29mm tuning

Hey guys, I have a 78 kz1000 with a set of 29mm smoothbores. I'm currently running a Vance and Hines sidewinder pipe w/ only slight valve work to the engine. I have been taking it to the local dragstrips and have a little problem. When I'm staging and set my RPM's I get a popping at the carburettor. It's almost like a slight backfire. There are no flames or any sparks apparent. Going down the track it does good except in between 5 to 6500 RPM, it has a flat spot you can hear more than feel. I'm also have a hard time with the idle. Can't get it set below 2500. Any suggestions I have 117.5 mains not sure of the pilot.

Really dont know why it's popping, but if u take the carbs off to tune them, check inside the intake ports for carbon from a leaking intake valve.

Welcome! Do you think the type airbox you have might make a jetting difference? What airbox are you running? What is the current jetting for the 29s? (jet needle clip position and pilot jet and air screw settings)? Last, check the voltage going to your coils. See the COIL REPOWERING article on our website (my sig) under wg's Tech Stuff Index. Last, talk about your ignition and ignition timing and have you adjusted your valve clearance?

Let me clairify a little. I got these 29's about a month ago, they came off a KZ of the same year and size. They had sat on the bike out in the elements for nearly 2 years, I cleaned them and that made an intant difference. They came with stacks on them and was told they worked better that way. I'm pretty sure that the main jets are 117.5, I don't remember the pilot size, I'll check it tomorrow. I run an aftermarket fiberglass tank with dual petcocks. I also thought that it might have been in the ignition, I was asking around at the track 2 weeks ago about the problem and a few KZ riders told me about the site and look up repowering. I really can't say that I noticed the difference. It's wierd, I turn the key on, pull up the choke, hit the button, it fires right up. I let it warm up a little, turn off the choke and it might drop to about 1000 RPM, when it does that there is no throttle response I have to pump it a couple time to get it going, then it won't drop below 2500. This old rescue project has come a long way in a short time, and I just want to get all the bugs out before the winter and she is put away.

Let me clairify a little. I got these 29's about a month ago, they came off a KZ of the same year and size. They had sat on the bike out in the elements for nearly 2 years, I cleaned them and that made an intant difference. They came with stacks on them and was told they worked better that way. I'm pretty sure that the main jets are 117.5, I don't remember the pilot size, I'll check it tomorrow. I run an aftermarket fiberglass tank with dual petcocks. I also thought that it might have been in the ignition, I was asking around at the track 2 weeks ago about the problem and a few KZ riders told me about the site and look up repowering. I really can't say that I noticed the difference. It's wierd, I turn the key on, pull up the choke, hit the button, it fires right up. I let it warm up a little, turn off the choke and it might drop to about 1000 RPM, when it does that there is no throttle response I have to pump it a couple time to get it going, then it won't drop below 2500. This old rescue project has come a long way in a short time, and I just want to get all the bugs out before the winter and she is put away.

Well after taking the carbs off and checking the jets, I was wrong about the size, the mains are 122.5's and the pilots are if I read them correctly 12.5. I'm thinking now that is too big of a main and the popping is from to much fuel. Any sugestions?

I would consider buying some air filters for the bike. K&N, UNI or Emgo... anything is better than no air filters. The inability to throttle down and poor response off idle indicates the carburetors may need to be cleaned and tuned properly. I doubt you have #12.5 pilot jets. That size is very difficult to find in VM22/210 type pilots. The #122.5 mains are fine, try some #20 pilots in type VM22/210 and turn the mixture screws out 1/4 turn. The clip on the jet needle should be 5DL31-3 (3rd clip position). If the 5-6K rpm flat spot remains after making the changes I recommend, reclip to 4th position.

sounds like its running lean on the pilot curcuit, double check all passages and make sure u can spray carb cleaner though each and every one. And like george said double check the pilot jet size, if its too small it will not run right at mid and high rpm.

There's no baffle in the pipe...correct?

If there is, yank it and then ride it.

Agree with George on the main jet and pilot. You probably have 17.5 pilots and the 7 looks like a 2.

Yank the air correction jets right out and see if it gets worse or better.

I would drop needles to 2nd groove from the top for a stock motor....especially if removing the a/c jet helps the situation.

Make sure someone didn't swap the O-6 needle jets to O-4 needle jets.