Xj issue run away throttle

Hey everyone, I’ve been watching this website and using everybody’s forums fixing this 1980 xj650 bike For over a year now as this is my first bike, and I finally hit my breaking point I’m stuck.

I finally got it running consistently, but I have a major issue. My throttle is sticking open, as soon as it starts, it goes from zero and revs its way all the way up to 6 in about a second I have a video of it, but I don’t know how to put videos on here If you even can.

if anyone knows anything I would love the help everything I know is from this website.

 

Check that one of the clamp bolts on the intake boots isn't jammed against the throttle cable thingemie. On the carbs.

 

Post on youtube, then post the link here.
Are you sure the throttle is sticking? When you twist open the throttle, the carb butterflys are not closing (look at the linkages of the carb movement as you open and close throttle.
Sure your idle screw is not just turned in too much?

If butterfly linkages are not closing lets troubleshoot

start with the simple stuff. Divide and conquire your troubleshooting.

Pull your tank off. If you don't already have an IV bottle aux tank, order one from amazon. Troubleshoot with the IV bottle so you can get to the carbs.

Unhook the throttle cable from the carbs. the easiest way to do that is to open up full throttle, then take a small screw driver to Jam the carbs at full throttle. then turn the throttle back down to produce slack, now pop off the cable from the carb.
Look at the cable now, Is that sticking? Unhook that and see if the throttle cable has friction in it or if its the carb that is sticking. If the carbs are sticking, pull the carbs is your next step.

 

Here’s the video this one’s mild but it got worse

 

It’s not firing on all 4 to my ear.
What have you done so far?
Was the bike in running condition when you got it?

 

It was running the day before I got it then it would barely start on choke and I couldn’t give it any throttle.

so far I’ve rebuilt the carbs fixed the wiring to the Start button new sparks and oil

 

When mine did this, it was a combination of badly out-of-sync carbs and idle speed knob turned up enough to keep the engine from stalling at idle. Basically, the #1 carb was completely closed at “idle” throttle setting, so when I compensated by turning the idle knob up so it wouldn’t slowly slow down and die, it would run away if it got much over 2500 rpm in neutral.

Doing a proper sync with vacuum gauges fixed the problem.

 

Yep, bad sync. It only takes one carb open to pull the rpm up. if you bench synch them carefully they should be close enough to idle, once the idle knob is set. So have you bench synced them?

 

FWIW, I had bench synched mine (the “RCH under butterfly” test) before I had this run-away problem. The bench-synch at least allowed the bike to start and run. But I think a proper synch with vacuum gauges is required to get it anywhere near well-behaved.

One thing: if you don’t have vacuum gauges, note that you don’t need a four-carb set like you do for, say, a Kaw Z-1. The XJ’s carbs are synched to each other in pairs, so you only need a two-gauge set. I found a very adequate two-gauge set on Amazon for forty bucks. Made in Taiwan, not China…

 

If you bench synch carefully using the edge of the hole method I guarantee you it will be good enough to ride, and idle happily. Sorry, what is an RCH?