Very weird problem.

[TROLLCAT]

bad gas

 

[TROLLCAT]

just had a 120 in the shop tank was empty added new 91 sled fired up then sat for 4 days until customer came to pick it up

did a test run around parking lot got a lap and 1/2 and sled quit

the old gas had left a bad residue in tank and mixed with new gas = no go

change gas again and rock and roll

 

[TROLLCAT]

oh I been dooing this for 50 years LOL too HAHA

 

[Captjacksparrow]

bad gas

I don't think so...... but who knows. It runs so good when it starts.
I put the primer injectors in the case so they inject fuel on the engine side of the reeds. I left it outside the shop for 4 hours. Went out and pulled it 10 times with choke on full, nothing. Then I primed it 3 times, nothing, then 3 more, nothing, then 4 more, nothing. Then I pulled the plugs, they didn't looked soaked, believe it or not, so I gave three squirts with my gas bottle down the plug holes, I figured I might as well really flood it, lol....... it fired up clean on the first rotation of the crank, and idled nice, it was fat for a bit but cleaned out quick. I've never seen a machine that ran beautiful, but couldn't pull fuel from the case cold no matter how much is in there. Yes, the primer is pumping tons of fuel. I sprayed the cranks seals again with brake clean, which kills the motor quich when there's a leak and not one RPM change. I'm done, customer won't be happy, but it's almost not possible for it to do this. Never seen a machine that didn't fire up with 2 or three shots of a primer...........

 

[SUMMIT TREE]

I'm working on a 98 Cat, ZL500. It runs beautiful, pulls normal and starts normal warm. It will not start cold unless you put fuel down the plug holes, then fires up first pull and runs normal with choke for a bit then stays idling and running normal. Been through the carbs and choke system, every thing is clean and good and choke set right. I thought I would just put a primer on it if it can't pull enough fuel cold through the choke. So I put a primer on it. Weirdly enough, makes no difference, 3, 4 or more primer shots, still won't start. put gas in the plug hole, fires right up. The primer is injecting the gas right at the carb book like every other primer machine. Never seen anything like it, just won't seem to pull gas from the intake unless it's primed through the plugs. I'm lost, reeds look ok too. It starts normal when in the warm garage too.........Anyone ever seen this before?

I would be curious to check the strength of your spark when its cold and wont start. Could it be weak? Enough to light off the gas you dump in the cylinder and then once running the spark would be stronger due to higher Rpm. Also when warm engines tend to start better, so explains why it starts ok warm. I would be going down the ignition path at this point. Can’t be fuel , u covered pretty much everything. And the fact that it runs good says fuel is being delivered properly while using the machine. I had a sled I would have swore did not have an ignition issue. Turned out the spark plug leads were completely shot. Another time replaced spark plugs and was baffled at how Huge the difference was between old ones and new ones. ( because “old” ones weren’t very old, or visually worn). But went from weak pathetic spark to Bolt of lightning! Anyway food for thought.

 

[TROLLCAT]

I don't think so...... but who knows. It runs so good when it starts.
I put the primer injectors in the case so they inject fuel on the engine side of the reeds. I left it outside the shop for 4 hours. Went out and pulled it 10 times with choke on full, nothing. Then I primed it 3 times, nothing, then 3 more, nothing, then 4 more, nothing. Then I pulled the plugs, they didn't looked soaked, believe it or not, so I gave three squirts with my gas bottle down the plug holes, I figured I might as well really flood it, lol....... it fired up clean on the first rotation of the crank, and idled nice, it was fat for a bit but cleaned out quick. I've never seen a machine that ran beautiful, but couldn't pull fuel from the case cold no matter how much is in there. Yes, the primer is pumping tons of fuel. I sprayed the cranks seals again with brake clean, which kills the motor quich when there's a leak and not one RPM change. I'm done, customer won't be happy, but it's almost not possible for it to do this. Never seen a machine that didn't fire up with 2 or three shots of a primer...........

Maybe the seal between cylinders on crank is gone that would cause this very issue you have described.

 

[mclean]

I'm beginning to realize how little I know about 2 stroke engines

 

[Clode]

I fixed a sled for a guy once that had sat for years and it would idle, but not right. When I tore the motor down the center crank seal was mush from fuel going rotten in the bottom end. I messed with that sled for hours trying to get it to run. Sent the crank out for new seals, put it back together and it ran like new. The fuel nowadays is horrible stuff if it sits to long.

