Any carb tuning wizards?

[Daveyd]

I have a 68 289 2 bbl that I recently got up and running and driving again. Anyway I rebuilt the carb and it still seems to me to be running rich. Idles nice and starts right up when cold but doesnt like to as much when it’s hot. The timing is good and shouldn’t be the issue. I ran the numbers on the carb it’s a c3af stamped round back carb with a 1.14 cast on it. 300cfm, and 51 or 61 jets. From what I can tell it came off a 1963 galaxie 289. Attached is a pic of a similar carb except without my manual choke. Under the diaphragm arm and cover looks different than the others I’ve see and just has a ball under the bolt coming from the top of the housing. From what I read there’s supposed to be a little buffer pad type thing. After looking at the diagram it’s the pump cavity filter. Could this be causing trouble as well? Thanks for any help, sorry if that was confusing.

 

[Daveyd]

Here is the picture of a similar one

 

[jckkys]

A '68 Bronco would have had an Autolite 2100 carburetor with 1.08" venturis instead of 1.12" venturis and a manual choke. The 1.12" venturis were used on 289s too, but in other vehicles. The automatic choke will need a heat source to open the choke as the engine heats up. Not a problem. The '63s used a check ball in the accelerator pump. Starting in '65 the 2100s got a red rubber umbrella type check valve. It's not a pad or a filter. Both check valves work.
I doubt a 1.12" venturi would have more than a .050" size jet. The 1.08" venturi carbs got 0.047" jets simply stamped 47. If your jets are 60s that would explain a rich condition. Do you still have the original '68 Bronco carb?

 

[Daveyd]

A '68 Bronco would have had an Autolite 2100 carburetor with 1.08" venturis instead of 1.12" venturis and a manual choke. The 1.12" venturis were used on 289s too, but in other vehicles. The automatic choke will need a heat source to open the choke as the engine heats up. Not a problem. The '63s used a check ball in the accelerator pump. Starting in '65 the 2100s got a red rubber umbrella type check valve. It's not a pad or a filter. Both check valves work.
I doubt a 1.12" venturi would have more than a .050" size jet. The 1.08" venturi carbs got 0.047" jets simply stamped 47. If your jets are 60s that would explain a rich condition. Do you still have the original '68 Bronco carb?

Thanks for the help! No I don’t. This one came with the bronco. I’m wondering if it’s worth it to get this one in nice order or just buying and rebuilding a holley, since I have a performer manifold laying around. I’ve heard these things are pretty good off road. It has the check ball, so that is correct and it seems to have been macguyvered with a manual choke.

 

[MS73HD302]

Sounds like heat soak to me. Fuels boiling and pushing past the needle flooding the carb. Mine does that with ethanol fuel but doesn’t with non ethanol. From my understanding a return line is the best fix with a flow through pressure regulator.

 

[gnpenning]

Why do you think it's running rich and when?

Did you replace the float and how did you set height?

Where are the idle mixture screws set and why?

Have you checked for vacuum leaks?

You said the timing is good, does that include vacuum and mechanical advance?

What is your dwell?

Early broncos came with manual chokes. Many have been converted to manual properly and some not so properly.

The 2100/2150 carb is a great carb both on and off road. About as simple as you can get as well. I wouldn't change to another brand unless your motor could use a little more.

 

[blubuckaroo]

I've found sometimes that, even when the float level is set correctly, the fuel level is wrong.
To check this, you'll need to remove the top cover from the 2100/2150 and check the fuel level, with the engine running.
The fuel level should be 13/16" +/- 1/32" measured from the top of the fuel bowl. Check the specs from your carb kit instructions.
I'd set it lower rather than higher to avoid boil-over.

 

[jckkys]

The 2100 is a far better carb than a Holley. The one you have would work fine if rebuilt and set up correctly. As blubuckaroo said the float level is just a preliminary step to get the engine running. Then you can set the fuel level that is the real adjustment. A rebuilding kit will have that spec and several others. I do recommend a rebuild since you don't know the history. An electrically heated choke thermostat would be the easiest way to get an automatic choke that never had heat tubes function. Here;https://www.carburetor-parts.com/2150-th1031.html is a late model electrically heated cap made to function on power from the alternator's stater post. Autolite/Motorcraft 2100/2150 don't convert to a manual choke easily. Here; https://www.ebay.com/itm/Ford-289-H...utolite-2100-4100-w-Choke-Shaft-/153526114665, is a real manual choke conversion. It's not cheap but it is real.

 

[707Bronk]

I was having this same issue on my brother in law's 69 bronco with a 302. It too had the 1.14 venturis and a manual choke. He wasn't having the hot start issues.

Initially it was running very rich, at idle, and cruising speed and under load. Just plumes of black smoke out the tailpipe. After resetting the timing and setting the idle screws it was better, but still way too rich across the board.

During the rebuild I noticed it had 53 jets. I went back to Mikes Carberator Parts site and ordered 51, 49, and 47 jets. I tried the 49 jets first and it was much better, but still too rich. Tried the 47 jets and its almost there. Still running rich, but much improved.

Its driveable now, just a light smell of fuel and slight puffs of black smoke when you accelerate, and a decent amount of black smoke until it warms up. Still want to get some 45 and 43 jets try try that out. We are at around 1200ft, btw. I still want to tune the vac advance and play with the timing a bit more, but I think with the 45 or 43 jets its gonna run great.

Wasn't expecting to have to jet it soo much, but the 1.14 venturis I'm pretty sure aren't typical on the bronco's or even typical on the 302's. But those stock 2bbl carbs are really good running carbs. If I had a 2bbl manifold for my 351W I'd consider switching out the 4bbl truck avenger for the stock 2bbl. But I do like the TA, its pretty easy to work on and hasn't failed me yet.

 

[jckkys]

The 1.14" venturi 2100s were all used on 289/302 engines. But none on EBs, that were all 1.08". The 1.08" 2100s appear on ebey regularly and are preferable for EBs. With a little patience you can get one. I don't trust the big rebuilders that often lie. They seem to toss all the ID tags to hide their lies too. They also offer near nothing for cores that are usually better carbs than what they sell you.

 

[707Bronk]

The 1.14" venturi 2100s were all used on 289/302 engines. But none on EBs, that were all 1.08". The 1.08" 2100s appear on ebey regularly and are preferable for EBs. With a little patience you can get one. I don't trust the big rebuilders that often lie. They seem to toss all the ID tags to hide their lies too. They also offer near nothing for cores that are usually better carbs than what they sell you.

Good info. Do you know what the stock jets were for the 1.08” and 1.14” for sea level conditions.

 

[jckkys]

The 1.08" venturi 2100s were usually equipped with 47 jets. The few 1.14" venturi 2100s I've been able find the specs on, had 50 jets.