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

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Mattax said:
Or better yet, take a look at some of the timing tables for late 360s with more efficient heads.
With more efficiency and more load (truck), less timing should be needed.
Only difference with carbs is the need for reducing HC and CO at idle is less a concern. No need to run 14 AFR idle mixes. So again less timing will be needed.
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Lok at post #8, and there's more in that thread further down.

Need some help with my timing curve.

So after running an eBay Ready-to-Run Hei distributor for the past 5-6 years, I finally got around to putting a timing light on it and mapping out the advance curve. Come to find out, the curve was severely lacking! I ended up swapping out that distributor with a factory electronic distributor...
www.forabodiesonly.com

looking at the table
690 - 780 torr is atmospheric, so nearly to fully wide open throttle The timing in those columns is equal to the mechanical advance.
111 torr is very high vacuum, so idle and decel.
296 torr is part throttle with moderate load.

My take away is that engine could run a lean idle with as much as 17* initial, and rich idle as low as 10*. With a distributor, if you can split the difference, it should be OK. You'll have to keep iterating timing, throttle position, and fine mix screws until its where you are satisfied.
it also looks like it should be good with about 12 degrees of vac advance. You'll have to do the conversions from torr to relative vacuum to see when vac advance should go away (and enrichment begins) under load.
Read everything @TT5.9mag posted in there.
 
Okay so another update. I still need to graph my timing curve but I’d need to do it at night because my timing light is so dim I can barely see it during the day. I have for the most part figured out the stumble, opening the curb idle more has helped, though it does diesel but I may have remedied it by richening the mixture slightly (not sure if this is proper, but it works).

I had a sort of unrelated question. The ticking I have seems to be a pushrod length issue. I followed what people said on another forum, use the stock pushrod length with my cam (I even bought a length checker and didn’t use it on the stand, stupid I know). But I believe the issue is my pushrods are too short. I popped the valve covers off to retorque all of the rockers (HS 1.6 non adjustable) and they were relatively loose but not an insane amount, and to my ears it sounds quieter but could just be placebo. I am able to spin the pushrods relatively easily as well when the valves are closed, which leads me to my question.

With non adjustable rockers, how does one calculate preload? Do I just use the adjustable checker until it has resistance spinning then measure and add the amount of preload I want?
 
Another update now, I’ve flipped the carb around the proper orientation and now for whatever reason I can’t get rid of a stumble. I had it setup last night before I flipped it where I had crisp throttle and no bog. Flipped it and didn’t change the setup at all and it’s super bad and I’ve been tweaking everything and can’t seem to get it to be better.
 
jmanhoff said:
Another update now, I’ve flipped the carb around the proper orientation and now for whatever reason I can’t get rid of a stumble. I had it setup last night before I flipped it where I had crisp throttle and no bog. Flipped it and didn’t change the setup at all and it’s super bad and I’ve been tweaking everything and can’t seem to get it to be better.
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Since you’ve been tuning on it, please post up the tune up.

That includes the size and location of the emulsion, the size of the power valve channel restrictors, your timing curve and plug and heat range.
 
Everything is still the same internally, only changes were external. Timing is 13 initial, I have the accel pump cam on hole 2 as it liked it better before, 0.015 gap on the pump linkage. I have it a setup for the best rich idle and idles around 850.
 
jmanhoff said:
Everything is still the same internally, only changes were external. Timing is 13 initial, I have the accel pump cam on hole 2 as it liked it better before, 0.015 gap on the pump linkage. I have it a setup for the best rich idle and idles around 850.
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Ok


Edit: I just went through this thread and not once did you post your emulsion or anything else that matters.

Until you understate you can’t tune a carb until you unfuck it first you will struggle.

You can’t fix what you want until you measure ALL the bleeds and put them in the correct location.

You can’t fix turn screws, change pump cams and nozzles until you are blue in the face and you won’t fix it.

First things first. Move the idle feed restricters to the bottom of the well. If you don’t do that you are hobbling yourself.
 
