Fine Tuning a 360 Magnum with a Brawler "Double Pumper"

[jmanhoff]

I just checked it about an hour ago. Unhooked the throttle cable so there was nothing touching the throttle other than the return spring. If I lightly open the throttle and then slowly let it go back down (like I would just driving normally down the road for example) it sticks slightly open, increasing idle by about 150rpm. If I touch the linkage and push it back so its touching the adjustment screw it idles as normal. It does the same if I let the throttle snap closed like blipping the throttle. I did also check to make sure the accelerator pump wasn't binding on the cable bracket or anything, no interference.

Could that just be a tuning issue? If so what would said issue likely be?

 

[Hysteric]

Look to see if the throttle plates are rubbing against the side of the bores

 

[Mattax]

Yeah I’ve just been poking around with random things to see if I can get it dialed in again.

I'll say the same as three other guys said. Stop. Write everything down and approach this systematically.
These carbs (I'm including carters, Rochesters and most of the downdraft 4bbls we deal with) have a low speed circuit that is feed from the main or high speed circuit. Get the low speed established first, beginning with idle. The low speed or idle circuit works off of the pressure difference (vacuum) below the throttle plates. It is most effective with high vaccum in providing good distribution. It is by its nature somewhat slow to respond to changes. Get the idle and then off idle established so it works with slow throttle opening. Then use the accelerator pump tuning to assist with fast opening.
You can 'get away' with being off a bit more with a manual transmission because you control the clutch directly.
Anyway. Timing is first. Then carb. With carb, start with fuel level, then initial throttle position. Adjust fuel mixture next. This is all an iterative procseess - hence the need for written notes and one change at a time. Use small adjustments in timing to adjust rpm as needed to keep the primary throttles in their operating range at idle. Then work on off-idle.

Holley (and their variants) say to set the pump arm with a .010" gap. I've never done that. I set it at what I call a "light zero". In other words, I make sure the pump arm isn't depressing the pump diaphragm arm at all, but there's no clearance, either. This way, the pump starts to work as soon as the throttle is moved.

Yep yep yep.
I think its in one of Urich's books he mentions the 0.010" is the check at wide open thottle; and its not free play but that a feeler gage can be forced in between and the spring will compress (insuring the lever won't bottom out and damage something with our foot to the floor).

Jmanhoff. Sorry i thought it was this thread I mentioned that, but it was actually this one

Holley 750 "stumbles" on WOT

Hello All, I purchased a nice used carb from a fella a while back. It was on his 68 RR, 440 auto. The facts are these : Worked perfectly when new, but over time when stomping it to the floor from a dead stop, it would hesitate for about 1 or 2 seconds then WAHHHHHH He replaced it with an...

www.forabodiesonly.com

Is there any good write ups or maybe videos that go into detail about all the little parts of a carb that would be a good place to start looking? It seems like YouTube is flooded with the basic stuff and not the internals as much.

IMO youtube is flooded by self proclaimed experts in many fields but carb science and mechanical stuff in general suffer so badly I don't bother looking there. Sure its fine if you want to find a video of things like a restored up-down vertical saw mill in operation - especially if you know the name of the place, but otherwise there is a lot of chaff for the amount of wheat.

Basics: Used copy of Urich and Fisher for a good explanation of the carb circuits.
Alternatively (or additionally): Chrysler's Master Tech series as several books about Carb fundementals.
look 'em up here Master Technician Service Conference - Chrysler's Training for Mechanics
and if you prefer pdf format go to the www.mymopar.com to download and/or watch.

As far as understanding and mapping out the idle restritions, air bleeds, etc, yea sure do a search here.
A lot of what I posted will have links back to posts or threads by "Tuner" and "jmarkaudio" and "Shrinker" on other boards like racingfuelsystems. Those guys got their info through years of experience as well as reading real books on the subject - the type of books and papers engineers learned from and referenced when carbs were king and fuel injection was mechanical.

