Kind Of strange Carb Problem

So I was out riding my '77 KZ-1000A1 the other day and before I left I started up the bike using the choke with the bike straight up and down. Once it started I set it on the side stand to let it warm up and put my helmet on and the rpm probably dropped by about half. I up righted the bike and the rpm came back up. I thought that was odd. Anyway out I went and I noticed that when I am in 5th gear at about 65 to 70 mph I can feel a surging in the bike. Not a bad surge but it surges none-the-less. If I accelerate it takes right off without stumbling or other problem. When I let it slow back down to around 65/70 MPH I can feel it surging again. I don't seem to be able to feel this same surging situation in lower gears. And every once in a while the engine actually feels like I have let off the throttle, but I have not and it will slowly come up to speed again.

The carbs were overhauled, but I have my doubts on the work. Everything else should be up to spec in the bike including valve adjustment, points etc. I am running the stock exhaust with complete stock air intake system including the silencer. Just for grins I took the silencer box off and the bike really ran for crap with big time surging in all gears and hesitation. Now as part of my diagnosis procedure I stuffed one of my gloves in one of the air box silencer holes, there are two of them and the surging seemed to be much less, but acceleration was terrible. I only ran it that way for a couple of miles.

I think the needles are in the #3 position and I am running 107.5 main jet with a 17.5 pilot. Any thoughts on this would be appreciated.

Rick H.

If this only started after the carb overhaul it is obviously fueling issues.
Most likely lean as your glove experiment would have richened the mix.
The main areas to look at are float heights possibly being too low and air leaks at the boots etc.

>>> I took the silencer box off and the bike really ran for crap with big time surging in all gears and hesitation
Bike is running lean, check fuel valves sticky, low level of gas in bowls, clogged idle jet, clogged main jet, dirt in tank or bowls.

If the bike has been running fine previously, sounds like you could have been low on fuel.
It could also have been a drop or two of water in the tank.

Just make sure fuel flow is good before opening the jetting worm can.

Thanks to all for the responses. I'll be doing some carb work this weekend to try and figure this out.

Rick H.