mderoy340
Well-Known Member
Well those appear to have the E tubes in them.
Holley stumble trouble
- Thread starter SSG_Karg
- Start date
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SSG_Karg
Enhanced member
MAB - #72 bit (.024”)
IAB - .053“
This hole at bottom of main well .031”. (Idle jet)
IAB - .053“
This hole at bottom of main well .031”. (Idle jet)
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SSG_Karg
Enhanced member
Hole at top of dogleg is .027”
yellow rose
Overnight Sensation
Are the vertical holes in the e well drilled or blank?
SSG_Karg
Enhanced member
yellow rose
Overnight Sensation
Yep that’s what I was asking. That seems strange to me.
I’m going to post a couple of pictures of a metering block I have here that is very strange too.
I'm not a guy with a lot experience in removing the well plugs and e-tubes.
All I can say is look at some of the things Mike (GNTKLLR) found and discusses in this thread.
New and improved 1850...?
One of them is a block where the e-holes were drilled in one air well and not the other.
In post #6 he has a 11761 metering block with flat caps but no e-tubes...
All I can say is look at some of the things Mike (GNTKLLR) found and discusses in this thread.
New and improved 1850...?
One of them is a block where the e-holes were drilled in one air well and not the other.
In post #6 he has a 11761 metering block with flat caps but no e-tubes...
mderoy340
Well-Known Member
The two orifices that is out of whack to me is the .053 IAB and the .024 MAB.
The .024 MAB delays the primary start, a .026 or .028 is what I run with 2 hole emulsion blocks.
The .053 IAB is normally .070 or .073 with today's carbs. On a 650 or 750 I run a .033 IFR and .067 or .070 IAB.
I believe your issue is a combo of to lean on idle/transition and slightly delayed primary coming in at light throttle. When you continue getting in the throttle the signal increases and primary have full flow.
Threaded brass set screws are the way to go if you really want to dial in. 6/32 x 1/8 for IFR, EML, MAB. 8/32 x 1/8 for IAB, PVRC, TSR.
Today's pump gas contains ethanol and it takes more fuel to equal the same BTUs real gasoline produces. Old carbs were setup for pure gasoline.
The .024 MAB delays the primary start, a .026 or .028 is what I run with 2 hole emulsion blocks.
The .053 IAB is normally .070 or .073 with today's carbs. On a 650 or 750 I run a .033 IFR and .067 or .070 IAB.
I believe your issue is a combo of to lean on idle/transition and slightly delayed primary coming in at light throttle. When you continue getting in the throttle the signal increases and primary have full flow.
Threaded brass set screws are the way to go if you really want to dial in. 6/32 x 1/8 for IFR, EML, MAB. 8/32 x 1/8 for IAB, PVRC, TSR.
Today's pump gas contains ethanol and it takes more fuel to equal the same BTUs real gasoline produces. Old carbs were setup for pure gasoline.
yellow rose
Overnight Sensation
I agree with that but did you see the picture of his metering block? It has a weird kill bleed location and some other stuff I forget without looking at the picture again.
mderoy340
Well-Known Member
I've run a 600 1850 without E tubes 2x.028 EML with the same kill bleed location with no issues.
Read the discussion I linked to. Especially the discussion between Deep Roots and Tuner toward the end. This seems to be one of those situations where sometimes the kill bleed in the dogleg is just enough to really kill the start of the boosters and sometimes its not a problem at all.
When I get my car running, I'll be curious to see how well my 650 carb does with those dogleg holes now plugged.
I agree the IAB in particular seems very small. Maybe that's the secondary block??
Deeproots and Gntkllr posted a fair number of combos that should be good guidance for getting this into the ballpark. IIRC numbers are all in the same range as you (Mderoy) suggest.
Also in the same range as my 650 VS. I don't have 600 or 650 DP or I'd post that too.
So primary IFR is just over .033" and IAB is .073"
I decided to drill regular kill bleeds in both blocks. I'm not sure if the ones in the primary block will help or hurt. On secondary block that was specifically done as a siphon break.
