Bucking at constant rpm?

[maxed66]

My bike has been like this for, well, since I picked it up. At constant speeds it sort of bucks and kicks, making it difficult to do a constant speed. Going downhill seems to aggravate the issue. My dealer flashed the ECU a couple times, and this actually seemed to fix it, for a day??? I am at a loss of what is wrong with it. On my rx7, I would figure the throttle position sensor is off. Anyone have this and find a cure???

[SIN138]

Sounds like the dreaded "kink in the breather hose syndrome" - -easy fix.

Check your gas tank. Is there a certain lack of pressure? There has been a few other threads on this issue. It happens to majority of these bikes.

Most likely one of your breather hoses are pinched or tipover valves are stuck, creating a vacuum in the tank.

Fixes:
1) wiggle hoses loose (prob. will return)
2.) remove tip valve / cut hose shorter

[maxed66]

Funny thing, I have zero vacuum problems with the gas tank. Any other suggestoins?

[Limey]

Mine hade a slight hesitation problem at 4k rpm. it went away after I changed the pipes and cleaned the 02 sensor, it was black with soot.

[kuhlka]

Is your clutch cable properly adjusted? Chain stiff at all (a stretched and/or siezed up chain will make the bike lurch a lot)?

[Sparti]

I had a similar issue when i put an aftermarket exhaust on. The bike was running lean I ended up installing a TOR's map and it fixed the problem. Not sure if this is similar to your problem but may another option to consider.

[maxed66]

My bike is bone stock, less bar-end mirrors. Chain is adjusted on the loose side, lubed but always dirty. The bucking effect is really bad when going down a hill with the throttle just touched to keep a constant speed of whatever. Up hill it is less pronounced, or not there, as I need a bit more throttle. I am thinking it is the FI system not adjusting well tot he barely open throttle. But what gives???? Brand new it did this, so this cannot be dirty fuel injectors. I have now clocked near 6000 km. I just hate to leave it at the dealer while the sun is shining and the roads are calling!!!

[Dobieman]

There is an annoying surging around 4 K with the stock set up. I didn't notice it much before until last week running the twisties in the mountains around the Dragon. I think this was a tune issue that was necessary to pass strict emissions regs. From what I have heard Tuneboy or PCIII and a pipe is the answer if this is your problem. Not an issue if the bikes pulling but when I would keep the throttle cracked open to maintain speed on a downhill slope it was annoying.

[Curmudgeon]

I wouldn't be surprised if it's a problem with throttle body balance. I rode GS-series BMWs from '99 through early '06 and they tend to surge at small throttle openings at the best of times. If the throttle bodies were out of balance, the problem was worse. I'd ask your dealer to check the throttle body balance.

[BUCKET]

I'm with Kuhkla,mine lurchs when the chain needs adjusting.Also when my right hand turns that throttle thingy to quick. :hammer: