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XT500 won't start/idle with choke on

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Can't seem to get the bike running properly. Can't use choke at all or it will not start. Idling is very unstable with lot's of coughing and if you touch the choke lever it will immediately kill the engine. Running way too rich I think? Pilot adjuster screw seems to be correct by Haynes, 1 1/4 open. Idling seems a little low, just about 1000rpm...New header gasket, so no leaks there. I think I got the timing right. Compression stroke, points open when F lines up. Still need to double check that it isn't 180 degrees out...

Any adviced? Carb rebuild?

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How about valve clearance? Timing? In warm weather, my SR500 (same engine with electronic ignition) didn't need choke, but if cool it did. How about flat level? Sounds too rich to me; way too rich.

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What year is your bike ?

It's '81 but in europe models we had points in all years so it's technically '79.

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Need more history. Did the bike ever run well or has it sat for years and now your trying to get it running?

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How about valve clearance? Timing? In warm weather, my SR500 (same engine with electronic ignition) didn't need choke, but if cool it did. How about flat level? Sounds too rich to me; way too rich.

Ok. We had 10 °C (50 °F) this morning and the bike won't need or want choke. I think it should. A few week old spark plug is black and smells petrol. Very easy to foul it. I think I have pull out the carb...maybe the jets have been changed by last owner...or try to lean it by adjusting pilot screw. Tho I don't have any idea how to spot correct adjustment.

Valve clearences are checked to be ok. Maybe I will re-check those with the timing. :thumbsup:

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Need more history. Did the bike ever run well or has it sat for years and now your trying to get it running?

It has been sat for years with minimal use before I bought it...It was running ok tho (without choke), but after I replaced header gasket (or what was left of it!) idling got all screwed up. Sounds horrible now. Maybe carb have been adjusted with leaking header?

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If the exhaust was plugged up and the exhaust gases where blowing out the leak you fixed, it could very well be as you suspect. I would be curious as to what the jets are and if the carb is crudded up, but don't over look the exhaust, it could be partially plugged as well.

Sounds like you're on the right track to me. It would be nice to know what the motor compression is if you can measure it, or have someone else measure it. If things don't start adding up, definitly do a compression check.

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If the exhaust was plugged up and the exhaust gases where blowing out the leak you fixed, it could very well be as you suspect. I would be curious as to what the jets are and if the carb is crudded up, but don't over look the exhaust, it could be partially plugged as well.

Sounds like you're on the right track to me. It would be nice to know what the motor compression is if you can measure it, or have someone else measure it. If things don't start adding up, definitly do a compression check.

The whole header was moving to all directions, so there was a massive leak. Pilot screw is adjusted correctly by the Haynes manual, so I think someone has been playing with jets. I gonna order a carb repair kit and we'll see from there.

Low compression is my worst nightmare, so I really hope that I don't have go that far. Strange is that bike is not smoking in any way. You can't see the smoke when bike is running. That was one of my reasons to buy this bike. Running ok and not smoking.

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As long as the exhaust silencer isn't plugged it's probably carb related. Changing the main jet does nothing for the idle. Idle is controlled w/ the pilot jet and needle jet. My Mikuni vm36 runs w/ the pilot at 2.5 turns and the needle at 3 from the top. Something is plugged. Check the silencer. You could remove it and see what happens. If no change check the carb. The pilot jet has been a culprit for me at idle. The choke could also be damaged. A rebuild my be called for. BTW my XT500 engine was built by an old timer with years of knowledge and experience. I run a Mikuni vm36 round slide w/ a 200 main jet and a 540cc bore, big cam, down pipe w/Supertrapp universal. Since I'm new to this site I haven't posted pics yet as I'm in the middle of a frame up restore (just dropped the motor in). Good Luck.

