If it's dual exhaust, I highly recommend two.
Fine Tuning a 360 Magnum with a Brawler "Double Pumper"
- Thread starter jmanhoff
- Start date
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I plan to run 2 eventually but getting it close enough is really my goal for now since wide bands cost so much. Worst case I can set it up on one bank then swap banks and make sure the readings are the same and tune accordingly.
Yeah they ain't cheap.
Alright so I’ve been tinkering and seemingly am not really getting anywhere. If I have the idle exposing the t slot enough for it to not have a stumble, it diesels like crazy, but if I get it to where it doesn’t diesel it stumbles pretty bad still. Is there a secondary idle adjustment on the brawler carbs?
Where is your initial timing set?
13 degrees according to harbor freights cheaper dial back light. I went to the point where it would knock under a load and backed off 2 degrees. Vacuum advance is on manifold so it’s idling around 28? degrees.
It may not need manifold vacuum on the advance can. Not everything does.
It seems to be happier that way. On ported vacuum the idle is much lower and to keep it where I want it I need to open it so far that it diesels.
Try it on ported and pull in more initial timing.
Would it still not have the same result with pinging? I thought once the blades are open ported and full manifold are the same?
It also backfired a little through the carb at the same timing when on ported but I feel like that’s more of a pump shot issue?
Ok. Then leave it like it is.
What would my next step be into diagnosing this? I’m still not entirely sure how all of the air bleeds and other internals of carbs work.
I told you what my next step would be.
Ported with more initial timing?
That's what I would try. Maybe pull in about 16-18 with the vacuum hose disconnected and plugged. Then you will need to likely idle it down. THAT would probably stop the dieseling. If it continues to spark knock, then you know for sure you need to limit the mechanical advance in the distributor. That's what I would try anyway. It costs nothing and at the very best will solve the problem and the very worst will tell you the mechanical advance needs limiting. What's the down side?
Sounds like a plan, I’m sure more initial advance to begin with wouldn’t hurt anyway. I already have the spring kit so hopefully it’s pretty easy to limit the advance should I need to.
Is there really any idle I should shoot for or is that really more of I’m stuck with whatever the engine gets when the carb is setup right? I have a larger than stock cam like I said a couple pages back but it’s not really a big cam, I think comp considers it a towing cam for the 5.9.
Is there really any idle I should shoot for or is that really more of I’m stuck with whatever the engine gets when the carb is setup right? I have a larger than stock cam like I said a couple pages back but it’s not really a big cam, I think comp considers it a towing cam for the 5.9.
The spring has nothing to do with limiting the amount of advance, but only WHEN the advance comes in. You limit the advance by disassembling the distributor, welding up and then filing the distributor governor slots back out to a certain length, or by one of those fancy and very inaccurate FBO limiting plates. The distributor has to be disassembled either way, so I would just keep doing what you're doing. See how much initial the engine likes on ported vacuum and go from there.
STOP using manifold vacuum on the vacuum advance. You don’t need or want it.
That thing should run with 14-16 initial and 35 total at 5000 rpm.
What you can’t do is what you are doing, and that’s jamming a bunch of timing in it with manifold vacuum, and then setting the curve up super fast with some light springs. That’s bad.
You don’t have that much cam. Not even close.
Start over and lose the vacuum advance FOR NOW. Plug it off and tune from there.
I don’t know what YOU think an appropriate idle speed is but for what you have I’d say 850-900 rpm is where it should idle. Without any vacuum advance. Certainly no lower than 800 rpm.
Set your T slot exposure to where you have the slot exposure square. Then start the engine and set the timing to 15 initial and start tuning.
If you have to open the curb idle screw up a bit to get the idle speed to where you want it then do it. It’s not a crime if the T slot exposure isn’t square.
Unless the plugs are too hot or you have the coolant temperature too high it shouldn’t diesel.
Once you get the timing sorted out you can go back to tuning on the carb.
Once all that is done and you’re happy with the timing curve and carb tune you can hook the vacuum advance back up to PORTED vacuum and tune that up.
You may have to delay when the vacuum advance starts and how much timing it adds.
Alright lots of stuff to try. Going to attempt to brave the cold and get this stuff knocked out. This is probably a stupid question but I’d imagine I should do everything to AVOID closing the idle screw even if the idle is high? I need to leave the t slot exposed at least enough so it’s a square?
Do one thing at the time. Get the timing sorted first. Then you can come back and fine tune the carburetor. From what it sounds like, you at least have the carburetor where it will run fairly well, so leave it alone for now.
Alright. I definitely think it’s not coolant related when it comes to dieseling because my truck actually struggles to get up to temp lol. I have cardboard on the grill just to get it to actually warm up. It sits around 160 and doesn’t really get any hotter.
