stuttering issue - with video

deadchef

deadchef

xsbobblehead
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petoskey, michigan

i can't seem to figure this out. starts and idles fine. i feel like it's a lean condition but i've tried larger mains with no change. i've cleaned carbs, tank, rebuilt petcock, new plugs, set cam tension, valves, set floats, new float needles, new carb boots and gaskets. i've checked the battery and voltage is good at idle and goes up with throttle.

i'm just at a wall at this point and i'm not sure what else to check.

:banghead:

thanks
 
81 has TCI so timing is rather fixed wouldn't hut to make sure it advances.
Synced the carbs?
New o-rings on the float valve bodies?
Throttle shaft seals? are the throttle shafts loose in the bodies?
Are the carbs still the BS34s, foam floats?
Does it hunt like that under load too?
Are you using the correct float height for the foam floats measured in the right spot on the floats.
Sure the vacuum diaphragms in the petcock and carbs are hole free?



How many miles on it?
 
gggGary said:
81 has TCI so timing is rather fixed wouldn't hut to make sure it advances.
Synced the carbs?
New o-rings on the float valve bodies?
Throttle shaft seals? are the throttle shafts loose in the bodies?
Are the carbs still the BS34s, foam floats?
Does it hunt like that under load too?
Are you using the correct float height for the foam floats measured in the right spot on the floats.
Sure the vacuum diaphragms in the petcock and carbs are hole free?



How many miles on it?
Click to expand...
carbs synced
new o-rings on the float valve bodies
throttle shaft seals are good. not loose.
yep, bs34s with the foam floats set to 22mm
i can ride the bike and it rides fine until >4.5k rpm
petcock was rebuilt with new diaphragm
carb diaphragms passed the 'thumb over the hole' tests

bike only has 4100 miles.
 
What aircleaners you using? If not stock air boxes then you should try UNI pods. K&Ns and other pleated pods will cause a similar "hunt" condition.
 
gggGary said:
What aircleaners you using? If not stock air boxes then you should try UNI pods. K&Ns and other pleated pods will cause a similar "hunt" condition.
Click to expand...
got me there. i do have the infamous mike's xs pods. the stock box that the bike came with had the original filters in them. they weren't pretty. didn't even start the bike before putting on the xs pods so no beginning reference. although, every time i have either rebuilt the carbs, changed jets or anything else, this exact symptom persists with every test.

sucks but i guess i'm going to buy the uni's now just to cross off another possible issue that may be causing this.
 
You have quite a pronounced carb problem there. Stumbles in the upper midrange don't usually show unless you're riding, not just revving at a stand still like that. What is your current jetting? And yes, dump the current filters and get UNIs. As a quick test, just take them off and try revving it.
 
ok, UNI's on the way, although i'm a bit skeptical if that is the true issue. i've read many people having success with xs pods, but have also heard just as many people having issues although i haven't come across any issues exactly like mine. i have also tried running without the pods on with the same result.

after studying the carb guide, the symptoms seem to point towards a too small main jet. i have tried stock, 135 and 137.5 with no change whatsoever. i do have some 140's that i'm going to try just for the helluvit.

symptoms manifest whether riding or standing still. idle and off idle response is fine and haven't seen any issues there.

just to toss this out there, could the TCI be the cause of this issue?
 
Will the bike power through that rough spot and continue on up to red line? Or is about 5.5K the max it will rev? The slide begins to lift around 4K. You may have small pin holes in the diaphragms. That would allow partial but not full slide lift. Some vacuum is being generated but not as much as should be. I would pull the slides and carefully inspect the diaphragm condition. Hold them up to a good light, gently stretch them, and look for pin holes, especially around where they connect to the slide.
 
That should rule out the TCI as your problem. Have you replaced spark plugs? One of those visible spark indicator you put on the spark plug is a nice way to know you have strong spark. What are your compression readings?
 
it won't go up to red line. won't get past 5.5k-ish. i'll check the diaphragms again but they really look cherry.

haven't done a compression test yet as I assumed with a low mileage bike they it would be ok but i'm going to go check. i have changed the plugs and have about 70 miles on them. i'll post up a pic in a bit.
 
here is a pic of the plugs. i don't know if that can really tell you much with only 70 piss poor miles on them...

plugs.jpg
 
yes, they are black. they are NGK bp7es plugs.

apparently i have lent out my compression tester so i will have to check it tomorrow.

could i have coil issues?
 
Hate to use the O word and would like to see a sharper pic but those plugs look oily.... how does the spark look? If it's fat and blue the coils probably fine. Never hurts to run it in a dark area and look for high voltage leaks. Spritzing with water from a spray bottle will show them up in a hurry
 

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