Bike quits after a mile.


XS400 Member
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Willmar, Mn
Hey everybody I'll start off by saying that this is my first post, but i have been using this site as a helpful resource to this point, and I am thankful it exists. :thumbsup:

I purchased my first motorcycle, a 1978 Yamaha xs400, in January. Well aware that it wasn't running great at the time.

Basically, I can ride it for maybe a mile before it starts to sputter out and quit. Then i can start it back up a minute later.

My dad and I have been working on it for a few weeks now. Neither of us are great when it comes to these things, but we can usually manage.

Battery is new.
Coils tested good.
Points are new.
Gap is set.
Oil is new.

I'm just wondering if anybody had any idea where we could go from here?

If it's getting into the realm of something too advanced for two untrained people to handle, please let me know.

If more information is needed let me know. Spring is here and I'm very anxious.


P.S. I'm new to this so take it easy on me. :D
Battery is new.
Coils tested good.
Points are new.
Gap is set.
Oil is new.

Welcome! make sure you cleaned the carbs really well.... and then do it again and set carb float heights... search the forum there is tons of info and videos on here to help. once you have gone through the carbs sync them with a manometer
Also check your petcock. I know that when I have it set to 'on' it works for like 3 mins then not enough fuel is getting to the carb. I believe that it needs to be rebuilt. When I have it set to prime though the bike runs fantastic.
also will be helpful if you threw up some pictures so we can see your set up and model.... and everyone like pictures.
Isn't running the bike on prime bad? I thought I read somewhere that it can flood everything and cause the gas to mix with the oil?
Its should be harmless. Prime just means that the valve is always open. The carb float should prevent gas from excessively flowing, provided its set to the correct height.
Thanks! I'll clean out the carbs two times over and get them all nice and shiny. Make sure the floats are nice and tasty. Then see about running it on prime.
Sounds good. Let us know how it goes. Also just to make sure, is your vacuum line hooked up from you intake boot the end of your petcock?
If gas only comes out of the petcock on prime then you need to rebuild it. If you forget to turn it off you may wake up in the morning with an engine full of fuel. Mcawesome it sounds like a carb/fuel issue. Welcome to the forum.:)
Check the gas cap. It should vent. If it won't vent then after a bit a vacuum builds upin the tank and fuel slows and stops.
Ride the bike till it quits, Open the gas cap, do you hear it sucking air as you open it?
If you do you need to take the cap apart and clear out the vent.
About a mile, give or take, of running distance is what I got on a good battery when my alternator/stator wires were severed. The bike ran fine until the battery was depleted. I'd check the voltage on the battery after a run if the problem is repeatable.

Alternatively, run the bike with leads on the battery. Rev the engine and measure the voltage. Make sure you're seeing something like 14 v across the battery when you rev it up to a few thousand rpms.
Thank you everybody for the extremely helpful suggestions. I'm pretty busy this week with school and work but this Saturday I'm hoping to get a lot of testing done. I'll post an update once I try out these suggestions and hopefully find the problem.
Check the tank to see if is venting. My bike did the same thing and it was a clogged vent hose (two stroke enduro). do you have a clear fuel hose? put a piece clear hose in the line ride it look at the hose fuel? swapping to clear fuel is what I do to have qiuck visual refference.
Okay. It's been a while, but I cleaned out the carbs as well as I could. After I got them back on I got it running. And now it died after making it a couple hundred feet. The tank is venting alright and it's not the pet cock. Sometimes it'll stall at an idle out of nowhere, it idles at around 1200 rpm. Does this sound like the carbs are still dirty or could it be something else entirely?

Also what kind of charging system is in these older bikes? I've seen a few different answers. Does it use an alternator?

if the carbs are dirty try running some SEAFOAM to clean it out before you pull the carbs out sounds stupid but try it.

if it stall thats a fuel delivery, so the SEAFOAM may clean the delivery passages. but your carb probably need to be tuned.
Man this forum is so helpful. I am hoping I am close to fixing the issue. The stalling is for the most part gone. Haven't had it happen for a while. But I recently noticed a little bit of white smoke coming from the left exhaust pipe. I haven't yet synched the carbs, and I think it's running a little rich. Could this cause the little bit of smoke. It's only noticeable at idle.

Edit: The smoke starts at around 4k rpm.
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