Air/Fuel Ratios from bottom to top of RPM curve?
#434617
08/11/09 11:09 AM
08/11/09 11:09 AM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
OP
Taking time off to work on my car
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OP
Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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For you guys that have either dyno data or use the on-board wideband O2 meters, do you find that your "tuned" WOT air/fuel ratios from bottom to top of RPM curve are fairly close, or do they tend to swing one way or the other?
I spoke w/ Dwayne Porter about seeing this on the dyno data for my engine where we tested a few different carbs. In this case, my Claw had a lean bias (not a "spike, a more gradual change) in the mid-range of a 3500-7000 RPM pull (i.e. ran richer near the bottom and peak RPMs). His "dyno mule" Holley 850 annular carb showed much more consistent a/f ratios across the pull, as did an 8896 HP 4500 we tested.
We know this can be the result of a combination of things... emulsion settings, booster signal, air bleeds. However, pinpointing the reason for going lean in that manner isn't so cut-n-dry. It just "is" at this point.
EDIT: I'll throw another related question on here... do you "want" to see a different air/fuel ratio at peak torque than at peak HP?
So... what have you guys seen from your own tests?
Last edited by BradH; 08/11/09 12:16 PM.
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: aarcuda]
#434622
08/12/09 11:35 AM
08/12/09 11:35 AM
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Joined: Aug 2003
Posts: 43,127
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,127
Bend,OR USA
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Is the immediate rich the accelerator pumps? Leaning out at the upper RPM needle and seat size?
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: Cab_Burge]
#434623
08/12/09 01:25 PM
08/12/09 01:25 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
Posts: 15,478
the boonies
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Quote:
Is the immediate rich the accelerator pumps? Leaning out at the upper RPM needle and seat size?
thats what Im thinking. I get a dump of gas and go rich. then it runs out and I get a lean spike. Why it creeps back a little lean at the top of 2nd gear and then again in 3rd, i have no idea.
Im going to try 2 things next week end. take out my 34 squirter and try a 28 and see if that mellows the initial rich and spreads the squirt longer to prevent the lean.
I also have a brown 500cc pump cam I want to try.
For the lean creep in second, maybe its the outboards fully opening??? I have plain springs in there now. I would think the outboards would be wide open at 6000 in first and stay that way thru 2nd and 3rd. I want to try some others.
I wish I knew when the outboards were opening/fully open. I need to figure out how to rig a tps to the outboards
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: mopar dave]
#434625
08/12/09 03:18 PM
08/12/09 03:18 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
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the boonies
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Quote:
the lean condition on top end may be high speed air bleeds. try two sizes smaller. that should richen it up a bit. do this with an air/fuel gauge so you can see whats going on.
how do you change them on a car with pressed in bleeds? Do i have to try and drill the old ones our and screw in the screw in type? I'd hate to do that on my original carbs. Is there a way to change something on the Promax jet plate that would accomplish the same thing?
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: Thumperdart]
#434629
08/12/09 10:56 PM
08/12/09 10:56 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
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the boonies
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Quote:
I`ve heard of guys putting epoxy in em and drillin em to the desired size AFTER measuring em w/a pin vise. Or, you can use a fine wire in the existing ones and see if it improves and if so, modify the carb for screw in bleeds. 
ya, the wire method... duh, i knew that. i used that years ago on my idle bleeds (used bent over paperclips).
cool, more tests to follow!!
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: aarcuda]
#434631
08/13/09 07:34 AM
08/13/09 07:34 AM
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Joined: Jul 2007
Posts: 531
Virginia
JimG
mopar
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mopar
Joined: Jul 2007
Posts: 531
Virginia
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Quote:
how do you change them on a car with pressed in bleeds? Do i have to try and drill the old ones our and screw in the screw in type? I'd hate to do that on my original carbs. Is there a way to change something on the Promax jet plate that would accomplish the same thing?
