What jets for my 625 Demon? - Lateral-g Forums

Moabdude · #1 10-04-2011, 11:47 AM

I have a 400 small block with lots of fancy stuff but almost no power modifications.
I have a dual plane intake and some TriY headers.
For the rest the engine is stock. I guess 200 hp or so?

I purchased a 625 Road Demon and I installed it on my car directly from the box.

The car runs okay.
It spits out black residu on the ground when I hit the gas a couple of times while in park.
Also the car is smoking a lot when the engine is cold and first started.
I also notice a very heavy usage of gas. I remember about 18miles to the gallon(I had a 500cfm Holley) but now it is not more than 9 miles to the gallon.

Are the jets of the 625 to large?

kennyd · #2 10-04-2011, 11:59 AM

take that carb off and throw it in the trash ! i have had 3 of them on cars and never made any of them run right . i just took a speed demon off a bigblock and replaced it with a 750 holley out of the box and now it runs perfect and 2 times the gas mileage .

**GregWeld** · #3 10-04-2011, 01:16 PM

Well said Kenny! Those things are junk... Explains why they went tits up.

HRBS · #4 10-04-2011, 01:47 PM

another vote for the trash can. i am with kenny, i had an 850 "mighty" demon on a 510ci street motor. couldn't get it tuned for the life of me. i put a 925cfm holley 4150 out of the box and it ran 10 times better. 90 seconds worth of tuning and it was dailed in....... done !
the only thing "mighty" about that carb was that it was a "mighty" PITA !

Moabdude · #5 10-04-2011, 02:19 PM

Okay, bad investment I suppose...

What Holley do you guys recommend for my setup?

67ragtp · #6 10-05-2011, 05:25 AM

How about this one: http://www.holley.com/0-80452 Single feed- square bore- electric choke- vacuum secondary, can also have it in a 650cfm.

Rich