Ok.. I recently purchased a Barry Grant Mighty Demon 800cfm Annular booster, mechanical secondarys carb to replace my worn out 850cfm Holley race carb on my 67 GTO.

After reading the instructions carefully I find that up to around 3grand the car seems to run fine. It's when I lay into the throttle that the car stumbles and misses bad. It is NOT an ignition issue at all. Something with the carb, I've adjusted that damn thing now for two days and still does not perform like my 850 Holley did.

What gives? Anyone have one of these carbs?

My engine

462ci + 0.030 over
87c E-heads with 1.65 Harland sharp roller rockers
CC292 hydraulic cam
4 tube heddman headers
th400 with 3500 stall 3:73 gears

Ran best of 11.5@118 on motor with holley carb. Now with the demon I'd be surprised if it got into the 12's!!!

Could I have a bad carb, or am I missing something here?

My holley has no power valves and 83 primary and 87 secondary jets If I remember correctly.

Ok.. I recently purchased a Barry Grant Mighty Demon 800cfm Annular booster, mechanical secondarys carb to replace my worn out 850cfm Holley race carb on my 67 GTO.

After reading the instructions carefully I find that up to around 3grand the car seems to run fine. It's when I lay into the throttle that the car stumbles and misses bad. It is NOT an ignition issue at all. Something with the carb, I've adjusted that damn thing now for two days and still does not perform like my 850 Holley did.

What gives? Anyone have one of these carbs?

My engine

462ci + 0.030 over
87c E-heads with 1.65 Harland sharp roller rockers
CC292 hydraulic cam
4 tube heddman headers
th400 with 3500 stall 3:73 gears

Ran best of 11.5@118 on motor with holley carb. Now with the demon I'd be surprised if it got into the 12's!!!

Could I have a bad carb, or am I missing something here?

My holley has no power valves and 83 primary and 87 secondary jets If I remember correctly.

Hi,I am running an 850 Mighty Demon Annular carb on my engine in my sig below,and it seems to do great.Are the jets bigger in your Demon than they were in your 850 Holley,maybe causing it to run rich?

Nick there was a post on here in the race section somewhere and a Barry Grant tech was answering questions about their carbs. I'll see if I can find it and post the address.

Greg

Don't know what they are actually. The 800cfm mighty demon is new. They don't even list that carb on their website yet. I would say it's using 79 primary and 84 secondary jets.

It sounds like it's jetted too lean. Have you checked the plugs? I would suggest stepping up the jets 2 sizes and try again. (also eliminate the possibility of a vac. leak) I'm running an 850 Mighty Demon on a 470 BBC with E-heads and solid roller. I blocked the power valves, and run it square jetted with 94s in it.
I know what works for Chebbies doesn't always work for Pontiacs, but it's worth checking into.

Have you gone over the basics and checked all circuits. On mine the secondary squirters were blocked on one side.

Time to strip it and clean and verify all passages etc are clean and then reassemble and adjust

Also check the internal ring on the annular boosters. One of mine fell out !!!!!!

I been there with a new carb, True story: after days and lots of expert help I found a little fly in the idle circuit! Ran like a champ after that.

With any product there can be exceptions and somebody always gets a "Friday afternoon" part (latley it seems as if its always me)

But when employee No *** signs off all circuits as wet flow tested and approved and when it gets to you and its a POS it gets a little frustrating. I hope employee No*** was having a bad day that day (if he even exists) and if not I feel for any future purchaser if that is the standard of quality control

I hope the level of quality control has improved and calibrating your carb is a simple matter

Good luck and let us know how you get on

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by meanken:
It sounds like it's jetted too lean. Have you checked the plugs? I would suggest stepping up the jets 2 sizes and try again. (also eliminate the possibility of a vac. leak) I'm running an 850 Mighty Demon on a 470 BBC with E-heads and solid roller. I blocked the power valves, and run it square jetted with 94s in it.
I know what works for Chebbies doesn't always work for Pontiacs, but it's worth checking into. </div></BLOCKQUOTE>

Well, I actually thought about blocking the power valves. My original holley had both power valves blocked. I checked for vacuum leaks there are none. With my cam I have about 6 inches of vaccuum. The demon has a 6.5 power valve in the front and non in the secondaries. I wonder if that what is causing my stumbling and missing?