 

[Captjacksparrow]

Spark might look a bit whitish outside, but almost looks blue?........ Hard to get it dark enough outside to tell. It looks good inside, nice concentrated blue spark. but it fires right up after a few minutes inside, LOL. I'm going to start on ignition system now. Everything tests ok but I'm gonna throw a coil on to start and go from there. I'll let you know if I get it fixed.

 

[rusty]

i have a zr500 parts machine if you need anything.

 

[team dirt]

Tighten your plug gap

 

[rsaint]

Could be a crank seal, colder it shrinks and when it warms seals up. Reason i think this my work truck sits outside no leaks on rear wheel seal, brought in garage to change transfercase and both rear wheel seals leaking on back end 3500 truck so pain to change.

 

[ZRrrr]

It my days of older Cats stators would sometimes go bad and do weird things like what you describe. A few degrees in temperature change would make the stator work or not work. Would get rewound stators from a local company. They would overbuild them. Never an issue after the stator was fixed.

 

[Luke The Drifter]

It my days of older Cats stators would sometimes go bad and do weird things like what you describe. A few degrees in temperature change would make the stator work or not work. Would get rewound stators from a local company. They would overbuild them. Never an issue after the stator was fixed.

Ditto. My dad had an 01 Mountain Cat 600EFI that started doing exactly this. Would run, then die, wouldn't start unless fuel was dumped down the cylinders. Ended up being something in the stator was intermittently failing even though it tested good by service manual specs. We pulled our hair out trying to figure out what was wrong with it. Ended up being a stator going wonky.

 

[JMCX]

Ditto. My dad had an 01 Mountain Cat 600EFI that started doing exactly this. Would run, then die, wouldn't start unless fuel was dumped down the cylinders. Ended up being something in the stator was intermittently failing even though it tested good by service manual specs. We pulled our hair out trying to figure out what was wrong with it. Ended up being a stator going wonky.

That stator had to power up a whole EFI system. This one seems that it can't get cold fuel above the piston at rope pulling RPM.

 

[TROLLCAT]

if you want to try a stator I should have 1 or 2 kicking around

pm me

 

[mountianguy]

Have you bypassed those goofy magnetic switches on the carbs? In 1998 AC went to a N/O ignition on the EFI sleds, the carb sleds should still be N/C something to be aware of when dealing with electrical. Is the air intake box, exhaust, carb / fuel tank carb vents, fuel filter, fuel lines, pickup in tank, fuel shut off clean and working properly? Have you checked the pulse line with a gauge to verify proper operation? Certainly is a strange issue.

 

[Captjacksparrow]

Have you bypassed those goofy magnetic switches on the carbs? In 1998 AC went to a N/O ignition on the EFI sleds, the carb sleds should still be N/C something to be aware of when dealing with electrical. Is the air intake box, exhaust, carb / fuel tank carb vents, fuel filter, fuel lines, pickup in tank, fuel shut off clean and working properly? Have you checked the pulse line with a gauge to verify proper operation? Certainly is a strange issue.

I did bypass those at the begining of all this, wasn't the problem. Trollcat had said "bad gas" and I said to myself that wasn't it.............but then it got me thinking, it only would start when I put gas from my squirt bottle in it, where the primer and choke were both using gas from the tank.........Now in my defence, the customer said it wasn't old when he dropped the machine off(I always ask) and it smelled fresh and it looked fresh(not the darker yellow you have with older gas) but I thought I'd try it for chits & giggles.......and sure enough, it would start cold but only with the primer after 5 or 6 pulls and didn't start good, wouldn't rev at first but could get it to run by playing with it, and then it would run good when it warmed up a bit. It was better but still not right. Then I threw a new coil on it because they are cheap and this morning it started second pull with only choke, revved up to high idle instantly and ran perfect. So I guess I was fighting a weird gas problem and a weak coil. Anyway, thanks for all the help guys, really appreciated it!!

 

[bobsledder]

Good to hear and thank you for reporting the cure. A learning opportunity for all. So often on forums the OP never posts what they find solved the issue

 

[ferniesnow]

Congratulations for being persistent and dragging us along with the results.
It is amazing that for 39 posts this thread has remained on topic. Not everything has gone to the dogs on this forum.