Vintage Mustang Forums banner

1 - 3 of 3 Posts

·
Registered
Joined
·
1,963 Posts
Discussion Starter #1
I'll try to keep this short. I'm having trouble dialing in a 625 cfm Road Demon carb. The car: a '65 fb 289-2v 3-spd stick. Relevant mods: 4-bbl dual plane, tri-y headers, 2-chamber Flows, Pertronix Ignitor II and coil, 3.50:1 lsd 8-inch. Factory 2-bbl camshaft still in place.

This engine ran well enough on the factory 2-bbl, no smoke or anything, pulled hard to guesstimated 4500 or 5000 rpm.

Road Demon was bought used. For jets, it had 61's in the primaries and 73's in the secondaries. Now it's 61's x 70's. Float levels are slightly below the middle hash mark. Don't know what spring is in the vacuum motor. Choke works properly. I've set idle speed and base timing with a vacuum guage, adjusting both to achieve maximum idle, then backing off the bell crank set screw to slow the idle down to an acceptable level.

The problem: starts and idles, idles rough till warmed up, but settles down. Will accelerate if I ease into it, and will run at steady speed under load, including at highway speeds. If coasting at low speed in second or third, will run slightly rough. I might call it surging if I knew for sure that this term is accurate. But apply any throttle at all and it bogs badly. Will run at steady 60 mph, but always on the verge of a stumble.

Barry Grant's trouble-shooting page says to set the idle screws then readjust the butterflies. I have done part one but not part two. Part two requires to remove carb and turn it upside down and check the transfer slot openings, which should show .020" of the transfer slot. Next, BG says to change the squirter size.

What do you guys say? Do I have an accelerator pump problem?

TIA
Seven
 

·
Registered
Joined
·
1,106 Posts
What is your vacuum at idle, cam specs and compression ratio? The surging and bog kind-sounds like a lean condition to me. The BG 625 came with 70 primary jets and 78 secondary jets. If you can set up a vacuum gauge while driving, what is the vacuum when it starts to surge or bog? The stock power valve opens at 6.5 HG and you might need to go down and inch or so. Hope this helps and report back :)
 

·
Registered
Joined
·
6,911 Posts
Ditto the reply.....61 is a bit lean with today's gas.......maybe on a 390 20 years ago.....


The accelerator pump has nothing to do with the cruise behavior.


Here' my setup for my Holley 600vs on my built Cleveland, FYI;

66 primary jets
7.5" power valve
.028 accel. shooter
#466 pump cam
stock secondary plate (IIRC, equivalent to about 70 jets)
lighter yellow secondary spring

The idle mixture screws are about 1.25 turns out from gentle bottom and I set the idle speed on both primaries and secondaries so you can JUST tell the transfer slots are there.


That being a 625 on a near stock 289, I'd say a bit more primary jetting than my 600 would probably be close.

Best of luck!!
 
1 - 3 of 3 Posts
Top