Gotcha gotcha, that makes sense. Basically close but not identical is the goal
Fine Tuning a 360 Magnum with a Brawler "Double Pumper"
- Thread starter jmanhoff
- Start date
-
Mattax
Just the facts, ma'am
No. The point is that if they are very different then the question is why.
The goal is to make it run strong.
Whatever makes it idle the best with the screws and the IFR/IAB relationship is wacky.
Something like a .036/.084 and the screws out between closed and 3 turns. That’s an issue.
I mention this because I had a carb come in several years ago and thats what it was. How it got there is anyone’s guess. He bought it used at a swap meet.
But yes, close and identical if you can get it. If not make it happy within reason.
Alright so the sun sort of came out so I let the engine warm up and messed with the idle screws. What I did was started 1 turn out and slowly turned them in until it bogged and then backed it off. Each ended up about 3/4 of a turn out, and I added a smidge of a turn on each because I heard a very slight stumble when I slowly open the throttle.
Afr is sitting around 12.5, vacuum is 22 inches, but the exhaust doesn’t burn my nose. Seems happy, going to take it for a drive
Afr is sitting around 12.5, vacuum is 22 inches, but the exhaust doesn’t burn my nose. Seems happy, going to take it for a drive
Just finished a short drive home, a lot of 45mph steady cruise but there’s a couple lights on the way. Cruise is pretty stable now, no surging. I still can kind of hear a bog when I give it a bit of throttle and the vacuum drops to about 10.5 or so, but it’s not as bad as before.
I did have a random point when I came to a stop after going over a railroad crossing where the vacuum and rpm dipped, but I couldn’t recreate that so I wonder if it was just the shaking and the nose going up and down that made some fuel slosh out of the vent tube into the throat and it was overly rich for a second. I guess this whole time it’s been a combination of my idle screws weren’t even and they were too far in.
Obviously there is still more work to do, but I’m glad I can actually drive this thing again. I noticed the difference immediately when I left the parking spot at work, the truck practically jumped out of there.
If it matters and I know we’re not looking for afr data right now, but my cruise afr sits around 15:1, kinda jumps between 14.6 and 15.2, but when I give it more throttle (around 10.5” vacuum) the AFR doesn’t change, it stays at about 15:1.
My 10.5PV did just arrive in the mail today, but I’m curious if I should even look into installing it yet or mess with some other things first. What do you guys think my next step is? I can pull plugs when I get to work tomorrow as well.
I did have a random point when I came to a stop after going over a railroad crossing where the vacuum and rpm dipped, but I couldn’t recreate that so I wonder if it was just the shaking and the nose going up and down that made some fuel slosh out of the vent tube into the throat and it was overly rich for a second. I guess this whole time it’s been a combination of my idle screws weren’t even and they were too far in.
Obviously there is still more work to do, but I’m glad I can actually drive this thing again. I noticed the difference immediately when I left the parking spot at work, the truck practically jumped out of there.
If it matters and I know we’re not looking for afr data right now, but my cruise afr sits around 15:1, kinda jumps between 14.6 and 15.2, but when I give it more throttle (around 10.5” vacuum) the AFR doesn’t change, it stays at about 15:1.
My 10.5PV did just arrive in the mail today, but I’m curious if I should even look into installing it yet or mess with some other things first. What do you guys think my next step is? I can pull plugs when I get to work tomorrow as well.
So the idle is nice? What’s the AF ratio at idle?
That tip in bog at that point may not be the carb. Too much timing at and around peak torque can do that.
Like I said…PROGRESS!
The idle is very stable and to my ear sounds healthy. I can’t smell raw gas, AFR sits around 12.8-13.1.
So just for clarification, you start by leaning out the screws until it idles down, and then back it out until stable. Then you go rich until it idles down and then back lean until it’s stable? Wouldn’t that leave it richer than it needs to be or can you almost immediately hear an rpm change?
I may be circling back to an earlier thing but I figured I would ask again. I have a ticking sound still, it sounds like a single cylinder, but I don’t know why it’s happening still. I had a tick from before the engine spun a bearing, but I rebuild everything in the bottom end, and the cam, lifters, pushrods, and valve springs are new. Leaving the rockers as the only thing that isn’t new (Harland 1.6 non adjustable rollers).
Hughes with this cam and lifter combo calls for .120-140 preload, I have .126 right now. I still hear a ticking, and it’s rhythmic following a single cylinder it sounds like. It doesn’t go away with oil pressure at least completely, and it is quieter on a cold start and progressively gets louder. It doesn’t sound like an exhaust leak. What are the odds that it is a failed rocker? I’m planning when I have time to pull the covers off and use a screwdriver on my ear on each pedestal to see if I can pin point it, but I feel like rockers usually don’t go bad this soon?
