No spark on one side at low rpm's

jasonschumacher

jasonschumacher

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I just got my bike back from the shop. I have been having an issue with backfiring so I decided to let a professional clean my carbs/ check out my electrical.
They don't want to mess with my electrical since it is not stock.
What they did tell me was that the left side isn't getting spark at low rpm's but it does at higher rpm's.
Ideas on where I should start?
I have a 1975 with the PAMCO ignition, high output coil, and the banshee permanent magnet swap.
Thanks in advance for any help
 
Since the Pamco is a wasted spark system and the spark travels from the coil to the first plug through the head to the second plug and back to the coil it would seem that the ignition is working. What do the plugs look like? You may try another set of plugs or try swapping the plugs as you could have a bad plug. Or you could try swapping the plug wires to eliminate a bad wire.
 
Ok, I checked the plugs and wires. Replaced the plugs with new and then switched plug wires from side to side.
Still backfiring at idle or with throttle applied.

Edit: it should also be noted that I redid my timing. Was only slightly off.
It doesn't want to backfire while I have it sitting at idle when first cranked, but as soon as I give it gas, it backfires, then backfires at idle.
 
Last edited:
It's hard to find a "professional" that really knows what they're doing when it comes to working on one of these old 650s. Besides, yours looks all chopped up. Have you properly re-jetted and tuned your carbs for those hacked off pipes and non-stock air filters? If not then that's probably at least part of the problem, if not all of it.
 
I know I shouldn't really trust the P/O, but he said that it wasn't backfiring before it stopped running, and that it had been jetted for the setup. I'm actually not sure what the jettings are, but I may have to look. What would you suggest? BS38's btw.
And also, would that explain it only having a weak fire on just one cylinder?
 
When you checked the plugs and moved the wires did the backfiring change sides? If not it could be in the carbs or a vaccum leak some where. Probably the best place to go would be the normal .... cam chain tension, valves then timing. Then start trying to tune the carbs with a sync. As far as the carb jetting it really depends on the year of the carbs not the bike as they can be swapped around sometimes so you will first need to properly identify the carbs to find out what the original jets were and where to go from there. Have a look in the tech section there is plenty of info in there about these carbs to get you started down the correct road. What kind of pods are those that you have? Some of the cheap ones are pieces of crap. Have you tried it with no filters on the carbs yet to see if there is a difference?
 
That "mechanic" may have just called the bad low speed running and misfiring a "weak spark". It could very well be carb tuning related instead. The Pamco system usually doesn't act that way if something's wrong with it. You usually have spark or you don't. If it's producing spark, it does so everywhere. It won't not fire at just low RPMs. It's possible the plug cap to wire and/or wire to coil connections are poor. You might try redoing those. I like to cut the wire insulation back about 1/8" then fan the wire strands out before screwing the cap on or the wire into the coil. This makes a good, solid connection .....

PlugWireEnd.jpg
 
Have you considered it is a carburetor problem? Air leak? Mechanical, like a tight or bent intake valve? A compression check is in order if you are still stymied. Both plugs must fire at the same time in a wasted spark so maybe a fouled plug? At only $2 a plug it is a good test to have a replacement.

If it is ignition then there is only one place the Pamco unit could possibly act different on one cylinder, the magnets. The early Pamco had a problem with the magnets loosening and coming out the top of the rotating plate. Pete made up a large washer that fit over the top and fixed that problem. Now if this is an early unit and a magnet was somehow installed backwards or there was never the washer installed and a magnet has loosened and is too far from the Hall sensor then the spark may be inconsistent from one cylinder to the next.

Tom
 
I just came across this thread,
I started my 83 bike yesterday, below freezing outside, started fine but seemed to run rough, I noticed that i could pull off the right side plug wire and no change. Took it out for a ride, and at higher speed it would catch and run fine. and don't know if it is bad to remove a plug wire while engine is running. Removed the plug and grounded it against the engine and it has spark, seems a little weak though. So i swapped wires and now it runs fine, any ideas.? Bat is good and charger putting out 14.5V when at 2000RPM

Thanks
John
 
I figured that might be the problem, but when i swapped the plug leads it idles and runs fine, on both sides. so now I am thinking that i have a funky plug wire. Swapping it over may have improved its connection. What about pulling a plug lead while the engine is running, is it bad for the ignition? I had an outboard motor once and with a CDI ignition you were not supposed to do that.
 
Sorry, I did not thoroughly read your post. As said above, it is never completely safe to pull a plug wire on a running electronic ignition such as your TCI system. Yes, swapping the wires may have improved the connection. I wouldn't worry about it until it starts acting up. Yes, may just be a bad plug wire.
 
Edgewood RI said:
I figured that might be the problem, but when i swapped the plug leads it idles and runs fine, on both sides. so now I am thinking that i have a funky plug wire. Swapping it over may have improved its connection. What about pulling a plug lead while the engine is running, is it bad for the ignition? I had an outboard motor once and with a CDI ignition you were not supposed to do that.
Click to expand...
bad on electronic ignitions, points don't give a damn, none of those pesky little transistors to blow out
 
The problem isn't so much you hurt the ignition but you hurt the coil. With one plug pulled the high voltage that is supposed to go to the plug can't and will find an alternate pathway. Often arcing from the windings to the steel core to ground.
The stock coil may srvive a short time but the higher the out put the quicker this happens.
Leo
 

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