The reason I've reduced the primary high speed air bleeds was because the AFR on the dyno was showing increasing need for correction corresponding to the reduction in jet sizes. Only when I take it to the track with a working logger will I know whether this was a move in the right direction, and if it was, whether it was sufficient, too much or too little.
When I get my car running, I'll be curious to see how well my 650 carb does with those dogleg holes now plugged.
I agree the IAB in particular seems very small. Maybe that's the secondary block??
Deeproots and Gntkllr posted a fair number of combos that should be good guidance for getting this into the ballpark. IIRC numbers are all in the same range as you (Mderoy) suggest.
Also in the same range as my 650 VS. I don't have 600 or 650 DP or I'd post that too.
So primary IFR is just over .033" and IAB is .073"
I decided to drill regular kill bleeds in both blocks. I'm not sure if the ones in the primary block will help or hurt. On secondary block that was specifically done as a siphon break.
The reason I've reduced the primary high speed air bleeds was because the AFR on the dyno was showing increasing need for correction corresponding to the reduction in jet sizes. Only when I take it to the track with a working logger will I know whether this was a move in the right direction, and if it was, whether it was sufficient, too much or too little.
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mderoy340
Well-Known Member
2x.027 and .026 or .028 MAB has always given me a flat fuel curve with a fuel delivery system that can feed the motor.
SSG_Karg
Enhanced member
^^^^This is what I’ve suspected the whole time. Question is, how to correct it? I’m not sure I’m interested in trying to drill out these tiny holes or press in new ones. Perhaps a replacement adjustable metering block is in order here. I briefly considered a ProForm main body but they do not come with blocks and there is no provision for a vacuum advance port if using my existing block.
Negative. It’s the primary. I’m gonna measure again to be sure but I was pretty careful the first time around.
yellow rose
Overnight Sensation
Don’t let drilling and tapping a few holes screw you up. You can do it.
I have a metering block that’s more whacked than yours, and when it cools off I’ll post a couple of pictures. Waiting to hear from Tuner. I suspect he’s pretty busy, but when he calls me back I’ll fill him in and see what he says.
He is a sharp guy.
mderoy340
Well-Known Member
I would drill the Primary MAB to .026, the IAB to .067, and the IFR to .033
Here's a good read for modifying and tuning. It's not rocket science, but is time consuming. You will also have a lot of folks looking at your tail lights.
Carb Tunning
Go make a sheet or table like I poisted or there's ones on Racing Fuel System as well.
Write everything down.
Since the mains started at different rpms, it wouldn't hurt to pin every bleed and restriction. One side could be different than the other.
Take out the jets and see if there are tubes. I'm betting not but......
My approach is normally the slow approach.
I'd do each of these seperately and take it for a drive.
* Plug those holes in the primary block's doglegs with fuel resistant epoxy - like for fuel tanks.
* Open the IAB's to something normal, but start on the small side - like .070
* MAB to .026
* IFR to .033, and then open the IAB a hair if needed
First one because I think it serves no purpose and is likely to be the root of the evit - assuming no e-tubes.
If there's e-tubes, then plug the eholes in the channel with some lead or a set screw.
Second because I agree this is an odd combo - maybe due to the holes in the doglegs but it aint doing the trick if that was the intent.
Third, if the above isn't doing it, then maybe the MAB is too small. .026 is not unreasonable.
Finally, if it really is running out of fuel in the idle circuit, then a larger IFR should keep it flowing to a higher rpm. A larger IAB may be needed to trim it to the same AFR as before.
yellow rose
Overnight Sensation
Here is what I’m working on.
This has an IAB of .082 and it doesn’t even look like it has any idle feed restriction. I pinned it at .080 but that can’t be right. And the upper bleed is .040 and the lower one is .028. Definitely has tube emulsion.
This has an IAB of .082 and it doesn’t even look like it has any idle feed restriction. I pinned it at .080 but that can’t be right. And the upper bleed is .040 and the lower one is .028. Definitely has tube emulsion.
You think it has IFRs in the idle up wells?
