Trying to get a 390 Holley to work on my stock 225
(but with Clifford headers). I have had a 400 AFB work well on this motor.
On the Holley when you mash the pedal it bogs bad and stalls out.
There is a good squirt from the accelerator pump.
Is it too rich or too lean. What should I be looking for.

Good luck!
...then why in the sam-hell did you take it off

Conventional wisdom sez too lean, therefore stumble, but it could be very well be too much gas (or wrong accelerator pump timing) putting out the fire. Rule of thumb: holley's are usually too rich, that's why they are usually run on shivvies where they need to be eye-wateringly rich to mask all the other shivvy related problems.

D/W

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If it ain't broke, fix it!

Thanks Dennis- I see your obvious bias against the Holleys.
I must say that I tend to agree, except the reason I'm trying
to run this 390 is I got a Holley NOS top shot kit which sprays thru the top of the carburetor. I'm trying to get the car ready for Vegas and Slantzilla is going to help me baseline it. I got that kit to reduce hood clearance.
Turns out I have enuff for an NOS plate anyway, but that's another expense. Also I must say that this Holley idles great- better than the AFB.

Anyway I will be tweaking- maybe playing with the accelerator pump
circuit to try to get this thing not to BOG before I start test spraying.
I

I was thinking of putting a nitrous/fuel spray bar right thru the side of the offenhauser intake under the carb... There is a 1/8 NPT hole there already that just needs opening up.

D/W

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If it ain't broke, fix it!

I'm gonna take a shot at the idea that the throttle plate is not at the bottom of the transfer slot like it should be and when you mash on it...the pump shot isn't enough to mask the lean out where the plate passes the blank spot in the base between the idle port and the trans slot....

Check plate position, or move screw from spot #1 to spot #2...also check to make sure the pump arm per specs has .015 between the spring loaded bolt and the pump lever at WOT...if not setup right this will a weaker shot, or a delayed shot (if there is a massive gap).


-D.Idiot

Duster Idiot- maybe you are right- what do you mean by moving #1screw
to #2- I'm not sure I know about these screw numbers.

...some kind of secret holley code!

D/W

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If it ain't broke, fix it!

Too lean jetting will make it bog, but don't jet up till the bog quits, it may then be too rich. If acceleator pump squirt isn't enough, it can bog even if jetting is fat. Adjusting one of the cicuits to eliminate bog will make that circuit too fat.

First, make fairly sure your jetting is right. Also check float level, too low will make it lean and bog.

Next adjust the pump linkage. Remove all play between springed bolt and pump lever, if any, but not so that linkage bottoms out. With carb at full throttle, you should be able to push the pump lever another .050 or so.

Next try different cam positions, as D.I. mentioned. Pump cams have 2, some have 3, adjustment holes. There are also different pump cams. What this does is to adjust how aggressive the pump lever moves. Each cam or adj hole change will require the linkage to be readjusted. This is time consuming, but try as many possible as you can before going to the next step.

If bog is still there, then go to a larger squirt nozzle. You want to use the smallest you can, that why you need to try pump cam and positions first. Don't over tighten the screw when changing or you can throw the carb away. Your 390 probably has an .025. Go up one size at a time. Sizes are .028, .031, .035, .037, .040, .042, .045, .047, .050, .052.
If you have spare nozzles and pin drills, drill some larger and mark them so you know what they are. Once you get as big as .045, you'll need to use the hollow screw, or drill your own. I had a #3310 750 cfm vac sec on a big block Mopar motor that needed a .055, yes bigger than whats available, I had to drill it myself. Same carb on a different big block Mopar only needed a .042. Carbs need to be tuned to the motor combination, very seldom are they perfect out of the box.

Fine carb tuning takes patience, because once you get one circuit correct, you need to go back and check the other circuits because all will have a small effect on each other.

Circuits to tune;
idle
transfer slot - not adjustable
jetting
power valve
accelerator pump

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Slant Cecil

slant cecil- thanks for going out of your way to outline that.
I'm going to print this out and get to work on this is
the next couple of days.