Throttle Stopping 2 circuit Carb VS. 3 circuit

cujo3116 · 05-25-2011, 11:45 PM

I know most of the "throttle stop" carb builders seem to be using 3 circuit carbs on their applications and I'm trying to completly understand the advantages to this?

I was told that the intermediate circuit is what is used when a car comes onto the throttle stop. So the tuners are leaning out the intermeditat circuit to help keep the engine from wanting to make power and climb on rpm while on the stop. This makes sense but is it only useful if you have a 565+ cubic inch motor? what if your still living in the 499 or less area like myself and a buddy?

I have been using 2 circuit carbs on both my combos (S/g and S/St cars) and had luck with them. However a friends car has a 3 circuit carb, so I'm trying to determine what effect this style carb may have vs the 2 circuits.

If one was to start changing air bleeds in the intermediate circuit what should they be looking for in regards to a A/F ratio while on the stop using a 3 circuit ?

What have others seen that only use a 2 circuit?

Thanks,

Andrew

C and W Racing · 05-26-2011, 10:23 AM

I have used nothing but 3 circut carbs on my applications so I can't comment on the 2 circut deal. That being said, not all combinations like to be lean on the stop. It has a lot to do with heads and intake. I had a carb built for me last year by one of the throttle stop carb guru's that is a believer of being lean on the stop. When I got the carb from him it had no intermediate air bleeds in it. My combo did not like the carb set up that way and was very hard to dial. My combo also wanted a lot more jet in it than he had thought it would need as well. I run Q-16 and the carb was supposed to be set up for that. I ended up putting an intermediate air bleed back into the carb and going up quite a bit in jet and now am very happy with being able to dial the car. Does not idle quite as well as I'd like but going down track runs great. At Atlanta last weekend I went 9.900 out of the trailer followed by a 9.901 on the next pass. I've also been 174 mph on a 9.90 run.
Chuck

jmarkaudio · 05-26-2011, 09:27 PM

If the carb is tuned correctly you won't find any issue with a 2 circuit carb, and a much cleaner running carb as well. I've converted all my Dominators to 2 circuit, between my brother and I we have a 1050, 1150, and 1250 on gas, all 2 circuit. Also a 1050, 1150, and a newly built 1250 to run E85 and all 2 circuit as well. The 1250 gas carb will go from idle to wide open even on my 23˚ 427 SBC, and is the fastest on either SB2 engine we have. The 461 ci SB2 head engine has been 7.62 @ 172...

05-25-2011, 11:45 PM	#1
cujo3116 Junior Member Join Date: Nov 2004 Location: Canada Posts: 53 Likes: 0 Liked 0 Times in 0 Posts	Throttle Stopping 2 circuit Carb VS. 3 circuit I know most of the "throttle stop" carb builders seem to be using 3 circuit carbs on their applications and I'm trying to completly understand the advantages to this? I was told that the intermediate circuit is what is used when a car comes onto the throttle stop. So the tuners are leaning out the intermeditat circuit to help keep the engine from wanting to make power and climb on rpm while on the stop. This makes sense but is it only useful if you have a 565+ cubic inch motor? what if your still living in the 499 or less area like myself and a buddy? I have been using 2 circuit carbs on both my combos (S/g and S/St cars) and had luck with them. However a friends car has a 3 circuit carb, so I'm trying to determine what effect this style carb may have vs the 2 circuits. If one was to start changing air bleeds in the intermediate circuit what should they be looking for in regards to a A/F ratio while on the stop using a 3 circuit ? What have others seen that only use a 2 circuit? Thanks, Andrew

05-26-2011, 10:23 AM	#2
C and W Racing Senior Member Join Date: Jul 2007 Posts: 557 Likes: 6 Liked 13 Times in 3 Posts	Re: Throttle Stopping 2 circuit Carb VS. 3 circuit I have used nothing but 3 circut carbs on my applications so I can't comment on the 2 circut deal. That being said, not all combinations like to be lean on the stop. It has a lot to do with heads and intake. I had a carb built for me last year by one of the throttle stop carb guru's that is a believer of being lean on the stop. When I got the carb from him it had no intermediate air bleeds in it. My combo did not like the carb set up that way and was very hard to dial. My combo also wanted a lot more jet in it than he had thought it would need as well. I run Q-16 and the carb was supposed to be set up for that. I ended up putting an intermediate air bleed back into the carb and going up quite a bit in jet and now am very happy with being able to dial the car. Does not idle quite as well as I'd like but going down track runs great. At Atlanta last weekend I went 9.900 out of the trailer followed by a 9.901 on the next pass. I've also been 174 mph on a 9.90 run. Chuck

05-26-2011, 09:27 PM	#3
jmarkaudio Junior Member Join Date: Apr 2008 Posts: 83 Likes: 0 Liked 0 Times in 0 Posts	Re: Throttle Stopping 2 circuit Carb VS. 3 circuit If the carb is tuned correctly you won't find any issue with a 2 circuit carb, and a much cleaner running carb as well. I've converted all my Dominators to 2 circuit, between my brother and I we have a 1050, 1150, and 1250 on gas, all 2 circuit. Also a 1050, 1150, and a newly built 1250 to run E85 and all 2 circuit as well. The 1250 gas carb will go from idle to wide open even on my 23˚ 427 SBC, and is the fastest on either SB2 engine we have. The 461 ci SB2 head engine has been 7.62 @ 172...