81 XS 650 fuel situation and ON FIRE

[sgtsteve]

I've been battling carb problems, fuel leaks, etc. Finally thought we had it solved but I can tell there is still a choke problem...at a certain point it RACES!

Anyway we had some half decent weather here last Saturday so I took all 3 bikes outside in the driveway and started them, took em' around the block. Problem: the Yamaha started, idled for a while and then started to sputter so I rev it a little. THe whole left side shut down or it sounded like it shut down. Then "bang"! I'm talking a backfire and I mean "fire". I shoot firearms and that backfire from the Yamaha made my .357 Ruger look like a sissy-boy flame. Yeah, I shut down the Yamaha. What the heck!

I know, I have the carb PDF and I've read through it guys but there's 1,001 different possible causes. Ideas? Why the backfire? Why the idle/start up/choke that wants to sputter or race? Can't believe it but I'm at the point where I feel like throwing a sheet over the bike and letting it sit for a year!

Sgt Steve

[preston]

SgtSteve:
Ethonal it could be, it causes all kinds of issues ! ( and clog carbs,) ,, but what do your plugs look like ?
best to you,,, Preston

[flea]

have you checked your advance and retard,maybe sticking.

[sgtsteve]

Feb 4, 2014 21:32:40 GMT -5 preston said:

SgtSteve:
Ethonal it could be, it causes all kinds of issues ! ( and clog carbs,) ,, but what do your plugs look like ?
best to you,,, Preston

Pres,

Yeah, ethanol is what the guy said that rebuilt most of the 81. Plus I think I narrowed it down somewhat; I had the bike sitting on the sidestand and from what I can tell there's a little bit of a fuel leak and it's weeping on the left side. So I'm thinking it's loading up the left side cylinder and BANG! Now I've got it on the center stand and we'll see what happens.

Another side to it all: I believe the leak is due to the petcock so if it's allowing gas to seep into the cylinder, well that could cause the problem.

Know if the petcock rebuild kits have material that won't disintagrate with the current fuel?

Sgt Steve

[sgtsteve]

Feb 5, 2014 23:20:01 GMT -5 flea said:

have you checked your advance and retard,maybe sticking.

Thanks flea but from what we've been able to determine the retard/advance is working fine.

Sgt Steve

[jetmechmarty]

Mar 23, 2014 20:42:29 GMT -5 sgtsteve said:

Feb 5, 2014 23:20:01 GMT -5 flea said:

have you checked your advance and retard,maybe sticking.

Thanks flea but from what we've been able to determine the retard/advance is working fine.

Sgt Steve

Check again. Make sure the timing is set correctly before you start fooling with the carburetors.

[sgtsteve]

Mar 24, 2014 9:31:11 GMT -5 jetmechmarty said:

OK will do, done and ok.

So fired it up again yesterday. Starts fine. Running. Don't know why I checked but the right side exhaust fine, heat building. THe left side, just air, no heat! I shut it down, pulled the plugs. Both were black as in "soot". Cleaned both and put em' back in and all was fine. I couldn't believe that the soot was bad enough that the left side wasn't firing, these plugs are new!

I still think there's something in the choke system that isn't right. Unless I let the bike run and heat up fully...if I rev the throttle the bike races...doesn't come back down. I have to let it warm up to the point where I can fully shut down the coke the whole way. I made a post in another section; ordered a petcock rebuild kit, getting some leakage.

Sgt Steve