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Weird throttle/carb issue...

  • Thread starter Thread starter DannyMotor
  • Start date Start date
D

DannyMotor

Guest
Before you ask... airbox, orings, all gaskets, top air screws at 1.25 turns out, bottom screws at 1.5 turns out, oiled drop in k&n aftermarket exhaust and the valves were just checked... 120 main... needles 1 notch up... the throttles were also bench-balanced.

Bike starts and idles fine. Once it warms up the throttle gets sticky and it starts to pop out of the exhaust. Shut it off... as soon as the bike is off, the throttle frees up. Fire it back up and after about 15 seconds the throttle sticks again and it pops...

What on earth could this be?? The petcock operates correctly... just derusted the tank... running 93 octane with a shot of marvel mystery oil in it.

Its obviously leaning out and the slides in the carbs are either becoming vacuum locked or are drying out... or something is adversely affecting throttle motion as soon as the bike is running...

Running it on PRI does nothing to fix the issue. The throttle cables are slacked all the way off on both ends. I have NEVER experienced anything like this before.
 
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What do you mean by "the throttle sticks"? Do you mean the rpm's increase while the bike is just idling?
 
No, I mean the throttle PHYSICALLY sticks! It becomes hard to turn, and hangs up when trying to return to full close... it's not the carbs doing it... you can feel it in the twist-handle.

But as SOON as you shut the bike off... it's gone... perfect. You can blip it, twist it, and crank on it and it snaps shut every time.

It JUST started doing this tonight, I was playing around with it all day yesterday and it was fine.
 
... I am really at a loss here. What the hell would change between running and not running that would cause the throttle to stick IN the carbs? Vibration?

All the pipes are hot, so it's definitely firing on all cylinders. So baffled.
 
I don't know but I'd look at your throttle cable and make sure all the slides and the throttle cable piece are all properly snugged to the throttle twist bar (or whatever it's called).

BTW, 1.5 turns open on the fuel screw is about double what it should be for a stock bike.
 
Check the clutch cable. Mine was wandering and holding open the throttle wide open at times. Had to resecure it so it could not touch anything. Took a while to figure it out too...
 
Nessism said:
I don't know but I'd look at your throttle cable and make sure all the slides and the throttle cable piece are all properly snugged to the throttle twist bar (or whatever it's called).

BTW, 1.5 turns open on the fuel screw is about double what it should be for a stock bike.
Click to expand...

Mines not stock... see above... however would dropping it to 3/4 of a turn out across tje board help?

nejeff said:
Check the clutch cable. Mine was wandering and holding open the throttle wide open at times. Had to resecure it so it could not touch anything. Took a while to figure it out too...
Click to expand...

You mean choke cable? I dont have one. Its a lever choke.
 
Taking the carbs off, checking EVERYTHING, then doing a re-bench balance and float-height check. Just to be sure...
 
2 hours later....

Took the carbs off... clean as whistles.
Adjusted fuel screws to 3/4 out from soft stop.
Adjusted air screws to 1.25 out from stop.
Re-balanced on bench.
Re-adjusted throttle cables.
WD-40'd the slides, from the top....

Slapped it back together and symptoms are gone!

I don't know if it may have to do with the humidity/heat, or something like that... the bike hasn't been 'run' just idling with a fan on it... so who knows. I'm going to lube the throttle cables and slide before I run it as well with some silicone dry-lubricant, just in case.

I'll leave it til tomorrow and try it out.
 
Did you put a thin coat of oil on the linkage rod too? if not, then dont disasseble to lube them. Take a Qtip and spray a bunch of that white lithium grease in a can lid. Dip the Qtip in and smear some right where the rod passes thru the rubber seals on the carbs. Squish it in there a bit and work the throttle a bit to work the grease around as well. And as was stated many moons ago, the recycling of the breather thru the airbox also serves to lube the slides. Yes they can get dry and as Josh ( Cafe Kid ) has noted, moisture in between the slides and tower ( being dissimilar metals to boot ) tends to make corrosion that makes them stick and hang up.
 
chuck hahn said:
Did you put a thin coat of oil on the linkage rod too? if not, then dont disasseble to lube them. Take a Qtip and spray a bunch of that white lithium grease in a can lid. Dip the Qtip in and smear some right where the rod passes thru the rubber seals on the carbs. Squish it in there a bit and work the throttle a bit to work the grease around as well. And as was stated many moons ago, the recycling of the breather thru the airbox also serves to lube the slides. Yes they can get dry and as Josh ( Cafe Kid ) has noted, moisture in between the slides and tower ( being dissimilar metals to boot ) tends to make corrosion that makes them stick and hang up.
Click to expand...

My concern is that it only happens when it was running... will lube the boots tonight. I also ordered a few new bits and pieces from z1. Mainly float needles and fuel screws... noticed mine were scored up during cleaning... and a carbtune.
 
I have seen something similar on carbs that sat in carb dip too long. A greyish coating rolled up in the slides and dried out. After a good cleaning and brushing the film was removed and no more problems.
 
I ran into a similar issue with sticking slides after using brake cleaner spray instead of carb spray. The brake cleaner residue must have reacted with the petrol and left some dark gummy smears on the slides that caused them to stick.
 
I did notice a grayish film in a couple of the motor-side venturis... I'm goinf to have to take them offf again this weekend anyway.
 
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