Bike not starting

1974yamahaxs650

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So I just bought a 1974 yamaha xs650 electric start and the bike is almost 100% complete. I knew it didn't run when I bought it, figured I'd have it running pretty quickly... I tried starting it and It didn't start. Looked like whoever had it before me was trying to change the ingition timing... we messed with that and timed it right according to a YouTube video. Still not starting. So we replaced the points because they looked worn... readjusted them properly and its still not starting. I have spark and compression. Sometimes when I try to start it, it will pop one or twice but not actually start. :( Is there anymore things I should try before just trying to rebuild the carb...
 
It is very common for bikes to have gummed-up carbs - that prevent starting - as they sit with fuel in them when improperly stored. Still it's good practice to eliminate other possibilities before working on carbs.

What is the compression reading? What is the points' gap setting? Did you check timing with a timing light and verify spark @ the "F" mark for both sides?
Do the chokes operate properly? Are the spark plugs wet or dry when you remove them after a failed start attempt?
 
I haven't officially done a compression test with a tester but it very clearly has at least SOME compression because the kicker doesn't go straight to the floor. Haven't checked gaps but they look fine. Haven't used a spark light (how would u recommend doin that?)
 
The proper tools aren't expensive: feeler gauges for gaps ~$9 (and other measurements), timing light ~$27, compression tester ~$26. Online service manual ~27.

You can "ballpark" adequate compression by removing both plugs and pushing your thumb over spark plug hole tightly - one good kick should force air past your thumb sounding like a balloon squealing. Adjust gap to .014" right points first, then left points. The points should just begin to open as the F mark on stator is aligned with mark on rotor and must be done with a timing light, a voltage tester or some other electrical means (cannot be done by eye).
 
So now I have it to where it will pop on the ignition stroke but it won't start and when it tries to it will backfire and kill itself :( is that still a timing issue or just a fuel issue?
 
If this was me I would move the ignition timing step wise.. In small steps Kicking
No starter because it takes power away from the spark.
Observe if it gets better and a small step again And back again in small steps the other way
And the battery needs to be good.

I am stubborn so I would probably do it many times ..
I dont normally see both sides carbretors gum up it can appen of Course depending on time and weather
I would expect one cylinder behave better ..
 
Spray some carb cleaner in the carb throats. Will it start and run for a few seconds?
If still only a backfire pop then; swap the points leads left to right.
 
Last edited:
Spray some carb cleaner in the carb throats. Will it start and run for a few seconds?
If still only a backfire pop then; swap the points leads left to right.

That is a good idea ..
Have flipped the wires myself on Boyer Bransden
I sometimes have sprayed starter fluid into the spark plug hole.
And then put the plug back in + tryig to start
Not sure if it is dangerous but I have done it
 
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