Author Topic: Engine Misfiring 3100-4900 rpm (Read 11099 times)

Summit670 · « **on:** July 11, 2011, 07:42:04 PM »

I had this prob last year but it was at 3-4k rpm. At that time I adjusted the pickup coil gaps to be the same and within spec and problem was cured.

Now, 3k miles later, the problem seems to be back and idential symtoms. I checked the coil gaps and they were equal and within spec. Hmmm, I bumped both to .73mm rather than .63, just because I was already there.

Now though, still missing.

It idles great and runs great at all other RPMs. I can downshift to 4th gear to keep RPMs around 5k when cruising and it runs great. I can accelerate and upshift and it runs great.

Gas - Ok
Carbs - Ok, cleaned last year.
Coils - stic coils installed year with new plugs.

Pickup coils going bad is my thought. 1987 with 71k.

Any ideas?

syntor · « **Reply #1 on:** July 11, 2011, 08:04:01 PM »

Quote from: Summit670 on July 11, 2011, 07:42:04 PM

Pickup coils going bad is my thought. 1987 with 71k.

I'd second that.

Summit670 · « **Reply #2 on:** July 11, 2011, 09:03:16 PM »

Are pickup coils a common prob on an older bike?

Maybe last year I bought more time (3,000 miles) by adjusting the air gaps to be equal. Maybe good pickup coils would not notice .1mm diff in setting but poor ones might? Now they have been equal for 3k and maybe they are finally on their last leg.

If I knew how and which wires to check with an ohm meter I could. I know where the plug is by the rear of the tank.

Let me throw this out there for more info - I rode the bike a minute ago. Cooler temps. The bike didn't act up till after 10-15 minutes of running. The problem seems to coorelate with temperature/engine temp. When it gets hotter the bike acts up more consistently.

Temps outside are now 82 and yesterday it was 96 or so and very humid.

George R. Young · « **Reply #3 on:** July 12, 2011, 06:44:40 AM »

If you haven't checked ignition, the resistance between plugs 1 - 4 and 2 - 3 should be around 22 K ohms.

Just adding this because you mentioned 'humid'.

Summit670 · « **Reply #4 on:** July 12, 2011, 05:50:36 PM »

George, I am not sure how to check that figure with the stic coils. ?

I am pitiful. I don't know how to connect an ohm meter to the pickup coil pigtail because the shop manual doesn't say but if I set it at 2000 and touch the yellow and black wire connection I get a reading that is within range on the meter, 540 range for both sets of wires. The shop manual indicates to ground to the frame but I can't get a reading at all if I do it that way.

When the bare ohm connectors are touched together the reading is O. Not touching the reading is 1. Digital.

George R. Young · « **Reply #5 on:** July 13, 2011, 07:20:05 AM »

Ah rats, the technique I suggested was for the stock coils which fire 2 plugs. Please ignore.

Leo · « **Reply #6 on:** July 13, 2011, 08:35:26 AM »

When the bike starts acting up, ride it home keeping the rpm's right where the problem is. When you pull in the driveway, do not let the bike idle, just shut it off. Pull the plugs and look at them. If they all look exactly the same, at least you have narrowed down the problem by process of elimination. Even though the plugs are pretty new, they can fail. I have zero experience with the stick coils, but I am certain that they can fail, just like any electrical item mounted in high temperature, intense vibration areas. While the plugs are out, I would do a compression test. An engine with a weak jug will often idle ok, and at high rpm's it is less noticable, but at 3000 rpms in high gear, the bike will buck like crazy. Let us know what you find, and we can get this narrowed down. Good luck.

Summit670 · « **Reply #7 on:** July 13, 2011, 11:01:50 AM »

Leo, last year I had virtually the exact same symtoms and after checking plugs, etc, it ended up being the pickup coil gap.

Now, the bike does run ok in this range once in a while but will start missing as time goes by.

Also, this morning, I noticed it was missing more as it warmed up, in the lower rpm range, then that subsided and it ran fine at all rpm's for the next 5-10 minutes. Then it started missing again in the 3100-4900 range.

I will check plugs tonight though to make sure. I've checked the caps and wiring visually and physically made sure the caps were pressed down and the connections were tight. Don't see any wires rubbing.

Leo · « **Reply #8 on:** July 13, 2011, 01:49:05 PM »

Summit670, I just remembered that several years ago, another COG guy was having an intermittent miss problem. Since he had two bikes, he just started changing things one at a time. As a last try, he transfered the pick up coils and the problem went away. If it is pickup coils, do the ride test like I said. If it is a pick up coil, TWO of the plugs will be fouled out and black. It will be either the pair on cylinders 1 & 4 or the other pair on cylinders 2 & 3. It would show up on an oscilloscope, but without a dyno to put it on, I don't know how you would read it with the bike under a load. I guess you would have to have a technician that could run really fast

Steve in Sunny Fla · « **Reply #9 on:** July 13, 2011, 03:31:43 PM »

pickup coils or ignitor. HTH, Steve

Summit670 · « **Reply #10 on:** July 13, 2011, 04:57:31 PM »

Guys, that helps. Thanks.

