Was running and riding, then running, now won't start.

[Sigurd8404]

I recently bought an 81 xs400 special, picked it up on Tuesday afternoon since the weather in WI is finally riding weather. She had been sitting in the sellers garage for half of the winter without a battery tender, so I knew the battery was dead. Brought a new battery with me to pick it up. Installed battery and she started right up with the electric start and I road her appx 6mi home. The only issues she had on the ride was she backfired a lot when you let off the accel and at one stop the rpm's hung high, but slowly dropped back down.

Yesterday in my free time, I take the air filters and carbs off to look at them. Carbs valves and floats were actually clean and free moving, so I did not take the carbs fully apart as of yet. Boots from the engine to the carbs are intact and secure, re-secured the carbs and re-secured the filters. Had her up and running to make sure she was good to go last night around 830pm, I did no adjustments to her and had no issues.

This morning, I go to start her up, choke on, gas on "pri", electric start...starts no problem. She's idling under choke, warming up, no issues. I swap the petcock over to "on" and start to back the choke off and she drops to idle, then just slowly fades out until she dies. I re-choke and go to start and she won't fire, I try again and nothing. So I hit the electric start and give her a touch of gas and she fires, the moment I let go of the accel, she dies. Do it again, same result. Choke on or off didn't make a difference.

Over my lunch break a couple hours ago I run home, pull the gas tank off, vacuum seal on the petcock is still working fine, tank isn't rusted. Pull the air filters, still no issue there. Pull off the carbs again, they were a little flooded from giving it the extra gas trying to start it this morning, clear out all the gas, valves and floats still look good, still move freely. Re-install carbs, filters and tank. Try to start her and nothing yet again. Gave one quick twist of throttle just to see if she'd fire up the same way she did this morning and I got the loudest backfire I've ever heard and that was it.

Parts note: The bike has aftermarket pod filters and an unknown brand aftermarket 2-2 exhaust system that is loud as balls from the previous, previous owner. Unknown if the carbs were re-jetted and synced after the pod filters and exhaust installed, so I still have to look into that.

Anyone have any ideas as to what I should look at first for diagnoses and repair to at least get her up and running again so I can hopefully get her in to be tuned, re-jetted if necessary and synced (I don't have the capabilities in my apartment garage)? Thanks.

 

[arfstrom]

My first thought is

1. vacuum line from petcock got forgotten
2. Floats, don't float anymore
3. Pilots, not at 3.5 turns

www.amckayltd.com/carbguide.pdf for backfiring Check sparkplugs to see current running health, (wet = not sparking, black = rich, white=lean...)

Floats, when my floats were bad, I could get it run on day one of the carb rebuild, day 2 was a nojoy.

everybody forgets the simple thing from time to time, (petcock vacuum line)

http://www.iwt.com.au/mikunicarb.htm -- another carb site...

 

[Sigurd8404]

So I had checked the vacuum lines again and they seemed fine. Took the carbs apart and cleaned them again. Checked to make sure the screws were at 3.5 turns. Still had nothing. I read that there were a lot of problems with the vacuum systems of these old bikes having leaks in gaskets and such, so I opted to switch out the vacuum system for a classic on/off/res petcock system from an older style XS. Mikesxs has systems already tapped for the newer xs, so I picked that up with some other parts.

I swapped bars to tcbros drags, put all the original controls back on the new bars while the gas drained out of the tank. Swapped in the new petcock, new fuel line and capped the vac line with a blind plug. Put some gas back in her and gas is feeding fine, carbs "should" be fine and she still wasn't firing.

To add to the confusion, not only will she not fire still, I've now somehow lost electric start. All other electrical systems are working, but electric start won't even attempt to turn her over anymore. Going to take the throttle housing apart again tomorrow to see if something happened during the bar swap, but other than that, I have no idea how electric start just suddenly won't work anymore. Any thoughts as I tear back into her tomorrow would be much appreciated. Thanks.

 

[xschris]

If you new bars are painted you have to remove the paint under where the left and right housings mount. This is how the grounding system works.

 

[Sigurd8404]

Aha, roger that. They are black bars. I'll have to strip the bars under the housings then. That's kind of a b*tch. Should have just bought non-painted bars and painted them myself after the fact then. Thanks for the heads up. This is the first time I've tried to use non-chromed bars on a bike.

 

[xschris]

That's why these bikes never came with painted bars.