Engine races on start up

another pic

Looks like some type of aftermarket "cruise control" device that's likely jammed or been left in the ON position (which is supposed to help keep the throttle from automatically pulling itself closed).

Good Luck!

It is an aftermarket inexpensive "so called cruise control". It is actually a throttle position holder, but is missing the top lever. Dropping the lever, it tightens the grip on the throttle, up the levver loosens it. For your purposes, just take if off getting it out of the way.

About the second throttle cable. I have '91 Zephyr 750 with Keihin CVK32(Yours would be CV32). It does have two cables, but I understand the second return cable is not needed. It is there only for safety. The carb return spring does the returning. Even if it had it before, the carb should return.

yup, the guys are right. remove what is left of the cruise control.

I have never seen one of those "cruise control" thingies and like the replies above I would guess it's the root cause of your racing problem and would suggest you get rid of it

I have the same CV34 carbs and they have only one cable. The big black idle adjsutment knob should be about the middle of it's range of travel.


Then check that the spring on the linkage where the cable attaches to the carbs has enough power to snap the throttle flaps closed

Then lube the cable and when you get the handlebar piece sorted out you want about a 1/4 inch of free play in the twist grip (you twist thw grip about 1/4 inch before it starts to pull the cable) and like the guys say you want it to snap closed when you release the grip.

Once you get this issue figured out you will likely need to synchronise the carbs


Just thinking about the smell of gas in your oil and wondering if this was a result of the gas overflowing experience of your earlier post.

Good luck

OK here is the update. I removed the leftovers from the aftermarket cruise control and that freed up the throttle so that it returns on it's own. I refitted the carbs into the boots that connect them on the engine. I thought maybe they just weren't seated well. I have ordered new ones just in case. The bike starts on a full choke and chugs for a bit till it warms up and then BOOM it races to over 5000 rpms. After I shut it down with the kill switch I opened the choke all the way and it would restart and race each time. So I know it is not the throttle sticking, and while it was warming up I was spaying carb cleaner around the boots and there wasn't any change (unless it took a few seconds to get though?)

I was reading the book about synchronisation of the carbs and it says I need a vacuum gauge. I found them at Z1 for about $60. I guess I need to order them as well.

I was also thinking about rechecking the floats to see if they are alright. I keep thinking that I might just have them out of adjustment.

So does anybody have any tips on carb adjustment and synchronizing?

Go to www.wgcarbs.com He has a similar forum and if he has time can answer your carb question.

Thanks I will post there and hope for the best.

With the carbs off the bike and the idle knob about where it should be are the throttle flaps or - butterflies or whatever one calls them - on the engine side of the carbs closed shut?

On the air filter side of the carbs with the choke lever in the fully off position are the choke flaps fully open ? ie not restricting the air flow ?

I'm just thinking along the lines of "never underestimate what mayhem a previous owner may have committed"

Thanks for all the ideas. I am going to pull them off today and check everything out again. Since I have new boots on the way I figure they need to come off anyways.

I have the same bike and had the exact same problem with mine. If I backed the idle screw all the way out, the bike would not stay running without the throttle being opened. If I tried to set the idle, it would race to 5000rpms and just hang there. The issue with my bike was the sealing of the intake boots. They were not cracked; the boots happened to be loose as in not screwed in tightly to the engine. I was able to reuse boots just by tightening the screws (with thread locker) and it fixed the idle trouble. I was able to diagnose the problem by spraying starter fluid on the carbs boots while the engine was running. When I did that, two the cylinders cause the idle to increase.
I hope you find the problem.

Thanks for the tip I ordered new boots and hope it is something this simple.