 

[Mattax]

I just checked it about an hour ago. Unhooked the throttle cable so there was nothing touching the throttle other than the return spring. If I lightly open the throttle and then slowly let it go back down (like I would just driving normally down the road for example) it sticks slightly open, increasing idle by about 150rpm. If I touch the linkage and push it back so its touching the adjustment screw it idles as normal. It does the same if I let the throttle snap closed like blipping the throttle. I did also check to make sure the accelerator pump wasn't binding on the cable bracket or anything, no interference.

Could that just be a tuning issue? If so what would said issue likely be?

if that's all it is, I would think even a single return spring should close it. But that does seem to confirm its mechanical.
Double return springs are mandatory by a lot of sanctioning bodies.
Having had a throttle cable fray and stick (on a public highway no less!) I can understand the requirement.

 

[jmanhoff]

I'll say the same as three other guys said. Stop. Write everything down and approach this systematically.
These carbs (I'm including carters, Rochesters and most of the downdraft 4bbls we deal with) have a low speed circuit that is feed from the main or high speed circuit. Get the low speed established first, beginning with idle. The low speed or idle circuit works off of the pressure difference (vacuum) below the throttle plates. It is most effective with high vaccum in providing good distribution. It is by its nature somewhat slow to respond to changes. Get the idle and then off idle established so it works with slow throttle opening. Then use the accelerator pump tuning to assist with fast opening.
You can 'get away' with being off a bit more with a manual transmission because you control the clutch directly.
Anyway. Timing is first. Then carb. With carb, start with fuel level, then initial throttle position. Adjust fuel mixture nect. This is all an iterative procseess - hence the need for written notes and one change at a time. Use small adjustments in timing to adjust rpm as needed to keep the primary throttles in their operating range at idle. The work on off-idle.



Yep yep yep.
I think its in one of Urich's books he mentions the 0.010" is the check at wide open thottle; and its not free play but that a feeler gage can be forced in between anbd the spring will compress (insuring the lever won't bottom out and damage something with our foot to the floor).

Jmanhoff. Sorry i thought it was this thread I mentioned that, but it was actually this one

http://[URL]https://www.forabodieso...ey-750-stumbles-on-wot.575305/post-1974937100

[/URL]


IMO youtube is flooded by self proclaimed experts in many fields but carb science and mechanical stuff in general suffer so badly I don't bother looking there. Sure its fine if you want to find a video of things like a restored up-down vertical saw mill in operation - especially if you know the name of the place, but otherwise there is a lot of chaff for the amount of wheat.

Basics: Used copy of Urich and Fisher for a good explanation of the carb circuits.
Alternatively (or additionally): Chrysler's Master Tech series as several books about Carb fundementals.
look 'em up here Master Technician Service Conference - Chrysler's Training for Mechanics
and if you prefer pdf format go to the www.mymopar.com to download and/or watch.

As far as understanding and mapping out the idle restritions, air bleeds, etc, yea sure do a search here.
A lot of what I posted will have links back to posts or threads by "Tuner" and "jmarkaudio" and "Shrinker" on other boards like racingfuelsystems. Those guys got their info through years of experience as well as reading real books on the subject - the type of books and papers engineers learned from and referenced when carbs were king and fuel injection was mechanical.

Thanks for this info Mattax, I'll take a look at that post and start from there. Fortunately my dad was a gearhead around the same age I am back in the day, and he probably owned a car with every Mopar V8 family at some point, unfortunately, I don't think he ever dove deeper than jets and timing, so I had a foundation but I'm missing the building blocks so to speak. I guess I'll add reading a bunch of articles, books, etc to get more into the complex carb stuff.

 

[jmanhoff]

if that's all it is, I would think even a single return spring should close it. But that does seem to confirm its mechanical.
Double return springs are mandatory by a lot of sanctioning bodies.
Having had a throttle cable fray and stick (on a public highway no less!) I can understand the requirement.

Yeah, I had the opposite happen with my old throttle cable where it fell down onto the header and melted the shielding and the cable just pushed itself out and all of the pedal throw minus maybe a quarter of an inch was just bending the cable. Had to limp into a parking lot with maybe 10% throttle when my foot was to the floor lol.

