Running Issues

[MotorPsycho]

So I've finally got my 1981 XS400 back together, but it still won't run correctly.

We put the carbs back on after a mild cleaning (because I don't know how to correctly do a full tear down and clean; if I did, I would definitely do that), and the bike will start and run with a shot of starter fluid and revving the engine. However, bike won't idle without revving, and won't start without the starter fluid. Also, when revving, there is some minor popping through the exhaust.

Everything is stock on it, air filters, exhaust, jets, if that helps with the diagnosis.

It was gratifying to hear it run today, but still frustrating that it's not running right.

Thanks for your help, guys.

 

[16VGTIDave]

You already have your answer - clean the carbs properly! There are plenty of threads here about it. Use the search function to find a couple hundred...

 

[Scorpio1963]

taking apart and rebuild our carbs for our bikes is very simple.Its so easy even a caveman can do it

 

[MotorPsycho]

taking apart and rebuild our carbs for our bikes is very simple.Its so easy even a caveman can do it

Okay, so here's an update:

Took the bike back apart. Removed the carbs. Watched a YouTube video by a dude about how to take them apart and clean them. Followed step-by-step, did everything he did, and clean the S#*T out of the carbs, inside and out, top and bottom, front to back, and everything in between. They were spotless. Rebuilt the carbs, step-by-step. Set the float height, per the Haynes manual AND the guidance of the knowledgeable gentlemen on here. Used the recommended height setting on here, as opposed to the manual.

Put a clear fuel line in, as well as a clear filter. Replaced old gas with about a gallon of 93, and half a can of SeaFoam.

Put the freshly-charged battery back. Lights and everything nice and bright. Fuel a nice, almost clear color in the fuel line.

Put the key in the ignition. Turned it to ON. Flipped the kill switch to RUN.

Hit the START button.

SAME S*#T as before. No dice.

Now what?

 

[corruptmind]

Whats your exhaust and intake situation? Stock? Clean filter? Exhaust leaks?

-Edit-
Did you adjust the mix screw, when tearing down did you remove them and check to make sure they werent broken off?

 

[MotorPsycho]

Whats your exhaust and intake situation? Stock? Clean filter? Exhaust leaks?

-Edit-
Did you adjust the mix screw, when tearing down did you remove them and check to make sure they werent broken off?

Stock intake and exhaust. Good filters. Not sure what the mix screw is?

 

[corruptmind]

http://www.13graphics.com/xs400/img00322.jpg

Allows you to adjust the idle mixture. I dont remember off the top of my head the amount of turns out, easy to find with a search though, but sometimes the screws will break off inside the carb.

Dumb question but has to be asked, starting with choke (enrichener) on?

 

[Brian43204]

I'm horrible with the bike, but I am learning, and even I was able to remove and clean the carb and it makes ALL the difference

 

[corruptmind]

These bikes are very temperamental about the carbs. If they're not squeaky clean they wont run right.

 

[MotorPsycho]

http://www.13graphics.com/xs400/img00322.jpg

Allows you to adjust the idle mixture. I dont remember off the top of my head the amount of turns out, easy to find with a search though, but sometimes the screws will break off inside the carb.

Dumb question but has to be asked, starting with choke (enrichener) on?

Enrichener? Location? Complete noob here, too. LOL!

 

[corruptmind]

Its all good. On the left hand side of the carbs theres a (generally black) pull knob. Pull it out. The bike has to run with this on for a short while until the engine is warm enough to vaporize the fuel completely.

 

[MotorPsycho]

I'm horrible with the bike, but I am learning, and even I was able to remove and clean the carb and it makes ALL the difference

Me too, complete noob here. I have a guide and this website and that's all the knowledge I have to go on right now.

I got the carbs off and very clean. So, now on to why it still won't run at all.

 

[corruptmind]

http://s20.postimg.org/df0vqrvd9/20130523_085229.jpg

That black knob is the one you're looking for.

 

[MotorPsycho]

Mine doesn't have that, unless I just missed it or it's gone.

 

[corruptmind]

Im not 100% familiar with your model, is it on the handle bars. Left side, a lever that slides towards you?

 

[MotorPsycho]

Im not 100% familiar with your model, is it on the handle bars. Left side, a lever that slides towards you?

I'll have to check tomorrow. Too dark to see now. It's a 1981 XS400SH, and I haven't seen a choke, but I may have missed it. Not hard for me to do at all. LOL!

 

[MotorPsycho]

One more thing that I just noticed on another website. The guy I got it from said it wasn't running. When I removed the carbs to clean them, the rubber vacuum line from the petcock (not the fuel line) was missing, completely. Would that prevent it from running altogether?

 

[corruptmind]

Yes/no. Without the vacuum tap closed off itll run very lean. Youll need that line ran from the engine/carb boot to the petcock unless you plan to leave the petcock on prime. If you're fine with leaving it on prime then just cap off the engine side of the vacuum.

 

[MotorPsycho]

Yes/no. Without the vacuum tap closed off itll run very lean. Youll need that line ran from the engine/carb boot to the petcock unless you plan to leave the petcock on prime. If you're fine with leaving it on prime then just cap off the engine side of the vacuum.

Is it possible that it just doesn't have a choke at all?

 

[corruptmind]

Pretty sure it has one. When you reassembled and attached the carbs, there were 2 cables right? 1 goes to the throttle, other goes to the choke.