel pump, can have a break,slit in it and it wont pump fuel
2.) if the pulse line is good take apart the pump and see if the diaphram is good or the pump is full of silt/dirt.
Devilin AblueDress!
New member
This is the exact opposite end of the spectrum from your question about fuel BUT, Way back when (like 15+ years ago) I had a early 90's style Jag (newer body style than yours) and I was at my witts ends. Sled had ben stored outside covered with an old boat tarp. Went to fire it up and was doing the exact same thing you describe. Pulled carbs and cleaned them, checked over 100% of everything I could think of. On the 3rd day of
(keep in mind I was young and dumb) I came to the conclusion I was just gonna keep priming it until it finally took off. When it finally ran for more than a minute I noticed it was trying like hell to blow the pipe off the can. Popped the springs and had a WTF moment. Apparently it was sitting at the perfect angle for the only hole in tarp to drip water onto sled that ran down the hood then dripped onto pipe and FILLED the can with water that froze. 20 minutes fighting with bolts to get can off, sat by wood stove upside down overnight.....ran like a champ! (well as good as a cat can LOL!)
(keep in mind I was young and dumb) I came to the conclusion I was just gonna keep priming it until it finally took off. When it finally ran for more than a minute I noticed it was trying like hell to blow the pipe off the can. Popped the springs and had a WTF moment. Apparently it was sitting at the perfect angle for the only hole in tarp to drip water onto sled that ran down the hood then dripped onto pipe and FILLED the can with water that froze. 20 minutes fighting with bolts to get can off, sat by wood stove upside down overnight.....ran like a champ! (well as good as a cat can LOL!)Thanks Mr..Viper for the troubleshooting ideas. I'll try it tonight.
As for Devillin story. I will definitely check that out. My sled was sitting under a tarp for a long time and could very well be possible. I'll let you guys know once i figure it out. Thanks.
As for Devillin story. I will definitely check that out. My sled was sitting under a tarp for a long time and could very well be possible. I'll let you guys know once i figure it out. Thanks.
Yamaha Nutz
New member
like mr viper said also it sounds like a symptom of water in the fuel make sure you have all fresh fuel too
got-wood
New member
My Rupp was doing this. I had that Keihin off so many times I can't count em. Finally realized the needle valve was sticking in the hole! DUH!
Okay.. Now that the christmas holidays are over I had a chance to take a look at the Cat again. Pulled the full line off the carb and what do you know.... Fuel is being pushed out of the line when I pull it over a few times. Clearly the fuel pump works. Removed the carb and caught all the fuel from the carb as Mr.Viper suggested. Problem now is, When i remove the bowl and examined the needle it moved freely but the floats seem to also slide easily. Could the floats have a small crack which causes them to sink overtime? Should i submerge the floats in gas again to see if they float over time?
since it has gas in the bowl being pushed in from the fuel pump, the needle and seat are working, so the problem goes to the pilot jet circuit of the carb.
remove the pilot jet, can you see light thru it when you hold it up and look thru it?
with the pilot jet out of the carb, take a spray nozzle tube of carb cleaner or brake clean and squirt it up into where the pilot jet goes, does the fluid come out of the idle orfice hole in the FRONT throat of the carb?
remove the pilot jet, can you see light thru it when you hold it up and look thru it?
with the pilot jet out of the carb, take a spray nozzle tube of carb cleaner or brake clean and squirt it up into where the pilot jet goes, does the fluid come out of the idle orfice hole in the FRONT throat of the carb?
Removed the pilot jet and sprayed with carb cleaner and an atomized mist came out of the flow orifice.
Just brainstorming here but if the floats would fill with gas and sink over time wouldn't this stop the flow of new gas into the bowl and in turn give the air pocket in the fuel line.
Just brainstorming here but if the floats would fill with gas and sink over time wouldn't this stop the flow of new gas into the bowl and in turn give the air pocket in the fuel line.
Does it stay running with the throttle partly open? When you pulled the carb and caught the fuel, had it just quit running and was the bowl full of fuel?
I believe that sled had a Mikuni VM30 on it. It should have a starter plunger instead of a primer, but someone may have converted it. If it still has a starter plunger, then leave it on until it runs rich and the drop it to the middle setting, and repeat to off when it runs rich again.
Can you post some pics?
