Max fuel pressure for Carter 3705 carbs?

[4406bbl]

Where the vacuum advance starts is kind of built in around 8", to get the 10 degrees you need will be tough to get working reliably at idle if you can't keep 10-11" of vacuum at idle in gear. A custom made at least $1000 torque converter is one way, you put it in gear and it does not pull the engine down, making tuning easy. I would get the initial to 18- 20 maybe 24 degrees is the number, you know the engine wants that and more at idle and see how good you can get it to idle in gear, then decide if you want to chase the vacuum advance or limit the mechanical. I would not drive the car with that much initial and unknown mechanical. In your case 30 degrees inital with the mechanical limited and little ported vacuum advance for a clean cruise might be as good as it gets until you get a looser converter at idle, manual trans is so much easier.

 

[4406bbl]

There was a good write up on for a bodies only years agoon vacuum cans you might want to research.

 

[fmahannah]

There was a good write up on for a bodies only years agoon vacuum cans you might want to research.

Thanks! Some really useful info in there about how vac advance actually works and how to correctly adjust it and limit the total if needed!

 

[Geoff 2]

Forrest,
There is getting to be too many chefs in the kitchen with this thread, some with bad advice. I have been setting up MVA for 30 yrs. Here is my take on where you are now & where to go.
[1] You have an intake that has a 3000-6500 rpm power range, that was NEVER designed to idle at low rpm because it is DEAD at low rpm & has poor carb signal 'low vac ]. To make matters, worse these intakes were designed for engines with 11-13.5:1 CR, which I doubt you have, & this will further reduce vacuum & response.
[2] A smaller c'ter would help slightly, but you probably do not want to go there....
[3] So you are probably going to have to compromise. Maybe you will have to run a run a higher a higher speed than you would like.....
[4] I emailed you a VA chart. Not very useful, but it DOES show the VA units starting to activate at 4-5" of vac.
[5] If you want to optimise this poorly chosen combo, then you need to perform step 5 in post 21 to find the optimum idle advance. This works every time, no exceptions, & is a must do if you want VA to work for you.
[6] Another option for better VA control is run a lot of static initial adv, which will increase vacuum & therefore the vac starting point for the VA. I think your combo could need at least 40* at idle from the above test. Say you use 28* initial. If the starter baulks at that much timing, the fix is easy. I have this on my car & it also acts as an anti theft device. Get a miniature on/off sw & mount under the dash. Connect one terminal to grd, the other terminal to either one of the pick up wires. Wire used can be very thin, only small current in milliamps; crank the engine with the switch grounding the lead [ no spark ] & flick switch & engine will fire up.
[7] Turn the AK adjustment fully CW on the VA unit & leave it there. It's job is now done.
[8] The plunger on the VA unit will likely have to be limited in travel to provide the correct amount of VA to add to the static initial timing. There are two ways of doing this, but because of the low vac, only one is reliable. One method is to put a stop at the end of the arm to reduce how far it comes out of the VA unit; the other method, which you should use, is to limit how far the plunger goes into the VA unit. I silver solder a small metal piece onto the plunger arm to do this; this method uses the lowest vacuum function.
[9] Do not worry about the centri curve, it comes last!!!! You need to make sure that you are not getting centri action with the higher idle speeds. Fit a heavy springs, tie up the weights with wire, whatevder, just make sure

 

[Geoff 2]

Pressed the wrong button!
Continuing on: disable the centri weights so that they do not interfere with idle set up.
[10] Check with a timing light that timing does not change going from N into gear. If timing is erratic in gear, VA is not holding. About all you can do is increase idle rpm. All this assumes that the idle mixture screws have been adjusted for best idle.
[11] It is OK to test drive, just don't hammer it. You are checking idle quality, idle stability & tip in response.

 

[fmahannah]

Forrest,
There is getting to be too many chefs in the kitchen with this thread, some with bad advice. I have been setting up MVA for 30 yrs. Here is my take on where you are now & where to go.
[1] You have an intake that has a 3000-6500 rpm power range, that was NEVER designed to idle at low rpm because it is DEAD at low rpm & has poor carb signal 'low vac ]. To make matters, worse these intakes were designed for engines with 11-13.5:1 CR, which I doubt you have, & this will further reduce vacuum & response.
[2] A smaller c'ter would help slightly, but you probably do not want to go there....
[3] So you are probably going to have to compromise. Maybe you will have to run a run a higher a higher speed than you would like.....
[4] I emailed you a VA chart. Not very useful, but it DOES show the VA units starting to activate at 4-5" of vac.
[5] If you want to optimise this poorly chosen combo, then you need to perform step 5 in post 21 to find the optimum idle advance. This works every time, no exceptions, & is a must do if you want VA to work for you.
[6] Another option for better VA control is run a lot of static initial adv, which will increase vacuum & therefore the vac starting point for the VA. I think your combo could need at least 40* at idle from the above test. Say you use 28* initial. If the starter baulks at that much timing, the fix is easy. I have this on my car & it also acts as an anti theft device. Get a miniature on/off sw & mount under the dash. Connect one terminal to grd, the other terminal to either one of the pick up wires. Wire used can be very thin, only small current in milliamps; crank the engine with the switch grounding the lead [ no spark ] & flick switch & engine will fire up.
[7] Turn the AK adjustment fully CW on the VA unit & leave it there. It's job is now done.
[8] The plunger on the VA unit will likely have to be limited in travel to provide the correct amount of VA to add to the static initial timing. There are two ways of doing this, but because of the low vac, only one is reliable. One method is to put a stop at the end of the arm to reduce how far it comes out of the VA unit; the other method, which you should use, is to limit how far the plunger goes into the VA unit. I silver solder a small metal piece onto the plunger arm to do this; this method uses the lowest vacuum function.
[9] Do not worry about the centri curve, it comes last!!!! You need to make sure that you are not getting centri action with the higher idle speeds. Fit a heavy springs, tie up the weights with wire, whatevder, just make sure

