'83 XJ750 Dies shortly after starting

Hey everyone - I have a few issues that I am having a tough time wrapping my head around.
Bought a 1983 XJ750 recently - rebuilt carbs and got it running. Rode it 60 miles home recently. When I got it home, I left it outside not knowing it would rain that night (never doing that again). The next day I got it in the garage to give it some TLC and work on the brakes and couldn't get it to start. Brand new battery died while I was trying to get it to start. Swapped the battery out and tried to start it and I got it running for 10 seconds a few times before dying and burning out another battery. The batteries were very warm when they died.

I installed an inline fuel filter, so I can see fuel is getting into the carbs. 3/4 exhaust pipes were warm. The first exhaust pipe (furthest on the left) was not. Spark plugs look good. I have one of the batteries on a trickle charger so I will be testing spark on the first spark plug when I get it charged and installed.

Airbox and air filer smelled heavily of gas as well. Not sure if they are supposed to or if that would make a huge difference.

I am very new to working on motorcycles, so any pointers in the right direction would be greatly appreciated!

 

Magafurlong, sounds to me, you are doing all the right things. I however, think you need to pull the carbs again. If one exhaust pipe is not warm, then no fuel or spark is happening on that cylinder. Just giving these carbs a good once over will not get the small jet in the bottom of the float bowl. I hate to say it but give them carbs a good look again and see if you find more stuff in there. Stuff could have come from the fuel lines from the tank to the carbs. Could have been stuck in some small spot and then make it way to the carbs.

How does the inside of the tank look. Finding a really clean tank on our older bikes is hard. Even if they look good, old gas that was stuck to the bottom can come loose after you put fresh gas in and then move the bike around. I have started these bikes that have been sitting and road them home after buying them. Once at home, the small layer of varnish that was in the carbs turned into jell and that was it for the bike. Found that issue once I pulled the carbs off.

https://xjbikes.com/forums/threads/in-the-church-of-clean.14692/
Church of clean link. This is a really good read for cleaning the carbs.

 

Ok quick update. I went through the carbs. Everything was relatively clean. Jets looked great. I replaced them a couple of weeks ago so I was glad to see those were alright. BUT… the small vent hole in the bottom of the float bowl was clogged on 3 of the 4 bowls. So I cleaned all of those up with some carb cleaner, a sewing needle, and plenty of compressed air. Shined a light through it to make sure it was clear. Put the carbs back on, got fuel into them and the motor started right up. My hose clamp holding the inline air filter fell apart so I didn’t put the tank on yet. However, when I put the tank back on, it had a really tough time starting. Noticed that if I didn’t choke it, it was able to start initially but wouldn’t stay on. I had to find a sweet spot in the choke for it to barely lug along.

Could this be a vacuum issue? Did I do well enough cleaning the carbs out? Is this a sync issue?

I have not synced them yet and probably don’t have the proper equipment to, but it sounds like this might be the next logical step? Any advice?

edit: gas tank looks clean on the inside honestly. PO removed rust before I bought it. Gas looks good going into in-line filter, and no debris caught up in the filter yet.

 

Good work on cleaning the jets in the float bowls, easy to miss.

So you are saying if you have AUX gas tank going to the bike it will run, but then you put the gas tank on, and it will not run? If that is the case, there is an issue with either the petcock not working or being plugged. The fuel line or that gas cap is not venting right and not enough fuel is flowing. A bench synch is just find and as long as the bike is not running supper funny when you have it hooked to an AUX gas I would guess they are okay enough to get the bike running.

 

Not even an aux tank. I was putting the tank on and noticed that I had a hose clamp that fell apart when I unhooked the fuel line when I first took the tank off. So I just let the carb bowls fill with gas until the carbs wouldn’t take anymore. Motor was off, petcock was set to “On”. Carbs filled up and I took the tank off so I wouldn’t flood my garage with gasoline. That’s when I start the motor with just what was in the bowls. And it ran better than I have ever heard it run before lol.

When you say fuel line or gas cap is not venting right, are you referring to the gas cap at the top of the tank? I do have an aftermarket petcock I will be installing today. Found one of the tubes/screens fell off when I first bought the bike. Bought an aftermarket one but was able to just put the tube back on the original petcock so I never replaced it.