[RA462]

I was just looking at a long on my air fuel ratio meter from last Friday. I start out the run with an air/fuel ratio of around 12.2:1 and finish the pass around 13.5.

How can I adjust the carb for a more consistent air fuel ratio?

Basically what I did was copy what 79TA455STROKED did to his 1095 demon (THANKS!) with Proform 2 circuit metering blocks on my own 1095 King Demon.

89-97 jets(prim&sec)
.063 t-jets(prim & sec)
.026 emulsion holes in #1&3 holes,#1 being top hole.
#2&4 emulsion holes plugged
opened angle channels up to .161(top of main well that feed boosters)
.028 kill bleeds
.039 ifr's(relocated ifr to bottom of block,left top hole open)(drilled and tapped for 6-32)
.089 primary pvcr(drilled and tapped holes for 10-32 setscrews for adjustability)
3.5 prim p.v
no p.v in rear(plugged)
.024 high speed air bleeds(prim&sec)
.076 idle air bleeds(prim&sec)
I drilled a .156 hole in the baseplate for an idle bleed
Air/fuel adj screws are 3/4 turn out.

Injun is a 463 with 14.6:1 compression
112-octain fuel
Stock High Ports (330 cfm)
Victor Intake
279/283° cam at .050”
1095 King Demon carb

I had 8-1/2 psi of fuel pressure at the beginning of the run and I am down to 6 psi by the end (I need a larger return line). Could the fuel pressure also be the cause?

Many many thanks!
Todd

[screamingchief]

Originally Posted by RA462

I had 8-1/2 psi of fuel pressure at the beginning of the run and I am down to 6 psi by the end (I need a larger return line). Could the fuel pressure also be the cause?

This line of reasoning is all wrong.

From the comments,you suggest your using a bypass style regulator.

When that is the case,the pressure regulation is happening after the carb is being supplied with fuel,thus dropping fuel pressure during the run should have absolutely nothing to do with the return line sizing,as that would not cause the pressure to drop under a high demand situation,if anything,with an undersized return,the pressure would remain more stable than it would with a larger return line,as the restriction in the return would help to keep the pressure from dropping as much.

Your problem is on the supply side of the system.

Either not enough volume (pump) capacity for the engines fuel consumption needs,or an overly restrictive supply side of the system.

Usually improper return line sizing manifests itself under low demand situations,as the return side is unable to allow enough bypassing fuel to return to the tank,and then the pressures on both sides of the regulator will try to equalize,and then you become completely unable to maintain the fuel pressure via the regulator no matter how you adjust it.

And yes,the fuel pressure drop could easily be the root cause of the lean out,if the pressure drop signals insufficient supply to the bowls (which it does,re-read above paragraph),the lower level of fuel in the bowls aboslutely can lead to reduced flow across the jets,less flow thru the jets,less fuel to the engine,engine goes lean.

HTH

Bret P.

[ponjohn]

How was the fuel pressure with old combo?

[tininjun67]

if the fuel press was set to 8.5 with a return line incapable of dumping the proper fuel, then I could see this happening. When the engine consumes enough fuel that the pump is no longer providing more fuel than the return line can dump, I could see a drop in pressure happening. increase the size of the return line. Then add a non return style regulator on each line between the carb and return style regulator you already have on the car. (assuming you run a line to each bowl, which I'm sure you do)The dead heads will keep the fuel press to 8.5 no matter what happens, but the return style regulator will dump unwanted fuel back and protect the pump like it's supposed to. If for some reason there is a spike in pressure the dead heads will keep the carb from flooding. a gauge on each regulator is required of course. If you're spraying it, another dead head regulator with gauge goes between the fuel solenoid and the return style regulator and keeps your nitrous tune consistent.

[screamingchief]

Originally Posted by tininjun67

if the fuel press was set to 8.5 with a return line incapable of dumping the proper fuel, then I could see this happening. When the engine consumes enough fuel that the pump is no longer providing more fuel than the return line can dump, I could see a drop in pressure happening.

No offense intended,but this comment seems to contradict itself ?

Is the return insufficient @ 8.5 PSI,or is it insufficient @ the lower PSI ??
Why would it affect both low and peak demand situations ???
What exactly would the regulator be doing in all that scenario ????

