Carburetor help...

Hello,

I need some help with my carburetor. I have a 1971 Ford Mustang with a inline six 250. I have a Carter RBS single barrel carb on it (Carter RBS 1V Carb w/Electric Choke, P/N 1-283). As of now, I cannot start my 71 Mustang. Here is the story thus far...I went to start my car last week and while it turned over it would idle briefly and then stall. It did this repeatedly. I tried to spray some carburetor cleaner in the carburetor, but this didn't help. As long as I kept my foot on the gas peddle it would continue to run, but as soon as I let go...it stalled.

I thought maybe it was the carburetor having problems so I tried to change the idle mixture screw to no avail. I turned it out so that it would be a richer mixture, but this didn't work. While the engine would sporadically try to turn over, it stopped starting all together even with my foot on the gas peddle. I tried various idle mixture screw positions and tried to find my original setting, but while it would sometimes try to start, it wouldn't any longer when I pressed the gas peddle. I was also starting to get some backfires in the carburetor itself. I continued trying to make adjustments to no avail.

So, I finally decided to replace the carburetor with another Carter RBS single barrel. The following is a picture -


Before installing it I had a question about a hole in the lower gasket, which I assumed was for a vacuum port under the carburetor, but the hole on the gasket didn't match up with any holes under the carburetor. I am not sure if this is causing a vacuum problem, but my old gasket didn't have any holes at all. See picture below of my current re-manufactured carb.



At any rate, I installed the carburetor with the gasket supplied, and it is acted exactly like my old one was after I made adjustments to the idle mixture screw. It seems like it wants to start idling, but it stalls, or backfires depending on the mixture screw setting. I am not sure what is wrong. Before on my old carb before I made any adjustments at all it at least ran when I kept my foot on the peddle when the engine was revving, but no longer. I don't understand what has happened. It is frustrating. I can't even take it to a mechanic without calling a tow truck to take it there because it won't start. I believe it is possibly something with my setting on the carburetor, but I understand it could be other issues with my engine, ect.

I would like to know if anyone has any experience with my type of engine and carburetor to see what they think. Also, I would really like to know what is the recommended idle mixture screw setting for this carburetor. I have been told after gently seating it that I am to turn it out one and half turns. It came with two turns out. And, I have heard someone in a video say to start with three turns out. I tried just about every position, starting at 1.5 turns out and make one quarter adjustments and trying to start the car all the way to having the screw adjusted to 5 turns out. Afterwards I noticed that the fast idle screw was adjusted almost all the way in. So, I turned that back until it wasn't touching and then back in until it was pushing a little bit. I thought maybe it was letting too much gas in previously by being turned in to far. At any rate, now that it is turned back I am going to wait and try adjusting my idle mixture screw again back to what the carburetor re-manufacturer sent it to me with (two turns out).

Before all of this my car has been running great (other than rough starting for the first minute or so on a cold start). Any thoughts?

Thank you.
 
Howdy,
I don't want to sound like a smart mouth but did you adjust the choke correctly? Did you adjust the cold idle choke? The car should run even with the vacuum port blocked off, it'll just run like crap, all mechanical advance. Check for vacuum leaks, did you plug the EGR plug on the carb? Is the float set properly (it should be if you bought a reman) ?.

Id start with the mixture screw at 1.5 turns out, that'll get you running if there's no prob.
Possibly your timing slipped? Try advancing it or retarding it.
Have you checked fuel pump pressure? Or the float bowl?
My 61 Studebaker Lark had issues getting gas. I had put a new pump on and all but it refused to start, the needle and seat had permatex in it (I bought the car after it'd sat for 10+ years. I swear that wasnt me haha).

Good luck,
Ryan
 
Mustang71":1sz3dqkj said:
Hello,

I need some help with my carburetor. I have a 1971 Ford Mustang with a inline six 250. I have a Carter RBS single barrel carb on it (Carter RBS 1V Carb w/Electric Choke, P/N 1-283). As of now, I cannot start my 71 Mustang. Here is the story thus far...I went to start my car last week and while it turned over it would idle briefly and then stall. It did this repeatedly. I tried to spray some carburetor cleaner in the carburetor, but this didn't help. As long as I kept my foot on the gas peddle it would continue to run, but as soon as I let go...it stalled.

