Mid last season I got a SMOKIN' deal on a brand new Barry Grant Demon carb. Put it on my '83 Z28 (350 5Spd ) and WOW! The car was quick before but then OMG! I love the carb. Pulled the car out after hibernation in the spring and it fired right up like it was run that morning. Warmed it up and, with a big grin, blew out of the driveway. The car ran like a bag of @#&%! Noticed it was almost out of fuel. We're talkin FUMES so assumed water, bad gas maybe some debris. Stopped and filled it up. No different. So bad had to flatbed it home because it would only run 5 to 10 seconds then die. Car sat for about 2 weeks before I had time to dig into it. When I did, car fired right up and ran beautiful WTF, right? Put some miles on it and when tank got low again, ran bad. Figured something on bottom of tank, or water. Drop tank. Clean as a whistle. Drain EVERYTHING out, blow out lines etc. Filled it up. My baby was back. Or so I thought. Started to happen again. This time decided to go after carb. Pulled front bowl off, went to remove jets to clean and they FELL OUT! WOOOO HOOOO (pissed off, but found it) Ran MINT. Happened AGAIN. Went right for jets. Ok this time. Put back together to pull out of shop and it ran mint. Sat for 2 days now doing it again. Car will run like its missing on 4 cylinders and worse when under a load. In neutral will rev, does skip, but will rev. under a load car wont rev at all without bucking, jerking, missing. All ignition stuff good. runs a little rich but wasnt a problem before. What am I missing? Any insight would be greatly appreciated. Thanks guys.

With this…

How are you so sure on this… ?

How old are the ignition components?

What is the fuel pressure when the car misbehaves?

Could be ignition module ready to take a dump on you.

my Speed Demon 650 does the same thing when the engine is cold, i don't know the problem but I'm about to put the Edelbrock back on and send the Demon to "hell" where it belongs.
mine everything is new from spark plugs to distributor, fuel pump, pressure regulator

All ignition components are fairly new (prob about 600 or so miles) and have been tripple checked. I was refering to the "misfire" as a way to describe the way it felt. It is not actually "misfiring" but feels as though it is. Like a shake/stumble. Like I said all ignition stuff is good and have even swapped distributor out and still did it. I have NOT checked fuel pressure but, like I said, if I remove the front bowl and then reinstall, all is well until it sits again. Almost like draining the bowl is doing something to help. BUT WHAT!!!!????? Thanks for taking the time to read this guys. Sorry I was vauge. Hope maybe this will be a little clearer.

Todays gas is crap (especially with the 10% ethenol). It will evaporate quickly in a carb. My Demon bowls will be completely empty after 5 days or so. Could your floats be sticking in the down position after the gas evaporates out of the bowls?? Your stumble/miss sounds like a lean issue. The only issues (other than tuning) I have had with my demon are the floats sticking. Mine stuck in the up position twice after making jet changes at the track. Now I look for it!

My Demon ran like an animal on the track but was an absolute nightmare on the street. It was just unpredictable behavior that made me get rid of it and put a Holley on. Never had a problem again.

There may be nothing wrong with your carb but the best way to tell would be to borrow someone elses and see if the problem goes away.

Again my advice so far would still be….

If you know the ignition is up to par I would ensure the fuel pressure is as well… before touching anything on the carb. Just MHO.

i did some research about this demons and it appears that if you not running a big cam and your engine has high idle vacuum you have to lower the float level to the minimum.
Today i lowered the fuel level to the first mark and it started right up, no smoke no jerking no missing

Well, not sure I totally agree with that. I have never adjusted float level depending on cam specs. Float level is really more dependent on what the carb needs to perform as desired on the engine it resides.

A high float level can cause excessively rich conditions. Too high and it can bring the mains in too quick and cause some low rpm cruising hiccups. It will effect the overall fuel curve if the carb, from idle to WFO. I like to set it midway on my Demon and get the carb tuned otherwise and if needed as a final step, make small tweaks of the float to get it dialed in, talking a flat or two.

This is why I stress the basics with carb issues.

1) Be damn positive timing is at least close before looking at anything else.

2) Then make sure float levels and idle speed, more importantly transition slot is within acceptable range. Then set idle mixture.

Without 1 and 2 nailed down you are pissing in the wind.

3) Then see how it reacts and what it needs/wants to behave to your acceptance.

How does it drive now?

well it sure fix it for me, after lowering the fuel level to the lower mark i haven't have a problem at idle, i didn't drove it yet, it's getting a 02 rear end (already in) and a rebuilt transmission (this weekend) but it starts fine and idles at 900 even when cold no fast idle needed.
I think I'm starting to understand how they work, I'll remove the wideband out of the truck to tune it properly