Here's how I see this:

When the fuel pressure is set to 8.5 PSI @ low demand and it's stays stable,then the system has to be capable of dumping the required return fuel volume at that setting,otherwise were the return line incapable of dumping the necessary return fuel volume,well then the pressure would almost certainly continue to climb and try to creep up to the max pressure the pump is capable of putting out,or at least to a pressure where the regulator more or less equalizes the pressures on both sides of the system and cancels out those two forces.

Could that "equalized" pressure point just so happen to be 8.5 psi,I guess it could,but that would be a longshot possibillity in most cases.

In a fuel system:
Resistance = increased pressure.
Zero or reduced resistance = no or lower pressure(s).

Resistance = reduced flowing volume.
Zero resistance = maxed out flowing volume.

And then there is this:
When the engine consumes enough fuel that the pump is no longer providing more fuel than the return line can dump, I could see a drop in pressure happening.
With a return style regulator mounted up front by the engine,this is totally wrong.

Anytime the pump is putting out "more fuel" (volume) than the return line can dump,the pressure wont drop,it has to increase as that is seen as a restriction in these systems.

When the engine consumes enough fuel to affect system pressures,the return style regulator will start closing off more and more of the return path to try and maintain the pre-set pressure in the pump/supply side of the system,it'll do such to the point of closing off the return path completely if it has to,so there is less and less resistance build-up in the return side of the system,as it is flowing less and less volume,and there is just no way that greater engine demand equals more fuel volume for the return path in these systems when that is the case,thus there is no way that there would be more fuel than the return line can move,and therefore no drop in pressure due to such.

If the return paths volume capacity is an issue in a system with a fixed output pump (electric pumps),it will almost always be found @ times of lowest engine demand.

That situation is usually encountered when one is trying to adjust the fuel pressure regulator.

Remember,the return style regulator feeds the engine first.
Then whatever fuel volume is left over gets returned to the fuel tank/cell.

Lowest engine demand = max return volume.
Higher engine demand = reduced return volume.

If the peak engine demand is great enough with a return style regulator,the regulator essentially becomes a dead end street,and at that point,the pumps output capacity and the "pre-regulator" system restriction becomes the defacto fuel pressure regulator.

All the fuel volume is going to supplying the needle and seats at this point.

Now when that is the case,if the pump cant keep up with the engines demand,then indeed the pressure will drop,though if the system is too restrictive @ some point,pressure will increase,but only in the portion of the system that's behind the restriction,any part of the system that is after the restriction will likely see a pressure drop as well.

As for the solution,well no doubt there are many possible solutions,but IMO the first thing that should be looked at is the supply side of the system,and the pumps output capacity,if those check out OK,then go looking into the system design aspects for better answers.

I stick to my diagnosis,the problem here is on the supply side.

Now that does'nt mean there wont be a problem on the return side when the root problem gets fixed,that could easily end up happening,especially if the pump capacity is drastically increased without addressing the systems volume capacity on the supply side.

Designing a properly functioning fuel system is a balancing act.

And dont confuse the "big" fuel pumps that use popet style bypasses with the systems that use return style regulators instead,they're usually not set-up in the same way,although the basic idea is similar,their practical application is often quite a bit different.

There are a million ways to skin this cat,but ya' gotta understand the basic dynamics at work in these systems,as essentially when a guy throws together his fuel system,he's just become his own fluid dynamics engineer.

Honestly,we need to know a lot more about his fuel system to make any serious diagnosis here,just too much that is yet to be known...

[RA462]

I have an Aeromotive A2000 pump and 13202 regulator. #12 line from the fuel cell to the pump, #10 from the pump to the regulator, #8 from the regulator to the carb, and a #8 return line. I have the regulator turned way down because this thing will supply enough fuel for 2 engines like mine. I just got the air/fuel meter so this may have been happening some time. No spray, I don't trust the stock block with Crower rods. I think this is a carb tuning thing. Just wanted to stated that i do have fuel pressure.

How do I make the carb richer at the top end?

Thanks guys!

[wrench]

I agree. Your fuel supply(pump/regulator) is more than enough. But, if you are losing fuel pressure during a run, something is wrong. I run the smaller aeromotive pump and regulator on my Procharged 505" and the pressure is steady always. What are you using for a fuel filter? Have you done a volume over time test? Maybe the return being too small is not letting the regulator do its job correctly. So its set at 6psi, but can only bleed off enough fuel to get it down to 8 psi until the fuel demand increases?? I would make sure the fuel supply is correct before doing any tuning. Just my opinion.

