Holley/Demon Carb stumble

[cookietruck]

Every time you go smaller on the MAB you make the booster come on later.

And the larger bleed will delay the start of the booster.

which is it?

 

[yellow rose]

I’d look into a chassis dyno in your area........ tune for power....... bring the old main body with you, and some notes on how to put that carb back how it was when the car went the quickest/fastest.
In fact, that’s probably the place to start.

I’ve tested a number of home brewed carbs on the dyno over the years....... some have been so far off(both from a power and/or fuel curve standpoint) that no amount of jetting or air bleed changes were going to fix it.
They needed more reworking than that.

The best luck I had with building a carb from readily available parts was the original Proform HP 750 body, using stock Holley 4779 metering blocks and a plain Jane 4779 type baseplate.
I built a few of those, and they required minimal tuning to get dialed in.

I built a similar carb with a Holley HP body, QFT billet metering blocks and baseplate.
I haven’t had a suitable candidate on the dyno I could use to dial it in....... so at this point, it’s still an unknown.

When we were selling BG stuff, and the Demon carbs........ I found the calibration of those things to be properly set up for.......almost nothing.
The Speed Demons in particular always seemed to have idle, driveability, and wot fuel curve issues.
Often all three!!
It got to where if I was going to be using a new one on the dyno for a build we did, I’d just modify them for adjustable air bleeds before ever being run.
By that time we had a better handle on what changes to make to the baseline calibration so they’d be closer to “right” from the start.
Some of those things as they came ootb were particularly bad.......they’d hardly even run.
Wouldn’t idle, super lean at wot, headers start glowing right away at part throttle, etc.

But......they looked good.

Eventually, it just got to the point where they were just more trouble than they were worth........ and we stopped selling them.

"...I found the calibration of those things to be properly set up for...almost nothing".

Post of the month right there.

 

[skrews]

The best luck I had with building a carb from readily available parts was the original Proform HP 750 body, using stock Holley 4779 metering blocks and a plain Jane 4779 type baseplate.
I built a few of those, and they required minimal tuning to get dialed in.

I've also found this, my best carb is an older ProForm main body with a 650 doublepumper baseplate using a pair of metering blocks off a couple of 4412 500cmp 2bbl carbs.
Primary metering blocks off the 3310 750 vacuum sec are my favorite as they have the same calibration and can be found for cheap on Ebay.

 

[yellow rose]

which is it?

Got over my skis. Now I have to think about it for a minute. I need new glasses and any more than about 10 minutes on here and I start getting a migraine.

A smaller bleed will start the booster sooner, and the fuel curve will turn rich sooner.

A larger bleed will start the booster later and lean the fuel curve sooner.

I hope that's right.

 

[cookietruck]

Got over my skis. Now I have to think about it for a minute. I need new glasses and any more than about 10 minutes on here and I start getting a migraine.

A smaller bleed will start the booster sooner, and the fuel curve will turn rich sooner.

A larger bleed will start the booster later and lean the fuel curve sooner.

I hope that's right.

about ten minutes on any forum is probably the sweet spot.

i don't like to type long messages so posting an image is easiest.

i pulled this from the tapatalk carb forum,
holes A and B would be the emulsion bleeds in your holley carbs.
Hole D would be the high speed bleed...i guess this is the way it works. people that know more than I do seem to agree with it...

 

[mderoy340]

mab work in conjunction with the emulsion bleeds. A smaller mab starts later and gets richer. All the old holleys had two emulsion holes .026-.028 and worked great. Use the mab and emulsion size to get a flat fuel curve and jet it to maintain what you want to run at WOT. I run a Mighty Demon and it works great.
Trashing a carb brand is easy. Reading a plug after 1 year and basing performance of a car with a 2000 foot DA change is ridiculous.

 

[Cudafever]

I'm reading what your guys are saying and trying to exorb it.
I get the MAB's and think i get the idle bleeds (haven't messed with them but bought a idle air bleed kit as well). so will dabble into them in a while.

The thing i'm just not getting my head around is the holes in the metering block that you guys keep saying i should drill out and instal a .oxx this or that.
I will get it!
skrews i have a a #3310 vac sec 750 carb...But i guess i would need 2 of them to try them valve bodys.

cookietruck, that chart look confusing to me but i just don't have time to study it right now. Works craze)will be asking question when i get a minute to really check it out.

 

[skrews]

If you can find another one, or a primary off a 4779, (ie 750 DP), or one off of a 4412 500 2bbl you'd be set as they are all the same as best as I have measured them. I'd be willing to bet the 4780, 4781 are the same too.
You do have the rear powervalve blocked off right? And are running jet extensions on the secondary side?

 

[Cudafever]

Hmm! now that's a question i have been meaning to ask.
At what G force or 60 foot time does that become important.
To answer your questions rear pv blocked, NO jet extensions in the rear.

 

[yellow rose]

Are you using Holley metering blocks?

