borrowed a Holley Demon double pumper...how do I adjust the idle mixture

This thing looks almost new, and starts right up, and choke works great, but it smells really gassy when idling. How do I adjust the idle mixture on this thing.

A friend was having difficulty with getting his 80s mustang to run right with it, so I let him borrow my Edelbrock Performer and he let me try out the holley.

Other than the very rich idle, I think it is working fine.

If it works well for both of us, we might make a permanent switch.

Is this as good a carb as my Edelbrock...would it be an even trade?

Not sure exactly what model, but picture is included.

 

looks like a barry grant demon of some type. should have a part number on it. probaly worth more than your carb, unless u dont care for bg carbs. find out what size it is. too big wont really help u.

might be as simple as a bad power valve.

 

Should operate much like a Holley.
Does it have 4 corner idle?
Could be the idle or PV just as stated earlier.

You definately got the better end of the deal!
Dave

Edit: If it does not smooth out with the idle mix screws, check the float level first, then dig into the PV.

 

the carb in the pic looks like a vac sec carb to me...did the previous owner play at all with the jets? If so I would find out what they were and use that as a baseline. Make sure floats are adjusted properly..then when warmed up(use a vac guage on Manifold vac) turn the idle screw in wards slowly until the carb begins to stumble...the turn out to get the highest vac reading...do this at each point(slow down idle if it rises to much)and once you are done..do it again starting with the one you started with(just to fine tune it). Ideally the mixture screws should be turned out the same number of turns(I check mine by counting the # of turns inward to bottom out then make sure the match. The car should run cleaner and have a much crisper throttle reponse.

 

That Demon has idle mixtures at each cornor of the metering blocks. Sometimes the idle circuits in these carbs are too lean and cannot be adjusted so they come with a air bleed kit. Once installed they cannot be removed, at least not very easily. If you tried the adjustments and cannot get it leaned out, he probably installed them. You can call Demon's tech line at 706-864-4712 and see what they suggest.

 

The newer demons have an adjustment screw in the middle of the carb down the the hole the air cleaner stud goes. It helps fine tune the idle. Check to see if this one has one.

 

The guy that had it did not know anything about it, and had been turning two "knurled" screws on the passenger side only. There are four of them, two on each side, one at frong and one at back.

It appears that he has turned the two on the passenger side all the way in, or darn close to it, but has not messed with the two on the driver side.

So basically, you "tune" it like an Edelbrock, only there are 4 instead of two?

Just tighten them up, one at a time, until the engine starts to run bad, then back out a little, and move to the other 3?

Sounds easy enough. With or without vacuum gauges. I might do it by hand and verify that it fixes most of the problem, the vacuum gauge for "fine tuning."

 

bad idea go get a holley or anything but that. If you get them from bg and its calibrated for youre ride thay may be ok but otherwise not a wise choice.

 

Well, I got the idle mixture pretty good, it idles fine now (it was pulsing...kinda running 850 for a few seconds, then trying to die on itself, then recovering with an 850-900 rpm burst, and cycling like that), and doesn't stink so bad. But, like I had on my Edelbrock before I leaned out the metering rods, this one spits and sputters just a bit when I stomp it and open up the secondaries.

How do you adjust that, or do you?

I guess it is too big for my current car, or just running too rich. It is a 650cfm, if I am not mistaken. When you hit the throttle, you can see a really good burst of fuel squirt out, much more than my Edelbrock. I think this burst when floored is what is flooding the thing out, giving me the power loss.

This is not a permanent swap (at least, I don't think it is, YET). I am just letting a friend try out my Edel so he can see if he wants to buy one. If he wants to give this one up to me and I can figure out how to tune it, I might take it. While I have his, I will work out some of the bugs, and he can put it back on his car running a little better than when he loaned it to me.

AS far as model numbers, I see no markings on it. Just DEMON on both bowls.

 

like 71 stated, that is a vac secondary. if the power valve is bad or the diaphram spring is too soft or hard you will never get it just right.good luck

 

Need a smaller shooter.

 

Would this carb be worth keeping, especially with a 347 in the near future?

Or should I stick with my Edel Performer 600?

I have done a little research and found this to be a Barry Grant Road Demon 625 cfm. It is new, no modifications done, yet. I found that I had the wrong port hooked up to the vacuum advance, and the pcv port was plugged. I put my pcv tube on it and hosed up to the correct vacuum for advance, but haven't driven it again. I don't expect much change.

I guess it would need to be rejetted to lean it out a bit before it worked perfectly on my car (and my friend's also).

By the way, the guy I swapped with reports that his car is running much better with my Edel on it. His is a 5.0 mustang, the last year they had carburetors on them (84-ish?).

 

if you can get the adjustments sorted out, and its really only a 650, it should run fine on your setup. just have to get it tuned down to your engine combo.

 

I have a speed Demon 650 on my Sprint. Other than adding the air bleeds for the idle circuit, it runs like a bat out of hell right out of the box. I'm very happy with it.

 

Exactly what are the "air bleeds" and how do they affect the carb performance?