As soon as I have time I am going to follow your step by step process. I am aware of the limitations of the max wedge combo, but you are right I don't want to change it If I have to idle faster to make it work then so be it as long as it is not pig rich.
I already know this combo likes a lot of advance at idle, so my fear is that I will end up needing a combination of static advance and vac adv that would mean static plus mechanical would go too high unless I can limit the mechanical on this Summit distributor. Specs and details on this dizzy are not available so far, although FBO (4sceondsflat) says that their limiter plate should work with it. Supposed to be a Chrysler replacement but I am not sur what springs etc would fit it.

Thanks!

 

[fmahannah]

In case anyon is curious I finally got the specs back from Summit on the SUM-851018 distributor. But the mechanical advance specs seem off to me? With a recurve my MSD started mechanical advance about where this one is all in?

Hello Forrest,

Attached are instructions that may answer you questions on the SUM-851018 distributor. Here are some internal specs we also have.
Per manufacturer, mechanical advance starts @ 500 RPM and is fully advanced at 1750 RPM , with a total mechanical advance of 11 degrees. (22 @ the crank)

Thank You
Summit Racing

 

[Geoff 2]

Totally different construction, MSD & Summit dist. MSD uses the GM/Delco weights system. They came with a variety of weights, centre plates & springs to give a HUGE range of curves. Superb design, & easy to access too. The Ch & Mallory types are very limited in how they can be modified.

You are likely to have a idle speed over 1000, so that would be a problem before it starts. Stronger spring needed to delay the start. Once again, centr curve is the LAST of your worries & should be left until last. In your testing for best idle, I would disable the weights [ tie wrap, or wire ] so that it doesn't add timing during the idle testing.

 

[fmahannah]

Totally different construction, MSD & Summit dist. MSD uses the GM/Delco weights system. They came with a variety of weights, centre plates & springs to give a HUGE range of curves. Superb design, & easy to access too. The Ch & Mallory types are very limited in how they can be modified.

You are likely to have a idle speed over 1000, so that would be a problem before it starts. Stronger spring needed to delay the start. Once again, centr curve is the LAST of your worries & should be left until last. In your testing for best idle, I would disable the weights [ tie wrap, or wire ] so that it doesn't add timing during the idle testing.

Yes I am working only on the idle, but I did not think that idling at 1000 the mechanical would be already kicking in with stock springs. I have a plate coming from FBO that will let me cap the mechanical limit wherever I need it or even lock it out while testing. Also the spring kit that Summit says can be used to adjust the curve (SUM-850121).

In the meantime I can disable the weights. Should make real progress tomorrow.

Why are the MSD distrbutors with vac adv not adjustable? That combined with their easily adjustable curves would have been my first choice.

Thanks

 

[steve340]

There instructions may mean distributor RPM which is half crank speed.
So 500 would be 1000 crankshaft.

 

[Geoff 2]

Yes, exactly: why did MSD not fit an adj VA unit to their performance dists when these dists were most likely to be used in performance engines that have reduced vacuum. A very stupid error of judgement by MSD.

 

[fmahannah]

Yes, exactly: why did MSD not fit an adj VA unit to their performance dists when these dists were most likely to be used in performance engines that have reduced vacuum. A very stupid error of judgement by MSD.

I wonder if someone makes a vac can for MSD that is adjustable? Now that would make me happy, much easier access to weights and springs in the MSD for tweaking.

There instructions may mean distributor RPM which is half crank speed.
So 500 would be 1000 crankshaft.

Ok now that would make more sense .... then all in by 3500. Probably true since having mech adv come in lower than most idle speeds would ever be set makes no sense to me

 

[Geoff 2]

No adj can for MSD. I tried adapting one for a Delco points dist & it was unreliable.
From memory, the VA plunger on the MSD sits inside a plastic bush on the plate & the movement is unreliable [ can get stuck ].

 

[Geoff 2]

I don't know why you are persevering with the MSD dist. It is a POS. It is triumph of marketing over brains. The big, fat reluctor tips & large air gap that MSD use will give more cyl-to-cyl timing variation than the fine tipped Ch or GM reluctor & tight gap.

 

[Dragon Slayer]

Typically, and how Chrysler does it is that advances and RPM are distributor values. So you do double them for crankshaft value which you can measure with timing light. The values given so the distributor can be curved on a machine which are measured in distributor values.

