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Jerky throttle?

  • Thread starter Thread starter growler
  • Start date Start date
G

growler

Guest
I noticed something yesterday while riding that has me perplexed. Not sure if I'm posting in the right section. Forgive me if I'm not. :)

The throttle feels a little "jerky". Say for instance....you are riding down a side street around 30-35 mph and then release the throttle, letting yourself slow down (not downshifting, just staying in same gear and slowing down 5-10 mph). Then you twist the throttle again to speed back up. That's the part that feels jerky. That on/off moment in the throttle. I can also feel changes and very slight jerky sensations while going down a bumpy street.

At first I thought my throttle cable needing adjusting. I made sure I had enough play and that it wasn't too tight, making every small movement affect engine speed. Throttle tube is nice and smooth, throttle is snappy when twisted and released.

Then I thought maybe it was my riding position. Could I be putting too much weight on my wrists?

It's making for an uncomfortable ride. All I want is smooth acceleration.
 
The on/off throttle jerkiness is pretty normal, at least I think so. Once you add up all the play in the gears and mechanisms between the crankshaft and the wheel, the final amount can be considerable. Especially on an older bike. Especially one with quite a few miles. There's far less of it on our shafties than most chain-driven bikes, if that's any consolation. You can mitigate it a little by selecting a higher gear than strictly necessary. (I'm typically in 3rd when cruising through 25-30 mph zones when 2nd would do fine, as much for smoother riding as less noise.) You can eliminate it to a large extent by slipping the clutch a smidgen when rolling back on the throttle.

Jerky throttle over bumps... I get that on my 750 because it is much more sensitive in the lower end of the throttle range, but not the so much the 850 for some reason. Best advice I can think of is to make sure you're staying loose on the handle bars and put more weight on the foot pegs when you anticipate bumpiness ahead. This turns your legs into shock absorbers and keeps your body from bouncing around with the rest of the bike.
 
Your CV-type carbs are very sensitive at the very bottom of the range. The transition from "idle" to "just barely more than idle" is rather abrupt. As eil suggests, maybe try one gear higher to help soften the impact. It is also a matter of familiarity. I find that same phenomenon every spring, as I get back on the bike(s). And, to compound the problem, the two bikes that I ride regularly respond just a bit differently in this situation, so I need to re-train myself TWICE. :oops:

.
 
My 1150 was generally a little jerky at low in town cruising speeds. This past winter I rebuilt the carbs including an o ring kit and new intake boots. Now its quite smooth in town. Agreed with Charles on drive line slack. How is your chain tension?
 
There is a fair amount of play coming right from the propshaft. This is likely what you feel. Here's a quick vid showing the play in mine.

 
JTGS850GL said:
I believe his is a shaft drive since it's an 850. I guess that would make his chain tension VERY slack.;) -JK
Click to expand...
And that would be HER shaft drive.

"Growler" happens to be of the female persuasion. :oops:

Note her signature: Girls like to tinker, too. ;)

.

.
 
dorkburger said:
My 1150 was generally a little jerky at low in town cruising speeds. This past winter I rebuilt the carbs including an o ring kit and new intake boots. Now its quite smooth in town.
Click to expand...

What he said. What have you done maintenance wise to the intake/carbs/exhaust? It didn't do that when it left the factory, there's no reason for it to do it now.

Even something simple like carb synch or mixture being set a little wrong can do this.
 
Carbs completely disassembled, dipped, all new o-rings. Everything done exactly via the link on basscliff's site.

Airbox taken apart, resealed, new filter.

New airbox boots, new intake boots.

Valve clearances done.

Carb sync done again after valve clearances.

Stock exhaust. No mods.

Runs great. I'm only a few rides into the season, so I'll try the suggestion of going up one gear and see if that helps.


tkent02 said:
What he said. What have you done maintenance wise to the intake/carbs/exhaust? It didn't do that when it left the factory, there's no reason for it to do it now.

Even something simple like carb synch or mixture being set a little wrong can do this.
Click to expand...
 