 

[PRH]

I was assuming he’s using the Demon
3 emulsion hole blocks.

 

[yellow rose]

I was assuming he’s using the Demon
3 emulsion hole blocks.

Now that I read that I think you are correct.

In that case, I refer to your above post. As in...calibrated for almost nothing. My paraphrase.

 

[PRH]

The specs show those blocks to have the upper two holes at .031, and the lower at .033, whereas the original 4779 blocks that I used with the old Proform bodies would only have two holes at about .026.
That’s a pretty big difference in the emulsion package.

 

[j par]

I had the day off and wasn't on call, so i slipped out to the track and did some testing. no timing equipment up at the track. just the track surface to make some stomps on. If i just need one i will sneak out the back road. but i wanted to string a bunch of them together.

This is the the same plug i posted above. pulled it off the trailer and let it idle, nothing else until it was up to 180 degrees(were my cooling fan turns on. shut it down to Pull this old plug out for a new one
View attachment 1715367898 View attachment 1715367899
With the new plug install, i made a stomp down the track and clean killed as best i could. pulled plug out.
View attachment 1715367900 View attachment 1715367901
drove back to the pits and pulled the plug again
View attachment 1715367902 View attachment 1715367901
2nt and 3d stomp when i pulled the plug i cut the picture. didn't figure this out until i got home.
The last one is hot lapping! I did 3 runs back to back and then clean kill it at the top end to take these pictures
View attachment 1715367904 View attachment 1715367905

That's as accurate as i can get Sorry some are blurry............what do you think of the fuel/jetting.....timing....heat wrange........ i want to hear all the appinions even if they differ one from another.

View attachment 1715367903Disregard this one.

Call the NGK tech line. Those guys will get you straightened out.
How Can I Get Technical Support?

Thank you for that I called the tech line and from my indications to them they recommended one heat range hotter.
I've been showing some spark plugs looking quite the same as the ones pictured here as well. I had a stumble up high and it was cured by Richer main Jets. But I'm working on completely different carburetors with seemingly a lot of the same problems. Not severe problems by any means, just slight tuning to get it just perfect..

 

[PRH]

OT, I know...... but just continuing on the Demon QC theme......
I bought a King Demon 1090 when they first came out.
I was running a customers 540BBC on the dyno, dialing in a few carbs.
I had a 1050 and a 1150 Holley to try, along with his new 1250.
I figured I’d make a couple pulls with the new 1090 to see how it stacked up.
The Holleys were all on the rich side at WOT, and pretty fat at part throttle, but all idled fine and the motor exhibited no “weirdness” with any of them.
Bolt the 1090 on...... idle speed just wanders all over the place, and isn’t very responsive to mixture screw adjustments.
Made sure float levels were good...... attempted a pull.
Motor doesn’t take the load very well...... start the pull, it’s kinda surging, check the a/f...... waaaaay lean, abort run....... put it back in the box.

When I had a chance to look at it I found a few manufacturing defects.
The first was than one of the booster stake tubes had the booster end folded over and crushed...... so no fuel is going through that one.... hence the super lean at wot.
I looked for that right away when I got it apart........ because I had actually run into that on two previous BG built 4500’s.
The next issue was, one of the metering blocks must have moved when it was being machined because the hole at the top of one of the main wells was all oblonged.
There was a big gap on one side where the idle tube was pressed in....... and then someone filled the gap with clear epoxy.
The real problem there is, the epoxy ran down into the void and plugged up the idle tube.

I called and talked to the rep...... they said just send it back and they’ll take care of it.
I said no thanks, just send me two disassembled metering blocks and a set of booster stake tubes, and I’ll take care of it myself...... which I did.

 

[skrews]

^^^ Makes you wonder why they went out of business lol.

 

[skrews]

Hmm! now that's a question i have been meaning to ask.
At what G force or 60 foot time does that become important.
To answer your questions rear pv blocked, NO jet extensions in the rear.

You should run jet extensions on anything that cuts better than 1.8 60ft IMO.

 

[PRH]

Makes you wonder why they went out of business lol.

After being a dealer for a few years, it really wasn’t any surprise.

Here’s another quick one......
Guy who works the phones at one of my suppliers buys a BG Silver Claw when they first came out.
He updated the motor in his 69 Camaro from a pretty mild 350 to hotter 383.
The tweaked 1850 Holley from the 350 wasn’t cutting it, so he buys the Claw.

The thing will hardly run.
Very unresponsive to jet or air bleed changes.
I have him borrow a carb from a buddy of his with a hot little 406.
The 383 runs great with that carb, so we’ve ruled out everything with the car.

I have him send me the carb.
The air bleed channels in the main body are 90* holes that go from the air horn area to the metering block area.
Two holes drilled from each end, meet in the middle....... same as a Holley.
It seems they work better when they actually meet in the middle.
6 of the 8 air bleed holes didn’t connect the two sides.
The kicker is....... when we’d call to ***** about this stuff, they’d keep saying how its impossible they could be so far off...... cuz they’re all “wet flowed”.
Well...... they might have been wet flowed....... but apparently no one was looking at any gauges, or if they were..... they didn’t care what they said.