In terms of what some have stated, how do I see if the plates are rubbing on the bores? Or is it literally as simple as just looking over the top of the carb and visually looking for it?

 

[crackedback]

Carb should not hang up when you snap the throttle. Figure out why it isn't coming back to the idle speed adjustment screw.

Look on the other side for small linkage parts interfering with the manifold, etc.

 

[Mattax]

here's a few on some of the topics

small drill bits will do if you don't have a pin gage set.

Looking for a little advice on the timing numbers I just pulled from my 73’ Duster (backfire issue)

The best answer will require knowing the timing vs. rpm. For example, you set timing at 5* at 750 rpm What was timing at 900 or 1000 rpm, 1400 rpm etc.? My guess is the throttle was too far open,, so when the vacuum advance was reconnected, it added timing and the idle rpm floated up. (Just...

www.forabodiesonly.com

racingfuelsystems-Relocating the Holley Idle Jet

In the original Holley carbs the idle feed was located at the bottom and for good reason. NACA paper 49 states in one of the conclusions: "Submerged m

www.tapatalk.com

racingfuelsystems-Emulsion Tuning

Mark, just wondering if you could give a brief run down on what we are trying to achieve, and what the effects are, of tuning/changing the emulsion bl

www.tapatalk.com

if all else fails and you have to use TSRs or shorten the slots

Lean idle. Rich cruise.

@Newbomb Turk Are you suggesting T slot restrictors in the front and/or back? I run a 4 corrner Demon DP. Thanks Yes

www.forabodiesonly.com

But don't start there unless the measurements are really wacked and low speed stuff can't be tuned with normal adjusments.

Carb tuning, larger accelerator pump nozzle?

Hello All, so I finally got my GTS on the road and I'm now able to tune it. Been reading and playing with the carb (Quick Fuel 650 SS, Mech Secondary) and had a really bad lean stumble just coming off the clutch. The slower the leaner then it would catch up (I have a wide band o2). Installed 67...

www.forabodiesonly.com

Make spread sheet or in a word processor listing all of the variables as found.
I also include the variables that get adjusted such as turns out on the mix screws, and idle stop.
So one sheet or one column on the spreadsheet is the factory setup or whatever baseline you want.
Then note every change and have a method to evaluate its effect.
Such as idle speed, how well it handled slipping into first, any issues when slowly opening throttles (by hand) in neutral. If there are issues or its astep backward, then make another change. If it seems OK, try a low speed test drive.
Focus on steady state conditions because they are the baseline.

here's the approach I suggest for tuning any non-stock build
Tuning for Performance.

Here's a blank example of the spreadsheet I use. Not all of it is important but its good to a complete list. Sometimes its handy to know what otherwise seemed unimportant like the numbers on a metering block.

 

[MOPAROFFICIAL]

Alright well that’s a start lol. I guess I’ll have to order a throttle cable kit and flip the carb around. Do you guys think it would be worth getting a manual choke? I know those aren’t reversible once installed. At least from what I can tell with the lead ball.

Skipping readimg the previous posts, put the largest power valve, I believe it's 10.5, because your vacuum is way up there and I would like to see the timing maybe closer to 18 if you can get it there as in.. if it will still fire up when fully warmed up with 18 initial. I wouldn't have gone up bigger in the shooter, more than likely you need to change pump cam. You may try the orange or you may try the red and with each one you can try the first and second settings/positions. 35 is the largest i could imagine you would need.. but i kinda think the 31 should work.
I like what you did with leaning the jets till it surged at cruise and then back up 2 sizes. I wouldn't mess with the secondary jetting from out of the box however.
when you see the results on the primary.. move to dialing in the secondary opening
I believe the yellow spring might fit the bill.
Otherwise, you seem on the right track.
The pv is opening late, and you're compensating with that bigger shooter. is my opinion.

