Only firing on right side, Is it Carbs or Points?

Optic Bliss

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Hi all,

I have been working on getting my 77’ XS650D in running order, here’s some info for reference:

1977 XS650D
Mikumi BS38 - not well synced
Main Jet:#130
Hugh’s PMA
Fresh Coils
Points Ignition
NGK BPR7ES

A little bit of backstory:
The bike had sat for 10+ years and had collected rust in the tank. The carbs were seized entirely. Once the carbs had been cleaned and rebuilt, it only fired on the right side. The left carb flooded because of a busted float. I replaced it with some ElCheapo float that would let the needle slip loose and cause the carb to flood. To make it work, I had to use a needle that didn’t match the seat. The left side finally ran, then it was driven upwards of 150-200 miles.

The carbs are DEFINITELY dirty, but not dirty to an extent that a jet or the seat could be clogged. After I got to a place I could work on it, I put Kreem in the tank and flushed the carbs about a dozen times to get any rust or scum out. After coating the tank and flushing the carbs, the bike developed a sputter/backfire through the carbs on deceleration. I assumed it was the cheap floats. I swapped them with a float from MIkesXS. After that, I attempted to match a needle and seat set so there would be no possible leaks. I took it for a test drive and it backfired like a gunshot on acceleration instead. I think it may be too much fuel, or maybe I didn’t clean the carbs good enough.

I can no longer tell because the next day, the left side had stopped firing entirely. The plugs are fresh (1 day old) and I tested them for spark. I can smell gas on the threads and electrode, meaning it has to be getting something in terms of fuel. I feel like the 5-6 massive backfires may have filed out one of the points, but I can’t be sure. At this point I'm just pissing in the wind, waiting for my ineptitude to splash back on me. I know there is a problem with the carbs, but could a few backfires file out a point? Or is it just the carbs alone?

I intend to find out by cleaning the carbs, but if anyone has some advice or has had an issue like this and somehow resolved it, please help! SOS! (save our shitbox)
 
Always good practice to ensure the ignition is adjusted properly and there is good compression before chasing a possible (probable) carb problem. No, I don't think backfiring would adversely affect the points. I would though clean and adjust the point gap and reset the timing with a strobe light before heading back into the carbs.

PS - Yes, It does sound like there are still issues with the carbs (still cheap floats and maybe wrong jets); first things first....
 
Always good practice to ensure the ignition is adjusted properly and there is good compression before chasing a possible (probable) carb problem. No, I don't think backfiring would adversely affect the points. I would though clean and adjust the point gap and reset the timing with a strobe light before heading back into the carbs.

PS - Yes, It does sound like there are still issues with the carbs (still cheap floats and maybe wrong jets); first things first....
It has good compression and when I pulled it out of the shed the points were the first thing I replaced besides the petcocks. The timing was set when I put on the PMA, and the cam chain adjuster thingy is still flush with the nut as it should be. I'm glad that it might not be the points though, fiddling around with feeler gauges and holding them open is a hassle alone. Thanks for the advice!

Edit: I will likely still stick a file between them and adjust them again because they might have pitted since I put them on though.
 
Is strobe light available Yourself or a buddy if so I Would check with that first
If spark and at the right timing
Or holding plug against the cylinder head look at the spark please do the readup how it is done
My guess is Points .those are tricky and can be difficult .. Fault finding
 
I had a lot of issues similar to yours on my XS650E. Several issues caused the lack of igniting on my left cylinder.
It turned out that one coil was bad ( measure the resistance ) or swap the plug wire and see if that make left ignite and right to not fire. Second I forgot to tighten the screw that holds the condenser. When all that was fixed I realized that the point had a “leak” thus when it was open it still had continuity ( I had to take it off to figure that out. )
Now it’s running on both cylinders and timing are correct.
My carbs were refurbished and bench tested so I knew they worked.
Good luck !
 
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