Carb question... - Lateral-g Forums

intofx · #1 08-25-2010, 07:35 PM

The Speed Demon 750cfm on my built 383 has never run well. I bought the "finished" car with 250 miles and now has 800 miles and now I'm faced with de-bugging it. I have the car at a shop now that has sorted a few issues. They replaced the oversized mechanical fuel pump with a smaller one, replaced the fuel filters before and after the pump, and added a spacer with an additional vacuum nipple to allow a port for the PVC. The car runs MUCH better now but at idle with the car hot, the fuel pressure drops to around 3 and tiny bubbles of fuel "jump" out of the vent at the front of the carb. The mechanic thinks the gas is percolating. I've been looking around and it seems that some people have had boiling gas issues as a result of block mounted fuel pumps or even gas lines being too close to the exhaust. The shop is looking at a heat shield for the carb but would that really do that much to drop temps enough to prevent boiling fuel? Any experience here or suggestions?

TIA,
Matt

ROKN69 · #2 08-25-2010, 08:09 PM

I have a speed demon 750CFM double-pumper that I used to run on my car. It never ran right. From float issues to the rear metering plate not being drilled properly from the factory to metal shavings in the carb due to not being cleaned from the manufacturer, it was down hill the day I bought it. I could never get it to idle properly even after hours of having several mechanics work with it (and many hundreds of dollars later).

I gave up and purchased a Holly HP from the Carb Shop. It bolted on and has worked perfectly. I can't stress how much I love this carb! It's amazing.

As for fuel boiling, I thought I had that problem with my demon as well - so I purchased a phenolic spacer (1 inch). That didn't really help. I don't have a spacer with my new carb - it hasn't been needed. I've been running the Holly HP carb for about 8 months now.

intofx · #3 08-26-2010, 02:57 PM

Quote:

Originally Posted by ROKN69

I have a speed demon 750CFM double-pumper that I used to run on my car. It never ran right. From float issues to the rear metering plate not being drilled properly from the factory to metal shavings in the carb due to not being cleaned from the manufacturer, it was down hill the day I bought it. I could never get it to idle properly even after hours of having several mechanics work with it (and many hundreds of dollars later).

I gave up and purchased a Holly HP from the Carb Shop. It bolted on and has worked perfectly. I can't stress how much I love this carb! It's amazing.

As for fuel boiling, I thought I had that problem with my demon as well - so I purchased a phenolic spacer (1 inch). That didn't really help. I don't have a spacer with my new carb - it hasn't been needed. I've been running the Holly HP carb for about 8 months now.

I was afraid someone would say this. The mechanic has called and the manufacturer seems to have few answers...

I don't want to spend a fortune chasing my tail with any system. What did the new carb cost? If it was costly, why not just FI it?

ROKN69 · #4 08-26-2010, 04:12 PM

The new carb, with my color accents of choice, was around $1200. It was cheaper than FI and the FAST FI kit I was looking at wouldn't handle the 625+ HP my motor is putting out. I've since found some other FI kits that will easily handle the HP number I am running, and plan to run in the future.

intofx · #5 08-28-2010, 03:19 PM

Quote:

Originally Posted by ROKN69

The new carb, with my color accents of choice, was around $1200. It was cheaper than FI and the FAST FI kit I was looking at wouldn't handle the 625+ HP my motor is putting out. I've since found some other FI kits that will easily handle the HP number I am running, and plan to run in the future.

Wow that's expensive. But I'm afraid a carb is gonna nickel and dime me to that point pretty quick. For $1200 I think it may be wise for me to pony up the extra $600-$800 and FI the car with the FAST kit.

The shop said something about a fuel pressure regulator on Friday. The car should be done first of the week. Wish me luck...

ROKN69 · #6 08-29-2010, 04:29 PM

Quote:

Originally Posted by intofx

The shop said something about a fuel pressure regulator on Friday. The car should be done first of the week. Wish me luck...

Most definitely, good luck!

Vegas69 · #7 08-25-2010, 08:10 PM

Modern gas isn't ideal for carb's. Lowering the floats 4 flats may do the trick. Taller vents or connecting them with a hose with holes on top could help as well. Is the spacer wood or phelonic?

intofx · #8 08-26-2010, 02:52 PM

Quote:

Originally Posted by Vegas69

Modern gas isn't ideal for carb's. Lowering the floats 4 flats may do the trick. Taller vents or connecting them with a hose with holes on top could help as well. Is the spacer wood or phelonic?

Not sure of the construction. I haven't seen it in person since the addition was made.

When you say 4 flats, do you mean turning the bolts?