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Re: 950 too rich at cruise
[Re: Thumperdart]
#2846527
11/15/20 12:19 PM
11/15/20 12:19 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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Posts: 4,220
West Plains, MO
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Too big of a main bleed = no fuel through the jets needing HUGH jets up top to be happy which floods part throttle cruise when on the mains..... Thanks for the tip. Too rich part-throttle cruise is my whole problem! But "up top" won't the secondaries be coming in too, and I can tune them leaner to compensate? The Eddie RPM has a gap in the divider, not a 100% dual-plane. What would you recommend for a single-plane then? I'll probably put on the aluminum heads this winter (293.5 cfm at .600-up and also breathe better at lower lifts).
Last edited by DrCharles; 11/15/20 12:25 PM.
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Re: 950 too rich at cruise
[Re: DrCharles]
#2846535
11/15/20 12:31 PM
11/15/20 12:31 PM
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Joined: Jan 2003
Posts: 12,244
Benton, IL.
DaveRS23
Special needs idiot
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Special needs idiot
Joined: Jan 2003
Posts: 12,244
Benton, IL.
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How's your AFR and vacuum at cruise? Can you get it above stoich, or at least 14:1? I could go to a 4500 but then I'd also have to get a single-plane manifold to match... concerned about the effect on torque when not WOT (which is nearly all of the time)  Thread some aluminum bolts into the carb mounting holes and cut them off flush. Then drill and tap new holes for the Dominator carb. You might have to open the plenum up some, but that's no big deal either. I have done this on several different intakes over the years. Works fine and costs about $10 for the aluminum bolts. In my personal experience, I don't feel that the Dominator hurts the torque or drive-ability on the street once dialed in. I agree with Dominic that the Dominator carbs are the way to go on our hotter/bigger big blocks and Hemis. I have a 1050 Dominator with Dominic's metering blocks on my primarily street 540 Hemi. Drives great. On mine, the key was getting the mains to come in early enough (1,900 RPM +/-) so that I could keep the engine happy when on the slot, and then cruising on the mains in the mid 14s at that lower RPM .
Master, again and still
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Re: 950 too rich at cruise
[Re: DrCharles]
#2846629
11/15/20 03:23 PM
11/15/20 03:23 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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Posts: 4,220
West Plains, MO
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Did some testing this morning... As usual Dom is spot on (and madscientist too). I did get the t-slot lean enough for low speed cruising with .028 IFR, .074 TSR and .082 IAB. Have the screws out 1.5 turns in front and 2 turns in the rear with a bit of secondary air added to maintain 1200, 8", 14.5 idle.
But I popped in .080 PMAB for a trial - sure enough it leans out a lot on the highway as the revs climb (still only on the primaries) but it's too rich as the mains come in. At this point I agree with madsc. that I don't know what on earth the people in that Innovate-hosted article were thinking!
And the damn thing STILL wants to cruise (15", 3000) at 12.5 to maybe 13 at best! Fuel curve looks like a roller coaster. Craptastic. Although driveability is still good except for a too-lean spot at low rpm on the slot.
So my next move will be to go smaller on the MAB, actually below .030. Also drop the PMJ's from #75 one or two sizes, and try it again.
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Re: 950 too rich at cruise
[Re: DrCharles]
#2846657
11/15/20 04:13 PM
11/15/20 04:13 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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West Plains, MO
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Progress!  I have some air bleed blanks on the way (Tues.) so I popped in the only small PMAB I had on hand, .026, and dropped the PMJ to 73. Now it runs quite a bit leaner - cruise is up to 13.5 at 15" Hg, 3000 rpm (in 3rd gear).  The .059 PVCR probably could be a bit bigger but I'll save that for later. Don't have time today to go out to the highway and try it at 60 in 4th. But if the vacuum and the rpm are the same, the load should be the same (I hope). AFR gauge wanders less too. But the flat spot off-idle is a little worse now - guess I misdiagnosed the symptoms and there was significantly more contribution from the mains even below 2000 rpm than I thought. I may need to richen the idle just a bit (it's on the lean edge right now) and that's quicker and easier than pulling the bowls yet again. Also I haven't even looked at the pump cam yet (.035 squirters, pink cam). Anyway it's not bad and I can live with it. I also need to get out on the highway and make sure I'm not too rich at higher rpm's on the primaries. Then I can try (very) brief blasts on the secondaries (currently .030 SMAB, #86 SMJ).
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Re: 950 too rich at cruise
[Re: DrCharles]
#2846670
11/15/20 05:07 PM
11/15/20 05:07 PM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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Lower the float levels and turn the mixture screws in maybe a 1/4 turn but one at a time......
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: 950 too rich at cruise
[Re: Thumperdart]
#2846709
11/15/20 06:41 PM
11/15/20 06:41 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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West Plains, MO
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Lower the float levels and turn the mixture screws in maybe a 1/4 turn but one at a time...... Thanks, will try that on the next tuning session. How much lower? It has "HP" float bowls with the large sight windows, and it's about 1/3 up the glass at idle. Fuel pressure 5 psi. I can't turn the screws in any more, it's about as lean as I can idle it now...  That's why I put a little more on the secondaries (2 turns) than the primary (1-1/2). Could I go one size smaller on the mains (to #72)?
Last edited by DrCharles; 11/15/20 07:10 PM.
