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OK, I think we are getting this whittled down now. I don't know the Demon
carbs (except that they are improved from the Holley design) But one of the
screwy things about the Holley design is the way the jets work. The jets
control the fuel during moderate acceleration. I got a life lesson, one
time, when I somehow sucked some junk into one of the idle / fuel passages.
I could tell what happened because it idled very rough, but would straighten
out when I revved it. I was across town with the car, so the freeway seemed
the "smart" way to get home. After all, I would be on the jets going down
the freeway. As you can guess, I was in for a surprise, the car ran rough
going down the freeway at eighty! So getting on the freeway was fine, but
staying at speed on the freeway, I was back on the idle circuit. The point
is: the jets control fuel ratios at moderate acceleration. So here is how
it all works: (forgive me if you know this already)
Idle circuit: The "mixture" screws control the volume/amount of
emulsified fuel (fuel already mixed with air) into the engine. (Idle
Air/fuel ratio is set on
a Holley) A BG should have Air jets to adjust
the idle.
Transisition slots: Help a smooth transisition onto the main jets. No
adjustment (short of filing)
Accelerator pump: Help a smooth transisition onto the main jets. Lots of
adjustments, Cams and nozzles
Jets: Adjustment for the air/fuel ratio at part
throttle acceleration
Power valve: Adds additional fuel for Wide open acceleration. The
Power valve can adjust WHEN the extra fuel comes in, but no adjustment
(short of
drilling) for the AMOUNT of fuel. The power
valve only works when the carb is on the main jets, and fuel is flowing
through the booster
venturies (No effect at idle)
So, you can see out of the five fuel circuits in a Holley two of them are
just to help the motor onto the main jets.
OK, to give you your answer, going down seven jets is why you have your bog.
See, You have a big carb on a smaller engine, with a weak vacuum. Then you
went down seven jets! This not only leaned the carb on a engine that is
already lean, but it also delays the fuel from flowing; hence your bog. I
know you hate that answer, but let me defend it.
The rich fuel condition you detect is caused by the overlap in the cam. You
have close to a racing cam, it is designed to waste some fuel, to blow out
the cylinders on the exhaust stroke so you can get more Air/fuel on the next
intake stroke. That motor will seem rich with the two barrel off my 283!
Now bear in mind that ninety plus percent of the time you are on the idle
circuit. So if your plugs are sooty, it's because your idle is too rich.
As I was explaining at the top of the page, the "jets" only affect moderate
acceleration air/fuel ratios. The engine rarely runs there.
1. I would take the nozzle up to a .040"
2. Jump up five jets richer than stock. front and back. 85's and 95's
3. Put the floats back to the stock setting
4. Put the power valve back to the stock setting
What do you have to lose? You will be a happy guy!
Rob
The engine you have is
----- Original Message -----
From: "Paul Hernandez" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, November 28, 2001 1:22 PM
Subject: Re: [Chevelle-List] HEI ???? RESISTANCE WIRE QUESTION ANYONE?
>
> Replies to this message are sent to The Chevelle Mailing List
> ------------------------------------------------------------
>
>
> I have done lots of research and my car is apparently set-up correctly for
> HEI after internet investigation and giving various calls to vendors.
> I do run my HEI with MSD 6A instead of the module. using the moroso curve
> kit & Crane vac adj. kit.
>
> Here is some of the sites I visited most helpful.
>
> www.lectriclimited.com/frequently asked questions.htm
> www.oldengine.org/unfaq/hei.htm
>
>
>
> Well. I don't have the choke on my 850 demon so that can't be but, I know
> the original jets were high 80's front and 90's rear. That really gave me
a
> rich indication with fuel wash on the plugs. so I went with 74's/ 81's
> being the rule of thumb 7 jet sizes from the fronts if using the power
> valve. I looked into the 750 demon and that sucker comes with 76's front
> and 83's rear. I will try that combo to see where my engine stands and
also
> reading my plugs color. I think I might have a fuel starvation problem
like
> you said. You were right my vehicle stalls right off idle to take off. MY
> IGNITION HAS BEEN RULED OUT TOTALLY! My car is wired correctly for HEI.
:)
>
> 1.) It stalls a little when I start it cold.
>
> 2.) bogs then go. warm!
