Just got a '78 Yamaha xs650 special 2. Trying to find out if both cylinders fire at once. Figure out if I can swap the wires because one cylinder isn't firing right. Every once in awhile it misses if I touch the exhaust. It's cold but the other side's like burning hot and it's running really really strong on one cylinder. So I'm trying to figure out if maybe the coils just out and if they both fire at the same time should I go to a coil for a cylinder or just keep with the one coil for both?
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Does both cylinders fire at once?
- Thread starter roken
- Start date
Forgot to say it has pamco ignition on it and upgraded PMA sator and currently it's just running off a car battery strapped to the back of it. Currently don't have a motorcycle battery but 12 volts is 12 volts. And I can give throttle and it's just fine. It's just only misfying one cylinder running kind of rough
Not read through there can be INFO
https://www.xs650.com/threads/no-spark-on-left-side-w-pamco.29186/
If the bike been sitting can also be stuck float valve or so
https://www.xs650.com/threads/no-spark-on-left-side-w-pamco.29186/
If the bike been sitting can also be stuck float valve or so
The pistons rise and fall together, yes, but they don't fire at the same time. When one cylinder is at TDC on it's compression stroke and firing, the other is at TDC on it's exhaust stroke, pushing the spent gases out.
If the ignition has one coil with two leads then it is running a wasted spark system that fires at every TDC event. Yes, you can swap left side and right side HT leads and it will still run.
wildav
XS650 Enthusiast
Check the spark plug on the cold side for fouling. My 79 has a tendency for some reason to load up one side while sitting for extended periods, especially when I leave it parked on the side stand. Fuel can seep into the cylinder. Always the right side on mine.
JJames
XS650 Addict
Get a battery. Check out the start up threads here.
This yes you can swap to see if the problem follows the leads.
But troubleshooting 101 says at the beginning, you test and verify system by system.
Check and set valves, cam chain, test compression. Got compression both sides? 150 is great 80-100 is enough to fire and run.
Now: remove that plug, ground it and check that you have spark. With a pamco if one cylinder is timed to run so is the other.
One tip is to spray a bit of carb cleaner in the "dead cylinder", does it fire then? IF so carb/fuel is where your issue lies.
Open float bowl drains use a catch pan,
clean fuel both sides?
JJames
XS650 Addict
The mysterious jumping misfire. It's been discussed on this forum before but I can't remember the conclusion. Lots if help I am. Also threads on converting to other coils.
Last edited:
Coil !
In theory the spark at each plug should be identical.
When the ignition fires it should pull electrons through one plug gap, up the plug, along the HT lead, around the HT windings in the coil, then down the other HT lead, into the other plug, and across the plug gap.
Sounds like you got a leak somewhere inside the coil, electrons are getting into the LT windings somehow.
Try a substitute coil.