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by 455-4+1:
Have you gone over the basics and checked all circuits. On mine the secondary squirters were blocked on one side.

Time to strip it and clean and verify all passages etc are clean and then reassemble and adjust

Also check the internal ring on the annular boosters. One of mine fell out !!!!!! </div></BLOCKQUOTE>

Visually everything appears to look ok.

Even though I'm not a big fan of these carbs, we've seen units right out of the box than run flawlessly. I'm always trying to beat them on the dyno and track with our custom q-jet carbs. We have ran into others, that run like CRAP...and despite taking them completely apart and hand cleaning every single passage, still ran like CRAP. If it's a new part I'd chase the tuning a bit, but not extensively, send it back and get another one back to be repaired under warrantee....Cliff

The carb is brand new. I may call BG tech support today to see if I can exchange it out. I'm no expert, but a $500 carb should not be giving me this problem.

As meanken suggested- run the jets up 2 sizes- also if you have 6 inches of vaccum you should be running a 4.5 power valve.

Quote:

"Even though I'm not a big fan of these carbs, we've seen units right out of the box than run flawlessly. I'm always trying to beat them on the dyno and track with our custom q-jet carbs. We have ran into others, that run like CRAP...and despite taking them completely apart and hand cleaning every single passage, still ran like CRAP. If it's a new part I'd chase the tuning a bit, but not extensively, send it back and get another one back to be repaired under warrantee....Cliff"

I tried to fix Tom Richcreek's carb (the third one he got under warranty return from BG) and
did the normal cleaning, setting, adjusting, etc and got most of the issues resolved BUT it
still was not right at low speed. Bud Lyon bought the carb from Tom, put it on a trans
brake car, and leaves much higher, and loves the carb.

The vehicle application can sometimes overcome "flaws" that are apparent in other applications. FFT.

Tom V.

NikiVee1954,

If the problem is happening when you're getting into the throttle, but not once you're up to RPM you may need to up to a larger squirter nozzle.

Tom Vaught,

Not sure the whole story with Tom Richcreek's situation, but his carburetor was worked on once, and replaced once in 2002. Nowhere close to three new carburetors. We have made major changes since then.

My 850 Speed Demon has run great out of the box. Idles screws were almost perfect, rejetted on step richer for my combo.

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Tech @ BG:
NikiVee1954,

If the problem is happening when you're getting into the throttle, but not once you're up to RPM you may need to up to a larger squirter nozzle.
</div></BLOCKQUOTE>

It misses and bucks when the throttle is almost half way open. At any rpm below 3000 the carb appears ok. When I apply throttle slowly and steadily as soon as the cars rpm goes over 3000 and approaches 4000 and above it misses and breaks up. If I slam the throttle to the floor the cars seem to run fine, but the power is not there like with my holley 850.

This carb was recommended to me by a BG reseller based on what I told them about my combo.

Sounds like power valve /PVRC issue to me. The 6" vacuum with a 6.5 power valve may be fluttering there at slow throttle.

Tech at BG:

Quote:

"Not sure the whole story with Tom Richcreek's situation, but his carburetor was worked on once, and replaced once in 2002. Nowhere close to three new carburetors. We have made major changes since then."

Here is how I did the counting:

He bought the carb, It did not work to his satisfaction so "Carb number 1"

He sent the carb back for repair, It did not work to his satisfaction so "Carb number 2"

You sent him a New Carb, it did not work to his satisfaction so "carb number 3"

Hope this helps.

I worked on the carb too and I could not fix it, so it was impossible to fix! http://forums.performanceyears.com/g...on_biggrin.gif http://forums.performanceyears.com/g...on_biggrin.gif
(Manufacturing stuff happens!)

Bud Lyons is a very happy guy so you guys still had a happy customer, eventually.

Tom V.