Coming home tonight I payed particular attention to the missing and don't think it is missing bad enough where it can be in that range and I hit the kill switch and I will see something by reading the plugs. This is acting exactly as it did 3k miles ago except the affected rpm range has changed.

I do have a spare ignitor I will swap in tonight to see if it makes a diff.

I'm leaning toward pickups but the parts mgr at the local cycle place told me he has only ordered 1 of those in the last 17 months.

We'll see what the ignitor swap does first.

Summit670 · « **Reply #11 on:** July 13, 2011, 06:29:20 PM »

Ignitor swap was done and it didn't change anything.

Pondering biting the bullet and ordering $115 pickup coil and trying that.

If I take it to shop it will probably be $100 labor plus $140 for the part, so $240.

Wtg to see what you guys think or if you have any other thoughts.

?

George R. Young · « **Reply #12 on:** July 13, 2011, 07:56:51 PM »

1) Can you interchange the pickups to see if it makes any difference?

2) Anybody around you could swap pickups with?

3) http://cgi.ebay.com/ebaymotors/90-KAWASAKI-ZG1000-ZG-1000-CONCOURS-MAGNETIC-PICKUPS-4-/400065650629?pt=Motorcycles_Parts_Accessories&hash=item5d25c55fc5

Summit670 · « **Reply #13 on:** July 13, 2011, 09:11:13 PM »

Thanks for the ebay link. $75 buy it now for 1990 pickups with nearly 50,000 miles is too much for me. I'd rather spend another $50 and have new ones.

No, for me swapping in someone elses set isn't possible.

I think I'll order some new ones and take the chance. It may be about due anyhow plus it would help narrow down the problem if it doesn't fix it.

Should have looked at the wiring routing closer when I had the sidecover off. I think it is an easy install without removing the timing plate or anything. Anyone know if it is as easy as it appears to install new pickups?

Steve in Sunny Fla · « **Reply #14 on:** July 14, 2011, 05:34:05 AM »

Yes, it's totally easy. just drain the oil first, and I'd have another cover gasket on hand JIK - HTH, Steve

Roadhound · « **Reply #15 on:** July 14, 2011, 08:02:49 AM »

You don't have to drain the oil. You need to put the bike on the centerstand, put something about 1/2" thick under the left foot of the centerstand and you will have no trouble with the oil at all.

Summit670 · « **Reply #16 on:** July 14, 2011, 10:18:07 AM »

Thanks. I've had the side cover off numerous times without draining the oil, including just the other day but I see where it could be an issue if the oil level was too high.

Looks to me like oil comes off the cam chain and drains back into the case via a fingersized hole. Letting the bike sit overnight is the best way to avoid excess oil in the cover area.

I do seal the cover with Permatex Blue rtv and that has worked great time and time again. The only hassle is the cure time vs a gasket and that a gasket can probably be reused a time or two if careful.

bbroj · « **Reply #17 on:** July 14, 2011, 11:33:56 AM »

I'm watching with interest. My '06 still has a rough/flat spot in the 2k range, even after Steve's carb magic and Tony's stick coils. The stick coils and new plugs seemed to narrow the range of the trouble, but it's not gone. I have not looked up or measured the pick up coil resistance yet, but I expect them to be fine as I don't put a lot of value in static DC measurements on dynamic devices. They can measure just fine at a given temp with no rappid change, and behave differently when heated and subjected to continually changing (almost looking like AC) input. Thanks for keeping us posted.

Summit670 · « **Reply #18 on:** July 14, 2011, 03:52:55 PM »

BB - my plug coils were bad last year. The shop checked them and they tested ok and they found a bad plug cap so they replaced that, but then the perf deteriorated again within a month and they said the same as you, things can test ok but may not be. Installed the stic coils and it solved the problem.

Hoping that is the case here.

Unless my wiring is bad, it has to be the pickups on mine. Heck, in the last year I've installed stics and I have another ignitor coil as a spare so I'm pretty sure it isn't that since I put the spare on when it was running good and the spare seemed fine.

Also, I guess pickup coil resist is measured by probing 2 of the pigtails at a time with an ohm meter. Not sure, but that's what seems to get a reading on mine and they both appear in the range.

bbroj · « **Reply #19 on:** July 14, 2011, 07:57:49 PM »

I'll have to start shopping for a replacement set of pickup coils, or an ignitor to try first. Those are the last 2 ignition components that are not new, short of actual wiring. I don't suspect wiring, mine is a clean, low mile (17kmi) garage kept bike, corosion is barely an issue on this bike.

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Author Topic: Engine Misfiring 3100-4900 rpm (Read 11099 times)