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jmanhoff said:
Everything is still the same internally, only changes were external. Timing is 13 initial, I have the accel pump cam on hole 2 as it liked it better before, 0.015 gap on the pump linkage. I have it a setup for the best rich idle and idles around 850.
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Why a gap on the pump linkage? You want the pump shot to be part of the throttle movement without delay. You have to make sure there is no binding at WOT but other than that, you want that pump shot to start when you open the throttle. No delay.
 
Demonx2 said:
Why a gap on the pump linkage? You want the pump shot to be part of the throttle movement without delay. You have to make sure there is no binding at WOT but other than that, you want that pump shot to start when you open the throttle. No delay.
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Yeah I’ve just been poking around with random things to see if I can get it dialed in again. The arm is contacting the plunger it’s just not pressing down on it I’m assuming that’s the whole point behind the feeler gauge check. I did richen up the idle mixture slightly and it seems to be getting better in the sense that when I’m driving around it doesn’t fall on its face, but it still has a bad stumble when I blip the throttle, being at idle or when I’m downshifting for example. For a second it actually sounds like the exhaust goes silent.
 
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.
 
Newbomb Turk said:
Ok


Edit: I just went through this thread and not once did you post your emulsion or anything else that matters.

Until you understate you can’t tune a carb until you unfuck it first you will struggle.

You can’t fix what you want until you measure ALL the bleeds and put them in the correct location.

You can’t fix turn screws, change pump cams and nozzles until you are blue in the face and you won’t fix it.

First things first. Move the idle feed restricters to the bottom of the well. If you don’t do that you are hobbling yourself.
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You can say it till you’re blue in the face, repeat it on multiple carb threads, scream it from the fuckin mountain tops, and people still won’t listen. Your post should be a sticky.

@jmanhoff you can’t fix the carb by turnin screws on the linkage and changing jets. If you’re really interested in making a carb work properly on a vehicle that actually is driven then you need to dive in and get dirty on em. That starts by pinning every hole and writing down what you have. Then moving stuff (idle feed) to the correct location, then drilling and tapping to make everything adjustable, then making changes AND having a way to quantify the change.
 
TT5.9mag said:
You can say it till you’re blue in the face, repeat it on multiple carb threads, scream it from the fuckin mountain tops, and people still won’t listen. Your post should be a sticky.

@jmanhoff you can’t fix the carb by turnin screws on the linkage and changing jets. If you’re really interested in making a carb work properly on a vehicle that actually is driven then you need to dive in and get dirty on em. That starts by pinning every hole and writing down what you have. Then moving stuff (idle feed) to the correct location, then drilling and tapping to make everything adjustable, then making changes AND having a way to quantify the change.
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Yes...

They had a really nice set up in the first generation 3310 dual metering block carbs. The 3 emulsion package was good. Then some genius thought if three is good, five is better! It became a race of monkey see monkey do on who could screw up stuff the quickest. Less is more in this case.

Why holley didn't move the IFR down low after how many years? Lazy, shitty approach to providing the customer with a better, refined product. Been doing that change for 30 years, but the big multi million$ company can't find the time to do it on a mass production scale? OK. DP carbs have always been somewhat pig rich everywhere except WOT. The universal carbs seemed to get the same treatment 1850/3310/etc. At least it kept me busy for years!
 
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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.
 
jmanhoff said:
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.
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Search this forum. Lots of smart guys like TT5.9mag and Mattax have posted an incredible amount of information right here. You just have to search for it.
 
Guess I’ll add a pin gauge kit to my shopping list. Should I just bite the bullet and buy one of those tuning kits from Holley that has all the jets and valves and what not?
 
RustyRatRod said:
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.
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Absolutely correct! You want the FULL travel of the pump arm so you don't want it depressed at all when the throttle is closed. If it is partially depressed, you have "wasted" part of the pump stroke. But the moment you do open the throttle, you want to see the squirters squirting immediately. You have to add fuel to get a combustible mixture to the cylinders when the manifold pressure suddenly increases. It is simple physics at that point!

There used to be a video around that was filmed in the 60's of an intake manifold on a dyno engine that was using purple-tinted fuel. At light load, the manifold had wisps of purple fuel in it. As the load increased (holding rpm constant), the manifold becomes more purple. At WOT, the manifold is almost pure purple.