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As long as the exhaust silencer isn't plugged it's probably carb related. Changing the main jet does nothing for the idle. Idle is controlled w/ the pilot jet and needle jet. My Mikuni vm36 runs w/ the pilot at 2.5 turns and the needle at 3 from the top. Something is plugged. Check the silencer. You could remove it and see what happens. If no change check the carb. The pilot jet has been a culprit for me at idle. The choke could also be damaged. A rebuild my be called for. BTW my XT500 engine was built by an old timer with years of knowledge and experience. I run a Mikuni vm36 round slide w/ a 200 main jet and a 540cc bore, big cam, down pipe w/Supertrapp universal. Since I'm new to this site I haven't posted pics yet as I'm in the middle of a frame up restore (just dropped the motor in). Good Luck.

Still waiting for parts to arrive. I'm gonna rip the carb to pieces and see what I find. Last owner said that these carbs are tend to plug on longer standstills. Hmmm, makes sence. I also noticed that my intake manifold is cracked. I found out that you can't get it from Yamaha anymore(?!) but luckily you can source one from ebay.

Heh, you have some powerful beast there! My bike is in "classic bike insurance" so I have to keep it stock.

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Still waiting for parts to arrive. I'm gonna rip the carb to pieces and see what I find. Last owner said that these carbs are tend to plug on longer standstills. Hmmm, makes sence. I also noticed that my intake manifold is cracked. I found out that you can't get it from Yamaha anymore(?!) but luckily you can source one from ebay.

Heh, you have some powerful beast there! My bike is in "classic bike insurance" so I have to keep it stock.

Manifolds can be had from Mikuni through Thumper Stuff, Dennis Kirk or Sudco. Float level makes a very large difference. Be sure it is where you think it is. The rubber bottom of the starter jet plunger has to seal well against the carb body in the well to actually keep the "choke" off. The chokes are really additional jet circuits. Sometimes the rubber mentioned above gets hard enough that it no longer seals, so you get some additional fuel even with it off. I ran a VM38 with about 2.5 turns out on the air screw. Didn't need much choke when cold, but did need some. Again, check you float level.

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Manifolds can be had from Mikuni through Thumper Stuff, Dennis Kirk or Sudco. Float level makes a very large difference. Be sure it is where you think it is. The rubber bottom of the starter jet plunger has to seal well against the carb body in the well to actually keep the "choke" off. The chokes are really additional jet circuits. Sometimes the rubber mentioned above gets hard enough that it no longer seals, so you get some additional fuel even with it off. I ran a VM38 with about 2.5 turns out on the air screw. Didn't need much choke when cold, but did need some. Again, check you float level.

Thanks for a tip! Very important things to check! :thumbsup: What a great forum this is! :confused:

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What a great forum this is!

Most of the time....you're more than welcome. The one thing this forum lacks is a teleporter to allow us to show up and assist where we can. Or throttle some bozo that desperately needs it. Either way, it would be handy. Very handy.

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Most of the time....you're more than welcome. The one thing this forum lacks is a teleporter to allow us to show up and assist where we can. Or throttle some bozo that desperately needs it. Either way, it would be handy. Very handy.

Hehehe, I agree, that would be handy in bunch of other occations as well! Most you are from U.S. so you have at least a chance that someone who knows how to help lives around a block. Lot's of specialists in U.S. as we can see. One more thing that you do better than the rest :thumbsup:

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It really helps when you have a habit of buying unwanted beat motorcycles and resurrect them. If you do that enough, you have lots of knowledge. I still have a few left to finish, but cut over to the newer stuff a few years back, as I don't have the time with my job to be owned by a motorcycle, or motorcycles. Plus, it was time to get up to the present.

The guys from Oz have a lot of good background as well. They were good when I lived there, and they're still good.

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Carb is now cleaned and repair kit installed. Not a moment too soon, o-rings broke in half when removing them, very crispy content indeed. Pilot jet was #25 and main #260. Main sounds little too big? Very rich setup with needle position on second groove from tip? My new setup would be: pilot #30, main #220 and needle on the center position. What do 'all think of that? Sounds right? Kit came with those jets.

Still have to order new manifold before firing up.

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The found ones sound original to me. Kit ones not always correct. Maybe the needle is rich, but if gaskets and o'rings are dissolving, I wouldn't change anything before I tried it.

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