I may be circling back to an earlier thing but I figured I would ask again. I have a ticking sound still, it sounds like a single cylinder, but I don’t know why it’s happening still. I had a tick from before the engine spun a bearing, but I rebuild everything in the bottom end, and the cam, lifters, pushrods, and valve springs are new. Leaving the rockers as the only thing that isn’t new (Harland 1.6 non adjustable rollers).
Hughes with this cam and lifter combo calls for .120-140 preload, I have .126 right now. I still hear a ticking, and it’s rhythmic following a single cylinder it sounds like. It doesn’t go away with oil pressure at least completely, and it is quieter on a cold start and progressively gets louder. It doesn’t sound like an exhaust leak. What are the odds that it is a failed rocker? I’m planning when I have time to pull the covers off and use a screwdriver on my ear on each pedestal to see if I can pin point it, but I feel like rockers usually don’t go bad this soon?
Okay small tinkering update.
I put in smaller IABs just to see what the affect would be. (.070” to .067”). Idle screws are now about 7/8 of a turn out, I got there by starting at 1 turn out on all 4, then slowly turning one by one until it started to idle down, and backed it off a quarter turn. I did a quarter because it was unusually hot today, so wanted to give it a cushion.
Idle is nice and stable, cruise is nice and stable, vacuum is rock solid it only moves when my foot moves on the throttle. AFR gauge stays within a 0.5 deviation. Off idle is very strong, turning from a stop feels like the truck wants to light up the tires with barely any throttle. I do however have yet another question now lol.
It seems like pairing a .028” IFR with a .067” IAB has made the engine idle very happy and smooth, as well as cruise. Given this scenario, if I wanted to lean out the cruise (it’s a bit richer than before), should I put in smaller TSRs because the engine likes the smaller IAB? I know a larger IAB would lean out the transition, but it would also lean out the idle and change the ratio, which I would guess I don’t want to change because the engine is very strong where it sits right now
I put in smaller IABs just to see what the affect would be. (.070” to .067”). Idle screws are now about 7/8 of a turn out, I got there by starting at 1 turn out on all 4, then slowly turning one by one until it started to idle down, and backed it off a quarter turn. I did a quarter because it was unusually hot today, so wanted to give it a cushion.
Idle is nice and stable, cruise is nice and stable, vacuum is rock solid it only moves when my foot moves on the throttle. AFR gauge stays within a 0.5 deviation. Off idle is very strong, turning from a stop feels like the truck wants to light up the tires with barely any throttle. I do however have yet another question now lol.
It seems like pairing a .028” IFR with a .067” IAB has made the engine idle very happy and smooth, as well as cruise. Given this scenario, if I wanted to lean out the cruise (it’s a bit richer than before), should I put in smaller TSRs because the engine likes the smaller IAB? I know a larger IAB would lean out the transition, but it would also lean out the idle and change the ratio, which I would guess I don’t want to change because the engine is very strong where it sits right now
Rusty,
does anyone publish (Holley) idle fuel restrictions diameters per manifold vacuum at idle like Ruggles does for Rochester's?
The IAB & the IFR have nothing to do with rich or lean idle. Once the T-slot position is correct, there will always be enough fuel for idle; idle rich or lean is controlled by the idle mixture screw. The IAB is sized to work with the MAB so that there is a smooth transition from idle to main cct. Not rich, not lean. The IFR is sized to provide a clean transition to the main cct, not sized for idle. The transition phase happens with more airflow & correspondingly more fuel flow, so there is always enough fuel from the IFR for idle because it needs less fuel. This why T-slot position is so important.
If everything is ok now except for rich transition, you should reduce the TSR size.
If everything is ok now except for rich transition, you should reduce the TSR size.
Hey guys I’m back again, I’ve been mucking around with different bleeds and such. I ended up going back to a 28 IFR and a 70 IAB, and I’m still dealing with a stupid rich idle and lean transition, so my next step is to go with a .086” TSR (up from .082”) and a .073” IAB. My screws are only 3/4 out, so I’m hoping to get more control with a larger IAB.
I did want to ask though, how much of a difference would I notice with annulars? Would I be able to cut back on the TSR because the mains would come in sooner? I’m pretty hard set on getting them, just curious what I would actually notice. If I remember correctly, they reshape the fuel curve, and there’s more down low because it has a much stronger signal, which would allow me to run leaner “jetting” everywhere because the circuits start sooner, so I could have a very lean cruise/transition slot but still have good mains overlap so I don’t have a lean spot when I open the throttle more
I did want to ask though, how much of a difference would I notice with annulars? Would I be able to cut back on the TSR because the mains would come in sooner? I’m pretty hard set on getting them, just curious what I would actually notice. If I remember correctly, they reshape the fuel curve, and there’s more down low because it has a much stronger signal, which would allow me to run leaner “jetting” everywhere because the circuits start sooner, so I could have a very lean cruise/transition slot but still have good mains overlap so I don’t have a lean spot when I open the throttle more
-
Similar threads
