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Discussion Starter #1
So I have a 289,30 over ,line bored and decked, hypereutectic pistons, hi-po heads ported and polished with 1.835 intake and 1.540 ex valves, port matched for both intake and exhaust with polished hipo exhaust manifolds 2 1/2 inch exhaust. Weiland stealth intake with this cam :
Currently have a Autolite 1.12 , 4100 built by pony carbs a few years ago jets are 51 in the primary and 68 secondary
Aod trans with 4R70W internals 2200 stall going to a 9 inch with 3.55 gear.
Current carb has a hesitation or shudder at low rpm and slow acceleration.
Seems ok with a harder acceleration but if I slow for traffic and go to speed up again the throttle response is bad.
Thinking to either rebuild the 4100 or buy something new like a Holley 570 Street avenger, Edlebrock or summit carb. I have been told that my problem with the 4100 may be caused by worn a throttle rod and not something that I can just "tune" out.
Would like to stay with vacuum secondary, electric choke and annular boosters.
Looking for lo-end throttle response for some light to light fun !
 

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First step for your issue would be to replace the accelerator pump diaphragm, check the linkage and clean out the passages.
 

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Yeah accel pump may not be delivering enough. And may be jetted too lean on the primaries. I have a similar set-up but a 1.08 carb and it's happy. I dunno what the jets are in mine.
 

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You need to isolate your problem further. Is there an A/F ratio issue as the carburetor goes from idle to transition circuit? I'd start by disassembling the 4100 and giving it a thorough cleaning, including knocking out the welch plugs and running all the small passages to ensure they're not clogged. Depending on your engine's requirements you might find that some "resizing" of the idle air bleeds may help with delivering more fuel from the transition holes as the throttle plates open past them.

However, it's uncommon for a carburetor to cause a "shudder". A flat spot or "bog", sure, but a "shudder" is an indication of an ignition misfire. I'd be looking more toward that area... perhaps distributor/rotor/cap phasing, inductive crossfire, etc.
 

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Discussion Starter #5
a flat spot or bog may be a better way to describe the problem for sure.
So a rebuild may be in order for me ?
Not sure what "welch plugs " or how to resize the idle air bleeds, is there some reading available ?
Distributor is a non vacuum advance with electronic conversion and the wires, cap and coil are new.
I was thinking that modern technology and parts that are not 55 years old would be the easy way to remedy the issue...
 

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a flat spot or bog may be a better way to describe the problem for sure.
So a rebuild may be in order for me ?
Not sure what "welch plugs " or how to resize the idle air bleeds, is there some reading available ?
Distributor is a non vacuum advance with electronic conversion and the wires, cap and coil are new.
I was thinking that modern technology and parts that are not 55 years old would be the easy way to remedy the issue...
There's nothing new in carburetor technology. The 4100 is one of the best carbs ever designed. That said, sure, you can spend $500 to fix a $10 problem.
 

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Discussion Starter #7
if the problem can't be solved with a good rebuild, ie. bad/worn throttle shaft what are the chances of getting good quality parts?
I really would like to keep the 4100 but don't want to chase a problem that's not fixable and would rather put the $500 towards a permanent fix.
Also any comments on my current jet sizing ? I have tried 47's in the primary but that was worse !
Should I go bigger based on my engine set up ?
Hipo spec was 52 primary and 68 secondary however I'm not sure if I have hipo boosters in my carb.
 

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if the problem can't be solved with a good rebuild, ie. bad/worn throttle shaft what are the chances of getting good quality parts?
I really would like to keep the 4100 but don't want to chase a problem that's not fixable and would rather put the $500 towards a permanent fix.
Also any comments on my current jet sizing ? I have tried 47's in the primary but that was worse !
Should I go bigger based on my engine set up ?
Hipo spec was 52 primary and 68 secondary however I'm not sure if I have hipo boosters in my carb.
If you decide to scrap it I'll give it a nice home....
 

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Discussion Starter #9 (Edited)
I also have another 1.12 core and what looks like a rebuilt 1.08 that came with the car.
Is there a chart that shows the difference between the boosters ?
Also are there different "power valves"
 

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Bob Mannel's Small Block Ford has the listings for the small blocks only. There are a few 1.12's in there and not only on Hipos.
 

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Is there a chart that shows the difference between the boosters ?
If these IS, it's super-secret. I've been trying to get my hands on something of that nature for 20+ years. I wish somebody would take the time to photograph and measure the attributes of the different boosters and come up with a "guide". Besides the inner and outer diameters there are also the number and size of discharge holes, the size of the emulsion tubes, the air bleed holes, etc...
 

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Discussion Starter #12
So I did a couple checks to see if I had a vacuum leak.
First I covered the primarys with my hand and that caused the engine to stall, that's good right ?
Next sprayed the carb cleaner around the base and there was no effect on the idle at all, also good right?
My idle screws do make a difference in the idle and are set at about 1 1/2 turns out on both sides however when all the way in, the car runs poorly but does not stall completely.
I moved the accelerator pump link to the top hole at the carb linkage to try to give it a bigger shot but that didn't make any difference in the "bog" during transition

What can I check next ?
 

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I fought carb problems on my stock 289 for years. I swapped from 2V to 4V years ago and kept it that way a long time. From time to time would have problems with the Holley 4160. Got tired of fighting and went back to the 2V 2100 about 6 years ago. Had problems with two different carbs. Went back to the 4V setup, rebuilt the carb again and still had problems. 6 years of problems and just went and bought a Summit 500 carb. Just bolted it on, 1/8 turn out on idle mixture screws, 2 clicks leaner on electric choke and a bit slower on fast idle. Absolutely love this carb. After fighting it for many years, I consider it a good investment. Price was about $360 and I can smoke the tire again...:cool: Your experience may differ.
 

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You should consider installing an A/F ratio gauge. This will give you actual numbers showing what fuel mixture the engine is getting during the various driving conditions. With this information, you will know where to look when tuning.
 

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Discussion Starter #15
I keep thinking about a new carb but keep coming back to the 4100 and all the great reviews...
 

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Why not just rebuild it for the experience? A rebuild kit is cheap, and you may end up fixing things while you're at it. If a rebuild doesn't solve the problem, you can either determine that it's something else causing issues, or you can grab the Summit carb and sell off your freshly rebuilt 4100.
 

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Discussion Starter #17
The kit is cheap enough but it's the cleaning that becomes an issue.
With all the environmental stuff I don't think I can get stuff to dunk and soak the parts to clean properly.
 

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Thanks, how about this one ? Will it work as well ?
Meh... you get what you pay for. Also, if you're going to do a proper cleaning you need to remove all the Welch plugs and run the passages with a wire to knock out any junk. You'll find them at the tops of the boosters, the choke unloader piston bore, etc. DO NOT use anything that will enlarge the orifices! You may also want to check the throttle shaft looseness and rebush if needed.
 
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