cold lh exhaust at startup idle

gray am I

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my 79 special starts up ok needs choke at startup but at idle I can put my hand on the lh pipe at startup and it is almost cold to the touch, only seems to get hotter when I crank the revs up wondering if it may be blocked jet. other possibility the lh fuel tap, or electrical issue? did notice last time I rode it left the fuel taps on prime and it died on me , almost like it had run out of fuel, started it back up and rode home after a 30 second stop. Any ideas?
 

5twins

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Well, the fuel taps pull off of the reserve pipe when in the "Prime" position, so if you run out of gas, you're really out.

Check the carb sync. If off enough, one cylinder could be effectively shut off at idle speeds, only kicking in when you rev it up.
 

Tomterrific

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It almost surely is the idle jet. Pull out the mixture screw and use the little tube and spray carb cleaner to blast inside. Wait and do it a few more times. With luck it will melt and force out any blockage. Drain the float bowl after. This is the absolute, no brainer, don't worry about screwing up something else method I have found. And it works too.

Also, if little black bits drain out of the float bowls you may have a rusty gas tank leaking debris.

Tt
 

Paul Sutton

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Before taking out the mixture screw mark its position relative to the carburetor body with a felt pen. Then screw it in until fully seated (closed) counting how many turns out from the fully off position it was. When screwing it in fully just seat it gently at the off position so as not to damage the screw and seat. Then when you remove the mixture screw fully you can easily get it back to where it was. You need to be accurate with the mixture position e.g. a difference of 1/8 turn is significant and a 1/4 is very noticeable.
 

ThatXS650Guy

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Sounds like your pilot jet is plugged. Has the bike been sitting? When were the carbs cleaned last?
 

XSLeo

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I have found that most of the time when a bike has issues such as you describe the pilot circuit in the carb on the side that isn't running/ getting warm needs attention.
There are vey small spots in the passages and the ports in the cartb bell are very tiny and plug quite easily.
Flushing them as tomterrific mentioned often woprks if the stoppage isn't too bad. If that won't work you might have to pull the carbs to tear down and clean.
After you get them clean, checking carb sync comes into play. If not synced p[orperly one cylimder pulls harder than the other. This can cause excerss vibration.
Leo
 
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