AAR:
Another way besides the wires is to drill out the original air bleeds (after measuring them and recording the sizes), tap the channel (usually 8-32) and buy some brass set screws from an industrial supplier like McMaster-Carr. 3/16" length works well for IABs and MABs. Drill the brass set screw to the desired diameter and screw it in.
Wires work, but it can be kludgey. If the wire isn't inserted perpendicular to the orifice you're trying to reduce, its effective footprint becomes larger than the measured diameter of the wire. The upside, of corse, is that you don't risk messing something up when you drill and tap your carb.
In your case, yes the smaller MABs will richen it at the top end and delay the start of the mains at low airflow (thereby possibly making a lean spot off-idle). Juggling a larger jet and smaller MAB might be the ticket; only testing will tell.
Aren't you running aftermarket metering blocks? If so, how many emulsion bleeds and what size are they?
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: JimG]
#434632
08/13/09 07:50 AM
08/13/09 07:50 AM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
Posts: 15,478
the boonies
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Quote:
Quote:
how do you change them on a car with pressed in bleeds? Do i have to try and drill the old ones our and screw in the screw in type? I'd hate to do that on my original carbs. Is there a way to change something on the Promax jet plate that would accomplish the same thing?
AAR:
Another way besides the wires is to drill out the original air bleeds (after measuring them and recording the sizes), tap the channel (usually 8-32) and buy some brass set screws from an industrial supplier like McMaster-Carr. 3/16" length works well for IABs and MABs. Drill the brass set screw to the desired diameter and screw it in.
Wires work, but it can be kludgey. If the wire isn't inserted perpendicular to the orifice you're trying to reduce, its effective footprint becomes larger than the measured diameter of the wire. The upside, of corse, is that you don't risk messing something up when you drill and tap your carb.
In your case, yes the smaller MABs will richen it at the top end and delay the start of the mains at low airflow (thereby possibly making a lean spot off-idle). Juggling a larger jet and smaller MAB might be the ticket; only testing will tell.
Aren't you running aftermarket metering blocks? If so, how many emulsion bleeds and what size are they?
i have the promax metering block and the jet plates for the outboards. i dont think the jet plates have provisions for adjustment other than they accept holley jets. the center carbs metering block has the stock emulsion bleeds in their now.
I would imagine i'd want to be messing with the outboard MABs but I really dont want to go and drill and tap them. Im not really a numbers guy but on this, date coded 0500 original 6bbls carbs, I dont want to make a permanent change by drilling them.
Is there a way to change the center carbs metering block oriface to get this done? of maybe the jet plate oriface could be modified??
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: aarcuda]
#434635
08/13/09 12:09 PM
08/13/09 12:09 PM
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Joined: Jul 2007
Posts: 531
Virginia
JimG
mopar
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mopar
Joined: Jul 2007
Posts: 531
Virginia
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Quote:
i would imagine the cruise is only running on the center carb but without a tps, i am not sure. I am going to try the ol bread bag tie on the diaphragm rod trick this week and that will give me a redneck TPS.
as for the emulsion bleeds in the center metering block, i seem to recal they are .031 and there are 3 of the. the other 2 or 3 are plugged
First things first: be sure the outboards are out of the picture when the problem occurs. Next, try what Cab Burge said.
3 e-bleeds at .031" makes me suspicious, but do the other stuff first. I think you're on the right track.
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Re: Air/Fuel Ratios from bottom to top of RPM curve?
[Re: Cab_Burge]
#434636
08/13/09 01:38 PM
08/13/09 01:38 PM
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Joined: Mar 2003
Posts: 15,478
the boonies
aarcuda
I Live Here
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I Live Here
Joined: Mar 2003
Posts: 15,478
the boonies
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Quote:
Is this a six pak set up? If so let me know, I have several sets, one of them is really good    I may be able to help 
I guess its obvious now but yes, these are somehat modified 340 six pack carbs. i have the promax base plates and jet plates for the outers, and the promax metering block for the center carb.
the choke plate has been removed, the center jets are 64's and the others are 84's. running the plain springs in the outboards diags 50cc pump with he white cam. squirter is a 34 (i drilled out a 32 I had).
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