Is a 700 cfm 4150 too much carb for a mild 351?

Mike Braddock · #1 (**permalink**) 10-31-2006, 06:38 AM

Guys,

I have a question about the carb we're currently running on our engine. It's a mild 351C with a dual plane intake, 9.4:1 compression and a very mild cam (6k RPM max). A friend gave us a 4150 700 cfm double pumper that we thought would work pretty well. We're having trouble leaning out the idle mixture. Does anyone have enough experience to tell us whether this is just too much carb for this mild of a motor? I know I'm not running on the transition circuit, as I had to drill .1" holes in the primary throttle plates to allow me to close the butterflies enough to not expose the transition slots at idle. Do the main jets have any affect on idle? I thought the idle feed restrictions, idle air bleeds and the idle mixture screws were the only things that affected the idle but I wanted to ask someone with more experience. The carb is newly rebuilt and appears to be working properly with the exception of my idle tuning. The idle mixture screws are about 5/8 of a turn off their seats, which tells me something else is wrong from what I've read. Thanks guys!

NZCOBRA · #2 (**permalink**) 11-01-2006, 08:11 PM

Hi try this web site it will tell you were the fuel comes form and what you need to ajust. hope this helps. www.bob2000.com/carb.htm

Mike Braddock · #3 (**permalink**) 11-02-2006, 05:46 AM

Thanks NZ. I've read that site several times and am looking for advice tuning the idle air bleed restrictions in an older 4150. Does anyone know if the replaceable air bleeds on the newer 4150 HP carbs use the standard fuel main jets of something different? I think I'm going to modify my metering blocks this weekend for replaceable air bleeds and wanted to ask for any advice. Thanks.

Mike

Remod · #4 (**permalink**) 11-02-2006, 06:04 AM

The newer Demon carbs have a base plate they named "idle eaze" or something like that. It is designed to solve the very problem you are working on there.

I have a speed demon 850 on my 351, and the adjusters on this carb are a snap. Carburates perfectly.

ST · #5 (**permalink**) 11-02-2006, 06:12 AM

Quote:

Originally Posted by Mike Braddock

I think I'm going to modify my metering blocks this weekend for replaceable air bleeds and wanted to ask for any advice. Thanks.

Mike

There's a DIY bleeder kit on this page.
http://www.aedperformance.com/Tools.htm

Mike Braddock · #6 (**permalink**) 11-02-2006, 06:35 AM

Thanks ST, that looks like exactly what I need...

Mike

byron w · #7 (**permalink**) 11-02-2006, 07:50 AM

Mike, That is the exact carb that I have on my 351 C. All sounds about the same except mine has a weiand single plane. Mine idles just great at 600-700rpm and I have no Carb trouble at all. Yours should be fixable. I also use a 65 power valve with 71 primary jets.
Good luck,
Byron

NZCOBRA · #8 (**permalink**) 11-04-2006, 08:25 PM

I have a proform main body , the air bleeds are smaller than the main
jets and you need much smaller size holes, you can solder up and
re-drill the removable ones buy a nice set of wire drills and a small collet
chuck,tricky and risky unless you have a sniffer up the exhaust and a
rolling road.you may be able to sneak up on the correct mixture, buy
enlarging the holes .002" at a time,when you get the size correct it pays
to get new bleeds ,they will flow different to the soldered hole, I
welded a 18 mm socket in the front of my muffler (inside toward chassis)
and wired an oxygen sensor it will give you a good Idea of were you are.

cleandan · #9 (**permalink**) 11-16-2006, 01:30 PM

Quote:

Originally Posted by Mike Braddock

Guys,

I have a question about the carb we're currently running on our engine. It's a mild 351C with a dual plane intake, 9.4:1 compression and a very mild cam (6k RPM max). A friend gave us a 4150 700 cfm double pumper that we thought would work pretty well. We're having trouble leaning out the idle mixture. Does anyone have enough experience to tell us whether this is just too much carb for this mild of a motor? I know I'm not running on the transition circuit, as I had to drill .1" holes in the primary throttle plates to allow me to close the butterflies enough to not expose the transition slots at idle. Do the main jets have any affect on idle? I thought the idle feed restrictions, idle air bleeds and the idle mixture screws were the only things that affected the idle but I wanted to ask someone with more experience. The carb is newly rebuilt and appears to be working properly with the exception of my idle tuning. The idle mixture screws are about 5/8 of a turn off their seats, which tells me something else is wrong from what I've read. Thanks guys!

Mike, what tells you to lean out the idle mixture?
What vacuum reading are you getting at idle?
What power valve are you using?
You state a "very mild cam" What is the duration at .050, overlap, and lobe centerline? With a very mild cam and mild 6K Cleveland you should not have to drill air holes in the primary butterflies for idle quality.