Author Topic: What are the symptoms of a bad shift fork? (Read 9889 times)

tomacGTi · « **on:** May 12, 2007, 01:16:13 AM »

One thing I've noticed in the past couple of rides is a weird tendancy for the bike to "surge" or better yet, it feels like the chain skips a tooth. I've noticed it's more apparant when I use the clutch to shift up versus easing off the throttle and shifting clutchlessly.

The strangest part about this is it only seems to do it in 3rd gear between 8000 and 10000 revs, 3/4 to almost full throttle and no other time or in any other gear. It's a really weird sensation and it scares me to think it may happen mid-corner. So far it's only happened straight up and down.

Bike has a good, well-lubed chain, recent oil change and the carbs are in good shape. CDI is good and has been tested with a known good one (still did it then as well). Also checked the wiring to the coil and has new wires to the plugs as well. Could it be something internal? Any ideas?

-Randy

Banditmax · « **Reply #1 on:** May 12, 2007, 05:33:07 AM »

Clutch slipping maybe.

gsxr400 racer · « **Reply #2 on:** May 12, 2007, 12:53:04 PM »

lean surge

Red01 · « **Reply #3 on:** May 12, 2007, 03:30:40 PM »

NOT a shift fork problem.

tomacGTi · « **Reply #4 on:** May 12, 2007, 05:36:57 PM »

Thats a relief. So do I raise the needles a skoosh then?

The bike rides fine otherwise, just that third gear hiccup.

Herr Tod · « **Reply #5 on:** May 12, 2007, 06:47:55 PM »

I've had something like that, but I felt it as if the ignition would stop for a second. Usually it happened in mid-corner so I figured it had something to do with the fuel.

duane · « **Reply #6 on:** May 12, 2007, 07:42:41 PM »

No, a bad shifter fork usually means it slips out of gear and gives you a false neutral. Often, but not always, second.

What you describe sounds like a chain worn past it's limit or a badly worn sprocket. Check for wear on the counter sprocket too by removing the cover.

Quote

The strangest part about this is it only seems to do it in 3rd gear between 8000 and 10000 revs, 3/4 to almost full throttle

This is very similar to my VFR's behavior when my chain was fscked up.
Let us know whatever it turns out being.

tomacGTi · « **Reply #7 on:** May 12, 2007, 07:50:00 PM »

I adjusted the mixture screws 1/2 turn per factory's recommendation. I'll give it a ride tomorrow and see.

Duane, I looked over the chain/sprockets pretty closely and they appear fine, no pointy teeth/hooks and the chain rolls through without catching. The adjuster is smack dab in the middle and the measurement is within tolerance.

I was thinking the chain as well and have factored that into the equation for replacement at some point. I guess I'll see come tomorrow whether or not the adjustment to the mixture will make a difference. I just find it wierd that it only does it in one certain situation and nowhere else.

-Randy

duane · « **Reply #8 on:** May 13, 2007, 04:41:32 AM »

If this was a carburetion problem, and I'm not saying it's not, then you are not adjusting the proper fuel circuit.

To quote you:

Quote

between 8000 and 10000 revs, 3/4 to almost full throttle

That would put you in the main jet. The air/fuel idle screw, that you moved 1/2 turn out, will mostly effect the idle.

If your bike idles fine now, I would suggest not touching it. If it used to accelerate fine before, then most likely it's not the main jet. (Unless there's an obstruction, then it's a matter of cleaning not adjusting.)

tomacGTi · « **Reply #9 on:** May 13, 2007, 09:37:47 AM »

It did have a bit of slow return to idle after a rev and the needle is already shimmed up with a washer. Main jet is fine for the bike, it pulls like a truck up top. The issue happened as you rolled onto it in 3rd

Looking at the plugs, they were also a little light in color. Figured I'd give this a shot as it doesn't require major surgery.

Banditmax · « **Reply #10 on:** May 13, 2007, 04:24:03 PM »

Needle jet comes as standard with a plastic ring underneath. But you may have another washer in there too so correct nme if im wrong.

tomacGTi · « **Reply #11 on:** May 13, 2007, 09:30:46 PM »

Already have a jet kit (Dynojet, yes I know but it was in the bike when I got it) and I had shimmed the needle up earlier on.

FWIW on-off throttle application has gotten much better, not as abrupt as it used to be and also the idle isn't as lumpy as it was before. I still did get a very slight hiccup in second but only one at lower revs versus higher in the range but at the 1/4 to 1/2 throttle position. Getting closer..