We talked about this - maybe even found a pic - certainly a description - from Tuner.
I'm I seeing holes in the dog legs and a bleed into the angle channel? I sure hope there's e-tubes in that case!
yellow rose
Overnight Sensation
If the IFR’s are up there, I can’t find them. It looks to have e tubes in them, but I want to run this past Tuner before I change anything.
Haven’t seen any follow up on what you ended up doing. What and from where did you source the pin drills. I’m not seeing much for drill sets in searches for sourcing the bits needed especially for the IFR’s.
mderoy340
Well-Known Member
Amazon and McMaster Carr have the small drill sets.
Locally you can try a hobby shop if you have one close by.
https://www.amazon.com/dp/B0916CQPQ3/?tag=fabo03-20
Come on man, tell us whether you got that off idle stumble taken care of and what you’ve done
Edit: Cat got your fingers huh?
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SSG_Karg
Enhanced member
Well, kind of. I disassembled the carb as far as I was comfortable doing and gave it a very thorough cleaning. Reassembled and tested without making any other changes and surprisingly the stumble was almost gone completely. It still had a little bit of a hiccup at very light throttle while cruising at steady speed on a slight downhill road. This is ONLY when the vacuum advance was connected. Everywhere else was good.Come on man, tell us whether you got that off idle stumble taken care of and what you’ve done
Edit: Cat got your fingers huh?
I believe if I would get into the distributor and limit the amount of advance pulled by vacuum it would totally eliminate the hiccup. Just haven’t done it yet. It’s almost not worth messing with it now. Maybe if I get bored this winter.
make sure, make sure that the PV is truly a good one (think you said it's a 10.5). I've had a late-opening PV cause the symptom you describe.
DrCharles
Well-Known Member
I was also wondering how the OP made out 
I have almost exactly the problem described in the initial post (lean stumble at very small throttle tip-in and low RPM), except I'm running a QF 950 and I have a wideband AFR meter. My cam is a .652" gross lift mushroom ([email protected]) and idles at 1100-1200, 8" vacuum, 13.5 AFR, in a 451 with RPM dual-plane. 27 deg idle timing, 35@4000, vac advance.
At the very beginning of tip-in, the AFR will jump to 17-18:1 and of course there is a huge sag. Opening the throttle just slightly moves past that point, the AFR drops to around 14. No slack in accelerator pump linkage.
After much tuning last fall/winter (see the multi-page thread on racingfuelsystems Holley forum "Dialing in my 950"), I have concluded that I'm asking the impossible to have economical cruise AFR, correct AFR at WOT, and perfect driveability below 1800 rpm with this much cam! I may have to either live with it, or cover it up with squirters/pump cams...
The unique problem with really big cams is that the idle vacuum is much less than cruise vacuum. 8" idle, 15" at 60 mph cruise in my case. I think there's no way to achieve perfect tuning with the vacuum going the "wrong way". Anyway I'm living with it ;)
I have almost exactly the problem described in the initial post (lean stumble at very small throttle tip-in and low RPM), except I'm running a QF 950 and I have a wideband AFR meter. My cam is a .652" gross lift mushroom ([email protected]) and idles at 1100-1200, 8" vacuum, 13.5 AFR, in a 451 with RPM dual-plane. 27 deg idle timing, 35@4000, vac advance.
At the very beginning of tip-in, the AFR will jump to 17-18:1 and of course there is a huge sag. Opening the throttle just slightly moves past that point, the AFR drops to around 14. No slack in accelerator pump linkage.
After much tuning last fall/winter (see the multi-page thread on racingfuelsystems Holley forum "Dialing in my 950"), I have concluded that I'm asking the impossible to have economical cruise AFR, correct AFR at WOT, and perfect driveability below 1800 rpm with this much cam!
I may have to either live with it, or cover it up with squirters/pump cams...The unique problem with really big cams is that the idle vacuum is much less than cruise vacuum. 8" idle, 15" at 60 mph cruise in my case. I think there's no way to achieve perfect tuning with the vacuum going the "wrong way". Anyway I'm living with it ;)
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