Clunking/jerking under load

Well, I'm still struggling with a condition I had previously posted under Engine forum. The problem is I have this "clunking/jerking" feel during acceleration in all gears.

I have checked the front sprocket and everything is nice and tight. I re-aligned the rear wheel and tightened the chain to 1" travel. Chain has no visible kinks or damage. Bike has 12K on it. Transmission shifts great, although the sound and feel of shifting is "harsh" as compared to my GS650.

Everything checks out OK, but when I mentioned this to Rob at Z1, he suggested it may be the rear hub shock damper and/or bearings, even with the low mileage. The damper is rubber, and may have dried out after 26 years.

My question is if anyone has experienced this "clunking/jerking" condition and attributed it to rear wheel? I'd appreciate any guidance, folks!

Post edited by: Norseman, at: 2007/07/31 12:10

It takes ten minutes (maybe 30 if you're inept like me) to pull a back wheel and start inspecting parts.

I suppose you could put the bike on the center stand, in gear, and try to rotate the tire, to see what happens once the chain gets tight against rotation.

You could disconnect the shocks at the swingarm and test the swingarm for notchiness.

You could attempt to rotate the wheel to see if you can feel any roughness.

But if you do, the wheel is gong to have to come off anyway.

And since it will already be on the centerstand, with the shocks disconnected, 3 of the ten minutes are already taken care of.


:lol:

Boy that's a hard thing to diagnose in a forum, but it sure sounds alot like when my stock coils failed. It actually got worse as the coils heated up, too.

I posted alot about it a couple years ago, and I called it "stammering". While idling, it really wasn't noticeable, but the missing firing under load was hugely obvious, especially on my twins! I replaced damn near every part on my drivetrain trying to solve it... and yes, I bought a replacement cush-drive (drive damper or whatever its called), too...

Anyway, the way you can prove or disprove it easily, is to hook up a timing light to the various spark plug wires. When I did that I had a Gomer Pyle "Gooooolly" moment. The light wasn't firing all the time, therefore no spark some of the time. Apply Dyna coil, and suddenly I have perfecty even timing light and smoooooooooooooooth running.....

You're making perfect sense to me, Biquetoast, that describes my problem perfectly! I did put the bike on center and lifted of rear wheel - no slop, noise, loosness, wobling, everything nice and tight.

I have been thinking about the firing and had a feeling something is not right. In fact, that's what promted my call to Z1 inquiring about a new Dyna ignition/coils.

So, do I just replace the two OEM coils, or do I need to get the whole Dyna setup?

Norseman wrote:

....In fact, that's what promted my call to Z1 inquiring about a new Dyna ignition/coils.

So, do I just replace the two OEM coils, or do I need to get the whole Dyna setup?

Whoa! I want to make sure its the cause before you replace everything! Actually, replacing stock coils is a win-win situation if you have all that money lying around, but who does? Make sure to do the timing light test if you have one first.
If you're absolutely certain the coils are at fault, z1enterprises is the right place to go. As for whenther or not to get the ignition, too, I cannot say. I have Dyna coils on all my bikes, but I have a blend of points and electronic ignitions, I kinda' think each has their own strength and personality, and pros/cons. That's really up to you...

Thanks, Biquetoast, and I will confirm before going off spending money. I do have a question; my 1981 has electronic ignition - what is the best way to confirm the condition of coils? I do have the Morgantune Colortune, but I don't think that really allows me to observe whether or not it's firing correctly every time. Is there a tool that hooks up to the sparkplugs to measure?

Post edited by: Norseman, at: 2007/08/02 11:05

It occurred to me to offer this idea, to maybe help isolate whether engine or chassis related.

Run the machine up to about 70 mph.

Pull clutch.

Hit kill switch.

Coast with engine off.

Use seat of the pants method of diagnostics.

Be careful re-engaging engine and drivetrain after test.

Norseman wrote:

... Is there a tool that hooks up to the sparkplugs to measure?