Stop the dieseling FIRST. Then tune from there. You can tune out the hesitation. Stop fixating on the t slot... Idle should be around 800 rpm with minimal drop in gear. If it clunkes into gear, look at the stuff from the converter back to rear end for why there is so much slack in the system.
There is a secondary idle adjuster. It's from the bottom on pass side. Where the little arm at the end of the throtte shaft hits the baseplate. Little trick.
Take a piece of notebook/writing paper, open the gap, put the paper in the gap, let go of shaft. Secondaries now opened a little more. Allowing primary to close off. If that helps, turn the hex screw on secondaries into the baseplate about 1/8 turn or until the idle RPM matches your setting with the paper inserted. Hillbilly engineering so you aren't ripping the carb off to make that adjustment if it isn't there with carb installed.
There is a secondary idle adjuster. It's from the bottom on pass side. Where the little arm at the end of the throtte shaft hits the baseplate. Little trick.
Take a piece of notebook/writing paper, open the gap, put the paper in the gap, let go of shaft. Secondaries now opened a little more. Allowing primary to close off. If that helps, turn the hex screw on secondaries into the baseplate about 1/8 turn or until the idle RPM matches your setting with the paper inserted. Hillbilly engineering so you aren't ripping the carb off to make that adjustment if it isn't there with carb installed.
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That definitely seems like a useful trick lol taking off the carb 100 times is just sort of annoying lol. I luckily have a manual so a clunk into gear really isn’t a concern. The big thing though that I would like to fix with the off idle is when I start moving from a stop. I can’t just press the gas and let the clutch out because it bogs and stutters. I have to blip the throttle a couple of times to what I’d imagine dump some gas into the intake and then let the clutch out.
Seems like the next step will be limiting the mechanical advance, I have the timing at 15 degrees or so, vac advance unhooked right now and it seems happier. T slot is a square, seems to not stumble, no dieseling, but it does ping ever so slightly around 2k when floored in 3rd. Probably going to back it off a hair and leave it for now until this cold spike goes away.
Mattax
Just the facts, ma'am
I try not to post much these todays. But just saw this and even though RRR and I don't see eye to eye on this he is correct;
and I'll try to answer your questions, or point you to a post which does.
To better understand what is going on, do yourself a favor and measure and plot out the mechanical advance vs. rpm. Knowing the RPM of any timing measurement is critical. The vac advance can be used to crutch insufficient initial advance in some cases. Apparently not yours.
To understand the effect of changing initial look in this post at the factory timing curve specs for non-smog and smogged Hi-Po 440.
Observe how welding the inside of the slots on the CAP advance make it essentially the same as a non-CAP distributor.
More important, see in the last illustration what happens when the advance is 'limited' and the initial set to 12* at 700 rpm.
^^Once an engine is fully warmed up this is guarenteed to ping at street rpms when combined with vacuum advance^^
Lets just say for discussion that the distributor came was for a early 70s 2-bbl 318. And lets assume that 13* was measured at 700 rpm.
The timing curve then looks something like this, and with 30 degrees by 1800 rpm will ping unless you disconnect the vac advance.
You need a curve that looks more like this.
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.
You've seen the port?
Photo in this post.
Chrysler set up their mechanical advance and initial so vacuum advance was only used for when the mixtures were lean. Before emissions were a major concern, idle were relatively rich mixtures. This made for more power at idle, allowing lower idle rpms even with manual transmissions.
from the 1969 Master Technicians Conference
and I'll try to answer your questions, or point you to a post which does.
Not neccessiarily. It depends on the conditions when it pinged.
To better understand what is going on, do yourself a favor and measure and plot out the mechanical advance vs. rpm. Knowing the RPM of any timing measurement is critical. The vac advance can be used to crutch insufficient initial advance in some cases. Apparently not yours.
To understand the effect of changing initial look in this post at the factory timing curve specs for non-smog and smogged Hi-Po 440.
Observe how welding the inside of the slots on the CAP advance make it essentially the same as a non-CAP distributor.
More important, see in the last illustration what happens when the advance is 'limited' and the initial set to 12* at 700 rpm.
^^Once an engine is fully warmed up this is guarenteed to ping at street rpms when combined with vacuum advance^^
Lets just say for discussion that the distributor came was for a early 70s 2-bbl 318. And lets assume that 13* was measured at 700 rpm.
The timing curve then looks something like this, and with 30 degrees by 1800 rpm will ping unless you disconnect the vac advance.
You need a curve that looks more like this.
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.
Correct. Once the blades are open past the timing port the vacuum is the same.
You've seen the port?
Photo in this post.
Chrysler set up their mechanical advance and initial so vacuum advance was only used for when the mixtures were lean. Before emissions were a major concern, idle were relatively rich mixtures. This made for more power at idle, allowing lower idle rpms even with manual transmissions.
Backfire through a carb is some combination that results in ignition when an intake valve is open. So my bet is timing too early (too advanced) for that rpm.
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