79 kz650 loss of power

If you have to run partial choke then I would bet your carbs are still dirty or a vacume leak.

The carbs are squeeky clean inside. That was my first thought. First thing I did was check them. Look new inside not a hint of dirt. But the carb to head boots have seen better days. I'm going to inspect those for leaks this afternoon

Normally carb holder leaks don't affect performance much above the idle rpm level. The reason is that at very low rpm, when the throttle is closed, the slides are lowered in the carbs and the vacuum from the cylinders can't pull much air through the carb throats. As a result, the vacuum inside the carbs and carb holders will pull air through any minor cracks in the carb holders or any cracks in the carb holder/cylinder head mating surfaces. Once the throttle is opened up and the slides rise inside the carbs, air can be pulled much more easily through the carb throats so less is pulled through the carb holder cracks. Additionally, when the slides are closed the percentage of air pulled through the cracks vs through the carb throats is far higher than when the slides are raised. Still, if the carb holders are old, testing them and replacing them if needed is a good thing. If nothing else, it will help the engine idle smoother.

To test the carb holders I suggest you try the following. Get the engine warmed up and temporarily set the idle as low as possible without killing the engine (lower than 900 rpm if possible). The lower the better because with the idle very low the slides are nearly shut and the vacuum inside the carb holders is at its highest. Then spray carb cleaner around the carb holders, especially where they mate with the cylinder head and where the carbs attach to them. Carb cleaner works best for this test as it doesn't leave an oily mess with WD40 or evaporate so quickly that it is not drawn into the leaks as can happen with propane or starting fluid (ether). If the engine dies or reacts to the carb cleaner, you need to replace the carb holders. Carb holder leak related problems are noticeable at idle but generally don't have much impact when riding because the throttle is open. If you find you need to replace the carb holders soak the screws with Kroil for a couple days before attempting to remove them, and use JIS standard, NOT Phillips, screwdriver bits, and this will greatly improve the odds that you will not break or strip a carb holder fastener as so many have done. Let me know if you need info on JIS bits, I have a good link for making your own at no cost. Ed

bikerdave79 wrote: Should the accel pump adjustment be all the way out like this?

Not sure, but I think there should be a few threads showing beyond the pump rod nut. The 81 650 manual doesn't give a measurement --- it just says to measure the threads below the nut before removing the nut, then reinstall using that number.

Check the accelerator pump by supplying fuel to the carbs, then actuate the throttle pulley vigorously: fuel should squirt out each nozzle straight thru the carb bore without hitting the walls.

Also, each float bowl should have a ball, rod & clip; and each nozzle should have an o-ring at the carb body gasket surface.

OK so i checked with carb cleaner. Didn't seem to effect idle at all. I would think vacuum is higher at idle and suck air. So why does it seem to run better at higher rpms and under loads with the choke half on? Its my understanding that this carb actually adds gas when choked not closes off the air. So I guess that means I'm having a fuel starvation. I guess its possible the floats are set too low or something or there is some type of fuel restriction but everything looks very clean. Points should be here today or tomorrow. I'll wait until I get them on and then go from there. Because if I'm losing spark kV while at high rpm or load that could also be why richening the mixture helps

Its quite possible the point springs or condensers are pooped out causing all this

If the problem persists after changing the points you can perform the clear tube test to verify that the fuel levels in the carbs are good. Ed

OK so points smoothed out the idle and low end. Still bucking and lagging under heavy throttle high rpm without the choke half on. With it on it drives perfect (aside from the compromised idle and rich exhaust) carb boots are not leaking. Float levels look OK. So I guess my next step is to remove the carbs completely and check the main metering circuits. Something funky going on where fuel is dropping out from the main jets.

Had the carbs off once before and checked 1, 3, 4 and they looked clean. I didn't undo the accel pump and check 2. My fault cause that's probably where the damn issue is

I think no matter what else anyone says or what you want to guess or maybe avoid.... if you have to engage the choke, which GREATLY enriches the fuel mixture.... you have a carburetor problem and it rhymes with green..... :sick:

Yup... Smh

Could the airbox boots cause this problem. They only have spring holding them tight to the carb intake. Seems like it wouldn't be tight enough to make it air tight. Would that effect mixture at higher vacuum conditions?