PK1BCarb

Hi All, my PK1 Carb is running really rich..Even idling for very short period of time, it fouls the plug. Ive got fuel mixture screw turned almost all the way in. Even with mixture screw turned all the way in, the engine doesnt stall. Am i missing something here?? Its a brand new carb. Was thinking about a leaner pilot jet, but the one thats in it, as far as i can tell is an .020. Dont think they even sell a leaner one than that. Could this possibly be a float level problem or something else. While engine is running, when i shut the fuel valve off. As the bowl empties, the engine rpms come up and it smooths out. Obviously less fuel, leaner mixture, i get that. Im perplexed, dont know what to do next. This isnt normal for this carb, is it?? High speed circuit seems fine. But i cant tell if that mixture is right either because the plug is always full of soot from when it idles...Plz help
 

1fasttiller

Member
Is this a unrestricted engine or a plate engine? Reason I ask is plate carbs are VERY rich in order to pull fuel and correct the loss of the fuel signal due to the plates. These are race engines, they weren't meant to idle long at all...
 

flattop1

Dawg 89
Try a new float and needle .
Both orings on ?
Approximately how long is (not very long) 45 seconds or 2 minutes ?
 

alvin l nunley

Site Supporter
With 2 cycles, when the carb is tuned to racing conditions, none of them will idle. Depending on your air density, you didn't say where you're at, it could just be the engine is running rich because it's not getting enough air. I had a brand-new 1963 Plymouth 383, I went to Tahoe, 4000 feet, that 383 was spiting black smoke everywhere I drove.
 

flattop1

Dawg 89
Just noticed the fuel screw , Turned in .

I think it is but my mental picure is gone 🙄
 
Last edited:

1fasttiller

Member
According to Dover, that screw is all but useless once the carb has been blueprinted...

It is an air screw or fuel screw, anybody know? In the motorcycle world they serve different functions. An air screw works by backing out to let in more air or making the mixture leaner, whereas a fuel screw makes the mixture richer when you back out the screw by letting more fuel in.
 
According to Dover, that screw is all but useless once the carb has been blueprinted...

It is an air screw or fuel screw, anybody know? In the motorcycle world they serve different functions. An air screw works by backing out to let in more air or making the mixture leaner, whereas a fuel screw makes the mixture richer when you back out the screw by letting more fuel in.
It is a fuel screw
 
Something else i noticed, when running at high rpm, im actually seeing vapor coming out air filter...is that fuel vapor??
 
Something i read, fuel screws are always pointy, air screws have a blunt end
 

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flattop1

Dawg 89
with the idle set high to get it to run and the idle mixture screw closed all the way you are supply all of the fuel from the main jet. If it will not idle with the idle screw set properly and the air mixture screw at 1 1/2 to 2 turns out it indicates the idle circuit blocked or not allowing the passage of air to pick up fuel at the pilot jet. Was the carb bore touched at the throttle plate bore?
 
All i do know is this thing is running extremely rich, raw fuel coming out carb throat..could it be i need smaller main jet than what came with carb? Of course, im just guessing here..near as i can measure here, is main is .029...that comes from sticking tiny drill bit in hole and measuring bit with digital caliper. Does .029 seem like its even in the ballpark?
 
Main is stamped with what looks like 10...does that tell anyone anything...I live in Indiana, so i doubt altitude is a problem
 
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