Bike jerking issues CARB?...

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itsRICH
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Bike jerking issues CARB?...

#1

Post by itsRICH »

I have a panhead kit bike with STD 88" pandemonium eng, SS E carb(stock) have not increased/decreased jet sizes, electronic ignition, straight drag pipes no baffles or power cones
The issue is:
When I go into 1st gear whith no throttle bike seems to jerk/rocking motion, when i increse throttle it take a bit to smooth it out nad no more jerking, same thing with the beginning of 2nd gear, until i give it more throttle, and its fine, have not been into 3rd gear yet,
I was told to increase my idle, becuase it might be too low not allowing enough oil flow, it helped a little bit.
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Re: Bike jerking issues CARB?...

#2

Post by olpanrider »

solid engine sprockets and chains will jerk in low rpm range. hard to say from description. belt primary(not nearly as bad) and or compensator wont do that(that's why they have compensators)
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Re: Bike jerking issues CARB?...

#3

Post by panhead george »

When you say " put it in first gear with no throttle" does it feel like the clutch is not disengaging completely and you are feeling clutch drag? or are you riding away and it is jerking? If it gets better as you speed up you may need to re-jet the carb and it is a lean condition which is causing the bike to surge or jerk. Straight pipes with no baffles are for the drag strip and would cause the bike to have a lean condition. You need to have some back pressure for the motor to run correctly on the street, especially at lower RPM's or at slower speeds. It will improve the lower RPM performance and make the bike a lot more responsive on the bottom. Down load the tuning manual from the S&S website and make sure the carb is in the ball park with the jetting and the accelerator pump setting would be my first place to start. Oil flow I would say is not the issue. Air leaks and timing are other things that need to be checked to make sure you have correct settings also. Has the bike ever ran correctly since you got it? or is this the maiden voyage?

Good Luck,
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Re: Bike jerking issues CARB?...

#4

Post by itsRICH »

it has a BDL 2" open belt, no compensator, the clutch is working properly, check it multiple times, i tunes the carb per the SS instructions, for the first few steps, it was the maiden voyage. Havent gotten to test the main jet yet, in the higher speeds. when i shift into first and let off the clutch it will roll smooth (had it backwards previous post) , and when i give it throttle it starts to jerk more, untill i get to the top of 1st gear. it was timed at the factoroy with the electronic ignition when it was rebuilt. I just got som carb cleaner, so i will be checking for air leaks,could it be an air leak? since it runs fine as the speed increases..seems like it would be consistant if it was, but im not too familiar with air leaks. Also by the way, this is my first bike ever/first time riding one, except for a riders safety course i took. so im a "new" guy. Ive had someone tell me also that it is normal with a larger engine in low speeds, but it doesnt seem normal to me,
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Re: Bike jerking issues CARB?...

#5

Post by itsRICH »

Ive been looking at power cones for the pipes, trying to find the right type, will probly just go with a universal one from JP cycles
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Re: Bike jerking issues CARB?...

#6

Post by RUBONE »

Sounds like you are experiencing a condition referred to as "snatch". It is commonly caused by lugging an engine at too low an operating range usually in combination with overly high gearing. If it was a carb issue there would likely be spitting back through the filter or backfiring. If the ignition is not retarding at low RPM it will exacerbate the condition. If slipping the clutch smooths it out it is pretty classic "snatch" or "chain snatch", common terms for the same thing.
And the bigger the engine the worse it can be due to the power pulses.
Raise your idle speed, check your timing,and lower your gear ratio.
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Re: Bike jerking issues CARB?...

#7

Post by olpanrider »

if you was running a chain I bet it would be even worse.. a belt will give a little and smooth it out some.
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Re: Bike jerking issues CARB?...

#8

Post by Panacea »

I'd start by adjusting the primary belt and the rear chain, eliminate the easy stuff...
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Re: Bike jerking issues CARB?...

#9

Post by itsRICH »

Ill try to raise the idle speed a bit more and fine tune the idle mix, I only increased the idle speed last time I rode it, to do a quick check. Then I try to loosing the belt a 1/4in and give some slack in the chain, its about 1/2in right now. Ill also see if pulling on the clutch smooths it out, if that's what you meant RUBONE.
But right now im cleaning up my wiring job, so it might take a few days.
How would I change my gear ratio?...never heard of that before,
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Re: Bike jerking issues CARB?...

#10

Post by RUBONE »

How would I change my gear ratio?...never heard of that before,
Different sprockets.
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Re: Bike jerking issues CARB?...

#11

Post by itsRICH »

Ohh, that makes sense, would you do both tranny and rear tire or just one or the other, ive got a pretty large one on the rear right now

Image
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Re: Bike jerking issues CARB?...

#12

Post by besibela »

it may sound a little "off the wall", but do you have any freeplay in your throttle?
if your throttle cable is adjusted too tightly, vibrations and bumps in the road will make the bike seem "jerky" when you are riding with little/ no throttle.
you should have about 1/8"-1/4" of play (on the grip)
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Re: Bike jerking issues CARB?...

#13

Post by itsRICH »

ive checked the throttle already, and I made sure it wasn't user error (me).. but its got decent slack in it. and when I say jerky the bike feels like its lugging/lungeing. Ive tried giving it a slow smooth pull, and I lil bit faster pull, both are the same, jerk, jerk, jerk
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Re: Bike jerking issues CARB?...

#14

Post by nmaineron »

What do you have for a Cam...low speed ,low rpms and a cam that doesn't come on till 3000 or so will make a bumpy low speed ride...
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Re: Bike jerking issues CARB?...

#15

Post by olpanrider »

itsRICH wrote:Ohh, that makes sense, would you do both tranny and rear tire or just one or the other, ive got a pretty large one on the rear right now

you have to count the teeth.. then divide drive into driven to get the ratio.


a common setup would be 51 rear 22 trans or 51 rear 23 trans


51÷22=2.318 final drive ratio
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