Carb problem frustration level 10/10

[Cribbs74]

I hope I can encapsulate everything that is going on. (Autolite 4100) First start of the car and it ran and idled. Then it revved up and kept running then started shaking then shut down. Hard to restart, but when it does it does the same thing. Super rich

Removed carb, found that primary and secondary venturi’s were swapped, fixed that, reinstalled same thing all over again. I can’t get it running long enough to check timing adjust mixture or check vacuum leaks.

I have blocked off all vacuum and no love. Fuel is soaking the base gaskets so it’s flooding. Had a leak from the power valve, fixed that by doubling the gasket (two in kit) used one the first go around.

I have had the carb off and torn down close to 10 times now. check balls are in the right place, float level is triple checked, needles seated and pass blow test.

I am really at a loss here guys.

Ron

 

[MikeGriese]

Sounds like this carb really needs a complete rebuild. Stop trying to fix what is there. Tear it down, clean it up, put in a fresh rebuild kit and start from a known state. The mere fact that the venturis were swapped means that whoever worked on it before didn't know what they were doing, so everything else is automatically suspect.

 

[Cribbs74]

I dipped/ cleaned and installed a kit before I even put it on the car. The swapped Venturi’s are because I put it back together the same way I took it apart. I am really good at reassembling from memory, but not so good at paying attention If it was correct in the first place.

I do have a buddy that has a Holley 1850-2 that I was offered to me. I will only use it if it can accept my stock air cleaner.

 

[Hemikiller]

It's possible you have too much fuel pressure, or there is junk in the needle/seat(s), causing a high fuel bowl level. I'd remove the needle and seat assemblies and inspect them for trash and damage, then blow out the fuel passages with compressed air and/or carb cleaner. If everything looks good, set the dry float level to the lowest setting shown in your spec sheet. The lowest in the '66 manual is .571". See if that solves your flooding issue so it'll run, then perform the wet fuel level adjustment.

What's the stamped number on the carb baseplate?

 

[piper62j]

I agree with Mike.. The 4100 series carbs are simple and very reliable. It's worth going back to square one and performing a complete rebuild. Do not remove the throttle plates. There are two different power valve gaskets and you should not have had to use two of them to stop the flooding. The tapered hole for the valve requires a different gasket than the hole which is machined flat. The instructions from the rebuild kit will show which one is used.. One other thing is the lock down spring for the needle and seat. If that is not secured to the seat ring groove, the float will not be able to push down on the needle to stop the flow of fuel from flooding the bowl. Take your time and watch a few YouTube videos for even more information. I've rebuilt many of the 4100's and never had a problem.. Best of luck..

 

[Cleveland Crush]

Agree with Hemikiller. Sounds like excessive fuel pressure Cribbs. Use a hand-held fuel pressure/vacuum gauge (indispensable for tuning any engine setup) and look for about 4-6 psi. just before the carb. Anything over 7 psi is getting into the danger zone, overloading the needle seat. If it passes the pressure check, time to open the carb back up as mentioned by piper and Mike. If over 7.5 psi the fuel pump needs regulated or replaced. Good luck with it.

 

[Cribbs74]

I didn’t explain very well. This isn’t a dirty carb issue or a non rebuild issue. I was being serious that I have pulled and disassembled roughly 10 times. I thought for sure I found the smoking gun when I realized venturi’s were swapped. My float levels are correct and have been triple checked. Clips, needles and seats are correct.

Fuelpressure may be a thing so I will check that for sure as I already thought about that.

Every time I pull the top of the carb off My fuel level is roughly 1/2” from the top. I have not done a wet measure. So I will do that.

This should be working, it’s almost like I have a hairline crack in the bowl that only appears when the carb is tightened down. With the carb off I see no leaks underneath when I fill the bowls on the bench. However, when I pull the carb after runnin, underneath the carb up into the cavities and air passages it’s wet when it should be dry.

Also, I pulled the PCV line off and fuel came out and that makes no sense whatsoever.

Thanks for the help and suggestions as always.

Ron

 

[MAD IRISHMAN]

My bad on previous post. I was thinking 4300.

 

[MAD IRISHMAN]

I would agree on the checking of pressure as close as possible to the inlet. I'm assuming your using mechanical fuel pump. If it's an electric one, like a Holley, sometimes the pressure relief bypass can stick over coming the needle & seat.

 

[Mach I Pony]

Cribbs74
If it makes you feel ant better your not the only one going around the mulberry brush with a 4100 carb. After my third failed attempt I had to set it aside ( that was a month ago). I'm contemplating either having it professionally rebuilt of purchasing anew one. My research tells me that the two choices are about the same cost. I'd totally replace it but I show my 73 MACH I.
I received multiple awards on the car and don't wish to alert it.

So to the rest of you "Lead on McDuff" I'm hoping to end this trek with at least enough left to fill the tank once. When I first purchased my Mach I I could fill the tank for $16.76. The last time it $68.80

 

[Hemikiller]

Every time I pull the top of the carb off My fuel level is roughly 1/2” from the top. I have not done a wet measure. So I will do that.

