Carb Adjustments

[GeneralTso]

Okay so I know trying to troubleshoot over the internet is less than optimal and very open to interpretation but you guys have been able to point me in the right direction on other problems so lets take a crack at this.

So first my setup:

• Kazuma 200cc
• Valves Adjusted
• Brand new PZ30 Carb
• Main jet needle set to lowest grove on needle
• Stock airbox
• stock exhaust (but PO drilled out muffler)

Problem:
Bike idles, sharp response if you crack the throttle while idling, runs good wide open. Problem is at partial throttle bike sluggish, back fires, coughs through carb, hesitates. When decelerating it back fires sometimes pretty good.

So I've been playing with the idle fuel screw thinking the bike is running too lean but the more I read I think I'm not attacking the right issue. By adjusting the idle fuel screw I'm just making the bike idle to rich but not correcting the issue at partial throttle. I'm thinking I need to set my idle back and increase fuel at throttle but since I'm already at the bottom groove I need to add a washer and raise the needle a little more.

Does any of that make sense? Or have I been staring at this too long and not thinking straight?

Here is how the plug looks after a run, it was clean.

[GeneralTso]

So reading more and wondering if my CDI might be heat damaged? As you can see mine had been sitting on the pipe for a while, not too mention it's 12yrs old and was left to sit outside unprotected. So ordered CDI, Coil, Rectifier and relay kit from Amazon.

[BlackBike]

[Ariel Red Hunter]

Originally Posted by GeneralTso

Okay so I know trying to troubleshoot over the internet is less than optimal and very open to interpretation but you guys have been able to point me in the right direction on other problems so lets take a crack at this.

So first my setup:

• Kazuma 200cc
• Valves Adjusted
• Brand new PZ30 Carb
• Main jet needle set to lowest grove on needle
• Stock airbox
• stock exhaust (but PO drilled out muffler)

Problem:
Bike idles, sharp response if you crack the throttle while idling, runs good wide open. Problem is at partial throttle bike sluggish, back fires, coughs through carb, hesitates. When decelerating it back fires sometimes pretty good.

So I've been playing with the idle fuel screw thinking the bike is running too lean but the more I read I think I'm not attacking the right issue. By adjusting the idle fuel screw I'm just making the bike idle to rich but not correcting the issue at partial throttle. I'm thinking I need to set my idle back and increase fuel at throttle but since I'm already at the bottom groove I need to add a washer and raise the needle a little more.

Does any of that make sense? Or have I been staring at this too long and not thinking straight?

Here is how the plug looks after a run, it was clean.
Attachment 7732

I like to use fingernail polish on my twist-grip to help sort out carburetion problems. I open the throttle and close it several times until I am confident where 1/2 throttle is. I put a dot on the twistgrip, and a line on the mount, marking the 1/2 open point. Next I open the throttle all the way, and put a line on the twistgrip halfway between the dot and where the twistgrip is at wide open throttle. Repeat this action with the throttle at idle. Now you should have two lines and a dot on the twistgrip, and one line on the twistgrip housing. So now you have a line at 1/4 throttle, a dot at 1/2 throttle, and another line at 3/4 throttle. Now, as I'm sure you know, the pilot jet controls the mixture up to 1/4 throttle, the needle position controls from 1/4 to 3/4 throttle, and the main jet controls mixture from 3/4 throttle to wide open. It is not quite that simple, but that technique has worked to tune this type of carburetor ever since 1930.

[GeneralTso]

Ariel I actually saw where you posted that in a different thread and it's what helped me get my head around it. So I think my plan is after I get the new CDI and coil on I'll try adding that washer. Because like I said I'd idles good, runs wide open good it's that in between where it falls down.

[Ariel Red Hunter]

Originally Posted by Ariel Red Hunter

I like to use fingernail polish on my twist-grip to help sort out carburetion problems. I open the throttle and close it several times until I am confident where 1/2 throttle is. I put a dot on the twistgrip, and a line on the mount, marking the 1/2 open point. Next I open the throttle all the way, and put a line on the twistgrip halfway between the dot and where the twistgrip is at wide open throttle. Repeat this action with the throttle at idle. Now you should have two lines and a dot on the twistgrip, and one line on the twistgrip housing. So now you have a line at 1/4 throttle, a dot at 1/2 throttle, and another line at 3/4 throttle. Now, as I'm sure you know, the pilot jet controls the mixture up to 1/4 throttle, the needle position controls from 1/4 to 3/4 throttle, and the main jet controls mixture from 3/4 throttle to wide open. It is not quite that simple, but that technique has worked to tune this type of carburetor ever since 1930.

Merlin, do you think I made this clear enough? Seems like we get the same questions over and over. And thanks for the thumbs up!

[Merlin]

Originally Posted by Ariel Red Hunter

Merlin, do you think I made this clear enough? Seems like we get the same questions over and over. And thanks for the thumbs up!

Clear enough that Iam going to try it with my new carb. Thanks.

[Ariel Red Hunter]

Originally Posted by Merlin

Clear enough that Iam going to try it with my new carb. Thanks.

You're welcome!