Clone Carb Info


New member
I'm tearing down a clone (Huayi) carb to learn more about the structure and the porting of all the air holes and such and I have a few questions on what I see......

1. I've removed the butterfly and see a little needle like thing sticking out of the side of the throat. if you look down the throat, it's on the right side. looks like it's been covered over with lead or something to make it non-removable. what's this for?

2. on the same side of the throat, there are four small holes...are these part of the air bypass that lets the engine idle?

3. on the right side, one the outside of the case looks like a this the welsh plug that I've heard about and the one that you don't want to mess with?

4. still looking down the throat on the block side, I see three distinct "cuts" is the cut that matches up to the black plastic spacer...the next one is farther inside and it steps down to a smaller size throat...then the final one is smaller yet and it's right in the middle of the carb. I've measure the port at .650, the next step down was at about .620 and the final step down was at about .600...if you are going to enlarge this area, wouldn't it be the same size all the way through?

5. after pulling the low speed jet out, is there a need to do anything with the hole at the bottom? smooth it, enlarge it?

5. how do you remove the choke butterfly?

this is an old carb... and I don't have any use for it (I have five or six others in my race box and two s/a carbs packed away for this coming season. i'm trying to learn all I can about the carb to make me a better builder and more knowledgeable at the track to diagnose problems...
anything that anyone can tell me would be greatly appreciated!

Mike C.
The little needle like thing is the bleed screw. Some of them are removable and some are not. chances are on that model it is not removable as in a fixed needle. Yes on number 2. Yes to number 3. Can't answer number 4 as I have never tried it. Not legal to alter it in stock class. Never altered it for stock appearing either. Not to my knowledge on number 5. put a vice grip on the butterfly to the choke and give it a pull. then lift the shaft out.
excellent don!! thank you very, very much! i'm trying to learn and trying to make sure that we do things right the first time. understanding is key.....
On the huayi mikey, that little plug you mentioned in #3, is it black? If so, you should be able to pop it off and reveal the mixture screw. The plug is black and square i believe, havent seen one in awhile. It will be in the same place you see the little mixture screw on the RUI ING carbs, on the back side of the carb, just to the left of the name on the carb, next to where the carb fits to the head.
if u drill them 4 small holes to .26 it helps throttle response, but you have to remove the plug on the outside to get to them so youll need a new welsh plug there around 1 dollar. grind down the throttle shaft and butteryfly too every little helps. I drilled my low speed jet to .22 the bottom hole. I ported my huayip19 to .670 venture and .750 throttle bore. it made a huge difference in power on my set up. I have pics but cant get them on here if u go to oldminibikes web site theres pics of it
if you open those 4 holes up, you better have a clutch you can adjust for a higher stall.. choked on the grid on my first carb job... clutch got hot an shut it down.
The very small hole that you see with the needle is the idle air/fuel circuit, it supplies the engine when the throttle is closed, the remaining small holes are transition circuits as the throttle opens the gap between the plate and the wall acts as a venturi (restriction) air velocity is high and pressure is low, fuel is supplied thru these holes to the engine until the plate is far enough open to cause sufficient air to be flowing through the main venturi where the main jet can take over. Without the small openings the engine would suffer from a lean condition up to 1/4 throttle and would bog severely. These engine are designed for stationary use, cement mixers, generators, etc. and seldom operate through their entire throttle range, they do for our purposes benefit from these transition holes being enlarged. How big should they be, depends upon several factors. The adjustment screw is sealed, hidden, or made tamper proof in several ways, most of which can be tampered with, several suppliers can supply replacement screws. The welsh plug is right behind the adjustments screw, it is sheet metal, drill a small hole in it and pry it out with a pick.

Looking through the carb the smallest diameter is called the venturi, as a fluid (air) flows through a venturi it's velocity (speed) increases, the pressure exerted decreases. The piston descending causes a larger volume in the cylinder (low pressure) the atmospheric air will be pushed through the venturi, because the the fuel in the bowl has atmospheric air pressure acting on it, it will be pushed up the emulsion tube to the low pressure area at the venturi. So no do not bore it straight through the same diameter.

When removing the choke plate, I always slid a utility blade(olfa knife) into the slot to lift the plastic above the barbs then grasped the plate and blade when pulling outward, it saves a lot of wear on the plastic shaft.

Excellent description 43!! I drill a small hole in the welch plug just big enough to screw a small metal screw into it. be careful not to push the drill bit to hard or you will drill through and into the back side of the snake eyes. Same thing when screwing the metal screw in, don't go to far. Then I place the carb in a vise and with a pair of pliers I give the grips a tap with the hammer and the welch plug will come out. Flatten out the welch plug and solder the hole shut and you can reuse it.
I have never seen a welch plug soldered from factory wont that get you a DQ:cool:

No where in the rules (yes I have a brand new 2014 copy) does it say you can do this in box stock. Other classes, yes. Its been stated many times on here "if it doesnt say you can, you cant". So the answer to your question will vary from tech guy to tech guy, from track to track. Some will suggest for you to "ask the tech guy before you try it". That will only be OK that night at that race. Next week different tech guy or next month at a different track would be anyones guess. Some will argue the "performance gain" angle. Clearly its a performance enhancement modification. Good luck
Marv, you aren't looking close enough at my carbs when you tech my engines. lol No, it isn't legal in stock but I knew he was not playing with stock.
all excellent information and i really do appreciate it from everyone! specially the graphic! i've stripped the carb down to the base housing and now poking and prodiing in all the chambers and seeing where this flows to's all good! one thing that puzzles me is the bowl right below the on/off switch. fuel flows into the carb through this switch into the bowl where it's picked up and flows into the float bowl with the etube and jet...looking at this, i'm wondering if enlarging the hole delivering the fuel to the float bowl would help....
There is plenty of fuel supplied to the carb, Increasing quantity available before the needle and seat will not increase the quantity in the bowl. The opening through the needle seat is the narrowest point in the supply path.
thanks al...i'v ehad a few questions coming up about the carb and what does what. i want to get a better understanding of the operation and specially the air/fuel flow through the carb. like the four itty-bitty holes in the side of the throat...never saw those iuntil i tore the carb apart...this is good to know! and your right about the fuel entering....if you are getting enough, a bigger hole ain't gonna give you more....

astro...was thinking more along the lines of need to go over board.... :)