TOPIC:

O.K., quick history...I got a "free" 79 KZ1000ST from my brother some time ago, and rebuilt the carbs to get it running...didnt seem to run quite right kept poking around, exhibited the same symptons as my wifes Miata did until I changed her plug wires, (intermittent missing esp. under load) but my stock coils dont have replaceable wires, conviced myself to ebay a new pair, seemed to run a little better, but not quite there yet. new plugs make a world of difference but only for a little while. did the coil re-power fix (Thanx WG!) seemed good enough to ride into work. after about 10 minutes at 70 MPH(~4K RPM) it started surging and slowed to a crawl, I pulled off, checked thoings out, after a couple of minutes of finding no problems, it started up and ran fine for another 10 minutes or so, then again same thing...It would hold 70MPH for more than 10 minutes.
I did a search here this morning, and looks like I will be checking valve clearances, but wanted to get some more ideas on what else I can check...For what its worth, I took back roads coming home, and this caused the speeds to vary more, and not top at 70, this got me home in one shot, but I did still feel it surging at times, I put the petcock on prime, and didnt notice much difference, (maybe a small amount....but not much)

thoughts..ideas...

Just taking a guess, but, completely go over your fuel system. I have a bike that sat for a few winters and some damn bug got into a fuel line, caused all kind of weird running problems until I found the lil' bastards fuzzy nest in a fuel line. A real good reason to BLOW thru fuel lines, NOT suck..... don't ask!!!

medic24 wrote:

Just taking a guess, but, completely go over your fuel system. I have a bike that sat for a few winters and some damn bug got into a fuel line, caused all kind of weird running problems until I found the lil' bastards fuzzy nest in a fuel line. A real good reason to BLOW thru fuel lines, NOT suck..... don't ask!!!

I think medic24's on the right track. Sounds like your carb bowls are filling while you're stopped, and emptying out during the 10-minute ride. Also check to make sure your fuel cap is venting. Open the gas cap after it quits. If you hear a sucking sound, your vent hole is plugged.

Almost sounds like your fuel tank vent might be plugged up. If it happens again try opening up your gas cap if you hear a woosh sound you know you found your problem. My $.02

I KNOW that the problem sounds like a fuel starvation problem but it just pains me to hear that someone has neglected to check valve clearances. DO THAT before mucking with the carbs. Once the valves are adjusted, adjust tension on the cam chain tensioner... then... check for vacuum issues as has been suggested. Also check to ensure that the fuel lines are not kinked and that if you have a fuel filter on the bike, you will change it.

wiredgeorge wrote:

I KNOW that the problem sounds like a fuel starvation problem but it just pains me to hear that someone has neglected to check valve clearances. DO THAT before mucking with the carbs. Once the valves are adjusted, adjust tension on the cam chain tensioner... then... check for vacuum issues as has been suggested. Also check to ensure that the fuel lines are not kinked and that if you have a fuel filter on the bike, you will change it.

WG:
If the bike will go 70mph for 10 minutes, and then a few minutes later, go 70mph for another 10 minutes, why suspect valve clearances? Sounds like the motor is warmed up.

valve clearances are the first on my list to check, although the venting of the tank could be a possibility, and easy to check...thats exactly what I was looking for from ya'll is the hey you might also checks.... I find ALOT of the time there are so many of the "you might as wells" when your doing maintenance on things, I.E. timing belts on an import car, "might as well" change the water pump your right there... rear main seals when doing clutches, etc.. .the list goes on.. (sorry for the rant out of 7 vehicles only 3 are road-worthy right now!!!)

I also got a 'free' 79 kz1000 st a while back. I rebuilt the carbs and it started, but ran bad unless
you went really really fast.

Turned out to be the smog valve was stuck open. I removed the valve and the lines leading to the valve covers. Also removed the vacuum line going to the carbs.

Now it runs great. You might look into that on your KZ.

I eventually made new covers for the exhaust valve covers. Just flat aluminum plates.

Bob