Bike lurch at idle

[RichV]

I have a smoothness problem with my throttle. If I drop the throttle back to idle, like just before entering a turn, I get a sudden and heavy compression drag without a smooth transition. Same thing happens in reverse when I add throttle from idle. I did recently change the cable but I'm not sure if this happened or not before. It is a Motion Pro throttle cable and it's not binding. I did have to route it differently since it seemed a touch shorter. I messed with the adjustment by the grip making it tighter/looser without anything changing.

I like to use the engine compression when entering a turn to slow down and not apply the brakes. I also don't want to engage the clutch. My engine compression is real good since I just replaced the rings so I expect a good braking action from the engine. It's just that if goes into and out of the braking with out a smooth transition.

No other changes to the operation of the bike were made. Gas mileage is still constant and predictable in all riding situations. It's just as if there is not transition to and from idle when the throttle drops. I did just take the bike out of storage for six months prior to the trip.

[TopCatGr58]

Hey there Rich,

I, too, enjoy using engine/compression braking when approaching turns and such vs. actual braking..just ask Greg/BA80....he was looking for and relying on my brake lights to help in sensing when I was slowing down coming into a turn and such....but I just used engine braking instead. However, I also run it in a bit higher rpm range than most others to provide that better smoother transition back into/onto the throttle after the braking.

If you don't want to use the higher rpms ie. 2500-6k+, then you may want to set your idle speed just a tad higher ie. 1200 so that you're not completely closing/cutting of the throttle when using the engine braking, and that can then help you to be able to get back into the throttle a little easier and smoother with not as much of a jerk/jolt.

But keep in mind, there's also a fair amount of drivetrain slop that has to be taken up when you shift from engine braking mode back into throttle mode(middle gear/driveshaft/final gear), and that can also cause a bit of a jerk/jolt sensation.

T.C.

[RichV]

Hey there Rich,

I, too, enjoy using engine/compression braking when approaching turns and such vs. actual braking..

If you don't want to use the higher rpms ie. 2500-6k+, then you may want to set your idle speed just a tad higher ie. 1200 so that you're not completely closing/cutting of the throttle when using the engine braking, and that can then help you to be able to get back into the throttle a little easier and smoother with not as much of a jerk/jolt.

But keep in mind, there's also a fair amount of drivetrain slop that has to be taken up when you shift from engine braking mode back into throttle mode(middle gear/driveshaft/final gear), and that can also cause a bit of a jerk/jolt sensation.

I try to compression brake as much as possible. However, in a group it tends to be harder to do. I back off but find i don't like falling too far back which causes me to go back to a close position or to "speed up" making me enter turns too hot. Although falling back did prevent me from joining Greg's "incident" on the turn.

The first thing I tried was to raise the idle to about 1200RPM (using the highly accurate tach on the bike ). Didn't affect/fix it.

I worry that I'm dealing with too much slack in the drive train but I don't know how to fix it. The middle and final gears were only cleaned/repainted and not torn down. I did lube the drive shaft.

Before placing the bike in storage I didn't notice the problem. The only thing that changed was I put a new throttle cable on and only did a test ride to make sure it worked okay. I also messed with the adjustment tightening up all play without affecting the lurch at all.

[TopCatGr58]

Hey again,

There really isn't any adjustments you can make in the drivetrain slop, it is what it is.

But after posting last night, I got to thinking, and with your bike in storage, the pilot circuit may be partially clogged/restrictive....and so you're not able to get that FINE throttle response when just slightly turning the throttle/rolling back into it. You said the bike didn't have the lurch before stored....and replacing the throttle cable with all of the proper tension/slack adjustments you've made should not have contributed to this problem....
but partially clogged carbs could. SO...I would suggest a good dose of Techroline or Sea Foam run in it for a tankful and then see how it responds!? Otherwise, might need to take the carbs off and clean the jets and pilot circuits.

T.C.

[RichV]

I'll pick some up when I go out and give it a try.

When I put the bike in storage I drained the fuel system completely and let it dry out. I then fogged it and sealed it off. This "should" have reduced the chance of a clogging problem.

I'm putting my HD in storage now and it's a lot easier. Fill the tanks and put stabilizer in it. Run it for a while and it's ready to go. Thus is the advantage of fuel injectors.

It could also be just a perception I'm having after making so many changes just before storage. I replace the fork tubes and cables and the may be reacting to the change in handling. The nose dive for example may be adding to it.

[Radioguylogs]

I heard that a zip tie is useful on the throttle cable .