>
> 3.) I will play with the pump cams possibly one from the dominators since
> that's a longer shot! before going to the 50 cc pump
>
>
> P. Hernandez
> 68 chevelle
>
>
>
>
>
> "Rob Thorburn" <[EMAIL PROTECTED]>
> Sent by: To:
<[EMAIL PROTECTED]>
> [EMAIL PROTECTED] cc:
> velles.net Subject: Re:
[Chevelle-List] HEI ???? RESISTENCE WIRE
> QUESTION ANYONE?
>
> 11/28/2001 01:51 PM
> Please respond to
> chevelle-list
>
>
>
>
>
>
>
> Replies to this message are sent to The Chevelle Mailing List
> ------------------------------------------------------------
>
> Hello:
> I have found the best thing with a HEI is to replace the orginal 16
> gauge
> "coil wire", with a larger diameter 12 gauge wire, back to the connector
at
> the firewall. I take the wiring harness plug loose at the firewall, pinch
> the blade connector and remove it from the harness. Then solder the 12
> gauge wire on, and reinstall the blade connector into the harness and bolt
> the harness back into place on the firewall.
> My guess is: your hesitation is from lack of fuel. Because you have
very
> low vacuum, you are running out of fuel. The weaker vacuum pulls the fuel
> less, so you have to go richer to compensate. When tuning a carb, you have
> to trust me, if it falls on it's face, it is 'cause of lack of fuel one
> hundred percent of the time! A rich condition will cause a lack of
> crispiness in the throttle response and possibility black smoke out the
> exhaust, but it would take insane amounts of fuel to kill an engine such
as
> yours.
> First lets discuss the idle: does it tend to stall when you first start
> the engine? Are you running a choke? A tendency to stall, without the
> choke, when cold is OK, the idle should be set for when the engine is at
> running temp. If it idles fine when first starting, it will be too rich
> when the engine is up to temp. You can expect fouled plugs from this
> setting.
> Next, lets talk about the accelerator pump and nozzle. This will sound
a
> little stupid, but answer this question: Does the car go, then bog, or
> does
> the car bog then go? My guess is, that the bog is immediate, off idle.
> Your engine requires more fuel, and/or it wants it faster. I would also
> guess, the nozzle is too small. Try a nozzle in the high thirties. If
you
> see some improvement, try going higher. On a Holley, you have to purchase
a
> "Hollow nozzle screw" when going over .042" to prevent flow restriction
> problems. If the nozzle screw is center drilled with two side holes you
> are
> set. Then fine tune the pump circuit with the selection of the pump cam.
> You will need to pick a pump cam that gives you a bigger pump shot at the
> beginning. If all of that is helping, but you still need more, it will
> be
> time to purchase the 50cc pump kit. But remember, you only want to use
> just
> enough fuel to solve the offensive problem. Too much, will give you soggy
> performance as the engine has to "clear out". My guess is you are lean on
> the jetting too, for peak power, because your motor is more radical than
> most street motors.
>
>
> ----- Original Message -----
> From: "Paul Hernandez" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Wednesday, November 28, 2001 10:25 AM
> Subject: Re: [Chevelle-List] HEI ???? RESISTENCE WIRE QUESTION ANYONE?
>
>
> >
> > Replies to this message are sent to The Chevelle Mailing List
> > ------------------------------------------------------------
> >
> >
> > If the resistance wire was not replaced with a pink or what ever
> color
> > wire going from the ignition to the HEI, What would be affected and how
> can
> > you tell the vehicle is having problems.
> >
> > I currently installed an HEI in my 68 chevelle and the car seems to be
> > running fine at idle. I don't have the module but instead I use the
MSD6A
> > box. Someone help! I'm having hesitation problems while in gear at low
> > speeds. I don't think its the Demon carb 850cfm with 74 jets front &
> > 81rears, 31 scquirters on my smll blk 355, 11.0:1 555 lift cam. I want
> to
> > make sure its not the wiring so I can make either timing adjustments or
> > carb tuning adjustments. My power valve is a 2.5 since my vacuum is only
> at
> > 5inches in idle park mode. I also recently changed over to internal
> > regulated ALT. and that's been ruled out.
> >
> > P. Hernandez
> > 68 chevelle
> >
> >
> >
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> >
> >
>
>
>
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