Ok, I'm running a 292 with a 2100 2-barrel carburetor in my 55 F350. While driving the other day it was backfiring back through the carburetor on acceleration from a start. So, when I got home I put my tach, timing light, and vacuum pressure gauge on; I assumed the port where my distributor vacuum advance connected (on the passenger side, below the manual choke, and at the base of the carburetor) would be where to connect the pressure gauge. But at 600 RPM idle and at 3 degrees BTDC, I have zero vacuum. I sprayed WD40 around the intake manifold, base of the carburetor, and everywhere else I thought I may have a vacuum leak - no raise in RPM at all just stayed steady at 600. I thought maybe my pressure gauge was faulty so I switched it out for another I had - same thing zero vacuum. I disconnected the vacuum gauge and checked with my finger, no vacuum pressure. Checked the internet and one fella said at idle there is no vacuum pressure with the 2100. Started buttoning things up and accelerated and now it bogs down. So I'm confused

I set my valves cold at .20 and then rechecked them hot at .19 - sounds like a well tuned machine; so I don't think I have late valve timing. When I set the valves I started at TDC and then turned the engine over 90 degrees and so-on-so-forth, following the firing order.

I had rebuilt the carburetor two years ago; before I had the truck running but it didn't have any fuel in it until last year.

Any suggestions would be helpful.

 

A '55 would have had a Load-o-Matic dustributor, and a "Teapot" carburetor no? A lot can happen in 60+ years in terms of replacement parts though, what kind of distributor is installed?

An Autolite 2100 has no source of direct manifold vacuum, the port is plumbed above throttle plates. Consequently no vacuum at factory idle.

 

Tedster9 - I replaced the distributor with HI-PERFORMANCE PRO SERIES READY TO RUN DISTRIBUTOR, the original one seized up on me breaking the drive gear and teeth on the camshaft. Teapot carburetor? Don't know what that is. I'm running the original 2100 2-barrel carburetor.

Well, you confirm it - no vacuum at the port on the distributor. So, I set the idle speed at 600 and then adjusted the air. Verified the timing was on 3 degrees BTDC. Now, I'll just let that be it.

 

Y-Blocks like lots of advance, try 13° instead of 3° and it should respond nicely.

 

Does the carb have 3 bolts or 4 to the manifold? If it has 3, then it's a 2110, a later edition of the 94, and it will have a Loadamatic port. That port is useless for the distributor you have, you want manifold vacuum.

 

I am not in the shop so I googled it and found that I was correct in my thinking that there is a ported or timed vacuum port that goes to your distributor. In the photo I found, it is in the metering block that is attached to the fuel bowl. Hope this helps.

Later!
Mr. Ed

 

2100 doesn't have a separate metering block, that sounds like a Holley 2300.

 

The 2100 Autolite Was patented and fist built in 1957 so it is NOT the original carb.
The Holley 2300 and 4150/60 were also first built and introduced for 1957.

 

Autolite 2100




Holley 2110

 

If it backfires through the carb during acceleration, it could be running lean. I am assuming you have set your idle mixture volume screws. Another cause might be a bad accelerator pump. With the engine off, while looking down the carb, I would see if you get a nice solid shot of fuel while moving the throttle lever. The 2100 is a good carb. But if it has been rebuilt, and new needle and seats and floats installed, then setting the floats correctly can be quite a challenge. A 2100 (like a 4100) has no external float adjustment. For the precise 'Wet adjustment" It's (very carefully and have a fire extinguisher handy!) get the engine warm, take off the cover, measure the float level, make a tiny adjustment to a tab on the float lever, and then place the cover over the carb and let it warm up again, and then check it again. Sometimes the "Dry Adjustment" procedure that is used in the rebuild procedure works and gets you close enough. Here's a page from Mike's Carburetors that if you scroll down will give you a link to a free 4100 carb manual. The 2100 is just 1/2 of a 4100, so these instructions will work.
Ford, Autolite, Motorcraft

 

^^^^ This is useful advice. Weak or missing carburetor accelerator "pump shot" of fuel upon acceleration could cause carb "backfire" due to a lean condition. Check for this first, since modern fuel is known to cause problems in vintage fuel systems. If this isn't the problem, look for plug wire crossfire or intermittent ignition etc.

 

My carb has 4 bolts to the manifold.

 

You're right! My 55 was owned by the Forest Service and later owned by a Local Tree Service. One of them swapped the 239 Y-Block out for a 292 and the 3-speed Transmission for a T-98; I can't see the USFS spending that money so I'm thinking it was the local tree service company, which is no longer in business, did the swapping. Along with the swapping I'm assuming the carb was changed. From the stamping on the engine block it came from a 60 something galaxie 500.

 

From your photos my carb is the 2100.

 

That's what I thought so I turned the mixture screws out alittle. Now it hesitates when I accelerate. I did check the accelerator pump and I have a good steady stream of fuel coming out. I did rebuild the carb but don't remember having any challenge to setting the float. I'll try the wet adjustment and thanks for link!