Attached is spec sheet from the 66 manual. 1/2" wet fuel level is extremely high. Have you checked the condition of the floats? Brass floats can leak, nitrophyl floats get saturated.

 

[Cribbs74]

Floats are working well. No leaks or fuel inside. My carb is C4SE-B

supposedly off of a 64 Tbird. It is 1.12, but Installed the brass 1.08 restrictors

 

[Cribbs74]

So, quick update, I lowered the floats to .491 dry and .880 wet or roughly therabouts. I also completely disassembled soaked and then blew out every passage possible. I also ran bread tie wire through all holes accessible then reassembled. installed on car, started ran for 10-15 seconds somewhat smoothly and then the same thing again with the crapy running and shutdowns fuel everywhere. For fun and because I had it available I mounted the Holley, same exact thing happened. Fuel was actually shooting out of the bowl vent. So…. I need to test the fuel pressure. I installed a new Delphi fuel pump before I started all this and I am really curious as to the output. I don’t have a fuel pressure gauge and I am going away for a week. I’ll let you all know what I find.

Ron

 

[Hemikiller]

I'd say that rules out the carb with some certainty

 

[mrgmhale]

Agree with Hemikiller. Sounds like excessive fuel pressure Cribbs. Use a hand-held fuel pressure/vacuum gauge (indispensable for tuning any engine setup) and look for about 4-6 psi. just before the carb. Anything over 7 psi is getting into the danger zone, overloading the needle seat. If it passes the pressure check, time to open the carb back up as mentioned by piper and Mike. If over 7.5 psi the fuel pump needs regulated or replaced. Good luck with it.

I have another enthusiast who has a similar situation, but with a 1972 Cougar with a 2100 2v carb, of all things. I suggested he acquire a vacuum/pressure tester and test for his fuel pump's pressure and volume. I also provided him the fuel pump performance specs he is to compare his results to. My gut tells me his fuel pressure is too high, much too high, causing fuel flooding out the venturis. Nothing else makes sense with his symptoms. I have never seen a mechanical fuel pump put out more, much less significantly more, pressure than the spec in the shop manuals (less than, but never over), especially to an excessive degree that it caused an excessive amount to be dumped into the fuel bowl. But, he sent me a 2 videos where the engine is turned off, the top of the 2100 carb is removed, the float and liquid fuel levels look okay. But, when he presses down on the float "long end" of the fuel float the residual pressure being retained causes a bit of fuel spitting.

I have run 2100 carbs with their cover off in the past, when looking for specific dynamic behavior.
But, I never pressed on the float, with the engine on or off, to see what the result would be re: fuel spitting under pressure - especially residual pressure when the engine is not running.

The two short video files he sent are attached. Although the liquid fuel level in the fuel bowl does not look excessive, that could be on account of an excessive amount of fuel being dumped down the main venturis. When he presses the float down and get the kind of fuel being spit back at him, down it look like what he is seeing is normal, or possibly an indication of excessive pressure?

Once he gets a vacuum/fuel pressure gauge, and get me the performance specs, I will share it with the group.

Thank you, my fellow enthusiasts!

 

[Cribbs74]

Ok, back home, pressure gauge showed right at 7PSI. Now I know it was said previously that 7 PSI is marginal and anything over 7.5 needs to be regulated. The test setup was pressure gauge attached right at the steel fuel line before the carb inlet. I only used the starter to crank the engine as opposed to starting it up. I would assume that it should be the same as the engine running.

 

[Cleveland Crush]

Hi Cribs, I would have more confidence in a running fuel pressure test vs. a cranking test. Most all carb tuning guides recommend a running engine to let the carb stabilize before testing. I did a bit of research on the Autolite 4100 at Mike'scarburetorparts.com, he states 6.5 psi running pressure is the max for a Autolite 4100 (his page 16). You mentioned your caraking pressure is 7 psi; even Holley double pumpers start to struggle at 7psi. Again good luck with it. Keep us posted as you get it sorted out.

 

[Cribbs74]

Update on the problem. It was indeed the fuel pump. I installed the old original last night and it ran. Poorly, but no more flooding. Debating on returning the new pump, but highly doubtful that I won’t have the same problem. There isn’t much room to run a regulator between all the steel hard line.

 

[mrgmhale]

Update on the problem. It was indeed the fuel pump. I installed the old original last night and it ran. Poorly, but no more flooding. Debating on returning the new pump, but highly doubtful that I won’t have the same problem. There isn’t much room to run a regulator between all the steel hard line.

Many congratulations. I hope this means you have are now able to begin cutting around in the Mustang, once you have it running perfectly.

 

[Cleveland Crush]

OK Cribbs, based on your feedback, bite the bullet and put on a new pump; cheap and easy plus good odds at fixing the problem!