Anyway, after correcting that problem I tested it on a street/strip 396..... reworked the calibration..... got it running pretty good, and sent it back to the owner.
He said it worked good after he got it back.

 

[skrews]

I don't think I've ever seen one OOTB that didn't have something wrong. Holley can mess up too, but its more like 1 out of 10 not 10 out of 10.

 

[PRH]

10 out of 10?

I don’t know....... if there’s more than one actual defect/problem...... it counts twice.

So, it’s probably more like 12 out of 10

 

[yellow rose]

The specs show those blocks to have the upper two holes at .031, and the lower at .033, whereas the original 4779 blocks that I used with the old Proform bodies would only have two holes at about .026.
That’s a pretty big difference in the emulsion package.

Been along time since I've actually had my hands on one of those metering blocks but that does sound like a bunch of emulsion.

Sitting here thinking about it...it seems the holes were in odd places compared to Holley blocks. I may not remember that correctly but that's what I think I noticed with a 383 chev on the dyno in probably 2001 or so. They dyno carb went 590 HP at about 6800 and the Demon went 520 around 5500.

After that is just tell the customer to pass on that stuff.

 

[PRH]

I did a bunch of head and dyno work for a somewhat local builder here several years ago.
I sold him quite a few cams as well.
Mostly they were Dirt modified Chevies.
Fairly high compression, roller cams, high rpm.
He had a lot of customers that would come up with these goofy carbs from all kinds of various no name carb wizards.
I never understood it really.
We had a couple of shop carbs that just ran well. Not necessarily the most power, but just good running with pretty flat fuel curves.
We’d start out with one of those, get a baseline...... then put on the owners carb......... which 90% of the time didn’t even run good, much less make any power.
Owners just didn’t want to accept it was kinda junk, so you’d waste an afternoon getting it as good as you could.
Then of course, they’d get there asses handed to them on the track and whine about it.

At the time, the best carbs I’d tested on that type of build were done by Baker carbs.
They had it figured out for that combo.

One of the motors comes to be tested, and they borrowed a Baker from another racer, and brought it along with some other swap meet type thing.
Well, it was a pretty nice build, and with the Baker carb it was as good as we’d tested.
The swap meet carb, not so much.

They take the motor, and there is talk about buying a new carb.

After two nights racing, and getting whooped...... the new carb is ordered.
A Baker?? Nooooooooo.
A new Race Demon, right from BG.

They take it to the races, engine builder is there with them, he’s pretty sharp.
Motor will hardly even run.
They can hardly even get the car around the track in practice.
Carb comes off, old carb back on....... race for the night.
Calls to BG on Monday for some tuning advice........ parts are swapped..... back to the races the next weekend.
Seems to run “better”, but still def can’t race with it....... old carb goes back on.

They give up on the Demon for a couple weeks....... but then decide to pull the motor, and bring it back up to the dyno along with the new Demon to see if it can be tuned up.

Well, that thing was totally out to lunch.
I took it all apart and didn’t find any actual manufacturing “defects”, but the overall tune just didn’t work well at all.
I messed with everything. Air bleeds, emulsion, jetting...... and the fuel curve was exactly the opposite of what you wanted.
It started out too lean, and progressively richened up with rpm.
I could change the rate at which it got rich, and I could change how rich/lean it was overall........ but I never got anything close to a flat curve, much less one that slightly leaned with rpm.
In the end, I felt like the booster response curve and the booster feed hole sizing was just wrong for the motor.
I didn’t have a Baker carb to compare with, but it was down about 8-10hp from one of my dyno mule carbs.

I did have it to where it at least ran well enough to use.
They ran it in the car for a few weeks...... wasn’t really any better than the old carb.

He had talked to them(BG) after the dyno session..... they said it was the wrong carb.
He had to remind them it was what they sold him when he called to order it.

He ended up buying a new Baker....... which worked just fine right ootb.

 

[Cudafever]

You are not helping me with my confidence to learn to tune this carb!

NO it is still the original BG/DEMON metering blocks

So i called NGK and was amazed that the recording said i had 10 sec wait.........And that was all i waited.
After taking with him a bit he gave me three spark plugs that he recommended. A platinum and double laser platinum plug and a race plug.
I haven't priced them yet but the RACING plug is no resistor. What is your thoughts about no resistor plugs!?..?!

Going to scare myself on price now.

 

[Cudafever]

You should run jet extensions on anything that cuts better than 1.8 60ft IMO.

I run mid 1.7XX i have ran one 1.6 (1.698) in the real good air day we had a while back.
so jet extension is on my list.
Is this just a standard or is there different lengths brand exc.

 

[skrews]

This is all I use.

Holley Carburetor Float Kits 116-15