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81 XS400SH carbs issue


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Hi all!

Carbs seem to be an issue on this bike looking back through the threads a bit.

My bike starts right up, has new intake boots, carbs cleaned a few times, new stock filters, but it just is not right.

Engine revs, but is really slow coming back down. The throttle cable is working, and It seems like the carbs follow without delay. But it still takes it's time coming back down on the rpm's.

I put 6 miles on it yesterday, and as the bike got warmer, the idle speed wanted to climb up to around 3000. But bring the bike to a halt with the clutch in, and it would drop back down to 1000.

Anyone have a clue what causes this? Or how to fix it?

Thank you!

Frank 81 XS400SH

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Hi all!

Carbs seem to be an issue on this bike looking back through the threads a bit.

My bike starts right up, has new intake boots, carbs cleaned a few times, new stock filters, but it just is not right.

Engine revs, but is really slow coming back down. The throttle cable is working, and It seems like the carbs follow without delay. But it still takes it's time coming back down on the rpm's.

I put 6 miles on it yesterday, and as the bike got warmer, the idle speed wanted to climb up to around 3000. But bring the bike to a halt with the clutch in, and it would drop back down to 1000.

Anyone have a clue what causes this? Or how to fix it?

Thank you!

Frank 81 XS400SH

Hi Frank,

if you did a search, you would have found loads of threads on it

this would answer your problem the best methinks

here

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  • 2 weeks later...

She's running beautifully! Was certainly too lean, but now just right. Thanks for linking me to that info. After screwing around with those carbs several times, carbs are starting to make sense finally!

Put about 20 miles on the bike now. Would have been more, but apparently the tail light comes on when you lock the bars. Didn't see that, in the bright sunlight, but there is an extra key position I guess! Can't see that either on the ignition switch lol! So needless to say, the bike was dead as a doornail the morning after fixing the carb issue. Won't make that mistake again this week.

But now all good. Thanks again!

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She's running beautifully! Was certainly too lean, but now just right. Thanks for linking me to that info. After screwing around with those carbs several times, carbs are starting to make sense finally!

Put about 20 miles on the bike now. Would have been more, but apparently the tail light comes on when you lock the bars. Didn't see that, in the bright sunlight, but there is an extra key position I guess! Can't see that either on the ignition switch lol! So needless to say, the bike was dead as a doornail the morning after fixing the carb issue. Won't make that mistake again this week.

But now all good. Thanks again!

There is one extra position after lock that turns on the taillight. Not sure why they have that there, as the battery won't take it for very long, but if you make sure you look at it I find I can always tell.

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There is one extra position after lock that turns on the taillight. Not sure why they have that there, as the battery won't take it for very long, but if you make sure you look at it I find I can always tell.

in the uk it runs a pilot bulb at the front as well as the rear. Its still law that you have to leave lights on parked on an unlit road!!

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in the uk it runs a pilot bulb at the front as well as the rear. Its still law that you have to leave lights on parked on an unlit road!!

Ahhh, I remember that rule from Germany in the late 70's. My ford taunus would turn on both front and rear marker lights on the side it was left active for with the ignition off. Of course with it's POS 6v electrical system it would start if left like that for more than about 30 minutes or so. And it was rather fun getting a jump since most of the newer cars were 12v :blink: and would blow out everything.

IIRC the technique we came up with for those situation was to start cranking BEFORE hooking up and last cable and removing the cable just as it stared to fire on it's own. Sure did crank fast when being jumped though :D:D

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