Yeah - a timing light. You know, you hook it up to the battery positive and negative, then you clip the the sensor around the spark plug wire. Then you squeeze the trigger and shine it at your auto-advance unit. Exactly how you set the timing.
Except here, you aren't really setting the timing, you're trying to see if the power is going through the spark wire in question every time by watching the light blink.
Move the sensor across the wires and see if they all fire evenly. If they do, it's not what I thought, and you'll have to look elsewhere. If they don't, then replace the coils.
On the other hand, there are all kinds of ways to measure coil resistance and all that other crap that I don't understand. You can search for that in the forums and find a bunch of info on that, too...



Post edited by: Biquetoast, at: 2007/08/02 19:33

From an ignition standpoint, am guessing the coils are originals with built in plug wires and original plug caps. The coils may be okay but with old plug wires cracked and deterioated and caps possibily also worn out. With engine running in a dark garage, spray water mist from a hand sprayer all over the plug wires and caps. Any visible sparking will be evidence of leakage through the old wires and caps which might cause erratic misfiring.


Are the spark plugs NGKB8ES and are they fresh? Have the plugs been tested and found to exhibit a nice fat spark?


Has battery voltage been tested across terminals at idle (12 volts) and rising to 14-15 volts at 4000 rpm?


Has voltage been tested at coil to assure full battery voltage is reaching coil?


Are battery terminal connections clean and tight. And negative connection well grounded (wherever it connects to engine or frame)?


Am unfamiliar with the igniter type ignition system, so must defer to others regarding possible defects there which might cause eratic firing. But do believe all the electrical connections involving any ignition should be clean and secure.

Now, after all that, the jerking may not be related to any ignition problem. :ohmy:


But Keep the Faith!

Yep, coils are original. Plug wires/caps are brand new from Z1. Plugs are NGKB8ES. Battery voltage is 12 volts across terminals, but I haven't measured at 4K rpm. I will do that.

I did measure voltage at coils, and got 11.5 so I went ahead and did WiredGeorge's repowering coils wiring with noticeable improvement in acceleration.

Checked and cleaned all wiring relative to battery (pos & neg). Call me anal, but I also unwrapped all harnesses, checked all connections, cleaned everything, and re-wrapped with new harness tape (yeah, I know; I need professional help...).

That leaves either the rear drive, which feels tight with no excess play anywhere, or the coils. I did the "get up to speed - kill engine and coast test with every imaginable movement to the bike, but could not detect any anomaly or slop/clunking/noise.

There is also the Ignitor, but from what I read in the factory manual, it either works consistently or not at all. However, it did say that the pickup coils may be at fault in an inconsistent firing condition and may need to be replaced.

What do you folks think? I guess I should move this over to Electrical?

Post edited by: Norseman, at: 2007/08/02 23:32

Norseman wrote:

Yep, coils are original. Plug wires/caps are brand new from Z1. Plugs are NGKB8ES. Battery voltage is 12 volts across terminals, but I haven't measured at 4K rpm. I will do that.

I did measure voltage at coils, and got 11.5 so I went ahead and did WiredGeorge's repowering coils wiring with noticeable improvement in acceleration...

There is also the Ignitor, but from what I read in the factory manual, it either works consistently or not at all. However, it did say that the pickup coils may be at fault in an inconsistent firing condition and may need to be replaced.

What do you folks think? I guess I should move this over to Electrical?<br><br>Post edited by: Norseman, at: 2007/08/02 23:32

It IS important to check battery voltage at 4000 rpm.

How were the new plug wires connected to the original coils? If applicable, is there complete confidence in the "splicer" connection?

Would also follow up on condition of pick-up coils.

Have coil primary and secondary windings been measured with an ohmeter (and found within specs per manual)?

Keeping the Faith.

Thanks, Patton, I will indeed test voltage at 4000 rpm. However, you have got me thinking about the new sparkplug wires. The jerking/clunking seems to coincide with the installation of the set of wires. The original wires were connected with compression-style screwcaps, but since the new set didn't come with new compression collars, I had to re-use the originals. Perhaps I did not do a good job on installing the new set?

Unfortunately I used one of the plug caps off the old set to fix a shorted cap on my son's GS650. I will remove the new set connections and re-install - that may clear up the problem.

If that doesn't help, I will check the timing advancer, pick-up coils, and coil primary and secondary windings per the factory manual. Thanks again for your help!