deceleration after freeway speeds

my 78 KZ650 B has stock carbs, pods and kerker. I have it all pretty much dialed in now, it runs great but today I took it to work to show off and after riding about 10 minutes of sustained freeway speed (70), once I came to a stop at the stoplight it wanted to idle real low and died.

Once I started it back up and headed onto work on the regular roads it was just fine. Then on the way back from work, it was just the same. Ran fine on the surface roads, then 10 mins of freeway and pulled the clutch in while on the offramp and it wanted to die so I babied it with the throttle while sitting at the light. Then it cleared up and ran normal.

Anyone had this? or know what it might be?

this is a total rebuild bike - new carb boots, sealant on the boot - to - head joint, carbs overhauled, jets are stock, timing is set, etc, etc. please dont even mention the coil wire relay thingy..... sheesh thats the fix for everything these days! I have a new wire harness, handlebar controls and plugs, wires...

It is completely normal except for this.

have you run a compression test on it once it warms up?

Besides a compression test, are you sure the vent passage in the fuel cap is clean? When I redid my tanks I made sure the vent was clean with a generous dose of carb cleaner.

one question for the record, are these the stock carbs for a 78KZ650B??

heres how they look

That is the classic symptom of needing to do valve shims.

The valves heat up on the expressway just enough to not seal, but you can't notice the difference on the highway. At idle the leakage is just enough to kill the motor. After just a few minutes the valves shrink just enough to seal again and all seems fine.

The problem will be worse on hot days, and maybe not noticeable on cold days.

A valve-lash check is in order.

Also should mention, a compression test will not reveal any problem. The engine cools so fast that the valves seal back up in moments. By the time you do the comp test, everything is back to normal.

Only checking the lash will tell the story.

jzanutto wrote:

one question for the record, are these the stock carbs for a 78KZ650B??

With the air screw on the side, I'd say no, that they're not correct. Does the number 2 carb have the accelerator pump on it (you'll know it as it's much different than the other three)?

I believe there was more than one type of carb for the 77 and/or 78 650's. At least I've seem to come across more than one type. It makes air/mixture screw and jetting info confusing.

They look similar, though.

jzanutto wrote:

one question for the record, are these the stock carbs for a 78KZ650B??

i could be wrong, but the extra ribbing going horizontally on carb bodies is from an older style...???

every one of the valves are between .003" and .004". Just went through the engine. No accelerator pump

If you have pods and the kerker you may want to adjust the jetting.

I will also see if my advancer is hanging open.