Help! Only running on front two cylinders

[Schaef77]

Hello everyone
I recently purchased a 85 that had been sitting for over a decade and have been going through this forum to clean the fuel system and get the brakes and clutch in working order.

some things I’ve done are
-tear carbs completely apart and clean throughly and rebuilt with kits.
-new carb diaphragms
-new rubber in the entire as they were very cracked/hard and couldn’t even get the carbs back on without replacing them
-cleaned master cylinders and bled everything throughly
-cleaned gas tank as it had some rust in it and I didn’t want to f with it later
-put new oil and changed fuel, oil, and air filter
-put seafoam in gas and oil as well as a small amount in each cylinder to help things get moving
-replaced battery as previous one was quite crusty and didn’t hold a charge


When everything was put back together I fired it up and surprisingly started right up within a few cranks. I rode it around and tested the brakes and clutch to see how my handy work turned out and everything worked just as it was supposed to. After a short ride up and down the road a few times I parked it up and oddly noticed the rear two exhaust headers were much cooler than the front two. Checked the spark and sure enough the rear two cylinders had no spark at all. I tested the coils and they both checked out. My suspicion was then the pickup coil but I tested it and it checked out as well. So from reading around on her it seems like it’s the cdi/tci box. I’m curious as to if this is a known symptom of a bad igniter box or if it is likely something different like a bad connection.

any input is greatly appreciated (good or bad)

thanks

 

[Fire-medic]

Riding it on two cyl's if you've ever ridden a VMax before, would be immediately apparent. Also, a parallel-twin VMax isn't a VMax, even with 600 cc of power.

I'd check the pick-up coils as it sounds like the system is not fully-functional. A factory shop manual, if you haven't already found it:

VMX12- Service-Manual.pdf (vmoa.net)

The ignition has two pick-up coils, '85-'89, '90-'07 has one.



If they are checking out OK, then the CDI box is probably bad. Contact Sean Morley [email protected] for his traveling kit of replacement electrical parts, you pay for what you use/keep.

 

[Schaef77]

Lol yeah I knew something was up when I rode it but kinda brushed it off to it having a bad carb synch and bad mixture. Can’t wait to figure this out and get riding!

 

[Fire-medic]

I expect you've had some barn-burners in your riding history, but a well-running VMax can put a smile onto your face with every trip to VBoost.

 

[Craig Huckeby]

Check with Sean, I had the same problem and my relay for the kickstand Killswitch was bad. I unplugged it and the bike started running on all four cylinders.
Per Sean.