 

[TT5.9mag]

here's a few on some of the topics

small drill bits will do if you don't have a pin gage set.

http://[URL]https://www.forabodieso...-duster-backfire-issue.545100/post-1974388896

[/URL]

http://[URL]https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?f=31&t=18

[/URL]

http://[URL]https://www.tapatalk.com/groups/racingfuelsystems/emulsion-tuning-t42.html

[/URL]

if all else fails and you have to use TSRs or shorten the slots

http://[URL]https://www.forabodieso.../lean-idle-rich-cruise.560447/post-1974694861

[/URL]

But don't start there unless the measurements are really wacked and low speed stuff can't be tuned with normal adjusments.

http://[URL]https://www.forabodieso...ccelerator-pump-nozzle.492113/post-1973469374

[/URL]

Make spread sheet or in a word processor listing all of the variables as found.
I also include the variables that get adjusted such as turns out on the mix screws, and idle stop.
So one sheet or one column on the spreadsheet is the factory setup or whatever baseline you want.
Then note every and have a method to evaluate its effect.
Such as idle speed, how well it handled slipping into first, any issues when slowly opening throttles (by hand) in neutral. If there are issues or its astep backward, then make another change. If it seems OK, try a low speed test drive.
Focus on steady state conditions because they are the baseline.



Here's a blank example of the spreadsheet I use. Not all of it is important but its good to a complete list. Sometimes its handy to know what otherwise seemed unimportant like the numbers on a metering block.
View attachment 1716362757

See what I mean? This is an excellent post, not to discredit any of the other posts you made with excellent information in them, as there are more than a few. By not posting here you are doing this board a disservice. Thank you @Mattax for your contribution.

 

[Mattax]

See what I mean? This is an excellent post, not to discredit any of the other posts you made with excellent information in them, as there are more than a few. By not posting here you are doing this board a disservice. Thank you @Mattax for your contribution.

Thanks. But its now 7 oclock and I haven't started dinner or done my travel expenses and bills....
That and the fact that this board crashes my desktop computer - somethng to do withthe video adapter I think - is part of why I'm not posting here as much.

 

[TT5.9mag]

Thanks. But its now 7 oclock and I haven't started dinner or done my travel expenses and bills....
That and the fact that this board crashes my desktop computer - somethng to do withthe video adapter I think - is part of why I'm not posting here as much.

Well crap, go eat. Get the bills payed and relax a bit. You’ve done your good deed for the day.

 

[Slantsix64]

With that that combo I would suggest a vacuum secondary street warrior 600cfm 66/72 jets 10.5 PV 31 nozzle adjustable secondary pod, and rear jet plate.

More forgiving on that combo.

 

[jmanhoff]

Skipping the previous post, put the largest power valve, I believe it's 10.5, because your vacuum is way up there and I would like to see the timing maybe closer to 18 if you can get it there as in.. if it will still fire up when fully warmed up with 18 initial. I wouldn't have gone up bigger in the shooter, more than likely you need to change pump cam. You may try the orange or you may try the red and with each one you can try the first and second settings/positions. 35 is the largest i could imagine you would need.. but i kinda think the 31 should work.
I like what you did with leaning the jets till it surged at cruise and then back up 2 sizes. I wouldn't mess with the secondary jetting from out of the box however.
when you see the results on the primary.. move to dialing in the secondary opening
I believe the yellow spring might fit the bill.
Otherwise, you seem on the right track.
The pv is opening late, and you're compensating with that bigger shooter. is my opinion.

I need to check the timing once again but I am probably going to suck it up and run higher than 87 octane whenever I can, so I can probably get away with more timing. Right now I think its about 15. I do have a 9.5PV in it, switched from the 6.5 that came in it.

With that that combo I would suggest a vacuum secondary street warrior 600cfm 66/72 jets 10.5 PV 31 nozzle adjustable secondary pod, and rear jet plate.

More forgiving on that combo.

I was looking at vacuum secondaries but from what I've read about what people say who have them they're more well suited for an automatic than a manual, and I would be opening the secondaries a lot running the manual, especially with how numerically low my gearing is.

