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Bike richening out when hot

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Hey guys. My 80 2t richens out when it gets hot. I've already checked a few things - overheating, and compression while it has these symptoms. What happens is the bike runs great while warm and as soon as it gets hot, it gets boggy and the powerband is hard to get into. Any ideas? It doesn't sound lean and it smokes more too when these symptoms are occurring.

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Fuel tank vent working?

 

Might be getting warm enough to pressurize the fuel tank, pushing fuel through the carb.  Open/close the cap and see if that fixes things for a bit.

 

The little stubby vents don't take much dirt before they quit working.

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Fuel tank vent working?

Might be getting warm enough to pressurize the fuel tank, pushing fuel through the carb. Open/close the cap and see if that fixes things for a bit.

The little stubby vents don't take much dirt before they quit working.

Thanks I will try that. I think it's working but its worth a try to ride with it off while I have these symptoms. I don't have a stubby one, just a piece fuel line

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Fuel tank vent working?

 

Might be getting warm enough to pressurize the fuel tank, pushing fuel through the carb.  Open/close the cap and see if that fixes things for a bit.

 

The little stubby vents don't take much dirt before they quit working.

I bought a yz85 off a guy who couldn't get it to run right, first and only thing I bought for the yz was a vent tube..

I prefer the honda tubes, they come with the fat section on the end..

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Thanks I will try that. I think it's working but its worth a try to ride with it off while I have these symptoms. I don't have a stubby one, just a piece fuel line

Avoid the bumps, you certainly don't need nitro crotch, it is way worse than monkey butt, and going to happen with no vent tube!

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Avoid the bumps, you certainly don't need nitro crotch, it is way worse than monkey butt, and going to happen with no vent tube!

Oh ya I've had that happen many many times. I had no vent tube for a while and the first time I actually topped off my gas tank I stopped riding and went directly to the hardware store and bought some line for it

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Here's an update. Now that I think about it, the symptoms I'm getting seem more lean then rich, which would make the clogged vent seem even more possible. I adjusted the carb float a little more rich, and messed around with the air screw somewhat. I let the bike idle for 5 minutes until it was so hot that I couldn't touch the cylinder or radiator and rode. Nothing weird, it ripped pretty good. The engine was hotter then when I had the symptoms earlier in the day. I'm confused.

This is the second ride with bel ray mixed at 40:1 and the first ride I had this happen to me but I just dismissed it as overheating and let the bike cool and then it was fine. The second ride was today and the bike had no reason to overheat so I'm assuming something went wrong. Both rides with bel ray 40:1 I have experienced this but I have never had this happen with the cheap valvoline I was using before.

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If it bogs like a kill button, that is a lean condition

If it bogs like it's under water, that's a rich condition

Edited by TheKoolAidMadeMeSick
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air leak that appears with heat expansion as things warm up and expand. pray some wd40 in suspect areas while idling. if the revs rise then there lies your problem. the other thing could be fuel starvation a a result in an incorrect float height/blocked tank vent.

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Line mgtkr said, air leak!

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air leak that appears with heat expansion as things warm up and expand. pray some wd40 in suspect areas while idling. if the revs rise then there lies your problem. the other thing could be fuel starvation a a result in an incorrect float height/blocked tank vent.

No air leaks. I tested for them. I haven't lost any oil from the clutch, which would've told me if I had a bad clutch side crank seal. And I tested the ignition side with carb clean. Nothing. And the plug chop showed me that I am actually running on the rich side which makes sense because I'm running one size larger jet then what is recommended. I adjusted the float richer yesterday and it happened again today. I still have some possible causes to eliminate. The gas cap, air screw adjustment, air filter, gas mixture, and spark plug.

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well if its running rich or giving rich symptoms id look at wether the coil/lead/cap is in decent condition and make sure the cap is on nice and snug. as it gets hotter it will maybe struggle to give adequate spark meaning your already slightly rich jetting will manifest itself into a running problem. are you sure the choke is off fully? it could be a duff choke lever, in fact I would strip the choke lever and inspect/make sure it is not allowing the extra fuel through once you knock it off

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