My 1991 Jag won't idle??

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sir-switch

New member
I was given a 1991 Jag 440 in fair condition that I'm now tuning up for my son. I've completed all the basic tune items... replaced gas, fuel filter and cleaned and adjusted the carb but I still can not get her to idle. She starts everytime within a couple of pulls and will run as long I feather up the throtle. As soon as I left off the gas ... the rpm will drop right down and she stalls out. She doesn't even try to hold idle it stops as if the gas was shut off (which is not). Looking for other trouble shooting tips that I can try? This sled is pretty much as simple as they get...Fan cooled, single carb, with no TPS switches to worry about... Basically if you have spark and fuel this baby shoud run. I should also mention that the compression is about 120psi on both cylinders and I've also added a jumper to the main harness which will bypass the entire console/kill switch assy and leave just magneto and ignition coils in the loop. I'm running out of things to check.

Any tips would be appreciated.
 
indy_500

indy_500

Well-known member
spray some starting fluid behind the clutch, crank seal could be shot. (of course you need someone to help you keep the sled running) If the rpm's don't change then you can rule that out.
 
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sir-switch

New member
I thought about trying that...but wasn't sure if the would cause an idle issue. I should also mention that the sled has less that 3000 miles on her. Crank seals at 3k might be a bit sonn. I'll give it try and post the results
 
indy_500

indy_500

Well-known member
My sled seemed to run fine from 10 mph and faster, but didn't want to idle at all. It ran on 1 until about 10 mph. My crank seal was shot and so was my crank bearing. I doubt your crank bearing is shot, but your crank seal could be shot just from exposure to the "elements" i mean, it is 20 yrs old.
 
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sir-switch

New member
Thank for the tip...Can the seal be replaced with simply removing the primary clutch and installing it over the tapered shaft of the crank?
 
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jimfsr

New member
first, make sure the idle screw is actually adjusted, if you can feather it up to idle, try to turn it up some. Also, is the air screw clean and adjusted properly, 1 1/2 turns out to get started. Is the choke(enrichener) closing all the way or letting in extra fuel that cant be burned. Crank seal problems are doubtful, but you can check. A plug color test will help with that if you can get her up to speed for a bit. Make sure the pilot jet is actually cleaned out, and that the passage into the carb is too.
 
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sir-switch

New member
I had the carb completely disassemble eailier today. Removed and cleaned both the main and pilot jet. the pilot looked a bit cruddy and it took a fair amount of compressed air and carb cleaner to clear out all the orfices. I then throughly sprayed the entire carb housing (inside & out) with carb cleaner and compressed air...I believe that everything is now clean it's difficult to see down the pilot hole inside the carb. When I reassembled, I set the pilot air screw to 1 1/2 turns, and confirmed the choke plunger is fully seated. to keep her runnnig, I need to feather up the throtle to a point just before the clutch engages...the machine doesn't have a tach but I would estimate RPMs at 2500. The idle adjustment screw is set close to the point where the machince should idle. After I get the engine good and warm (throtle up for several minutes) I let off the throtle and the machine simply dies out and does not even try to stay running.
Could this be a fuel pump or a gas tank screen issue? I'm running out of ideas. If I had a spare carb I would simple swap them to see if my issue follows the original carb.

Thanks again for any help
 
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hank2613

New member
sounds to me your pilot is still dirty. Spray cleaner does not do much. It should be soaked. You can get a gallon pail of it at a auto parts store. Your fuel pump is a ez test. Pull the fuel line off and pull the sled over if it does not shoot five feet your problem is before the carb.

Dan
 
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trailshredder

Member
hank2613 said:
sounds to me your pilot is still dirty. Spray cleaner does not do much. It should be soaked. You can get a gallon pail of it at a auto parts store. Your fuel pump is a ez test. Pull the fuel line off and pull the sled over if it does not shoot five feet your problem is before the carb.

Dan
Click to expand...

I have never seen a sled shoot gas 5 feet!?! But yes you need to soak the carbs in carb dip to get a "real" cleaning. Carb cleaner in the spray can won't cut it. And on that sled you can change the PTO crank seal without pulling the motor, but you need the know how and right tools to do the job. Something you should leave to the profrssionals.
 
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arcticman

Member
Switch my old jag was bad on the diaghram in the fuel pump would run on choke but not idle. It got to where when I put one in I would pick up a back up.

Good Luck, nothing more frustrating that the little things.
 
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doomsman

New member
Try tightening the throttle cable, there is are two
little flip switchs near the handle that one has to close
before the other opens. See the little pin on the flipper,
it puses a switch. This is a frozen carb cable safety.
good luck
 
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sir-switch

New member
Thanks everyone for the helpful advice....
1st... I've check the crank seal using the starting fuild spray behind the primary clutch and there were no changes in rpm. (no seal issue ... yea)
2nd... I've disassembled the fuel pump to inspect the diaphram for cracks and didn't see any issues. Also confirmed that the fuel is flowing through the line when I spin her over....the flow rate however is not 5ft. The in-line fuel filter has been chaged, but I don't see it completely filled when I feather up the rpm's. I will pick up a $5 pump rebuild kit and also replace the fuel/vaccum lines tomorrow.
After reading the replies, I believe that my issue may still be crud in the carb (pilot jet and carb passage ways). I'll pick-up a new pilot jet and soak the carb for a couple days in cleaner then try it again. Does anyone have a favorite carb clearner?

I'll give everyone the final results once I get this baby purring again.

Thanks again to all

sir-switch
 
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huttes99

New member
Had the same problem on a friends old single carb Jag and it ended up being that the choke was not coming off completely. Check your choke over very good. We messed with his for 2 weeks and had the carb apart 10 times and thats what it was. Good Luck.
 
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sundown

New member
A bad crank center seal will cause it not to idle. This was a common problem on the old engines with rubber seals. I have only seen it once on an engine with a labrynth seal. If all else fails this might be the problem.
 
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sir-switch

New member
T

Well my saga continues..... I've tried everything listed in the posted replies with no change in results. The latest was a two day carb chem dip soak to insure the all passage ways within the body were clear and installed a new pilot air jet. I've aslo replaced all the fuel/vacuum line and installed a rebuilt kit on the fuel pump. I've checked again the choke plunger for operation and confirmed that the crank seal (PTO side) is not leaking by spraying starting fuild near the seal while running and looking for any change in RPM. During my last attempt, I feathered up the throtle and let her run for quite awhile. After the initial start-up (2 pulls or less) within about 15 sec the motor begins to die but I can keep her running if I just feather the gas to about 2500-3000 rpm. I notice that the Y-pipe branch (pto side) becomes much hotter than the branch on the other side and the spark plug condition (non-pto side) is a bit more wet....could this be a result of an intake valve issue? I'm not quite sure if this machine has a reed cage or what. I do recall an issue that I had with another machine where the skirt area of the piston was damaged (basically missing)..... I guess I'll check that next
 
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