Dead Left Cylinder Turned Limp Engine (79’ XS650 Special)

Thraxxface

XS650 Enthusiast
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For anyone that’s not familiar with the issue at hand, we started this conversation over another thread I created about changing my OEM stator to a XSCharge PMA. Essentially, I started a 320 mile journey with my bike and at about 75 miles into the journey my left cylinder started to lose power. I got about 5 more miles in and the cylinder died completely. The left side of the engine was much hotter than the right side and the left exhaust was rainbow pretty. The bike was abandoned at an auto shop until I was able to get it back home.

When I got the bike home I took the plugs out and put a socket on the crank bolt. With two fingers the engine spun like butter. So I knew the engine was seized. I then checked all of my valves and found the left cylinder to be way over tightened. This was weird because I adjusted the valves myself and checked them 3 times before I left with them being within the factory specs at cooldown all 3 times. I checked and adjusted my points and found my top point wasn’t even touching at any part of rotation. About a dime sized gap between. With all that checked I put the key in and tried to start. It takes a few minutes but it eventually does start. Here’s her terms and conditions. Choke on startup, even when warm, 15% throttle always. No more, no less, or she says good night.

Here’s some things that I notice. When she starts, she only runs at 1k rpm. If I open the throttle it’ll go up to about 1500 rpm but will die immediately after. If I let go of the throttle it also dies. Choke must be on every time I start it but in order for it to stay on I have to turn it off right away. There’s a bad backfire through the carbs every 5 or 6 seconds. Both cylinders reek like petrol, the intake side of the carbs have a nice layer of unspent petrol around them, when the bike is off and sitting for a moment the carbs start to dump petrol out the intake side of carbs. Clearly there’s a fuel issue but I’m still trying to get into a school around here so I’m not terribly knowledgeable on the specifics. I do not have pictures of everything at this moment. I’ll share what I do have in hopes that it might help.
 
I would remove the carbs and give them a cleaning and inspect the inlet needle/seats and float condition. As you lost fuel supply to the left cylinder that would result in a lean condition and additional heat in that cylinder.
Since the points gaps have been adjusted I would check timing. Just, confirm or reset basic tune-up specs.
I am sure others will offer more info.
Good luck.
 
Perhaps check the valve play first ..feeler gauge and turn the motor with a wrench step vise so it is reasonably
within spec is closing and opening

I would try to flush trough the float valves if it is 34 .- s.one can take down the float bowls
with closed petrol line or it will flow petrol
then open so petrol flows and gently move the float up so it closes
a couple of times
get a feel if it is closing

and yes ignition timing
Try the startup
 
I would remove the carbs and give them a cleaning and inspect the inlet needle/seats and float condition. As you lost fuel supply to the left cylinder that would result in a lean condition and additional heat in that cylinder.
Since the points gaps have been adjusted I would check timing. Just, confirm or reset basic tune-up specs.
I am sure others will offer more info.
Good luck.
That's the thing though. The left piston is caked in carbon and has a good amount of fuel saturating the top. I can take my finger, stick it in the spark plug hole and wipe the crap off the piston. I'm going to do a compression test when I get home. I feel like I'm missing something real simple.
 
Perhaps check the valve play first ..feeler gauge and turn the motor with a wrench step vise so it is reasonably
within spec is closing and opening

I would try to flush trough the float valves if it is 34 .- s.one can take down the float bowls
with closed petrol line or it will flow petrol
then open so petrol flows and gently move the float up so it closes
a couple of times
get a feel if it is closing

and yes ignition timing
Try the startup
I just did a compression test and I’m getting 150 psi exactly on both sides. I’m wanting to check to timing next but the PO took the stator apart and never aligned anything correctly when replacing parts plus after he did all that I replaced the stator with a PMA so there are zero markings on the bike currently. What would be the next method to checking the engine timing. I’m thinking timing is the issue but I want to be certain. Is there any way to do this without dropping the engine? More specifically, how to do check to see if my tensioner is bad or broke?
 
I just did a compression test and I’m getting 150 psi exactly on both sides. I’m wanting to check to timing next but the PO took the stator apart and never aligned anything correctly when replacing parts plus after he did all that I replaced the stator with a PMA so there are zero markings on the bike currently. What would be the next method to checking the engine timing. I’m thinking timing is the issue but I want to be certain. Is there any way to do this without dropping the engine? More specifically, how to do check to see if my tensioner is bad or broke?
You use a timing disc. You'll have to adapt it to fit the end of the crankshaft. Find TDC and use the degrees on the disc to turn the engine to the number of degrees you want.
 
I have a Boyer Bransden and no correct timing marks after a rewind of the rotor Its been a long time --Above has one method
I try to find Top Dead Center with a wooden stick into the spark plug hole
Then ill try to start it with kick starter .If no success I change the ignition slightly try again.
Eventually something will happen ..shooting in the exhaust ... To late
or kick back on the kick starter to advanced .listening to the sound of the engine
Especially if it starts easily is a sign being over all correct
Blipping the throttle gives information

Sure it is a strange method .But Folks here are setting ignition a bit later runs smoother and fuels are different today.
Making pen marks .and adjust over time .I don't se any need to take the motor out
Dont set it to advanced that can hurt the motor
 
@Thraxxface , FYI this is what a timing degree disc looks like -

1000003037.jpg
 
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