'81 XJ750 - high rev

I finally got the carbs back on and cranked it up. It immediately starts revving up (like the butterfly valves are stuck open) and I have to kill the engine. Here's the basic setup:

- mixing screws at 2.5 turns
- I haven't touched the sync screws
- the rubber boots from the airbox to the carbs are not attached (I just want to see if it runs).
- I'm using an auxillary fuel bottle and just have the vacuum line that normally goes to the petcock plugged with a screw driver.

I screwed the idle screw out a bunch, but it never made a difference.

Any suggestions are much appreciated.

 

make sure you dod not bump the Idle screw on the bottom of the carbs. Try turning it out a turn and restart the engine. If it still does the high revs then make sure the manifold to carb boot clamps are tight. If there is a leak this could cause the high idle also. also the air box needs hooked up to put a restriction on the system and have the carbs draw the right mixture. Let us know what you find. Hope this helps

 

Tight, insufficient throttle cable slack is my first suspicion. Given that you had to remove the carbs to get the cable connected is my hint. Normally that is un-necessary. (You don't have to remove the carbs to 'replace' a throttle cable.)

Slack the cable adjustment up at the throttle grip?

Upside-down mount?

Improperly routed throttle cable?

You haven't turned-out the idle adjustment enough; yet?

Enrichment Circuit issue? Stuck? Needs slack; too?

The atmosphere of your work space contaminated with an odorless, highly volatile gas ... try striking a match!

 

Well, maybe I found part of my problem. After reading some of the DIY links, I think I may be missing the tiny o-ring associated with the pilot mixing screws. When I reassembled these screws, I had the screw, a washer, and a spring. From what I read, it sounds like I should have had an o-ring, too ('81 XJ750). Should I have an o-ring? If so, anybody know where I can purchase these? (I checked DennisKirk and they have a carb rebuild kit and it says it has the all orings). Could the missing o-ring cause the high revs? Also, I'm not sure I assembled them correctly. I first put the washer on and then the spring, but from the DIY links it seems like maybe it should be spring on first, followed by washer, and then the o-ring.

One last thing, how do you adjust the slack in the throttle cable? Up at the throttle, there is a lock washer and adjusting nut. The lock washer is on all the way (screwed on clockwise) and the adjusting nut is screwed on (clockwise) all the way to the lock washer. Turning the adjusting nut counter clockwise seems to tighten the throttle cable resulting in the throttle linkage being pulled up (not what I want). So, it appears I have no more adjustment in the throttle cable unless I'm missing something (which is very possible).

thanks for the help

 

Pilot screw, spring, washer, o-ring.

The o-ring just might still be in there. Those little tiny devils tend to stay put ... and, they are really, really small.

If you have absolutely NO adjustment available at the upper throttle cable "Slack adjustment" ... none ... There is the possibility that it's not the right cable and somebody Jury-rigged some other throttle cable on there.

The reason I suspect this are the clues provided from the previous discussion.

The throttle cable is a "Piece-'o-cake" to replace. You don't have to remove the carbs to do a cable swap. You just slack-off the upstairs adjustment ... lift the cable out of the downstairs mount -- through the slot in the mount ... slide the bullet out of the linkage through the linkage slot and the whole deal is done!

I strongly suspected something strange was going on when the discussion went to you having to "remove the carbs" to hook-up the throttle cable.

I'm absolutely certain that the cable should have enough slack available to disconnect and re-connect it at the carb linkage without removing the carbs; ever.
As Yogi Berra used to say: "You could look it up!"

 

I would guess that the airbox not being hooked up is part of the problem too. Had the same issue with my bike, tried starting it without the pods, would idle up to about 3k or so and not come down. Put the pods on and brought it right down to where it should be. They make a lot more restriction than you would think...

 

SWEET

RickCoMatic, you win the grand prize (that is if I could afford one; you'll just have to settle for the satisfaction of knowing you were right). Based on your hunch, I disconnected the throttle cable and cranked the bike up. Guess what, no rev..........just smooth idling. I used my hand to manually push the throttle linkage up and it revved nice and smooth and then settled back to a nice idle.

I'm going to move on to adjusting the valves and add a new throttle cable to my list of things to buy.

Once again, thanks to everyone for there input and suggestions. Keep listening and posting, I'm sure I'll have more questions as I keep moving forward.

99expytn

 

Keep plugging, you'll get to the bottom of it all and have an enjoyable ride when your done!

 

Hunch???

That was NO hunch! That was my "Diagnosis!"

How about my Grand Prize being that I want YOU to buy yourself a ColorTune Plug Kit (On sale - see thread) ... use it to set your mixtures up PERFECTO ... and, get that little baby of yours right on the hairy-edge of fine tuning!

I can hear that ... "Whoa .. whaaa .. aaah" happenin' soon!!!

Gid-did-don-bro!