Idle issue

So bike runs fine when I'm riding at first it ideal fine at 1100 to 1500 and then after a while it sits at 4000 rpm and no matter what I do it won't go down to where it should be the bike is a 1981 yamaha xj750r seca

 

I had a similar issue with my 82 XJ750. The issue was primarily getting the bike synced properly and ensuring there weren't any air leaks with the boots at the carbs.

 

So the carbs may be out of sync or air in the boots but wouldn't that make it run like crap

 

Have your carbs been to the church of clean? What condition are your intake boots in? Are you running stock airbox...or the dreaded pods? Has your valve clearance been checked and adjusted? How many miles are on your bike? I know lots of questions these are all things that can have an effect . Your synch is off when bike heats up can change as well you have a vacuum leak as well ...when bike starts doing this use a propane tourch( unlit lol) around boots see if rpm jumps this can help pin point. Another possible thing is the gasket between head and intake boot.

 

Yes. Which is exactly what it is doing now; running like crap.

You have a vacuum leak, which could be attributable to worn-out throttle shaft seals, among other things.

IN THE CHURCH OF CLEAN

 

I had a similar experience with idle fluctuation. After attending "church" and replacing the carb holder boots I still had problems syncing then maintaining solid idle. Upon replacing all four intake "band clamps" with better quality and style SS units syncing the bike took very little effort. I found the factory clamps became distorted/weak after several removal cycles plus the age of them doesn't help. The new style I chose are stainless steel, have a small shoulder which adds strength and stops cutting into to the rubber carb holders. They also cinch down with a 7mm socket and they don't back off. They are standard on British bikes and cost the same as factory clamps. What a difference at idle....zero vacuum leaks

 

do you have a link or supplier? photo?

 

I ordered mine from a place called Speedmotoco. The actual name is "9mm German style band clamps SS". I know they are just hose clamps but these ones are different by the way they built really robust and the thick gauge stainless used. $4.00 a piece plus shipping, one less thing to screw with: zero vacuum leak issues. Winner!

 

I don't know why I typed "British bikes" when they are "German style clamps". I was looking at Thruxtons last weekend. I don't know.....

 

those are the right kind of clamps, it's the flared or raised edge that does it. they don't cut into the rubber like regular ones do

 

Add this to your signature so you don't have to keep typing it.

Gary H.