Loud bang when trying to start

[Karkids]

Hi all. I bought a 1980 xs650 special II and it was running o.k. but the battery kept dying. I found out the rotor was shorted. It took me a few months to get around to swapping and the bike sat for that time.

I finally got the rotor in and tried to start with a known good battery. The engine chugs for a very short time and then stops.

My main concern is that there is this incredibly loud gunshot noise that comes from the bike every few tries.

I know I will have to rebuild the carbs since they sat but I just wanted to see if I fixed the charging.

Any ideas on what this bang is? There is no smoke or strong odor just a crazy loud bang on par with a rifle. I still feel it in my right ear as I’m typing lol

 

[Jim]

Welcome to the forum!!

Did you reinstall the woodruff key when you installed the new rotor? '80 was the first year of the electronic ignition... TCI.
The trigger magnet is on the rotor. If it's not keyed correctly, too advanced can give you loud pops.

Some pics of the carbs and rotor would be useful. Hell, show us the whole bike.

 

[gggGary]

Weak battery? The tci can throw off a random spark when the voltage is low.

 

[Karkids]

Thank you for the ideas, I will post pictures of the bike tomorrow it’s in a state… need new bars, tachometer, brake lever because neighbor backed into it. 99% sure the key is in there right, the curved part is facing the shaft. my tester says the battery is good but I can take it to autozone for second opinion.

 

[gggGary]

Clean, check battery cables +12 AND Ground strap. The fuse box is a notorious problem area, the thin metal fuse holder tabs rot and cause intermittent contact. Old glass fuses another aged out item. They can look good but the metal strip can be loose to a cap. Ignition and kill switches can be REALLY corroded inside.

 

[Karkids]

Good idea I’ll test the fuses tomorrow. Another thing, I only have the rotor torqued to like 15nm, the clutch slips beyond that. Could this be because I have the side cover off? I don’t fully understand how the clutch works, but it engaged fine when I was riding on the highway in December

 

[Jim]

 

[AUTOMAN]

15 NM!
Let's see.. 15x.737=11LB-FT!
and the clutch slips?

more to this to come

 

[YamadudeXS650C]

I know I will have to rebuild the carbs since they sat

Sitting for a few months won't be a problem for the carbs if the gas was fairly fresh.



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[Karkids]

Excellent idea, I have a filter wrench. Couldn’t work on the bike today here are a couple pictures if found for what it’s worth

 

[Karkids]

https://imgur.com/a/p6zmzqV

I went back to check my work. the stator might not have been fully seated, it was way easier to screw it in this time… I know I’m an idiot.
In any case it started and ran with the choke knob open, I used the push start because i was afraid of the kickback

Im getting 14.5v at what I’m assuming is 2k rpm (no tach) I didn’t measure the voltage with the old rotor is this good?

Also the bike slows down and dies when the choke is in

 

[YamadudeXS650C]

I know I’m an idiot.

All of us have our idiot moments.




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