Good info. Thanks :)

Steve said:
Your CV-type carbs are very sensitive at the very bottom of the range. The transition from "idle" to "just barely more than idle" is rather abrupt. As eil suggests, maybe try one gear higher to help soften the impact. It is also a matter of familiarity. I find that same phenomenon every spring, as I get back on the bike(s). And, to compound the problem, the two bikes that I ride regularly respond just a bit differently in this situation, so I need to re-train myself TWICE. :oops:

.
Click to expand...
 
growler said:
Carbs completely disassembled, dipped, all new o-rings. Everything done exactly via the link on basscliff's site.

Airbox taken apart, resealed, new filter.

New airbox boots, new intake boots.

Valve clearances done.

Carb sync done again after valve clearances.

Stock exhaust. No mods.
Click to expand...

I would certainly take another look at synchronization, idle mixture screw, and also make sure no one has altered anything to do with the pilot jet or needle position. If for instance it is too lean at idle, and not too lean at a tiny throttle opening, it will surge as it goes from one to the other. Like wise if it's lean at the barely opened throttle, but not lean as the slide comes up a tad, it will do the same thing. Like Steve says, it's very sensitive at low throttle openings. Even different atmospheric conditions from what you had when you set these parameters can have an effect.


Again, it didn't do this when it was new, there is no reason for it now. Starting out in second gear or short shifting or whatever is a band aid fix at best.
 
Last edited:
tkent02 said:
Starting out in second gear or short shifting or whatever is a band aid fix at best.
Click to expand...

We are not suggesting taking off in second gear. Instead, we are suggesting idling through the grocery store parking lot in second, instead of first. Or approaching a traffic light in third, instead of second. Times when you want to keep moving, but a lower gear requires so little throttle that the jerkiness is really enhanced.

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This makes sense. Next time the tank is off I'll sync again. The pilot jets are stock.

tkent02 said:
I would certainly take another look at synchronization, idle mixture screw, and also make sure no one has altered anything to do with the pilot jet or needle position. If for instance it is too lean at idle, and not too lean at a tiny throttle opening, it will surge as it goes from one to the other. Like wise if it's lean at the barely opened throttle, but not lean as the slide comes up a tad, it will do the same thing. Like Steve says, it's very sensitive at low throttle openings. Even different atmospheric conditions from what you had when you set these perimeters can have an effect.


Again, it didn't do this when it was new, there is no reason for it now. Starting out in second gear or short shifting or whatever is a band aid fix at best.
Click to expand...
 
Steve said:
We are not suggesting taking off in second gear. Instead, we are suggesting idling through the grocery store parking lot in second, instead of first. Or approaching a traffic light in third, instead of second. Times when you want to keep moving, but a lower gear requires so little throttle that the jerkiness is really enhanced.

.
Click to expand...

Steve, you of all people know if all is adjusted perfectly it shouldn't do any of this.
 
Trust me, my bikes are darn close to running perfectly, but I will NOT idle through a parking lot in first gear.

With EITHER bike.
tongue.gif


.
 
If I can get a hold of a GoPro this weekend I'll take a video while riding. I broke mine. :(
 
I'm experiencing a very similar occurance with my '80 850 shaftie, Growler. Although I am still playing with jetting to get the best fuel economy I can, I am considering a different throttle lever down on the carb linkage in the not-too-distant future.

If I can make the "off throttle/on throttle" action go slower at first, requiring more twist on the throttle grip, then I think I can get my bike to respond more smoothly and be easier to control at extremely low RPM. Also would like to eliminate the throttle cable free-play entirely if I can.

It's all about that off throttle/slowing then transition to on throttle - not even trying to accelerate, just holding a steady speed through an intersection. Getting the carb synchronization spot-on does help, in my case but does not 100% take care of making smooth on/off/on transitions. The excess drivetain slop in my "Little Suzy" doesn't help either (maybe a broken reaction spring) but that's a fix for another time.

I feel very strongly that if I can get the throttle action slowed WAY down just at the almost closed position, then I SHOULD have an easier time riding smoothly since the engine would not be as "sensitive" at slight throttle applications.
 
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