Do you have his number? With any luck, maybe he has a set he could ship me. Thanks.

If I go to daul carbs, do I need to do anything to the fuel supply system relative to volume? I currently have 1/2" lines from the tanks, into a 110 gph 12 psi mechanical fuel pump, feeding an aeromotive regulator with 5-12 psi set range and I have it set at 7.5 psi currently. Seems to hold 6 psi at 4500 rpm at the manifold to the current carbs.

Carburetors work based upon pressure differential. As your engine draws air through the carburetor it creates a low pressure in the center of the carburetor. The difference of this pressure, and the higher pressure (from the atmosphere) pressing down on the fuel in the bowls is what causes the fuel to flow through the carburetor into the engine.

Now with that out of the way, if you have to jet up excessively from a carburetors baseline it usually indicates one of two things. It could be the carburetor being too large for the combination, or your fuel system not keeping up with the demands of your engine.

Doug, I spoke with Steve in your office today. The biggest thing I learned was the need for the vacuum feed from the outlet under the primary bowl to the manifold under the blower; no one ever mentioned that to this "rookie" and I discovered by accident while speaking to Steve. Of course without it on these #5563020BM 850 carbs, the 4.5 PV will never open. Hooked up the lines tonight and will drop it in the water tomorrow evening to see what happens. In addition, I learned that I have 130 gph mechanial fuel pump; probably still on the "light" size, but then I don't run all out for more that about 30 seconds and then on rare occasions at that; call me chicken!

Steve, like you, seemed these 850's should work, all other factors being right. Thanks for the response, I appreciate the help.
With that being said, going to a larger carburetor is not going to help you at this point. The first thing to look at would be your fuel delivery system. A 110 GPH fuel pump would be on the small side for a supercharged engine.

As far as your original question, jetting by vacuum most likely isn't going to work on your current combination.

www.NickersonPerformance.com
It sounds like you are on the right track with help from RR. Not sure what others involvement is in your project and what cost you have sunk but Nickerson carbs are pretty foolproof if they are set up for your application. Just stating my experience.

Well, I got it in the water this evening with the boost referenced PV vacuum line hooked up; how should I say this?

A quote from the move Days of Thunder comes to mind......"Don't touch a thing Harry, she's perfect!!!!!!!"

This is the best these engines have every performed!!!
Ok, here are the facts:

- Twin 454's, 9:1 compression
- 250 Blowers from the Blower Shop set-up for max 4lbs of boost
- Single 850 Barry Grant Demon blower preped carbs with boost references 4.5 power valve with #98 jets in the proimary and #100 in the secondary.
- Initial timing set at 16 with Thunderbolt pack for anothr 14 degrees producing 30 degree total.
- 130 gph, 9 psi mechanical fuel pumps into Aeromotice regulators, 1/2 inch lines all the way back into the tanks

Pulled the nubmer 7 plug after streching her legs up to 5200 rpm, looks a bit rich but I think I'm going to leave it for now. After about 20 minutes of runing between 4000 to 5200 rpm, she never popped once!!!

Like I said, "don't touch a thing HArry, she's perfect. Hope someone finds this information usefull in the future.... believe me, it was costly getting here.

Thanks to eveyone that responded with input.... it was all helpful and I really appreciate everyone of them.

Al

PS: Even got to meet Mark from Precision Marine while at the ramp this evening. Thanks for taking the time to speak with me Mark about my set-up. Your comments put my mind at ease regarding the use of the 850's on this application. Look forward to seeing you on the Tickfaw run this weekend.

Is this vacuum setup only because it is a blower engine. I guess I am still a little lost. I am running a Barry Grant on a 496 N/A application. Seems to work fine but just wondering I dont have something hooked up correctly:eek:

Yes... Carburetors calibrated to run on top of a Super Charger need to have the power valves externally referenced. We manufacture them this way, so you would just hook up the hose. A naturally aspirated carburetor would not require anything additional hooked up.

Thanks, that makes sense. No more middle of the night posts:drink:

I had nickerson do mine this year and they work great, he is pricey but knows what he is doing. If you go to his shop he has more carb parts around than I have pennys.