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

Moabdude · #1 10-04-2011, 10:47 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, 10:59 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, 12:16 PM

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

HRBS · #4 10-04-2011, 12:47 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, 01:19 PM

Okay, bad investment I suppose...

What Holley do you guys recommend for my setup?

67ragtp · #6 10-05-2011, 04:25 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

Moabdude · #7 10-05-2011, 03:29 PM

What about an Edelbrock 1406?

70rs · #8 10-07-2011, 12:02 AM

If you are going to buy another carb, spend the money and get a new Holley hp in the correct size. You will be glad you did.

**Sieg** · #9 10-07-2011, 01:30 PM

I had a 1406 on my 355, in my opinion a good cruiser carb, not so good for top end performance. I had the strip kit and played with the jetting a fair amount and finally ended up buying a 650 Speed Demon pre Idle-Ez base plate.

The Demon and Barry Grant are two names I won't recommend. Though I have finally got the Speed Demon to work good enough without the assistance of the arrogant BG tech support team.

The keys to making it work for my motor were increasing the electric choke fast idle setting, bumping the accel pump discharge nozzle from .028 to .035 and running the green accel pump cam. 5.5 power valve, 68/76 mains, plain vac secondary spring. Due to the poorly engineered base plate the idle circuit still lacks the range of adjustability I would like but it does run decent and produces fuel milage similar to the 1406 and much better mid-high (3-6,500) RPM performance.

If I was going to replace it with one of the new carbs on the market I'd probably go Holley or Quick Fuel.

A lot depends on your driving style and your motor specs though. You're right on the fringe of a 750/770 cfm carb depending on the rpm you motor makes peak power.

kennyd · #10 10-07-2011, 01:46 PM

.

The keys to making it work for my motor were increasing the electric choke fast idle setting, bumping the accel pump discharge nozzle from .028 to .035 and running the green accel pump cam. 5.5 power valve, 68/76 mains, plain vac secondary spring. Due to the poorly engineered base plate the idle circuit still lacks the range of adjustability I would like but it does run decent and produces fuel milage similar to the 1406 and much better mid-high (3-6,500) RPM performance.

holly crap i dont remember what i had for dinner last night .