Just for your info your Car orig used a Prestolite IBB-4202 distributor with No vac can, had a 12degree cam. So 24 mechanical at the crank. Initial timing was 12.5deg. So about 36.5 total.
Your curve ""converted"" to Crank spec was:
0 deg at 1000 rpm
2 deg at 1080
12 deg at 1500
22 deg at 1920
24 deg at 2000 rpm

So it does start rolling in advance above 1000 rpm and is all in at 2000rpm at the crankshaft.
So I would confirm with Sum if the rpm they gave is distributor or crank values. If anything it looks slower than an orig max wedge curve.

I give you original values so you know the baseline you are departing from. Frankly I don't think the Chrysler engineer were "wrong" or "stupid" as some think they were.

It is a shame you have to go down this route of aftermarket parts, for what is otherwise a nice tribute Max Wedge. I do hope you get it running right.

 

[fmahannah]

OK, so the first test was to see what the car likes at idle. With engine warm (these don't run worth a crap until they are fully warmed up) and vac can disconnected, it seems to like 38-40* at idle, just like Geoff 2 said

If I set initial at 12*, with the vac can maxed out, It is only bringing it up to 28*. This is at around 1100 RPMs. I imagine if I brought the rpms up more then vac would come up and can would bring in more timing,
but I really don't want to have to idle at 1200-1300 if possible. I think the issue is that even at 1100 rpms I only have 7 inches of vacuum, and since the can is triggered by vacuum I am not geting everything it can add?
I notice that if I drop the idle speed it starts to surge like the can is bringing in timing but fluctuating as idle vacuum fluctuates.

Seems like getting just the right combination of initial, vac adv, and idle speed takes a lot of testing to get the best combination.

The other alternative would be to bring initial up to 22* and let the vac can do the rest, but right now I don't have a way to cap the mechanical so it does not go over 36. I will have a limiter plate Monday that is supposed to
work for this dizzy.

I am going to try bringing up the idle speed to see if that makes the can bring in more timing or not. The good news is that it does idle in gear now, no stalling, and smoothly. And it is only a little rich at idle until it warms up all the way.

 

[Dragon Slayer]

. I was reading up a little on the max wedge, I guess the early manifolds were prone to a crack near the carb flange. Later manifold which should include yours since you have a large carb were beefer. Hopefully you don't have an early one someone modified for larger carb. I am not a cam man, but that vacuum really seems low. Sure no vacuum leak? Those carbs were meant to work with 19" vacuum at idle at 900rpm, and the spec for manual trans was an idle of 900-1300 according to the carter documents.

 

[fmahannah]

Manifold is 2402726-1, cam is P4120237, -Adv. duration: 292 Int. 292 Exh./Lift: .509 Int. .509 Exh./Overlap: 76/Centerline: 108

Manifold looks good. Had another 63 Polara with 413/426 same cam single four barrel, it also only got 5-7 inches of vac idling at 1000 or so

 

[4406bbl]

OK, so the first test was to see what the car likes at idle. With engine warm (these don't run worth a crap until they are fully warmed up) and vac can disconnected, it seems to like 38-40* at idle, just like Geoff 2 said

If I set initial at 12*, with the vac can maxed out, It is only bringing it up to 28*. This is at around 1100 RPMs. I imagine if I brought the rpms up more then vac would come up and can would bring in more timing,
but I really don't want to have to idle at 1200-1300 if possible. I think the issue is that even at 1100 rpms I only have 7 inches of vacuum, and since the can is triggered by vacuum I am not geting everything it can add?
I notice that if I drop the idle speed it starts to surge like the can is bringing in timing but fluctuating as idle vacuum fluctuates.

Seems like getting just the right combination of initial, vac adv, and idle speed takes a lot of testing to get the best combination.

The other alternative would be to bring initial up to 22* and let the vac can do the rest, but right now I don't have a way to cap the mechanical so it does not go over 36. I will have a limiter plate Monday that is supposed to
work for this dizzy.

I am going to try bringing up the idle speed to see if that makes the can bring in more timing or not. The good news is that it does idle in gear now, no stalling, and smoothly. And it is only a little rich at idle until it warms up all the way.

I am thinking the mechanical advance is bouncing just a little at idle some stiffer advance springs would help any napa or advance auto generally has them unless you ordered the plate and springs. As Geoff said absolutely lock all mechanical out and get the idle/vs what the starter will allow balance first. The 7-8" vacuum with that cam is about right installed straight up, at least in my experience, anyway good to hear you are making progress, and how about some pics of the inside of the distributor when you get it apart.

 

[fmahannah]

Yes I ordered the plate and the springs, just waiting for them to get here as usual. Timing with vac advance is now at 31* with the 12 initial. Not going to mess with it more until the parts get here. I think I might have to go more static to get it where it needs to be and then limit total mechanical. That is if different springs don't help. If I was willing to idle at 1250-1300 it would be fine the way it is but I hate the slam when shifting into gear with the push button auto.

By the way shifting into gear does currently lose the vac advance (most of it) probably because of rpm drop and resulting vac drop...