My current setup is the 35 squirter, ~15 degrees timing, 66 primary jets, 71 secondary, stock pump cam on setting 2, 9.5PV (biggest I could order easily at the time) everything else on the carb is as it came stock. I did decide on the 9.5PV as when I was driving I watched a vacuum gauge and slowly got more onto the throttle in 4th gear until I felt it starting to struggle and it happened to be right in the 8-10Hg mark, hence the 9.5.

 

[Slantsix64]

I need to check the timing once again but I am probably going to suck it up and run higher than 87 octane whenever I can, so I can probably get away with more timing. Right now I think its about 15. I do have a 9.5PV in it, switched from the 6.5 that came in it.


I was looking at vacuum secondaries but from what I've read about what people say who have them they're more well suited for an automatic than a manual, and I would be opening the secondaries a lot running the manual, especially with how numerically low my gearing is.

My current setup is the 35 squirter, ~15 degrees timing, 66 primary jets, 71 secondary, stock pump cam on setting 2, 9.5PV (biggest I could order easily at the time) everything else on the carb is as it came stock. I did decide on the 9.5PV as when I was driving I watched a vacuum gauge and slowly got more onto the throttle in 4th gear until I felt it starting to struggle and it happened to be right in the 8-10Hg mark, hence the 9.5.

Hmm if you have a bog at Wot try a 4.5 power valve for the secondary block so it gets a dump of fuel later on during the throttle opening vacuum drop.

keep that 9.5 for the primary I think a 10.5 pv for the primary would be perfect. Also 31 primary squirter and a 28 for the rear.

She sounds like she’s getting too much fuel dumped at once secondary timing is key for the double pumpers.

 

[jmanhoff]

Hmm if you have a bog at Wot try a 4.5 power valve for the secondary block so it gets a dump of fuel later on during the throttle opening vacuum drop.

keep that 9.5 for the primary I think a 10.5 pv for the primary would be perfect. Also 31 primary squirter and a 28 for the rear.

She sounds like she’s getting too much fuel dumped at once secondary timing is key for the double pumpers.

I'll see if I can find a 10.5PV somewhere I think I tried ordering during a weird shortage period. IIRC, the secondary metering block on this carb doesn't have a PV port so I would need to buy a new block for it.

I am getting my new exhaust put on Monday meaning I will have ports for o2 sensors to run a wideband and I'm assuming that will tell me whether or not I'm having a lean or rich issue from the squirters? I also think it will help me tune the fuel more. I know people say that you should tune an engine off of what it likes, not an AFR number, which I believe and I have been doing, but I'd imagine I can use the gauge and blip the throttle and watch to see if it jumps up or down to figure out if its rich or lean.

 

[Mattax]

Nope

 

[RustyRatRod]

All the way to 18.5 and they work with gas just fine.

Holley Power Valves, High Flow, Alcohol

Holley Power Valves, High Flow, Alcohol Fuel System Single–Stage Power Valve High Flow

jetracinginc.com

 

[Mattax]

Shouldn't be needed for a mild Magnum in a light truck.

As far as the idle rpm, maybe somehting to do with the choke since that was a problem on page 1. Had no pull off on start up.

 

[RustyRatRod]

Shouldn't be needed for a mild Magnum in a light truck.

As far as the idle rpm, maybe somehting to do with the choke since that was a problem on page 1. Had no pull off on start up.

You'd think not, but..... LOL

 

[jmanhoff]

Nope

What’s the nope in reference to lol

 

[Newbomb Turk]

What’s the nope in reference to lol

Blipping the throttle and watching the gauge.

Learn to read plugs.

 

[jmanhoff]

Blipping the throttle and watching the gauge.

Learn to read plugs.

Gotcha gotcha

 

[Mattax]

Widebands can be useful but not for what you imagine.
Even if it was showing what was happening in the intake and combustion chambers - which its not -its reading 02 in the exhaust - its happening so fast that I don't beleive you can actually read it. And then I wouldn't beleive what it said anyway. Plenty of posts on WBO2 and loggers. Same actually showing what they can and can't do.

 

[jmanhoff]

Sounds good, so in terms of reading the plugs how do I differentiate between running rich and a rich squirt?