Troubleshooting wisdom: Firing on one cylinder

cacka_lacka

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Hello everybody,

I'm in the process of wrapping up my '81 bobber build. The build started 2 years ago and now I'm having a hard time firing the thing up. I was hoping to get some troubleshooting advice...

Info:
1. Bike ran "okay" before it was disassembled for the build... occasionally tough to start cold, but then always started first kick when warm. It pulled okay, but was in need of a good carb cleaning.
2. The engine hasn't been ran since the build began 2 years ago. Nothing has been done to the engine... it's the same as the day it was pulled.
3. I thoroughly cleaned the carbs as per the usual guide. I spent 2 nights and 3 cans of carb cleaner cleaning these things and swapped out jets to account for the pod filters/exhaust. Everything was squeaky clean... definitely the most time I've spent cleaning out old carbs before. However, the carbs were cleaned 1.5 years ago and have sat in a sealed ziplock bag since.
4. No changes to the ignition besides iridium plugs. Still running the stock rotor/pickup/coil/TCI.
5. Now that the bike is ready to be fired up, I rough wired the regulator, TCI, and coils to just get it running before final wiring. I have the whole works hooked up to a fresh car battery to hopefully eliminate any voltage drop issues with the TCI.
6. I confirmed that both plugs are getting a nice blue spark and both carbs are getting fuel by cracking the drain screw.
7. When turning over the motor with the starter, I get a fairly consistent pop on the left cylinder but nothing on the right. If I pull the right plug, I still get the left to pop.
8. Of the three choke settings, the middle position seems to be the best for getting the left cylinder to pop. The right still doesn't pop.
9. I've dribbled a little fuel through the carbs and into the plug holes, but with no real effect. Same thing with carb cleaner... it doesn't seem to help. I've always had luck using carb cleaner to get other motorcycles to at least fire for a bit. I have a can of ether laying around... but I'm going to hold off on using that until I'm desperate.
10. Kicking seems to have the same behavior... popping on the left and nothing on the right.
11. Timing. Shining a light through the plug hole and eyeballing the piston for TDC, it seems that TDC is exactly midway between the T and U marks on the rotor.


Seems to me that I may have a carb issue with the right cylinder? Before I tackle that, I'm going to check valve lash... just for good measure. Although I'm getting a clean spark, could all this be possibly related to a weak pickup magnet on the rotor?

Any suggestions from you experienced xs650 folks? I'm still going to be troubleshooting it, but just thought I start this thread to see what else is recommended.

Thanks!
Sam.
 

XSLeo

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Try unplugging the reg/rec. The TCI uses a small magnet in the rotor to tell the TCI box the engine position. They sometimes get weak. If weak the magnetism from the rotor hides the magnet from the pick ups. Unplugging the reg/rec removes the magnetism in the rotor, this lets the pickups read the magnet better.
If your engine runs with the reg/rec unplugged then it's easy to fix the rotor magnet. I don't recall the part number but Radio Shack sells rare earth magnets in a 4 mm / 3/16 inch size. A perfect size. A two pack for like $3.
You just glue one of these magnets on top of the magnet in your rotor. Any good epoxy will work, I like JB Weld.
It wouldn't hurt to go through the carbs again. Possible float height or plugged passages.
Leo
 

cacka_lacka

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Good news! She's alive! Turns out the right side valves were way out of spec. No lash at all. So I'm guessing the right side wasn't building enough compression to fire. The left side wasn't perfect, but it at least had some lash. I put everything back into spec, buttoned it up, and it fired up on the first try. :D

There's still a lot of tuning to do... it likes to pop/backfire a lot. But at least it's running. Thanks for the tip on the magnet, but hopefully I won't be needing that Radioshack magnet any time soon.

Video:
 
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