Need the carb guy's - Team Camaro Tech
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post #1 of 10 (permalink) Old Oct 20th, 19, 06:55 PM Thread Starter
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Question Need the carb guy's

I have 850 demon carb. It's one of the older ones. 2002? 2003? Not sure if it's a mighty demon or a street demon. Bought it off Summits bargain shelf back in 03'. Someone bought it, didn't like it, brought it back I imagine. So I was willing to throw down $100 on it. What the hell. LOL So that's how long I've had this thing. Sat in my shop for 10 years before I bolted it on, then ran it off and on for the past 5 years, knowing that it wasn't correct for the motor I had in the car, but it helped with hood fabrication ect. Researched how to ID these things, and there's an 8 stamped on the air horn. That's why I say it's a 850.
Now that I have a motor underneath it, it's time to clean it up and dial it in better.
I have a 10:1 427 BB with hyd. roller cam and big valves with a tunnel ram. ( Easy, I'm old school, and don't care.) LOL It's a double pumper manual secondaries, no choke.
I tore it down today and realized it has a 50cc accelerator pump on the primary side with 85 jets. The secondaries have a 30cc pump with 93 jets.
That just seems odd to me.
Maybe it's something normal. I'm not a carb expert, but.... It don't look right to me.
Any thoughts on why it would have jetting like this?
And yes, I am changing the power valve to a lower vacuum unit after reading my idla vac. in gear with a load. In gear its 8" vac. So I went with a 3.5 power valve.
So, hopefully, for me, somebody has some insight on these demons and has played with them.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
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post #2 of 10 (permalink) Old Oct 20th, 19, 07:12 PM
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Morgan
 
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Re: Need the carb guy's

Prosystems likes 50cc primary pumps and 30 in the back, so it must work. Power valve in the rear?

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post #3 of 10 (permalink) Old Oct 20th, 19, 07:15 PM Thread Starter
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Re: Need the carb guy's

No, just 1 power valve. It's the 93 jets on secondary side that has me stumped.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #4 of 10 (permalink) Old Oct 21st, 19, 06:16 AM
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Re: Need the carb guy's

Larger jets and accelerator pump size on the primary side seems pretty odd to me too. Any chance you have an AFR gauge? If not, that will tell you immediately what's going on. If you only have one power valve, your rear jets should be up to ten jet sizes higher, not lower. Personally, I would put it back to stock specs before doing anything else and start there. I would definitely have dropped $100 for it to, but who knows what the first guy did to it or the reason he returned it.

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

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post #5 of 10 (permalink) Old Oct 21st, 19, 07:34 AM Thread Starter
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Re: Need the carb guy's

Yeah, I know someone was in it prior because of the way they didn't put the bolt washers back correctly. lol So the secondary jets should be ten sizes higher without a power valve? 85's on the primary and 93's on the secondary side is what I found when I opened it.

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
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post #6 of 10 (permalink) Old Oct 21st, 19, 11:13 AM
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Re: Need the carb guy's

According to Holley:

https://www.holley.com/products/fuel...rts/FR-76850BK

That carb left the factory with 89 jets front and raer, and a secondary metering plate containing a power valve. Whenever you pull a power valve on a drag car that only runs at WOT you enrichen the main jet FOUR sizes to compensate for the missing fuel flow from the power valve (not ten).

The fact that it has a Reo pump on the primary (and not both) is because the previous user was compensating for a flat spot on hitting the throttle. It is called a REO pump because gas powered semi trucks made by Diamond Reo used a Holley with a 50 cc pump on their six cylinder motors to get a very heavy under powered vehicle moving.

Normally a 50cc accelerator pump is the last resort after changing the accelerator pump cam out for a different one (or moving location from 1 to 2; or both); and/or adjusting the squirter size to flow fuel over a longer or shorter time period by varying the size of the nozzle to cover the flat spot. These adjustments vary from car to car depending upon the car's gearing, weight and the engines power (displacement and cam).

