PDA

View Full Version : Dual carbs



Timer
04-14-2001, 03:11 PM
I have dual 4150 carbs (750 cfm) on a tunnel ram on a BBC 468 motor in a v-drive. I noticed that someone had reversed the shooters on the front carb. (The primary shooter is where the secondary shooter should be, etc.) The primary should be a 25 and the secondary should be a 32.
Question #1: Would there be any logical reason to have the shooters on one carb reversed?
Question #2: Should I go to bigger shooters, and if so, what sizes would be a good starting point. (I haven't really run the boat yet, but would like to have the right size shooters handy if these are too small.)
Thanks.

Racing Ray
05-15-2001, 07:13 PM
.
[This message has been edited by Racing Ray (edited March 12, 2002).]

Timer
05-15-2001, 08:12 PM
Thanks Racing Ray.

ponponracing
05-16-2001, 04:28 AM
There shouldn't be any gap in the accelerator
pump linkage. As soon as you touch the gas, there should be a acc. pump. diafragm movement. The accelerator pumps are there to give the engine some fuel when the signal to the ventury boosters is too low to make them work properly. If you have a backfire or a bug when you go off-idle, you need more fuel(larger nozzles). If you have smoke from the exhaust when you accelerate, that means you have too much fuel from the squirter. Of course you have to do those verifications when the engine is under load. Usually, longer is the distance from the carb. to the intake valves, larger the squirters. When Holley sale a carb, just remember that it is not tuned for a particular engine. Tuning is something that has to be done accordingly to the engine you are using. If a carb. works decently on an engine, that doesn't mean it will be alwright on a another engine since
the signals may be way different from an engine to the other one. In many occasions, I ordered many carbs. (same part numbers) in one order and when those babies showed up some of them where with different jets, others had different squirters sizes. My advice: Always take apart a new carb. You may have surprises!

Racing Ray
05-16-2001, 05:36 AM
.
[This message has been edited by Racing Ray (edited March 12, 2002).]

ponponracing
05-16-2001, 06:20 AM
If you use a larger acc. pump cam, you select the quantity and the duration of gas you're sending to the squirter. In the tunnel ram application, more gas is not a band aid, it's logic. Since the acc. pump is there to compensate for the poor off-idle signal, if the carb is further away from the valve, it will take more fuel to reach that intake valve in the very short time that last the off-idle fuel need. By the way, if you give your engine as much fuel as it can burn, that fuel will be transfer in heat, meaning more performance. That doesn't mean less squiter fuel won't work, that means that if you want to have the max response from your engine, you better give it as much fuel as it will accept. In the pleasure application, you simmply have to provide enough squirter fuel so there won't be any backfire (caused by a momentarly lean situation). We are talking about fuel economy since everytime you touch the trottle, squirters shoot gas. Never put a gap between the diaphragm lever arm and the acc. pump cam: that delay the moment the squiters feed the engine when it badly need fuel. I recommend the HP or S-A DESING books about Holley carbs. Those are basics books and they give very good hints about tuning, particularly about performance. No offense there.

Racing Ray
05-16-2001, 10:16 AM
.
[This message has been edited by Racing Ray (edited March 12, 2002).]

Timer
05-16-2001, 04:22 PM
Great information -- thanks to both of you. Racing Ray, whose Patrick and how would I contact Pro Systems?

Racing Ray
05-16-2001, 06:29 PM
.
[This message has been edited by Racing Ray (edited March 12, 2002).]

Timer
05-16-2001, 07:24 PM
Thanks.