EngineBuilding
Engine flooding (Help)
My carburetor is spaying way too much fuel into the engine and I can't get it to idle, the float bowls aren't overflowing and my Idle mixture screws are set according to factory settings, I can get it to crank but it won't idle and I'm lost on what to do next.
Discussion
So my bbc likes more around 22 degrees idle, no advance and 36 degrees total timing at 3k. I’ve found the big blocks like a lot of timing.
I also just had the same issue with a bad fuel pump and regulator. Flooding the carb even though float level was good but would just push past the seats
FYI Holley just put out a recall on a ton of regulators so might be able to get it for free
what usually happens is the power valves are opening early big cam = low vacuum, so a 6.5 power valve is already open at idle (6.5 =inches of vacuum) so the booster ventures are receiving fuel at idle . try a 3.5 in front and a 5.5 in the rear if it has one, also a hard backfire can rupture one giving similar problems
the other thing mentioned timing etc can affect this but it sounds like the wrong/damaged valve.
also once that's fixed and the idle is some what ok set the idle mixture screws at 2 turns out from bottom (gentle turning them in to bottom) if you can't get a stable idle, pull the carb and drill a .090 hole in each primary throttle blade. usually a cammed motor wants extra air and the idle screw open further exposes the transfer slots making the mixture screws useless
read up a bit on this with Google and it will make sense
don't forget gaskets when you buy your power valves
Check for vacuum leak and make sure your pump isn’t over powering your floats.
I ordered a fuel pressure regulator and guage, I'm think that's the issue
Fuel regulator won't help with dumping cas into the engine.. Edit. Unless the pressure is so high it's just forcing it through the carb.
Putting my money on a big vacuum leak guys.
No visible vacuum leak
Power valve
What kind of carburetor is
It
Barry Grant
Demon Dubble pumper
Not saying your doing it wrong just best to check, if not this the. You need to change out the size of the jets for ideal
Jets have nothing to do with the idle circuit.
I bought the carb brand new a couple of years ago. The jets should be fine, but I'll look into that
What’s your fuel pressure and timing?
The timing is at 12⁰ btdc, and I just ordered a fuel pressure guage and regulator, I'm hoping that's the issue
Retarded timing or not enough will come across or have the same symptoms as being rich.
I'll add some more initial timing and see if that helps
Give it a shot. I will do an initial startup at 34 degree just so it fires right off especially with a flat tapet cam
Hope it helps!
Is this a street engine or race engine?
In vehicle or onstand?
Steet/strip, should make around 630hp from what I've seen from similar build combinations
The Holley is a race-oriented carb. No choke means it's going to be hard to keep it running at idle until it warms up, even when properly tuned.
Does it idle whenever engine is up to operating temp?
Nope, the carburetor is a new Mighty Demon on the engine I rebuild, it cranks without any problems but stumbles and dies after a few seconds
Demon carbs are derivatives of Holley carbs. From tbe look of it, I would guess it's about 800-850 cfm.
Cranking will not depend on the carb.
Without a choke setup, until the engine gets to operating temp, you will have to use the throttle to keep the engine running.
Once you get to operating temperature, you should be able to get it to idle wirh tbe factory carb settings. You are still going to have to fine tune both carb and distributor timing.
cam specs please
Comp cams 248/254 @.050 and .560/.580 lift
Do you have a vacuum leak? If so, fix it.
Which power valve are you using?
No visible vacuum leaks, the power valve is the same as when I bought the carb a couple years ago
No, which power valve as in which number. When does it open, at what vacuum.
Vacuum leaks are almost never visible.
You know what, nevermind. Forget I asked.
Bail out....
Sometimes trash gets caught between the seal on the inlet needles. Happened to me once. Check those.
Float level
Vacumn leak
Fuel pressure. Modern fuel pumps are often sold for fuel injection, which requires a much higher pressure than a carb. The floats are often overwhelmed by the pressure.
I'm using a mechanical fuel pump, but I've ordered a fuel pressure regulator
Yes. Fuel pressure at the carb should be no more than 7 psi. Most fuel injection pumps operate in the 35-70 psi range
More timing 16 to 18 initial without vacuum please, and be sure you have all your vacuum ports capped.
If you see fuel dumping out of the venturis then you have the float height too high or the vents are clogged at the top or the carb. Could also be excessive fuel pressure you want 6-10 psi
If that's not that case make sure your throttle blades are set correctly so that about an 1/8th of an inch of the transfer slot is showing from the bottom of the carb, if the throttle blades are open too much you won't have any control over the idle mixture via the mixture screws.
If all that checks out I would see what size the idle feed restrictors are in the metering block as well as the idle air bleeds at the top of the carb and report back to us what you find
Too much fuel?
Lean it out before you crank it again. Then tune it. It's a carburetor, not a rocketship.
Double check the fuel bowl gasket and metering body gaskets. Had a buddy mistakenly put a wrong gasket in the wrong place and while it ran it dumped so much fuel that it drained by the pistons and ended up in the oil. I’m surprised he didn’t literally blow up the engine as well as himself.
Get it out of the rain.
It's going in a boat😂😂😂😂👍
Take the carb apart and go down a size or 2 on jets or up on the needle, repeat until it stops flooding. And make sure the floats are set properly, it may not be overflowing but can be overfilled
It could have 104's in the primaries and it still won't matter.
Jets have nothing to do with the idle circuit.
True, but It might make a difference if he revs it at start and it dumps fuel and floods before it comes down to idle, power valve might also be bad or set incorrectly. I still think it's a good idea to disassemble it and verify float level/seals, looks like a new carb so factory settings might be way off
Factory settings doesn't mean shit with an after-market intake, heads, headers and presumably cam flowing more than it ever did from the factory. You tune a carb for the engine it's on, not for the engine your car would have come with stock. Sounds like a tuning issue.
When I said factory settings, I meant the setting of the carburetor, which is obviously not stock to the engine, how am I supposed to tune the carburetor beyond baseline settings if I can't get the engine to run for more than a few seconds
I think he/she misread.
Kinda hard to tune it when I can't even get the engine to idle
Thats one part of tuning. Get help from an old carb expert.
I’ve never seen a “factory” edelbrock al headed big block, so kinda hard to tune when you don’t use a vacuum gauge to adjust the idle mixture screws.
Did I eat the onion or something?
How can I do that if I can't get the engine to run beyond a few seconds, what am I supposed to do beyond baseline tuning if I can't get the engine to run?
Well if your problem is flooding…..I think there’s a very clear place to start to get it to at least idle