that's interesting, maybe that is why I do have a hard time 'hitting the gas' in the morning to get a good launch, it will instead stall out.

here is my calibration sheet though, and it doesn't show any delay , the vacuum advance is connected directly to manifold. Note this is for a '78 and my truck is a '79 but probably not a difference. My calibration code on the valve cover indicated 9-97J-RO

There IS a reservoir though. I should probably connect that back up and it might help with the stalling.

 

Yes hook the reservoir back up you will notice an improvement in acceleration. This Calibration is a full on emissions calibration even though you have no catalyst (catalytic converter) it is a full-on emissions calibration with thermactor (air injection).

If you are not running all the emissions gear get off manifold vac for vac advance and move to ported you find that low and off idle operation will be far more stable.

I would mod this vac system to have an overheat ignition advance. See below modded vac diagram on how this would be done.

This set up will use a 3 port VCV in the 210-212F° range. (You can use whatever temp you want for when you think the engine is getting too hot.)

When the engine is cold or at normal operating temp the vac advance will work normally off the ported vacuum.

When the engine temp reaches 210-212F° temp the VCV will switch from ported vacuum to manifold vac, this will automatically speed up the idle speed and will increase cooling through the rad fan moving more air through the rad and by increased coolant flow. This set up is very commonly used on the 460s from the factory.

As a note ignore vacuum line orientation on the VCV it was done just the way it was so no lines would cross.

 

That your truck is manual will mask much of the off idle issues. Regardless still keep an eye on your plugs as you run the very real risk of burning valves with this carb.

Also the jets have NO effect on idle they are not used during idel. They are only used when the carb is on the main circuit. The Idle mix screws are your jets at idle.

And there is no argument for a manifold vac, that fact is the only time you would use it is for emissions applications or hot camshafts simple as that.

Also you are worrying about item X and ignoring the more important A,B, C,D

The VERY first thing you should be doing is making sure all your advance in by 2500RPM or os.
And quit trying to take out mech advance accept the extra vac from ported and increase the amount of mech you have and lower the base timing. You can not fix the advance at idle so ignore it.
Since you are on a manual you will likely not any off idle issues any way.
Also when you install the new induction system you will not have to mess with the Dist again.

You said you do not have experience with this stuff yet do not want to take the advice of those that have been doing it for almost 3 times as long as you have been alive, we are not trying to steer you wrong but trying to get your engine to be as efficient and as powerful as possible.

 

That is what I mean. That's why I have never even thought about using manifold vacuum because my cam is stock, but I understand why people argue that manifold is better because I may very well be for THEIR engine.

 

Do you mean I run the risk of burning the valves because of it being too lean in the higher rpms? Since the jetting has no effect on idle, should I still bump them up a few sizes (say 52 as a starting point) to combat it being lean in the higher rpms?

Since it is a manual, I won't worry about the 2 degree vacuum advance at idle unless I absolutely pinpoint a problem specific to the vacuum advance (stumbling, etc).

 

You run the risk of burning valves at cruise when the EGR would have been active (cruise light acceleration etc), with this carb.
The carbs leans the fuel-air mix in the fuel curve when the EGR would have been active.

The EGR introduces inert gasses into the combustion cycle, making less available oxygen for combustion, this lowers the temp of combustion lowering NOx emmisions. But less oxygen means less fuel is needed
So there is no point in providing the full measure of fuel just to have it go out the tailpipe in the unburnt HC (Hydrocarbons) there by increasing HC and the loading on the cats shortening their life span.

The EGR carbs from the 70's did not really cut back the fuel delivered during EGR operation. But by the time the 80's (the era these knock-off carbs are based on and calibrated from) rolled around, CAFE standards had increased drastically and emissions regs had become far more stringent, and they really dialed back the fuel that was being delivered during EGR operation.
So run one of these carbs remove the EGR then drop it on a larger displacement engine and then throw Ethanol laced fuel into the fray that requires an even richer fuel-air ratio over straight gasoline and you have pretty much just created the perfect recipe to start burning valves from too lean a fuel-air mix.

And now here comes the crappy part yes you can increase the jetting BUT it will not really help as the carb is calibrated to lean out during what would be EGR operation. Increasing the jet size will help but by the time you get it to a good point during what would be EGR operation you will be pig-rich everywhere else. Ask me how I know.

We played around with this back in the early 80's trying to find ways to trick EGR calibrated carbs to deliver appropriate fuel during what would be EGR operation without having to resort to new all-new carb calibrations for non-EGR Canadian spec vehicles, this was an exercise in trying to cut costs by minimizing part production variations and stock count. The end result.... new Canada spec calibrations for non-EGR vehicles.