My favorite carb for a 427 BBC with a tunnel ram was two 660 cfm center squirt Holleys:

https://www.holley.com/products/disc...t/parts/0-4224

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post #7 of 10 (permalink) Old Oct 21st, 19, 01:33 PM
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Dave
 
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Re: Need the carb guy's

Quote:
Originally Posted by Larger Dave View Post
According to Holley:

https://www.holley.com/products/fuel...rts/FR-76850BK

That carb left the factory with 89 jets front and raer, and a secondary metering plate containing a power valve. Whenever you pull a power valve on a drag car that only runs at WOT you enrichen the main jet FOUR sizes to compensate for the missing fuel flow from the power valve (not ten).
I said up to ten in my original post. I've never seen ten with my own eyes, but four seems pretty low. Not doubting you, but I'm running 6 sizes higher on my 950cfm right now.

'69 SS396 X66 L34 08D M21 BS
460ci Gen VI 9.75:1 AED 950 carb
241/249 @ .050" .625/.625 110 LSA

Semper Fi!

"The galleries are full of critics. They play no ball, they fight no fights. They make no mistakes because they attempt nothing."
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post #8 of 10 (permalink) Old Oct 21st, 19, 06:07 PM Thread Starter
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Re: Need the carb guy's

Okay, that gives me some info to work with. Thanks for the input. I'll post a pic of it after I get it back together. Before I re-assemble it, I'm going to read the plugs. If it seems fat, I'll most likely jet it down some.
One thing I read about some of these early BG demons was during the manufacturing process, quality control was a bit lax. I did find some pieces of aluminum in the primary bowl. One was a pretty good sized chunk. Looked like it never was properly cleaned. It did have an idle air bleed plugged to. It took alot to get it opened up. No, I didn't start probbing the aluminum with sharp steely objects enlargening the holes. LOL (Air pressure and carb cleaner.) I'm sure it was a piece of aluminum stuck in there. And this is probably why they brought it back.
One things for sure, When you crack the butterflies on this thing, it flushes gas like a 1948 ferguson commercial toilet. WHOOOSH!!! LOL
Motor seems to like it though, I have to stomp the pedal 3-4 times to get it to fire. Yeah, about a quarter cup. LOL

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
stevo camaro is offline  
post #9 of 10 (permalink) Old Oct 21st, 19, 06:45 PM
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Re: Need the carb guy's

Prosystems goes up 10 without power valves. It really depends on how large the pvcr was before you plugged it.

Demons were famous for alluminum chips. Every hole needs to be blown out and start fresh. That jetting is rich, but with a tunnel ram, everything changes. I have ran 50cc pumps in the front plenty of times.

Spend the $150 and get an AF meter, worth every penny

69 Copo 9560 ZL-1 automatic [email protected], 1.95 on f70-14 polyglas F.AS.T. Race June 2016
69 Copo 9560 ZL-1 4spd [email protected] 1.93 60ft on F70/14
PSMCDR 2014
71LS6 vette [email protected] PSMCDR 2012 SOLD
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post #10 of 10 (permalink) Old Oct 21st, 19, 09:06 PM Thread Starter
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Re: Need the carb guy's

The secondary metering block doesn't look like it was modified. It just looks like it never had a power valve. Yeah, a AF meter should be utilized. I agree. I'm going to install, permanently, a vacuum gauge too. I think pulling some plugs will send me in the right direction on the jets.
I appreciate the input.
I do have another tunnel ram for 2 4 bbls instead of a single like it's set up now. I just don't want to spend the time polishing on the damm thing. LOL
No, I won't bolt it on like it is. I would on the 55, but not this car. LOL

67 RS 327, 4-speed, posi, done.
67 Modified, 454, TH-400, posi, under construction.
67 SS 396, 4-speed, basket case.
72 RS, sitting, partially done.
55 210 post, 2 door, 327 4-speed runs good.
55 2 door post, gasser project
69 Cadillac ElDorado
69 4x4 suburban
59 ElCamino

Some mornings, it's just not worth chewing thru the leather straps"
stevo camaro is offline  
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