351C Carburetor Coughing

[patrickob17]

Hello everyone,

So my dad and I have been repairing his 1971 mach 1 mustang 351C 2V that he had in high school and college until it broke down. It's just sat for 30+ years until this past summer when we sent it out to a shop in town to get it to start, run, and stop. While they did manage to do that, they didn't do the best job in the world so for the past couple months, whenever I'm home from college, he and I always work on it together and I've gotten almost everything running beautifully now except for one big problem we have. The carburetor coughs. So when it's idleing in park it's just fine and in drive it's perfect too, but when driving it, when you step on the gas too quick the engine will "cough" out of the carburetor. I can't seem to find anywhere where someone's got the problem figured out. Some people say the fuel mixture is too lean, but when you accelerate in park it's fine so I didn't think that was the problem. Others say the Carb is just old and needs to be replaced or rebuilt, and others say it's the fuel pump itself. Honestly we're both lost on this one so if anyone has a list of things to try to identify the problem and try to fix it that would be a lifesaver. Thank you so much.

 

[Chopper]

Hello everyone,

So my dad and I have been repairing his 1971 mach 1 mustang 351C 2V that he had in high school and college until it broke down. It's just sat for 30+ years until this past summer when we sent it out to a shop in town to get it to start, run, and stop. While they did manage to do that, they didn't do the best job in the world so for the past couple months, whenever I'm home from college, he and I always work on it together and I've gotten almost everything running beautifully now except for one big problem we have. The carburetor coughs. So when it's idleing in park it's just fine and in drive it's perfect too, but when driving it, when you step on the gas too quick the engine will "cough" out of the carburetor. I can't seem to find anywhere where someone's got the problem figured out. Some people say the fuel mixture is too lean, but when you accelerate in park it's fine so I didn't think that was the problem. Others say the Carb is just old and needs to be replaced or rebuilt, and others say it's the fuel pump itself. Honestly we're both lost on this one so if anyone has a list of things to try to identify the problem and try to fix it that would be a lifesaver. Thank you so much.

Mate mine does the same when it's not quite up to temp, under hard acceleration it likes to cough at the carb.

Once it's warm it's much better.

Does engine temp change yours at all?

Sent from my iPhone using Tapatalk

 

[mustang7173]

patrickob17,

Accelerating in Park does not replicate the engine under load. It could be a bad vacuum diaphragm on the distributor, it could be the old carburetor does need to be rebuilt. You said it has been sitting for 30 + years. Time sitting is an enemy of automobiles.

All of the rubber components in the carburetor are probably rotted along with the vacuum diaphragm in the distributor. The coughing could also be timing related issues. The accelerator pump is suppose to elevate that issue when the carburetor and engine are cold.

Keep us posted on your findings.

mustang7173

 

[c9zx]

The accelerator pump diaphragm is probably stiff from age and not allowing the pump to work properly.

http://www.carburetor-parts.com/Carb-Type_ep_665.html

Chuck

 

[will e]

I would suspect the accel pump as well. A simple test. Start the car and let it run for about 30 seconds then turn it off. With the car off remove the air cleaner. Look down into the carb, hold the choke open if needed. Either have someone step on the gas, all the way to the floor or open the throttle quickly by hand. You should see a Spray of gas on both of the ventri's. Similar to what you might see from a squirt bottle when you pull the trigger. If nothing comes out or it just dribbles your accel pump is probably bad.

Good deal getting the old mustang on the road again!

 

[Don C]

I agree, likely the accelerator pump, possibly power valve.

 

[patrickob17]

Okay so I tested what Will C. said to do and it did spray just like you said it should from both ventris. Also the problem is actually worse as you drive. Like when we first take it out she'll run pretty well, then as we continue it starts to cough more and more. We tried to seafoam the engine like this guy did here http://diysrc.com/how-to-seafoam-your-cars-engine-to-clean-and-dissolve-carbon-buildup/ and that definitely helped out a ton, but after about a half hour of driving the cough came back. I don't know I'm starting to think that Mustang7173 is right in that it may just be that even though the place that did the repair either didn't do a full carb rebuild or just did a poor job of it because it doesn't look nearly as good as what I've seen from pictures when people say they do a carb rebuild. Any suggestions on what to do or what kit to use best works for this carb? Also I know this sounds crazy probably and it's something we probably wouldn't want to do simply because it's great to have almost all original parts, but someone said something about switching from a 2V to a 4V. What're y'all's thoughts on that?