IIRC the pilot circuit consisted of the pilot jet line from the bowl which connected to three other passages . . . 1 - the pilot air jet from the air horn, 2 - an orifice under the slide (bypass), and 3 - an orifice right after the slide (on the engine side). Looking closely in the venturi you should see 2 little openings in the bottom (must raise the slide to see the 1st one). All three of these need to be clear for proper operation. The flow of air and fuel actually changes direction in #2 (bypass) when the slide is opened (instead of air coming in #2 (as well as the air jet) and fuel going out #3 - fuel comes out both #2 and #3 when the slide is open)
To check your floats just fill the removed bowl with gas and set it on the bench to see if the floats drop over time.
Do check your pipe. I filled one with enough fuel to blow it completely off the engine once when I was being careless.
I did have a weak pulse cause one to quit pumping fuel when the engine warmed up. But it sounds like your issue is right after starting.
I believe that sled had a Mikuni VM30 on it. It should have a starter plunger instead of a primer, but someone may have converted it. If it still has a starter plunger, then leave it on until it runs rich and the drop it to the middle setting, and repeat to off when it runs rich again.
Can you post some pics?
IIRC the pilot circuit consisted of the pilot jet line from the bowl which connected to three other passages . . . 1 - the pilot air jet from the air horn, 2 - an orifice under the slide (bypass), and 3 - an orifice right after the slide (on the engine side). Looking closely in the venturi you should see 2 little openings in the bottom (must raise the slide to see the 1st one). All three of these need to be clear for proper operation. The flow of air and fuel actually changes direction in #2 (bypass) when the slide is opened (instead of air coming in #2 (as well as the air jet) and fuel going out #3 - fuel comes out both #2 and #3 when the slide is open)
To check your floats just fill the removed bowl with gas and set it on the bench to see if the floats drop over time.
Do check your pipe. I filled one with enough fuel to blow it completely off the engine once when I was being careless.
I did have a weak pulse cause one to quit pumping fuel when the engine warmed up. But it sounds like your issue is right after starting.
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Recheck the complete pilot circuit. See my previous post. Also can you answer some of the questions?
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In order for fuel to pulled up into the carb at low rpms, the pilot circuit must be working. You can override this by opening the throttle halfway while someone pulls the rope hard. This of course doesn't fix it but simply proves that it will run once you get the pilot circuit working.
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Have you determined which carb is on it, and whether it has a starter plunger?
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Will it start with the starter plunger open either halfway or all the way?
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Just to explain the fuel not getting from the bowl to the carb throat a little more . . .
At low rpms there isn't enough vacuum created by the venturi to pull fuel through the main jet. Thus fuel needs to be pulled via the pilot circuit (small amount) or via the starter circuit (large amount). If the slide is in the idle position then a small amount of fuel should be pulled from the rear (engine side) pilot orifice in the carb throat as long as there is open passage from the air jet opening in the air horn and the middle pilot orifice (under the slide). Plug any of these up and this doesn't work right. When working right this circuit is designed and tuned to supply fuel for a warm engine at idle and low rpms.
However, for a cold engine the starter circuit comes into play. Because fuel atomizes poorly in a cold engine a super rich mixture is used to get it started. The sled should start on the starter circuits with or without the pilots working.
You might try turning the idle speed screw (the one that raises the slide, not the air screw) in to raise the slide position a bit. Once you get it started and warmed up then you can go through the adjustments.
btw: where is your air screw set at?
However, the starter circuit should still supply plenty of fuel
At low rpms there isn't enough vacuum created by the venturi to pull fuel through the main jet. Thus fuel needs to be pulled via the pilot circuit (small amount) or via the starter circuit (large amount). If the slide is in the idle position then a small amount of fuel should be pulled from the rear (engine side) pilot orifice in the carb throat as long as there is open passage from the air jet opening in the air horn and the middle pilot orifice (under the slide). Plug any of these up and this doesn't work right. When working right this circuit is designed and tuned to supply fuel for a warm engine at idle and low rpms.
However, for a cold engine the starter circuit comes into play. Because fuel atomizes poorly in a cold engine a super rich mixture is used to get it started. The sled should start on the starter circuits with or without the pilots working.
You might try turning the idle speed screw (the one that raises the slide, not the air screw) in to raise the slide position a bit. Once you get it started and warmed up then you can go through the adjustments.
btw: where is your air screw set at?
However, the starter circuit should still supply plenty of fuel