The thing is it only takes a few minutes to pop another 6.5 PV in there just to cross it off the list.
Check the secondary throttle plates Back the screw off and seat the throttle bores Then when the screw barely touches the secondary lever, turn it in around 1/4 turn Some books show .086 in, some 1/4, 1/2 .. etc You can flip the screw upside down and adjust it without taking the carb off Also, do you have a good running vehicle you can try the 4100 on ?? Ricky.
I set the timing by ear and it turned out to be around 16BTDC. Didn’t make any difference to my issue though.
I did that when I rebuilt the carb, will double check I have another running car and carb but don’t want to mess with that till after the weekend’s racing.
I’ve confirmed that the new PV in there is ok but just because no one believes me I will put a different new one in when I get a chance.
Ok, another new power valve to keep you boys happy. Nope, no difference, it ain’t the power valve. Checked secondary adjustment screw, all ok
I have discovered that screwing in the right idle mixture screw all the way slows idle slightly but not much, screwing the left one in all the way (with the right one out) and it dies. Seems there is an issue with the idle circuit on the one side of the carb. I’ve swapped the Venturi/booster unit from the 2100 and it’s made no difference. I’ve pulled the jets and the aren’t blocked Passageways don’t seem blocked. I think I’m just going to replace the carb
I had to study up a bit again on idle air bleeds myself. And they seem to be pretty well concealed on the Autolite 4100 and their path is fairly convoluted. Looks like they could easily become plugged but not so easily cleaned. https://www.carburetor-blog.com/knowledge-base/autolite-4100-idle-circuit/ The thing to keep in mind I think is that the idle mixture screws don't just control the flow of strictly liquid fuel. They're designed to control the flow of an emulsion of fuel and air. If the bleeds are too large, or a small vacuum leak somewhere allows too much air into the circuit, the idle mixture screws can't richen the mixture enough to provide for a proper idle fuel mixture. If the air bleeds are restricted or plugged you'll see the opposite effect. The mixture screws can't lean out the mixture enough for the engine to idle smoothly. You can only attempt to screw them in so far before you end up shutting off the fuel flow completely. In the past when working with carbs that have readily accessible idle air bleeds, I got into the habit of momentarily blocking off the air bleeds while adjusting the idle mixture. Usually you could do so with your fingertip or a toothpick. If the idle speed or quality changed it indicated that the air bleed circuit was clear and working as it should. If the idle quality didn't change it meant that there was an existing restriction somewhere else in the idle air bleed circuit. The idle fuel circuit to the mixture screws needs to see an air/fuel emulsion and not just purely liquid fuel. The needle valve on the mixture screw isn't precise enough to deal with purely liquid fuel.
Also check that both idle mixture screws goes equally deep. Once overhauling qjet with both screws turned in other one is stil not bottomed, it had bad thread from the factory.
US fuel, in Worcester? Methinks you can't know how old that fuel is. I've been following along on the all two's thread but can't remember the full story of the car. If there's any doubt about the fuel it makes sense to eliminate it. What series do you race in? Bernies v8's by any chance. If so I'll see you running at Oulton in July. Chris
I’m going to try it from a can of new fuel next week. Yep Bernie’s V8s, Donington this weekend, should see you at Oulton.
I’ve replaced the carb with a Holley and sorted the rich running. It’s still not quite right though, there is what I’d describe as a non cylinder specific misfire. Couple of vids: https://oneball.smugmug.com/Cars/Merc-Original/n-5ZtcCv/i-ddPdrTq View my video at https://oneball.smugmug.com/Cars/Merc-Original/n-5ZtcCv/i-J2V6239 I’ve checked points gap, swapped to old coil and leads and rotor arm and it is no different RPM, mixture and base timing don’t seem to affect it If you pull plug leads one by one it doesn’t seem to affect it I can’t find any vacuum leaks Not sure where to go now The thing that’s really beginning to annoy me is there’s only been one car I’ve never been able to fix and that was a v8 BMW with a non cylinder specific misfire!!
If your 4100 is running rich at idle, and the float is right height, and your idle screws are somewhere near right…it is your power valve. Assuming you carb body is not cracked. You will not see the fuel in the venturies because it bypasses them and lets fuel go directly into the intake manifold via the vacuum port that signals the power valve. You can easily check the power valve on the 4100s and 2100s. Remove the carb, hold it level and remove the cap coving the power valve. If fuel is present in the cap…..you have a bad power valve. There were some bad power valves,made in past years. You may have some. These carbs are great carbs, but they are prone to rupture the power valves. Holley even started putting “ power valve saver valves” in their carbs. And the 4100 uses the same power valve as the Holley. Very easy check. I recommend it! Bones
Checked dwell, doesn’t change between 600 and 1500 rpm so don’t see a distributor issue. Checked compression, not perfect but not what I’d expect to cause a proper issue. Will see if I can pop an endoscope in there tomorrow, you can tell when you pull leads that it’s running better on the front 4 cylinders so I’m wondering if there’s an intake leak into the valley at the back.
I can’t give you a specific reason as to why it was running rich as swapping the Autolite for a Holley fixed that side of things and I’ve not dug any deeper. It wasn’t the power valve or float level or any of the other suggestions. You could be right that there’s a crack in the carb body or maybe a bunch of other stuff I can’t think of. The only real pointer for me was that I discovered one side of the idle circuit didn’t seem to be affected by the adjustment screw.
This, from the fordsix website re 2100 [4100] power valves: The early model 2100 Power Valve is not the same as Holley or the 2150 PV. I'm not sure yet if it is the cause of a rich cruise mixture/lean power mixture, but the Holley-type PV has some differences in size and design. The Holley PV on the left (removed), the 2100-specific PV on the right, just installed. One review of the 2100-only PV on Mike's Carb site said it cleared up a rich condition. Mike's also indicated that the early 2100's had this difference from the later model carbs, this new PV is sold as early 2100-specific at Mike's. The carb metered like it had PV fuel at all times. (Could not have been discerned without the AFR gauge- what a worthy investment!) I'll follow up after driving again. It doesn't seem likely this will make a difference, but stranger things have happened inside carbs! This not-expected-to-use on this build carb was cast 1/1964. . Still like it, not done working thru the mysteries and small bugs. It's more clean and unharmed than any old carb I've ever seen.
I had a dead miss in my T-Bird's 390 that turned out to be the brake booster; the bellows had ripped, causing a huge vacuum leak on that cylinder. If yours has a small leak, it could lean out cylinder #3 enough to cause an occasional miss. You might want to try blocking off everything to that vacuum port just to see. I don't know why Ford used a vacuum feed that largely affected one cylinder, but they did.
I disconnected the pcv but haven’t done that for the booster, it’s a new one as I had a leak from the old one but willing to give it a go to rule it out, thanks.
Tried disconnecting the brake booster and vac line to the gearbox and didn’t make a difference. If you leave the end of the pipe unplugged the rough running gets worse so I’m wondering if there’s a vacuum leak from the intake that I can’t pick up externally
Found the problem. Took one of the valve covers off and with the engine running ran an unlit propane torch around the join between intake and head in the valley and the revs picked up when I got to 7 & 8 so it’s leaking there.
No, it was running incredibly rich with the Autolite, I guess that was masking the intake leak which then became evident when I put the Holley on. So I had two issues; a rich carb and a leaking intake.
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