Help with troubleshooting 2100 Carb

[JWMcCrary]

I ordered a rebuilt carb from Rock auto last October, right when it showed up I went down with a kidney stone and by the time I was over that it was past my wheeling days for the year up here in Ohio. I bolted it on and fired it up, ran good. Put the cover on for the winter. Problem is now it won't run consistently. You start it up and it runs fine, warms up, starts are good but randomly it will act like it's out of fuel, but there is no fuel delivery problem. Get started back running and the idle is low, have to adjust idle to keep it running. I can adjust the idle mixture screws in and out and it makes no difference. Doesn't make any sense to me. Shut it off, let it sit a bit, go back and adjust the idle mixture screws to 1.5 to 2 turns out and it fires up and runs great other than having to lower the idle. Take off down the road and within 2 miles its acting up again.

Any ideas before I throw this carb in the trash and get another one?

 

[B RON CO]

Hi, maybe the gas is stale and that could be the problem.
I like to add @4 oz of Marvel mystery oil the each fill up on my class is cars.
Good luck

 

[Rustytruck]

See if it does the same thing with the gas cap off. I would check the fuel line from front to back for loose clamps or bad fuel line. I would check the fuel pump for pressure and volume. Bad move for changing a Bronco carb for an autoparts rebuild. You just dont know whats inside.

 

[blubuckaroo]

If turning the idle mixture screws makes no difference, I suspect the air bleeds are plugged up from storage.
Pull the idle mixture screws out and flush the air bleeds out with a spray carb cleaner like Chemtool.
Also, a nice thing about the 2100 carb is you can run it with the top removed. That way you can see what the needle valve is doing and set the actual running fuel level.

 

[72Sport]

Go to Wal Mart and buy a can of Sea Foam and pour it in the gas tank Sounds like you have had water condensing in the gas tank. The Sea Foam will help burn off the water.

My experience: I have owned a 72 boat with a 302 for 40 years. I never did anything to the engine except change oil and add gas. Four years ago I towed it to Austin Tx for my son to use along with the grand kids. While we were waiting on the moving van to show up at his new house we took the boat out to kill some time. It ran just like it did in Ca, perfectly. A few months later I started to get phone calls. Dad did you ever change spark plug wires etc etc etc. I think he spent about $1000 dollars fixing things. It was spring time when one of the shop mechanics said you know a lot of boat owners put Sea Foam in the their gas when they take their boats out for the first time. He took the boat out for a test run and got stuck out on the lake. Someone towed him back to the dock. He got a can of Sea Foam and poured it in the tank. After a few minutes it started to run just like in CA.

Went to Austin a couple of weeks ago and took the boat out. Ran like crap until he added a can of Sea Foam.

 

[JWMcCrary]

If turning the idle mixture screws makes no difference, I suspect the air bleeds are plugged up from storage.
Pull the idle mixture screws out and flush the air bleeds out with a spray carb cleaner like Chemtool.
Also, a nice thing about the 2100 carb is you can run it with the top removed. That way you can see what the needle valve is doing and set the actual running fuel level.

Thinking this is likely my next step. It's something with the carb and not fuel delivery or bad fuel (as some others have leaned toward fuel supply or water in fuel). It wasn't out but I poured 5 gallons of fresh in. 15 gallon fuel cell mounted in the bed with gravity feed directly into 4070 electric pump, I'm getting loads of good fuel to the carb, no issues there.

 

[jckkys]

Going to Rock Auto for a rebuilt 2100 is a problem. You now have no idea what 2100 you have. To ID the carb, you need the letters and numbers stamped on the front drivers side foot on the vertical surface, plus the venturi size cast on the driver side of the float bowl. The 2100/2150s changed every year so we need to what year and transmission you have to see if Rock Auto came close. The large scale rebuilders rarely get it right.

 

[Justafordguy]

If it ran good before you parked it I bet you just need to clean the carb out.

 

[Skytrooper15]

Have you checked for vacuum leaks on and around the carburetor?That may be why the air/fuel needles won't adjust any.Also check to make sure the choke is closed while cold and slowly opens up as the engine warms up.But like someone said you can take out the 4 screws holding the air horn on and remove the choke rod to carburetor vanes and see what is happening inside the carburetor is doing, as in float movement.If all else fails just put a repair kit in because the problem may be varnish build up.Just buy a can of carb cleaner to get it good and clean.If it worked when you first put it on it should work right after the kit installation.

 

[jckkys]

The automatic choke may be the problem, but we don't know what kind of choke Mr. McCrary has or should have, since he didn't tell us what year Bronco he owns. Nor did he relate the ID stamped on the carburetor. The '66-'69s had manual chokes.

 

[72Sport]

I guess no one here likes or has used Sea Foam. The instructions on the can mentions that it controls moisture in fuel, gasoline or diesel.

