Help, blip the throttle and bike goes to redline

I have a 1982 xj550 seca, I just finished the carb rejet and rebuild. I have entirely split the rack, dipped them, and replaced every last seal. Even the throttle shaft seals. Wanted to see if anyone would know what could be causing this. Every time I give it even a quarter way throttle, it revs out and I have to kill the bike. Also new throttle cable and throttle is not sticking, the butterflies return immediately. If anyone could help that would be great, thanks

 

Maybe you have leaky intake boots. You can propane test them. The other guys will know more about this.

 

Yup, first thing to check is for a vacuum leak at the carb-to-manifold boots. Dumb question....did you forget to put the caps back onto the vacuum ports on top of the boots?

First though, did you bench sync the carbs? What settings did you put your mixture screws at? Do you have the airbox and filter hooked up, or are you trying to run it with pods?

If there is no leak there, then the next thing that I'd wonder about is if you could have put some jets in in the wrong spots....

dave

 

Hi dave, so i have already replaced brand new boots and gaskets, there is a small vacuum leak still from around the boots while tight but i dont see how it would be causing this problem intermittently only when i touch the throttle. my air bleeds are at 2 and a1/2 turns out and the bike starts right up and idles well. I have those dual k&n filters but i haventt put them on yet. Vacuum caps should probably be replaced but they are on and i did bench sync the carbs, all the jets are in the spot they should be.

 

ANY vacuum leak will lean out the mix and cause that.. So, you have leaks, they must be eliminated. Also, are the caps on tight? If there's even a hint of play or looseness you can get vacuum leaks there too.

As soon as you touch the throttle, the vacuum leak will suck in exorbitant amounts of air, cause a lean condition and rev high.

 

If you just rebuilt the carbs, you will need to adjust the air mixture and vacuum sync . The high rev's is from running lean, but once you get all the adjustments done it will stop.

What you will need is get a carb vacuum sync tool or make one. Search on YouTube or on the forums here and a colortune. simply just screwing the air bleeds in at 2.5 turns is not enough.

 

He has a vacuum leak somewhere. Properly cleaned carbs, with no vacuum leaks in the intake system, will run perfectly fine with a 2.5 turns out baseline on the idle air screws without doing a color tune and vacuum sync. He should do both for optimum running, but that is not the cause of his problem.

 

To be honest i was told i must have a vacuum leak for when this happened to me on my carb rebuild and i checked and checked and nothing. I even used a propane blow torch(not on) to look for the leak. Nothing. It all stopped and ran like a champ when I color tuned and vacuum synced it.

 

Did you do a running sync? Out of sync carbs mean that one cylinder will carry all of the others, then when the throttle starts to open, then all come on.

How about the slides? Did they go "clunk" when you rebuilt the carbs?

 

so i had a major vacuum leak coming from my carb boots to the head. I bought new ones replaced them and no vacuum leak. A week goes by and now the same thing, the new boots are leaking. Leaking at the head surface. The head surface looks more than true and I cleaned the matting surface very thoroughly. I was thinking about spraying the gaskets with copper spray. any other suggestions?

 

the boot has a rubber o-ring in it......maybe the rings had hardened up. I'd say use a thin bead of rtv, or yamabond/threebond, or something similar.

dave

 

my carb boot set came with paper gaskets..
my gasket set also had carb boot paper gaskets.

 

There are paper gaskets, correct. But if you look in the end of the boot, you'll see the ring, too

 

Yep. The steel base has a o-ring in it. The groove is pretty shallow and it is easy to bump the o-ring out of its groove during instilation and end up with a leak.