[ponjohn]

Could be low voltage and/ or bad ground at the pump.

[tininjun67]

screaming chief,
no offense taken. I was thinking you're answer would be as such while I was writing it. What wrench said was what I was trying to get at.
Ra462, good luck with it, hope you get it solved. How's the glass front end holding up?

[chuckies76ta]

Originally Posted by RA462

I have an Aeromotive A2000 pump and 13202 regulator. #12 line from the fuel cell to the pump, #10 from the pump to the regulator, #8 from the regulator to the carb, and a #8 return line. I have the regulator turned way down because this thing will supply enough fuel for 2 engines like mine. I just got the air/fuel meter so this may have been happening some time. No spray, I don't trust the stock block with Crower rods. I think this is a carb tuning thing. Just wanted to stated that i do have fuel pressure.

How do I make the carb richer at the top end?

Thanks guys!

Reduce the size of the high speed air bleeds on the carb if it has them..

Charles

[meanone]

I set my carb up exactly like this also, thanks 79TA455STROKED, and it did the same thing. As soon as I would jump on it it would be down in the 12's, then go to 13.5for the rest of the run.I was only in the 12's for a second or two. Sounds like maybe what yours is doing to me. I just put smaller pump squirters in and jetted up two numbers front and rear. Seems to have straightened it out. My 2 cents.

[Skip Fix]

I'll let the carb guys like Tom or Jeff chime in but main air bleeds can lean or richen the circuits as it pulls on the carb. Pretty sure smaller bleeds richen it up.
Some one already posted while my computer was thinking!

[chuckies76ta]

Originally Posted by Skip Fix

I'll let the carb guys like Tom or Jeff chime in but main air bleeds can lean or richen the circuits as it pulls on the carb. Pretty sure smaller bleeds richen it up.
Some one already posted while my computer was thinking!

Smaller bleeds will richen it up..

Charles

[screamingchief]

Originally Posted by tininjun67

screaming chief,
no offense taken. I was thinking you're answer would be as such while I was writing it. What wrench said was what I was trying to get at.

Yeah,that's why I put that last line in about too much not being known yet.

Did'nt wanna look like a complete idiot if he had a decent fuel system,which we all now know he does.

Originally Posted by wrench

Maybe the return being too small is not letting the regulator do its job correctly. So its set at 6psi, but can only bleed off enough fuel to get it down to 8 psi until the fuel demand increases??

Yep,that was basically what I was saying when I said this:

Originally Posted by screamingchief

Could that "equalized" pressure point just so happen to be 8.5 psi,I guess it could,but that would be a longshot possibillity in most cases.

That is,when the regulator is wide open and @ full bypass,between the orifice flow limits in the regulator,and the flow restriction in the return side,the best it can do is maintain 8.5 psi.

Takes a lot of pump to make that happen,that's why I said it was a longshot in most cases,as most guys tend to underestimate their pump needs,and tend to use smaller pumps as SOP.

But as I was getting at in my posts,the problem is actually being manifest at lowest demand,that problem being the pressure is being kept artificially high as we cant set the regulator at peak demand,and then when demand infact increases,the pressure drops as the return path is likely still wide open,but the carb is taking more of the volume up.

So yeah,now that we know all about his entire fuel system,seems obvious that the return is what's messing with the fuel pressure settings,and causing the pressure drop issue,and it's highly likely the going lean situation is related to the carb tuning instead of any fuel supply issues.

And I agree testing the system flow to the regulator is a good idea,but it would seem to mostly be a "covering your bases" type deal here,as would be checking the voltages/grounds @ the pump,both are always good practice,but often those tests just confirm that all is as it should be.

His pump and system should be more than capable in terms of supply.

But for all I knew,he could have been using a holley blue,some -6 hose,and a 803bp reg.

I should know better than to speak in absolute langauge before all the facts are known...

[screamingchief]

I've been thinking about this more,yeah I know that can be dangerous...

Originally Posted by RA462

I have an Aeromotive A2000 pump and 13202 regulator.

Is'nt that the aeromotive pump with the diapragm style bypass built into the pump?

