Spark/no spark

[85 VMX 1200]

Hey all, thanks for the add to the group. I have an odd issue with my rear coils. Its an 85 VMX 1200 which I've owned since 1992.
They have spark at cranking, but not at idle. If i rev the bike past 2k rpm, they fire but not perfect.
Coils test= 3 ohm primary, 16.3 secondary. P/U test= 139.5 to 146.5. Both are a little high but not terrible. I have 11.82 supply volts to the coil for both. New battery and plugs.
Any help is greatly appreciated. Thank you!

Jim H.

 

[DMAN999]

It sounds like your rear coils are going bad, it's fairly common for them to fire when cold but not when hot.
I'd talk to blaxmax about getting a set of COPs to replace the OEM coils.
http://vmaxforum.net/showthread.php?p=441822#post441822
I replaced my OEM coils about 5 years ago with COPs when one of my front coils was acting up and I haven't had an issue since.

 

[maleko89]

Early models have two pickup coils...one for the front cylinders and the other for rear. I'm betting it's one of the p/u coils as it would be rare if two ignition coils go bad at same time.

Sent from my SM-G920P using Tapatalk

 

[DMAN999]

Early models have two pickup coils...one for the front cylinders and the other for rear. I'm betting it's one of the p/u coils as it would be rare if two ignition coils go bad at same time.

Sent from my SM-G920P using Tapatalk

Good call, that does sound like a likely cause.

 

[one2dmax]

The pickup coils are pretty robust but can be bad (I have a bunch of good ones I can sell you "cheap")

It's been pretty common over the last 5-10 years for the CDI box's to go bad as well causing all kinds of running issues.

 

[85 VMX 1200]

Thanks for the replies guys, I really appreciate it.
I would like to find the issue before throwing money at it and continuing my frustration. I just got done battling garbage in the gas tank, had to reline it. $750.00 at service shop just to have it mess up again when i got it back lol. So I bought a Carbtuner Pro and solved the issue myself, but now I have the dang spark issue.
Those electronic replacement parts are crazy expensive and hard to find. I believe the CDI box works or it doesn't, is this correct? At least that one I can rule out if true. So then it would be either my coils or my P/U coil?
Thanks again for all your help, you guys rock!

Jim

 

[Yoshimra]

Move the 1/4 coils to where the 2/3 are and see if the problems goes with the move.

 

[blaxmax]

Move the 1/4 coils to where the 2/3 are and see if the problems goes with the move.

You know 2 & 1 are on the left side right? With #2 coil being in front and # 1 coil being in the rear.
I would try rebuilding the wire ends first as they corrode.

 

[Bill Seward]

Over the years, I had to trim the ends of the hi-tension wires, and replacethe caps a few times. Installing the COPS solved all the ignition gremlins. Best mod I ever did.

 

[85 VMX 1200]

Thanks so much for everyone's help. I will be going with the cops from blaxmax. Cant wait to get em installed and be riding again. Keep up the great help everyone, good advice is getting harder and harder to find.

Jim

 

[one2dmax]

CDI boxes can drop cylinders at idle, or at higher RPM. Some run fine at idle but won't rev for ****. Some run like **** and idle but pick up the other cylinders under high rpm.

 

[Dorney]

Your test #'s on the coils are good don't think that's what it is.

Dave

 

[maleko89]

Things can test fine on cold engine. Electricals are finicky about heat.

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[Redbone]

CDI boxes can drop cylinders at idle, or at higher RPM. Some run fine at idle but won't rev for ****. Some run like **** and idle but pick up the other cylinders under high rpm.

This is what my Dyna 3000 is doing, runs normally while cold. When warm/ hot it will idle ok but not normal, runs on 3 cyls until 4 -4500 rpms then picks up the other cylinder and runs normally. It also likes to backfire when decelerating. I've yet to take it apart as I've been busy since I've been home, but hope to this weekend. I do have the stock CDI I can swap in if needed.
Dyna has been in use for 3 years from new even though I bought it 4-5 years ago.

 

[blaxmax]

This is what my Dyna 3000 is doing, runs normally while cold. When warm/ hot it will idle ok but not normal, runs on 3 cyls until 4 -4500 rpms then picks up the other cylinder and runs normally. It also likes to backfire when decelerating. I've yet to take it apart as I've been busy since I've been home, but hope to this weekend. I do have the stock CDI I can swap in if needed.
Dyna has been in use for 3 years from new even though I bought it 4-5 years ago.

Are you running the stock coils or Dyna coils and I'm sure you have resistors?

 

[Redbone]

Gannon's COP's with resistors. I still have to do an inspection and troubleshooting, so all I have until the weekend is symptoms.
I'm going to test components (COP's, COP's cables, sparkplugs), make sure all's well with carbs (do peashooter/ shotgun if necessary) but I'll report back what the issue was.

 

[wildweasel_pt]

For a new battery 11.8 is low voltage.