New bike troubles

900 rpm is just a tiny bit low. Normal idle for the KZ650 is 950-1050 rpm. Just use the idle stop screw (the big knob under the tank on the right hand side) to adjust. Often the cause of the revs being slow to return to normal is a vacuum leak. I would check the carb holders for leaks. They will eventually develop tiny cracks in the mating surfaces between the holders and the cylinder head that can cause them to leak at idle. These cracks cannot be seen with the carb holders in place. 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.

Here's some general info than may be helpful when working on the bike (see link). Ed

kzrider.com/forum/10-new-members/589649-...r-savannah-ga#594587

When the bars are straight or turned to the left, it snaps back without a problem but when I turn them to the right, it goes much slower. Would that be the problem or would it be the carb holders like 650ed has said?

That definitely sounds like a throttle cable routing problem. Remove the tank and take a look at the throttle cables while you turn the handlebars. You should see where it's hanging up. Ed

So I went out and adjusted the throttle cable so that it snaps back from all positions and the problem still remains. I also sprayed carb cleaner around the carb holders and the carb boots to see if that did anything and nothing happened. The strange thing is that when I physically roll the throttle forward the revs slow down like they should. There also seems to be some backfiring but I changed out the old muffler for a newer one of the same type and it seems air is leaking out where it connects to the headers. Gonna see if I can put a tight clamp to close off the leak or get it welded if I have to. Would that small air leak be causing the issue or would it still be the throttle cables since it drops when I roll off the throttle?

Could try tuning the pilot circuit by adjusting the pilot screws.

Would suspect in this case that a richer pilot circuit may reduce the "run on" tendency and exhaust popping on deceleration.

Remember that which way to turn the pilot screw is different, depending on the carb pilot circuit design (i.e., side-located air vs botton-located mixture.)

Good Fortune!

Interesting, I'll try adjusting the screws tomorrow and see what the outcome is.

Patton wrote: Could try tuning the pilot circuit by adjusting the pilot screws.

Would suspect in this case that a richer pilot circuit may reduce the "run on" tendency and exhaust popping on deceleration.

Remember that which way to turn the pilot screw is different, depending on the carb pilot circuit design (i.e., side-located air vs botton-located mixture.)

Good Fortune!

Bottom-located pilot screw -- turn out counter-clockwise to enrichen.

Side-located pilot screw -- turn in clockwise to enrichen.

Good Fortune!

When adjusting the screws, turn them 1/2 turn at a time. You can fine tune them by turning them 1/4 turn either way.

I don't understand what's going on with this thing, it's giving me a different problem every day I went out this morning to try a few things that you guys said might be the trouble so I started it up to get a baseline for the day and rolled on the throttle a little bit but this time rather than hanging, it dies almost immediately when the throttle is touched.

If you have carb problems, you have to fix them from the top down. Clean the tank thoroughly, clean the petcock assembly, install new filters. Check for vacuum leaks. Clean the carbs, adjust fuel levels with clear tube. Until you do that, you will have a hobby of continuously working on your carbs.

Onealjp wrote: I don't understand what's going on with this thing, it's giving me a different problem every day I went out this morning to try a few things that you guys said might be the trouble so I started it up to get a baseline for the day and rolled on the throttle a little bit but this time rather than hanging, it dies almost immediately when the throttle is touched.

Was this after letting the engine warm up to operating temperature? Ed