So when you open the throttle and increase the manifold pressure, where do you think the additional fuel carried on the manifold walls comes from? Either you supply the extra fuel through some means (pump shot!), or it comes from the normal steady-state fuel delivered from the idle/transfer slots, and then venturies. If you get it from the latter and don't supply it yourself, the physics wins and the manifold walls take the fuel until it reaches its equilibrium while the cylinders starve and you have the big hesitation. Again, simple physics that will always win out!
 
Yeah that makes a lot of sense. Out of pure curiosity is the reason a carb will “sneeze” on a lean condition because the lean mixture takes so long to burn that there is still combustion happening in a cylinder when the intake valve opens again? I’ve been trying to figure that out I’m not sure why lol
 
Does anyone have any possibilities for a sticking throttle at idle? Occasionally my throttle will stick ever so slightly open at idle causing it to idle up another 100-200rpm or so, and it’s slowly getting worse with how much it happens. If I manually open the throttle it returns to normal.

I have plenty of slack in the cable and 2 return springs and it still sticks from the pedal. If I put my foot behind the pedal and push it toward me it closes fully I’m assuming I’m pushing the cable into the linkage closing it.

I’ve read that it could be the secondaries being open too much forcing the primaries to open or a worn out bushing but my mind says neither of those would be the case if I haven’t ever touched the secondary adjustment and it’s only a 6 month old carb?
 
jmanhoff said:
Does anyone have any possibilities for a sticking throttle at idle? Occasionally my throttle will stick ever so slightly open at idle causing it to idle up another 100-200rpm or so, and it’s slowly getting worse with how much it happens. If I manually open the throttle it returns to normal.

I have plenty of slack in the cable and 2 return springs and it still sticks from the pedal. If I put my foot behind the pedal and push it toward me it closes fully I’m assuming I’m pushing the cable into the linkage closing it.

I’ve read that it could be the secondaries being open too much forcing the primaries to open or a worn out bushing but my mind says neither of those would be the case if I haven’t ever touched the secondary adjustment and it’s only a 6 month old carb?
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I would say it’s very likely not something to do with the carb. It’s in the linkage, cable, bracketry, pedal, or kickdown stuff. Easy to diagnose, just unhook everything for now while you’re tuning on it and see.

Disclaimer;
I did not say to drive it without kickdown linkage or throttle control.
:thumbsup:
 
TT5.9mag said:
I would say it’s very likely not something to do with the carb. It’s in the linkage, cable, bracketry, pedal, or kickdown stuff. Easy to diagnose, just unhook everything for now while you’re tuning on it and see.

Disclaimer;
I did not say to drive it without kickdown linkage or throttle control.
:thumbsup:
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I’ll have to see, the only linkage I have is for the throttle and it’s directly connected to the pedal. Manual trans so no kickdown and no cruise control. It did it with both the new cable and the original throttle cable when I had the carb flipped around as well.
 
jmanhoff said:
I’ll have to see, the only linkage I have is for the throttle and it’s directly connected to the pedal. Manual trans so no kickdown and no cruise control. It did it with both the new cable and the original throttle cable when I had the carb flipped around as well.
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Interesting, maybe it is the carb. But it’s pretty easy to find out.
 
Yeah I might try to adjust the spring bracket so there’s slightly more tension on the springs but I don’t want to have a super heavy pedal either so guess I have to experiment
 
jmanhoff said:
Yeah I might try to adjust the spring bracket so there’s slightly more tension on the springs but I don’t want to have a super heavy pedal either so guess I have to experiment
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Be careful. The carb has a return spring on both throttle shafts.

Any other spring you hang on there is just for safety. Too much spring and you’ll bend the throttle shafts.

Take the carb apart and make sure the throttle blades are fitted correctly in the bores.

You’d be surprised how many are not,
 
Doesn't make sense as I read it.
Its 'sticking' and the rpm is floating up ?
Do you mean the primary throttles are not closing to the idle stop position?
In which case the rpm shouldn't float up, it should just not fully return to slow idle.

If the rpm does not come down (sort of floats) that's not the throttles. That's the setup, by which I mean the tuning.
 
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