Upping jets will help and reduce the risk. But the best option is to either get the carb you want, installed sooner rather than later, or buy a quality rebuild that will work properly on the engine.

 

Thanks! This is great info. I will look into getting different sizes of jets in the low 50s and do some testing just to be on the safe side. The earliest I could get/afford a 4 barrel intake/carb would be in June or July. (I started real estate license school recently so I won't have a stable income for a while). I'm not really sure yet, but I think I'll just go with the motorcraft 4100 and matching intake. If I find a good deal, I'll jump on it.

When choosing this current carb, I was also looking at a few 2100's with the 1.21 venturi. They are available on eBay for $50 (very used) but since I just had a problem with a worn and leaking throttle shaft, I didn't want to end up spending another $30 to rebuild it and wind up having to replace the throttle shaft bushings.

I think the problem I was having with the egr wasn't with the unit itself, but because the other ported "nipple" on the front of the carb (where I had the egr connected) has the same amount of vacuum as the timed advance port. That must be why it runs a little better when I plug it off. Is there a thermostat controlled vacuum port I could use so at least the egr could be used when it's above operating temp? Thanks!

 

The later carbs (2150) typically have at least 2 ports. The S port or spark port for the vac advance and the E port or emissions port that controls the EGR. The E port should not have a vacuum except in times of higher venturi flow. The fact that the E port has vacuum at idle (which should be an impossibility ) just shows how completely screwed up the engineering is in these knock offs.

The EGR should not operate until the coolant is around 100-130° F this will be controlled by a VCV or a solenoid or one of a dozen other means to do so. And really unless you are in an area that requires you to run the EGR to be emissions compliant, take the EGR off and throw it out. In a carb'd engine all, it does is decrease power and efficiency.

Also any ports not being used on the carb should be capped off.

The 4100 is about the best 4 BBL carb ever made. And far and away my fav carb, I have played with them for basically 50 years and still have buckets of them kicking around, I have modified them and back in the 80's created the conversion for drop-on use in front of AOD's.

With the 4100 you need to be sure to get the right one for your engine displacement you NEED to find one from a 390 or larger displacement engine.
You can step the carb back to a smaller displacement engine then jet down. But they will not always work well being used on significantly larger displacement engines.
The most common 4100's out there are from the 352. And 352 Carbs tend to not work well on 390's 400's 406's 410's etc etc. but they do work fantastic on 351's C,W or M.

Alternatively, you could opt for the Summit M2008 this is a reworking of the old Holley 4010, which was a modernization and holleyfied version of the 4100 Autolite.
The 4010 was designed by the same group of engineers that originally designed the 4100. (not kidding)

The Summit M2008 is built and boxed by Holley, then supplied to Summit. All Summit does is sell it.

The advantage of the Summit M2008 over the 4100 is:

It shares the interchangeability of parts with other Holley carbs.
It is far easier to tune and set up than 4100.
The learning curve is far less steep
It comes with a manual to tune and set up the carb, the 4100 requires some dedication and understanding to get the most out of it.
Since 4100 knowledge is few and far between you either get to trial and error or try to find one the few old codgers left that have the knowledge on how to tune and tweak the 4100, and try to pry it out of them.

The Advantage of 4100 is:

When tuned in, almost nothing can touch them in terms of reliability and fuel economy.
They basically never drift once tuned/set up and will maintain dead nuts consistent reliable operation till the throttle shafts wear out.
The 4100 will digest absolutely mountains of crap and work flawlessly.
They look the part in period vehicles and can provide some neck-snapping acceleration, almost on par with double pumpers when they are set up correctly.

So if you are willing to put in the work and the frustration that may initially come with it trying to find a good and complete 4100 core with all original parts, and want the originality absolutely go for a 4100.
If you want to drop something on and go, opt for the Summit M2008, It still sort of looks like a 4100, and shares the 4100's lineage. And likely will prove to be far less of a headache to tune in and set up.

 

I will stick to not using the egr then. The egr port on the carb is the same height as the spark port, so it makes sense that if one has some vacuum, the other would match.

I have heard the 4100 is good and I have begun to enjoy the tuning process so that definitely sounds like it will be ideal for me. Is there any give away as to what engine size the carb originally came on (venturi size, etc)

 

Basically, there are 2 that you will find. 1.08 used on the 289 and the 1.12 used on everything else. So you can not use venturi size to determine what they were used on. But if you find something post the part number that is stamped on the base plate and I can tell you what it was from.

 

Thanks! I'll start looking around some local junkyards and Facebook marketplace before I turn to eBay. That way, I might be able to get some history on the carb instead of just buying it from a third party who doesn't know anything about it.