started w/ a Demon 750

Reply Subscribe

Thread Tools

Search this Thread

Apr 25, 2014 | 11:20 PM

Alwyn678

Thread Starter

Team Owner

Joined: Jun 2001

Posts: 43,136

Likes: 155

From: Thomson Georgia

started w/ a Demon 750

Too much Carb, switched to a Hollr 600 And it id ls much better, but secondaries are dumping gas into the carb at idle. Should I get s new HOLLEY. Or try anorher brand?

Any suggestions, thoughts

Thanx
Al

Apr 25, 2014 | 11:30 PM

7t9l82

Le Mans Master

Joined: Oct 2010

Posts: 6,938

Likes: 848

From: melbourne florida

2023 C3 of the Year Finalist - Modified

check your float level, and needle and seat what was wrong with the demon?

Apr 26, 2014 | 12:01 AM

TimAT

Le Mans Master

Joined: Oct 2006

Posts: 7,123

Likes: 433

From: Gladstone MO

C3 of Year Finalist (appearance mods) 2019

Any carb that has a design similar to the "dual float" design can have problems with fuel "dumping" into either the primary or secondary. Causes can range from mis-adjusted floats, dirt in the needle and seat, float saturated with fuel and too heavy, or high fuel pressure. Even the Q-Jet can suffer from the same causes.

Apr 26, 2014 | 09:33 AM

diehrd

Safety Car

Joined: Jan 2009

Posts: 4,000

Likes: 299

From: New York

750 is not to much carb ..

Tuning a carb can be to much for the cars owner though .. Read on how to set up a carb and all related info and the 600 or 750 will work just fine.

Apr 26, 2014 | 03:07 PM

larrywalk

Melting Slicks

Joined: Oct 2002

Posts: 2,317

Likes: 111

From: St Louis MO

Secondary fuel level is too high - why? Bad needle & seat, mis-adjustment, or debris? Might be time to rebuild the carb.

Aug 21, 2019 | 12:27 PM

ronarndt

Drifting

Joined: Jul 2015

Posts: 1,765

Likes: 254

From: Catlett VA

Pressure over 6 psi will overpower the needle and seat, which operate only by the small amount of force exerted by the rising float to close the needle valve. I had a high volume/high pressure electric fuel pump on my 68 convert and it frequently flooded the carb and in one case spilled so much liquid gas into the intake manifold it hydrolocked one of the pistons and the engine stopped turning as I was trying to start it.. I switched to a normal performance electric pump and was able to get my pressure regulator down to 6 psi and now it works fine.

Aug 22, 2019 | 03:26 PM

suprspooky

Burning Brakes

Joined: Jul 2016

Posts: 767

Likes: 74

From: Blaine MN

A quick look at your 355ci 284 cam info leads me to believe a 600/650 is about the right size carb for a non-track car as you should have better throttle response. (I'm assuming double-pumper). As others stated the Holley needle and seat are big and it doesn't take much over 5psi fuel pressure to start causing high levels.