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major backfiring

Posted: Sat Feb 15, 2020 12:08 pm
by jayvee43
Hi guys

Well, I have a new problem.
On the return from the afternoon ride in Chalk River, My 500 started to give me a lot of back-firing bangs and it progressively got worst as it went.
Today I went in the back field at my place, and I experienced a lot of backfiring. I replaced the spark plug, re-verified the plug cap that I got from Bruce, I disconnected my kill switch wires in case they were fraying and grounding onto the body, but nothing worked.

I fiddled with the carb settings, ran under load on the spot by spinning the track on ice, no go. Backfiring one after another. it gets worst the more RPM I give it. (it acts like turning off the ignition and on again a second later)
at times at idle, it seems to fire too early before the piston makes it to top end. It is bad enough I could blow a seal, or a gasket.

Is there anything else I can check externally before I have to remove the flywheel and look at the point and condenser. Cause I still do not have a tool to pull the flywheel.

And, I am supposed to be at a vintage ride this next Sunday 23 Feb. Any advice would help. Also what type of spark plugs are you guys running in your Diablos. NGK A-B 7 is what I have been using.

Thanks again for the help guys.


Re: major backfiring

Posted: Mon Feb 17, 2020 9:52 am
by Schoobytwo (Bruce)
Back firing is typically not an issue, but I have seen it.

I'd start by saying that the Bosch Ignition Coil and Condenser are typically very hardy components and rarely fail. So, I would start with the simple things first like a bad spark plug or carb sending too much fuel to the motor.

I use Champion D-14 plugs and have for over a decade with success. Not that I have never fouled a plug, but it is rare. I've seen what looks like a good plug be fouled, so if the motor is still not starting, back firing or not running right, change the plug again and again. Get yourself a few extra plugs. Sometimes it takes a few tries to get a motor cleared out and running good again.

If the carb and spark plug don't seem to be the problem, then it might be time to look at the ignition. You can check the points without removing the flywheel. Just pull the starter hub off and look through the flywheel windows. Clean the points if needed. Set them to 0.016" if needed. Then give it another shot and see how it runs.

If you are still struggling, then I'm not sure what else to suggest other than getting the flywheel off and getting a good look at the coil and condenser and plug wire. For those in Canada, I would suggest contacting Peter Purych for parts. I know he has these Bosch parts for sale. I do have the flywheel pullers for sale.


Re: major backfiring

Posted: Tue Feb 18, 2020 6:59 pm
by jayvee43
Thanks for the reply Bruce.

Yes, I pretty much did everything you described before I was forced to go to extreme. Thankfully for me I have a great helper in Gatineau, Quebec that was willing to meet me halfway to help me with the flywheel puller and a couple of armature plates with a few good points set and condensers.

To make along story short, I had to pull the engine out of the 500 and put it inside my messy garage and proceeded to remove and replace the entire armature plate assembly from a spare motor I have here. The point set was almost like new.

Today, I re-installed the motor into the frame of the 500,but I did not hook up anything yet. I do however have a nice blue crisp spark now. I'm hopeful this will fix my problem.

As best as I can figure, I blew the condenser on my last long ride in Chalk river. For a long time I have been ignoring a loose spark plug cap issue, and I think the excess amperage help prematurely kill the condenser. (The points were burned very badly)

Anyways, I will finish the repair this week and hopefully make it to Constance Bay vintage run this Sunday.

I'll update yous later


BTW: I came to the conclusion that I needed to replace the points set and the condenser, because I was seeing fat white spark at the sparkplug tests, and after I filed down the original points and re gaped to 0.016" and tried for one more ride it burned the newly filed down points almost right away. Big indicator that the condenser died.

Re: major backfiring

Posted: Mon Feb 24, 2020 7:47 am
by jayvee43
Alright for those that have been waiting on it, Here is my results from My major ignition repair on my 500.

After removing the engine and changing the stator plate with a good donor and cleaning the points set and timing the stator and finally putting the engine back into the frame in time for the run in Constance Bay over the weekend, I am happy to report that my little 500 made it all the way to Quyon, Quebec and back to Constance Bay Ontario with no issue other than one burned spark plug (due to excessive heat that day)

I want to thank once again a very good friend who helped me with this run. Roy Teske. "Merci Roy !!!"

Here is a couple pics of us that day. (watch a little commercial video of the day too) ... Yh-icsEEr0

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