Finally finished my first build

[michael whiteman]

This rat bike was constructed from mostly free discarded parts and pieces. The terrible vibration I was experiencing from the 100T drive pulley in my 7G trans that had .100 inch runout was eliminated when I replaced it with a 4G pulley. I know this glasspack muffler from Amazon is more quiet and flows better than the one in the kit. All that is left to do is to drill out the main jet because it's running too lean as verified by the fact it runs better with the choke half on. I want to thank you all who have helped me along the way with this build. I've learned a lot from all of your combined experiences.

 

[Sidewinder Jerry]

This rat bike was constructed from mostly free discarded parts and pieces. The terrible vibration I was experiencing from the 100T drive pulley in my 7G trans that had .100 inch runout was eliminated when I replaced it with a 4G pulley. I know this glasspack muffler from Amazon is more quiet and flows better than the one in the kit. All that is left to do is to drill out the main jet because it's running too lean as verified by the fact it runs better with the choke half on. I want to thank you all who have helped me along the way with this build. I've learned a lot from all of your combined experiences.

Does your carburetor have high, low, idle adjustment screws on it? Do you have similar screws like these on your carburetor?

Idle adjustment screw

.
High adjustment screw

Low adjustment screw under plug

If you do have these adjustment screws do not drill out your jets. To adjust the carburetor with the screws you will need a tachometer.

 

[michael whiteman]

Totally different carb Jerry. All I have is an idle air bleed needle valve. I'll have to drill the main jet a couple of thousandths.

 

[Sidewinder Jerry]

Totally different carb Jerry. All I have is an idle air bleed needle valve. I'll have to drill the main jet a couple of thousandths.

On the side of your carburetor this looks a lot like a high adjustment screw. Although the carburetors may be different if you have adjustment screws they'll be in the same area generally.

This could also simply be a jet access screw. An easy way to tell the difference is an adjustment screw will have a needle at the end of it.

If you're using ethanol gas, it can build up and clog the jets meaning you just need to clean them. Recently I became able to get 100% gas from a reputable station. Before I had to run E90 because that's all that was available in my town. Because of E90 I started carrying a spare carburetor with me.

 

[Sidewinder Jerry]

After watching this video I have a better understanding of your carburetor tuning techniques,



The screw I pointed to is the low adjustment screw. Unless you have a screw inside a bolt at the bottom of the bowl you don't have a high adjustment screw. Therefore when the throttle is in the low position you'd adjust the low screw until the rpm goes as high as possible; then turn it back to where it just drops favoring the rich side. Then adjust the idle screw to where the engine idles at 3000 rpm.

 

[Chainlube]

After watching this video I have a better understanding of your carburetor tuning techniques,



The screw I pointed to is the low adjustment screw. Unless you have a screw inside a bolt at the bottom of the bowl you don't have a high adjustment screw. Therefore when the throttle is in the low position you'd adjust the low screw until the rpm goes as high as possible; then turn it back to where it just drops favoring the rich side. Then adjust the idle screw to where the engine idles at 3000 rpm.

Or slightly less than the engagement point of the clutch.

 

[Sidewinder Jerry]

Or slightly less than the engagement point of the clutch.

Once tuned the recommended idle is 3000 rpm for these engines the centrifugal engagement point is around 4200 rpm.

 

[michael whiteman]

This is my Huayi Japanese carburetor. There is only an idle mixture adjustment. I enlarged the main jet today by .003 so we'll see how that worked out as soon as the weather gets a little better around here.

 

[Sidewinder Jerry]

The brass screw is the low adjustment screw. With no throttle it gets adjusted to the highest rpm. Then you turn it back until it just drops favoring the the rich side. What you have to do is remove the brass screw to determine if it's an air screw or a fuel screw. That'll determine the direction you turn the screw. The plastic screw is the idle adjustment after you set the brass screw.