Looking for some advice.
325” engine with a 750 Holley on alcohol. 10:1 compression. Currently has 150 jets all around and 4.5 power valves. 28 degrees at idle.

First fire up of the engine was yesterday and it’s so rich at idle there is literally raw fuel coming out of the headers and it’s clearly not firing on all cylinders. Took the idle air bleeds out to see if it would make a difference. No change. Plugged the power valves. No difference. I don’t see any fuel dribbling out of the boosters or the squirters. Idle mixture screws can be turned all the way in with no change.

Haven’t spent a ton of time on this yet but I haven’t had an engine run this rich at idle before so I don’t really want to guess and check my way into this. 150 jets don’t seem radically too big to me. Should I go way down and try like 130s? Something potentially wrong with the carb?

Thanks in advance.

no my combo is almost identical and doesnt do that. Pull carb and investigate issue look for leaky metering block gasket got to beleaking some place-lol

1. Are your throttle blades set correctly without excessive transfer slot exposed?
2. Keep the fuel pressure down, under 7 psi would be a good starting point
3. Don't have your float level too high
4. If you have closed cell foam floats, weigh them to make sure they aren't soaked and too heavy (and yes, closed cell foam floats will absorb alcohol)

Since you are using power valves here is something to be aware of.

When installing a power valve be very careful when using a socket (or worse a 12 point box wrench) to tighten the valve. The metering block has small, very thin ridges that serve as fuel dams to prevent fuel from leaking across the face of the metering block. These ridges are located directly under the area where the socket would ride. If you allow the socket to ride on those dams as you rotate the socket it will damage that sealing ridge. At that point the only way you would be sealing any leakage would be from the force of the metering block against the main body of the carb. Some gaskets have a sealant to help prevent leakage, some don't. Keep in mind as those gaskets age, or exposed to heat or sunlight that sealand degrades making it useless. Also the power valve is a fragile device, you can distort the valve by over tightening it, you are not dealing with a cylinder head bolt.

Your problem could very well be that those ridges have been compromised (damaged) and fuel is leaking across the face of the metering block.

One last thing I would recommend is to not use a power valve in the secondary metering block. As the car accelerates fuel is driven toward the back of the bowl uncovering the power valve. We installed jet extensions in the rear jets which allow a pathway to the fuel that builds up toward the rear of the bowl under acceleration. Unfortunately you can't install an extension on the power valve. Therefore I would remove the rear power valve and increase the size of the rear jets accordingly.

Good Luck hope you find this helpful.

Bob

quote:

Originally posted by team:
1. Are your throttle blades set correctly without excessive transfer slot exposed?

This ^^^^^

Also, don't rule out a lean misfire situation, most times mistaken for an over rich condition.

Do the idle mixture screws have any effect at all?

Carb gaskets are all new. Throttle blades are not exposing the transfer slots on either end.

Don't overlook the possibility of a junk spark plug(s) or inadequate secondary ignition components.

Compression?

I see you're in Wisconsin...is it just too cold to be running an alky burner?
There is a temperature threshold where gasoline just doesn't react, alky, I don't know about.

I do know a guy that sets his car on fire nearly every time he tries to cold start it.....he says he couldn't afford to race if he had to buy race gas.....I tell him I couldn't afford to race if I had to buy a fire extinguisher every time I want to go.

Have you considered gasoline lately?

On a different subject, having not run a carb in many years, is a hose between the bowl vents with a notch cut in the middle still a thing?

Plugs are brand new. It’s 65 degrees in the shop. Compression is 10.25:1.

The vents are completely open. Beginning to think this is an ignition problem.

Fuel pressure at idle?

Also check for vacum leaks if engine has set a while small blocks are famous for the intakes to leak at bottom of port at head

6psi at idle

quote:

Originally posted by CSRacing:
Plugs are brand new. It’s 65 degrees in the shop. Compression is 10.25:1.

The vents are completely open. Beginning to think this is an ignition problem.

In 50+ years experience I have found more bonafide defective spark plugs brand new, than ones that were in service. Just saying.

quote:

Originally posted by Big Steve:
On a different subject, having not run a carb in many years, is a hose between the bowl vents with a notch cut in the middle still a thing?

When it's needed yes. I went a different route when I needed to do that though. I used 5/16" pushlock hose ells with 5/16" brass tubing in between and 4 holes drilled into it. But the piece of rubber tubing notched at the top is cheap and easy.

In addition to the things others have said here, Check your boosters at idle and see if they are dripping fuel. If so float level or fuel pressure is too high. Possible needle and seats bad.

IR gun on the header tubes see if certain cylinders are cold. fuel coming out of the headers the fuel should be obvious pouring in the boosters.

How does a person know if their alky is water contaminated?

one other thought the air although cool in the shop gets very contaminated quickley and is not a good test .move it otside after checking al other possiblties.butterfly open too far is likely but usally it will start pulling through booster at that point

Why only 28 degrees? That thing should want 34 minumum, and 36-38 would not suprise me at all.

edit*

If your timing isnt locked, you need to lock the timing out, and get it set to 34-38 all the time.

quote:

Originally posted by 329L:
Why only 28 degrees? That thing should want 34 minumum, and 36-38 would not suprise me at all.

edit*

If your timing isnt locked, you need to lock the timing out, and get it set to 34-38 all the time.

^^^^^ First and foremost. More timing will allow you to close the butterflies more to lower the idle. Secondly, dont start it if you aint going to get some heat in it.