And you say you have the 13202 return regulator up front?

Are you saying you disabled the regualtor that's on the pump?

Or does this system have two returns on it???

Where is the fuel pressure being taken from?

Just wanna be sure we got the right info.

[Gach]

Yep, typical Pontiac motor wants more fuel in the middle, air bleeds for sure.

[joes455]

Sometimes the smaller hsb's will make the system go lean?I would try blocking the two lower emulsion holes 3 and 4.

[79TA455STROKED]

Originally Posted by RA462

I was just looking at a long on my air fuel ratio meter from last Friday. I start out the run with an air/fuel ratio of around 12.2:1 and finish the pass around 13.5.

How can I adjust the carb for a more consistent air fuel ratio?

Basically what I did was copy what 79TA455STROKED did to his 1095 demon (THANKS!) with Proform 2 circuit metering blocks on my own 1095 King Demon.

89-97 jets(prim&sec)
.063 t-jets(prim & sec)
.026 emulsion holes in #1&3 holes,#1 being top hole.
#2&4 emulsion holes plugged
opened angle channels up to .161(top of main well that feed boosters)
.028 kill bleeds
.039 ifr's(relocated ifr to bottom of block,left top hole open)(drilled and tapped for 6-32)
.089 primary pvcr(drilled and tapped holes for 10-32 setscrews for adjustability)
3.5 prim p.v
no p.v in rear(plugged)
.024 high speed air bleeds(prim&sec)
.076 idle air bleeds(prim&sec)
I drilled a .156 hole in the baseplate for an idle bleed
Air/fuel adj screws are 3/4 turn out.

Injun is a 463 with 14.6:1 compression
112-octain fuel
Stock High Ports (330 cfm)
Victor Intake
279/283° cam at .050”
1095 King Demon carb

I had 8-1/2 psi of fuel pressure at the beginning of the run and I am down to 6 psi by the end (I need a larger return line). Could the fuel pressure also be the cause?

Many many thanks!
Todd

Well,your setup similar to me except for jets and pvcr.Im in the lower 80's on prim and lower 90's on sec.And smaller pvcr.
You seem to be a little unalanced prim and sec,the front of carb is much fatter.

The only other thing i see different is my hsab is .026
That thing should def be runnin fat on a 463!I would take a look at the fuel sys issue like screamin chief said.
My smaller jettin on my 468 with same emulsion hole,kill bleed setup on my 1095 king demon is keepin me at 12.6 throughout wot.

[79TA455STROKED]

Ill get back to you with my final setup after tuning,need to find the paper or ill just pull carb off and check all holes for ya.
i know it was
.026 emulsion in hole 1&3
.028 kill bleed
.026 hsab

I think i ended up a tad smaller then ur .076 iab
I know i ended up smaller on jetting and pvcr.
The .089 pvcr ended up bein too big and was not balancing carb front to rear after seeing what size prim jet gave me a nice cruise afr.
I think i ended up slightly larger on the t-jets.

Ill get back to u but like i said,i think you have a supply issue,that thing should be way rich.The 12.2 at the begining of your run sounds more like where it should be at the end.Maybe even richer with that much jet.

[79TA455STROKED]

Im workin on carb now for summer tune.This is my 1095 king demon on combo listed below.It is still a little rich art cruise but here is a wot log to show u how urs should be with a similar setup carb.

PJ=82
SJ=93
PVCR=.070
IFR'S=.039
T-JETS=.099
P.V=6.5 FRONT ONLY
HSAB=.025
IAB=.076
EMULSION=.026 1&3,2&4 BLOCKED(1 BEIN TOP HOLE)
KILL BLEED=.028
ANGLE CHANNEL=.161
THROTTLE BLADES OPEN TO EXPOSE .020 OF T-SLOT FRONT AND REAR
IDLE SCREWS OUT 1 TURN
IDLE EZE=OPEN 2 1/2 TURNS
FLOATS SET FOR FUEL LEVEL BOTTOM OF GLASS IN PRIM,MIDDLE IN REAR
TIMING LOCKED AT 38 DEG

I am still gonna play with prim jet,pvcr,t-jets to get a better cruise but u can see im in the mid 12's afr at wot in this log.
Im running alot less jet then u on same carb and smilar combo.This is where u should be.