 

[73pony]

Okay so I tested what Will C. said to do and it did spray just like you said it should from both ventris. Also the problem is actually worse as you drive. Like when we first take it out she'll run pretty well, then as we continue it starts to cough more and more. We tried to seafoam the engine like this guy did here http://diysrc.com/how-to-seafoam-your-cars-engine-to-clean-and-dissolve-carbon-buildup/ and that definitely helped out a ton, but after about a half hour of driving the cough came back. I don't know I'm starting to think that Mustang7173 is right in that it may just be that even though the place that did the repair either didn't do a full carb rebuild or just did a poor job of it because it doesn't look nearly as good as what I've seen from pictures when people say they do a carb rebuild. Any suggestions on what to do or what kit to use best works for this carb? Also I know this sounds crazy probably and it's something we probably wouldn't want to do simply because it's great to have almost all original parts, but someone said something about switching from a 2V to a 4V. What're y'all's thoughts on that?

Were they suggesting switching the heads from 2v to 4v or just putting an aftermarket intake on the 2v heads that will accept a 4bbl carb? The head swap is going to be a considerable amount of engine work and the cost of the heads as well as new intake and exhaust manifolds. The intake swap with a 4bbl carb is pretty straight forward and is a common upgrade.

 

[patrickob17]

Okay so I tested what Will C. said to do and it did spray just like you said it should from both ventris. Also the problem is actually worse as you drive. Like when we first take it out she'll run pretty well, then as we continue it starts to cough more and more. We tried to seafoam the engine like this guy did here http://diysrc.com/how-to-seafoam-your-cars-engine-to-clean-and-dissolve-carbon-buildup/ and that definitely helped out a ton, but after about a half hour of driving the cough came back. I don't know I'm starting to think that Mustang7173 is right in that it may just be that even though the place that did the repair either didn't do a full carb rebuild or just did a poor job of it because it doesn't look nearly as good as what I've seen from pictures when people say they do a carb rebuild. Any suggestions on what to do or what kit to use best works for this carb? Also I know this sounds crazy probably and it's something we probably wouldn't want to do simply because it's great to have almost all original parts, but someone said something about switching from a 2V to a 4V. What're y'all's thoughts on that?

Were they suggesting switching the heads from 2v to 4v or just putting an aftermarket intake on the 2v heads that will accept a 4bbl carb? The head swap is going to be a considerable amount of engine work and the cost of the heads as well as new intake and exhaust manifolds. The intake swap with a 4bbl carb is pretty straight forward and is a common upgrade.

They were suggesting the intake swap with a 4bbl carb I believe

 

[patrickob17]

Honestly though, I just want it to drive without coughing and take off when I stomp on the gas because no new car has that same sound and powerful feel to it that this car does. It's intoxicating just to listen to.

 

[73pony]

The intake swap and 4 bbl carb will give you some additional seat of the pants feel over the 2bbl carb for sure. I still think you have a timing issue though. Could be slack in the timing chain.

 

[patrickob17]

Thank you so much. Unfortunately though, I'm just now getting back to school so it won't be until May 9th that I can get under the hood and change anything, but if anyone has any suggestions or ideas I would love to hear them and relay them to my dad so he can see what he can do about it. I'm starting to think a carb rebuild is going to be our first step then we'll continue from there.

 

[Don C]

Even though your accelerator nozzles are squirting they may not be squirting a large enough volume. You either need to build or replace the carburetor and do a complete tune up.

 

[c9zx]

It should be an Autolite 2100 2V carb. The original carb tag may or may not still be there to identify the carb. +1 on Don C's post. Chuck

 

[patrickob17]

Thank y'all so much. We would still be stuck wondering what we should try to change otherwise.

 

[secluff]

patrickob17, very good advice given so far. In the interest of not throwing a lot  of money at a problem that may not need it, I would do as others have suggested and give a serious look at your carburetor. Easiest thing to do before tearing into an engine. There are plenty of seals, gaskets, and rubber components than can deteriorate with age, especially when they dry out after being wet with fuel.

As Chuck posted, the favorite pastime of a lot of mechanics was to pitch any identification tags found on engines, distributors, carburetors, etc. If the tag is missing off your carburetor and it is original to your car, you can look on the left front of the mounting flange or base plate and you should be able to read a stamping. This number should be the same as the metal ID tag. If the tag is missing and you can't read the stamping in the base plate, just go to your favorite parts house and tell them to cross a Ford rebuild kit (D4AZ-9A586-A or Motorcraft CT-499-D). By the late 70's and into the 80's, that kit replaced the majority of the 2bl kits used until EFI was just about on all Ford engines.

 

[Don C]

The picture that Steve posted (thanks Steve) shows the lever and rod that actuate the accelerator pump. Make sure the rod is in the next to top or top hole on the lever, that will supply the biggest shot of fuel. And if there are two holes on the lever on the other end, make sure the rod is in the inboard hole.