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Re: 950 too rich at cruise
[Re: carnut68]
#2846739
11/15/20 08:25 PM
11/15/20 08:25 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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West Plains, MO
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Dr C what holley 950 do you have? The 830 cfm version? That's what I have and it acts the same way. I finally settled on 70 iab, 28 hsb .081 on the T slot. .031 ifr down low. Its better not perfect. What I need is more idle timing. Without locking out the dis. 34 total 24 initial. Sorry, didn't see your question. I don't know exactly, it's a "hybrid" (QFT/Proform 950 body with 1.42" venturis, QFT baseplate with 1-3/4" butterflies, billet metering blocks, Holley Ultra HP fuel bowls). The key seems to be a small enough IFR and a very small MAB (hsb). I have 16 cranking 27 initial 36 total, plus a vacuum advance hooked up to manifold vacuum (these blocks and baseplate don't have vacuum nipples at all). But 8" Hg at idle is not enough to provide any advance there. It could use more at idle (1200 rpm).
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Re: 950 too rich at cruise
[Re: DrCharles]
#2846984
11/16/20 12:09 PM
11/16/20 12:09 PM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
I Live Here
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I Live Here
Joined: Jul 2004
Posts: 19,318
State of confusion
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I'd ditch the vacuum advance myself cos like vacuum secondary carbs, they don't belong on a performance engine imo ever......
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: 950 too rich at cruise
[Re: Thumperdart]
#2848748
11/19/20 05:22 PM
11/19/20 05:22 PM
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Joined: Apr 2006
Posts: 4,220
West Plains, MO
DrCharles
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West Plains, MO
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I'd ditch the vacuum advance myself cos like vacuum secondary carbs, they don't belong on a performance engine imo ever...... A performance engine that also does street duty can benefit though At WOT there's no advance anyway... So, since last post I leaned the PMJ slightly, reduced the PMAB a hair, and also lowered the floats in both bowls 3 flats (half a turn on the nut). Finally got a chance to take it out for a run this afternoon. I warmed it up enough to idle while trying to determine the exact source of a right front corner oil leak, drove 15 min to town (2 mi slow back roads/6 mi 60+ mph), filled back up on oxygen-free premium, idled through the automatic car wash and 15 min back home). Current tune pri/sec: ------------------------ IFR .028/.028 IAB .078/.079 TSR .074/.074 MAB .026/.030 MJ 72/86 PV 9.5" PVCR .059 I'm getting close. Low speed cruise (below 2000) is around 15-16. 60 mph (15"Hg.) is 14-14.5, not too bad. 50-60 mph gentle acceleration (10") doesn't change much. Brisk acceleration (5") with PV open, about 13. With the primaries open at the secondary linkage start, it's in the high 12's. Looks like one more jet size to #71 might do it! I tried one brief blast with all four barrels open from 3000 to 4200 rpm (man, did it get there quick even in 4th!) and managed to catch a peek at the AFR dropping below 12. So the #86 secondaries are too rich, not a huge surprise since I'd expect a .059 PVCR to provide about 10-11 jet sizes worth from #72. Will drop them 2 sizes on next test. The only remaining problem (at least until I have the nerve to run it up to 6000+) is the lean flat spot during transition. I don't have enough experience to know if it's late mains, early end of t-slot fuel, and don't want to cover it up with squirt until I've tried my best to tune it out. Frankly it doesn't bother me, I'll just push a little harder on the loud pedal and get past it!
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Re: 950 too rich at cruise
[Re: DrCharles]
#2848764
11/19/20 06:14 PM
11/19/20 06:14 PM
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Joined: Sep 2014
Posts: 4,457
Washington
madscientist
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master
Joined: Sep 2014
Posts: 4,457
Washington
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I'd ditch the vacuum advance myself cos like vacuum secondary carbs, they don't belong on a performance engine imo ever...... A performance engine that also does street duty can benefit though At WOT there's no advance anyway... So, since last post I leaned the PMJ slightly, reduced the PMAB a hair, and also lowered the floats in both bowls 3 flats (half a turn on the nut). Finally got a chance to take it out for a run this afternoon. I warmed it up enough to idle while trying to determine the exact source of a right front corner oil leak, drove 15 min to town (2 mi slow back roads/6 mi 60+ mph), filled back up on oxygen-free premium, idled through the automatic car wash and 15 min back home). Current tune pri/sec: ------------------------ IFR .028/.028 IAB .078/.079 TSR .074/.074 MAB .026/.030 MJ 72/86 PV 9.5" PVCR .059 I'm getting close. Low speed cruise (below 2000) is around 15-16. 60 mph (15"Hg.) is 14-14.5, not too bad. 50-60 mph gentle acceleration (10") doesn't change much. Brisk acceleration (5") with PV open, about 13. With the primaries open at the secondary linkage start, it's in the high 12's. Looks like one more jet size to #71 might do it! I tried one brief blast with all four barrels open from 3000 to 4200 rpm (man, did it get there quick even in 4th!) and managed to catch a peek at the AFR dropping below 12. So the #86 secondaries are too rich, not a huge surprise since I'd expect a .059 PVCR to provide about 10-11 jet sizes worth from #72. Will drop them 2 sizes on next test. The only remaining problem (at least until I have the nerve to run it up to 6000+) is the lean flat spot during transition. I don't have enough experience to know if it's late mains, early end of t-slot fuel, and don't want to cover it up with squirt until I've tried my best to tune it out. Frankly it doesn't bother me, I'll just push a little harder on the loud pedal and get past it! Nice!!!!!!!
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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