Almost starting. I turn off ignition then it backfires.

I just bought the bike. It ran at buddies house. I had it running three times here. Now it won't start. It almost starts and like I said I turn the ignition off an then it backfires. Flames coming out of exhaust. Buddy said the petcock had to be on "prime" to run. It seems to me it must be getting too much fuel. The bike wasn't on the road since 2012.it has been running off and on. I just changed the oil and wanted to cycle the oil through but I can't get it running. Frustrated big time. Can anyone suggest something... Thanks.

 

How long did it run for those 3 times?

Not knowing the PO personally I would recommend you start with verifying valve clearances are correct:
(I do NOT know if the following works for your bike . . . 750?)

http://www.xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

 

Sounds like its flooded. Your carbs more than likely have dried gas in them. The best way to address the situation is to pull the carbs off. Thoroughly clean them , make all the adjustments , set your valves and do a complete sync. All the information you need to do this is here on this site. By the way welcome!

 

It appears you have a Maxim-X, these machines have a total of 20 valves compared to 16 for other XJs, and every valve shim is located inside a small bucket so it is a bigger job to adjust them compared to other XJs. FOr that reason, it is pretty common for this model to have very tight valves, and sometimes burnt valves. I'm not saying this is your problem now, but you will have to address it shortly, or at least check the valve clearances to make sure they are in specs.

Meanwhile, your friend was right and wrong at the same time. If the bike hasn't been ridden for a long time, the petcock should be set on PRIME for maybe 15 seconds to help fill the carb bowls before starting, then switched to ON when you start the bike. I'd remove and clean the spark plugs before the next starting attempt, though. It would be a good time to check if they are properly gapped. DId you checked the air filter?

Nice bike, by the way !

 

make sure your battery is fully charged. test starting voltage put meter on battery and try to start if voltage goes 10 volts or less your bike will not start, the tci needs 10 volts minimum to fire.
when you get it started check the running voltage.
charging voltages
* approximately 500-2000 rpms: 1.8 volts gradually increasing to 14.2 volts

* 3000+ rpms: 14.2 volts up to about 14.8 volts, with a maximum of 14.8 volts (all XJ700-X and XJ750-X)

 

did you use jaso rated motorcycle oil ?
some reading for you
The Ultimate Relay, Switch, Sensor, and Diodes Guide

IN THE CHURCH OF CLEAN

THE SECRET LIFE OF CARBURETORS

Something New, Something Naked


The Information Overload Hour

 

link to down load a free service manual if you do not have one
http://www.4shared.com/web/preview/pdf/pzHAlX2s

 

Hey there. It's a 750. I had the person I bought the bike come over this morning. He took the spark plugs out. They were soaked with fuel. I had bought 4 new ones. He installed the 4 new ones and the bike fired up right away. It just fired up ten mins ago. I think if this happens again it's probably the petcock leaking. If so it's an easy fix.

 

Welcome aboard. Nice looking bike.

@quebecois59: You mean 8 valves for other Xj's... 4 Intake and 4 Exhaust.

Gary H.

 

Yeah, wrong maths, I did 4X4 instead of 4+4..

 

The bike sounds amazing when running.

THANKS. I just downloaded the manual.

 

HI there. The guy I bought it off said the bike only runs on prime. I'm actually going out to try what you suggested. Prime 15 secs then switch to on . I will try taking a short video. This site doesn't allow for very long vids.

 

Vids can be any length you like. You just have to use a hosting site and link the vid in your message.


Also. Petcock failure does not allow carbs to flood (not on it's own anyway). If it's flooding then you will need to tear into the carbs.

 

check the oil level make sure gas is not filling the crank case.

 

Thanks for the info. I have went out to the shed 3 times today since changing the spark plugs and the bike has fired up first ice and I've ran it for 10 mins the last time. The guy I bought the bike off of said it had to be on prime to run. But that seemed wrong to me. I placed the petcock on run and it's working great. I'm thinking having it prime was the issue.

 

https://goo.gl/photos/HJ9wewY7FBCiWMa59

 

It had the cell flipped over a bit so video is off center.. If you flip ur device a bit it will straighten out. This is it running for 10 mins. After I put the petcock in the run position. Hopefully there are no more issues.

 

I'm checking the air filter tmrw. And changing the antifreeze tmrw as well. Already changed oil and spark plugs. Looking forward to spring already. I also have a 2006 1200 Custom HD. In mint condition..

 

Prime supplies fuel to the carbs at all times, and is mainly used to initially get fuel to the carbs after cleaning them or if the bike runs out of fuel. The bike can be operated on Prime and as long as the needle valves are fine and the carbs aren't leaking. The reason not to leave it on Prime is to prevent fuel from overflowing if the float needle valve(s) are leaking. It that happens you will probably get fuel in the engine oil and that's not good. Your petcock is designed to allow fuel to pass when the engine is running since it is vacuum operated when in "On" or "Reserve".

 

Exactly!! That's what I said to the former owner... I'm thinking he didn't know the bike at all.

 

I guess I can't change my user name!!

 

It is now an ironic name.