The thread says the Bronco was parked in October and it ran fine. I would guess that there are pretty wide temperature ranges on any given day from October to May in Ohio. A friend who lived in PA says he has seen a 50 degree drop in two to three hours. The reason for this info is that the gas in the tank stays warmer longer than the sides and top of the outside of the tank. When you get warm moist air heated by the warm gas the moisture will probably condense on the inside of the walls of the gas tank and will run down the sides into the bottom of the gas tank. The tank is probably vented to outside air at some point which brings in more moist air as the outside air temperature heats and cools. If the heat cool cycle goes on for several months you could have enough moisture in the tank to make a 302 run like crap.

This missing etc in my Son's boat did exactly that two weeks ago. I was surprised to see he had two cans of Sea foam in his box of spare parts. Within a minute after adding Sea Foam to the gas it began to run like it had in CA/NV for 40 years.

I don't know what 2 barrel carb was on the boat because I never worked on it. It did have a Mallory dual point distributor. I don't remember ever changing the points. The engine did have a leaky Bronco slip in dip stick pan which I fixed.

 

[Skytrooper15]

The automatic choke may be the problem, but we don't know what kind of choke Mr. McCrary has or should have, since he didn't tell us what year Bronco he owns. Nor did he relate the ID stamped on the carburetor. The '66-'69s had manual chokes.

I have a 66 carburetor with an automatic choke and I do believe that automatic chokes were on all models of Broncos.You may be getting heat riser chokes and electric chokes mixed up.

 

[JWMcCrary]

Sorry....It's a 68 body on a 75 frame with 76 axles, 302 engine out of god knows what, 2 barrel carb with electric choke, NP 435 trans, not a single thing here like came from the factory. The problem occurs with the engine warm and the choke open, it's an electric choke. The carb that was on it came off of a 73 with an auto, and it worked fine just needed a rebuild. Due to fact it had a few stripped screw holes I decided it wasn't a good candidate for a rebuild. I have no idea what the numbers stamped on it are, it may not be the "perfect" carb for this engine but it should run without the problem I am having. Even if it's the "wrong" carb that's not the issue I am having. I'll get it sorted out, just thought describing the issue might allow someone to save me a little troubleshooting. I'm feel like blubukaroo is right and I need to clean some grit or trash out of it.

I do appreciate all the feedback.

The automatic choke may be the problem, but we don't know what kind of choke Mr. McCrary has or should have, since he didn't tell us what year Bronco he owns. Nor did he relate the ID stamped on the carburetor. The '66-'69s had manual chokes.

 

[chrlsful]

also needs mods if run off rd (fuel slosh) due to the gradients (L/R, frnt/rear).
To me? they're one of the best carbs made (@ CFM, annular discharge, tuneability, 2v).

 

[JWMcCrary]

Well, the rock auto rebuild is the problem. Swapped out the carb and it’s running great. I knew the fuel supply was fine. Later on I’ll tear into it and see what I find since I’m sure I’ve had it too long to return.

 

[chrlsful]

"...too long to return."
doesn't matter, many of us have a rebuilding kit waitin for when the box arrives.
Never trust em...
Mike's carbs (on-line) hasa good rebuild vid, good parts...

 

[jckkys]

For anyone's info '66-'69s had manual chokes as produced at the factory. I kind of thought this was common knowledge. Also, electric choke is a misnomer. Some automatic chokes have electrically heated thermostats. They are not electric chokes. Most of these were originally heated by the exhaust manifold choke stove that rusted away or was replaced by headers, and not OE. The later '75-'77s had 2150 carbs using both a choke stove and an electrically heated thermostat. The '70-'74 2100s used the choke stove in the exhaust manifold alone to heat the thermostat. The year an EB was made is important so is the venturi size. The large scale rebuilders rarely get it right. It may be easier to ignore this reality. It's just not smart. The only off road modification worth anything is a slightly lower fuel level in the bowl. Fuel doesn't slosh out of the vents. It comes out of the boosters when the carb is shaken.

 

[Rustytruck]

1974 california had the exhaust heat stove with electric heat coil on the carb. Mine was built june
1974.

 

[jckkys]

There were a lot of "special" California emissions oriented variations that are irreverent to the rest of the country. Then again an electrically heated thermostat cap can be installed with .just 3 screws and a wire. The objective is to get the choke open asap, avoiding an over rich mixture after the engine has run long enough that the choke isn't needed. When using a manual choke I've found that I can fully open the choke after 1-2 min. in cold weather. I always used both systems to heat the choke thermostat. The electric heat works faster and the exhaust manifold heat stove stays hot for some time after the engine shuts down assuring an open choke on restart when the engine is still warm. '75 and later 2150s all used both thermostat heating methods plus a vacuum diaphragm pull off to open the choke faster.
Competent use of a manual choke is better than any automatic choke. Unfortunately there aren't many owners/drivers that know how to use a manual choke. The bureaucrats on the CARB (Cal. air research board) don't believe in trusting ordinary citizens to be competent.

 

[chrlsful]

and the 'heat stove' (lill tube drawing hot air up frm exh manny) brings dirty air up into the carb, less than desirable. I like the 'closed PCV system' 4 same + pollution control...