I thought maybe it was the carburetor having problems so I tried to change the idle mixture screw to no avail. I turned it out so that it would be a richer mixture, but this didn't work. While the engine would sporadically try to turn over, it stopped starting all together even with my foot on the gas peddle. I tried various idle mixture screw positions and tried to find my original setting, but while it would sometimes try to start, it wouldn't any longer when I pressed the gas peddle. I was also starting to get some backfires in the carburetor itself. I continued trying to make adjustments to no avail.

So, I finally decided to replace the carburetor with another Carter RBS single barrel. The following is a picture -


Before installing it I had a question about a hole in the lower gasket, which I assumed was for a vacuum port under the carburetor, but the hole on the gasket didn't match up with any holes under the carburetor. I am not sure if this is causing a vacuum problem, but my old gasket didn't have any holes at all. See picture below of my current re-manufactured carb.



At any rate, I installed the carburetor with the gasket supplied, and it is acted exactly like my old one was after I made adjustments to the idle mixture screw. It seems like it wants to start idling, but it stalls, or backfires depending on the mixture screw setting. I am not sure what is wrong. Before on my old carb before I made any adjustments at all it at least ran when I kept my foot on the peddle when the engine was revving, but no longer. I don't understand what has happened. It is frustrating. I can't even take it to a mechanic without calling a tow truck to take it there because it won't start. I believe it is possibly something with my setting on the carburetor, but I understand it could be other issues with my engine, ect.

I would like to know if anyone has any experience with my type of engine and carburetor to see what they think. Also, I would really like to know what is the recommended idle mixture screw setting for this carburetor. I have been told after gently seating it that I am to turn it out one and half turns. It came with two turns out. And, I have heard someone in a video say to start with three turns out. I tried just about every position, starting at 1.5 turns out and make one quarter adjustments and trying to start the car all the way to having the screw adjusted to 5 turns out. Afterwards I noticed that the fast idle screw was adjusted almost all the way in. So, I turned that back until it wasn't touching and then back in until it was pushing a little bit. I thought maybe it was letting too much gas in previously by being turned in to far. At any rate, now that it is turned back I am going to wait and try adjusting my idle mixture screw again back to what the carburetor re-manufacturer sent it to me with (two turns out).

Before all of this my car has been running great (other than rough starting for the first minute or so on a cold start). Any thoughts?

Thank you.

I have seen this same situation often over the years and most of the time it's not the carb causeing the problem. But let's start were we are now. The mixture screw has very little to do with the car not starting it's only used to fine tune the idle mixture to its the lean best idle. The mixture screw should be set at 1 1/2 turns out for the base setting on a rebuilt carb until it's running. The throdle stop screw should have a base setting of about 1/2 to 3/4 turn open after touching the throdle arm until the engine is running, then it's set to the curb idle RPM. You didnt state what else your car has for the transmission so some of the below specs like idle RPM and base timing won't be exact but the rest is.

Now let's go over what I think is the real cause if your engine is in reasonably good condistion. The condistion of the ignition system.
A good tune up follows this order of work and settings for a non electronic ignistion system.
1. Set the spark plug gap to .034.
2. Set the points basic setting to .025 after its runing set the Dwell Angel to factory spec of 38 degrees.
3. Now you need to set the timing at 8 to 10 degrees BTDC base timing
4. Set the Idle mixture to its Lean Best Idle.
5. Set the curb idle speed to 500 RPM.
6.Repeat 4. & 5. To see if it improves anymore.
You might also test your coils output with the volt / ohm meter as well as the plug wires and cap for their resistance readings are in spec.

An engine needs three things to run Air, Fuel, and Ignition! Since you said it did run but was hard starting we know that you have air and fuel. So I would first look at the condistion of the spark plugs. If they are good condistion (pictures would help) you could clean then regap them to .034, reinstall or you can replace them especially if they look worn on center electrode. Next check the condistion of the points if they are good (again pictures would help) i.e. they haven't transferred metal from one point to the other. If they look good check the gap opening is at least .020. What's the condistion of your Coil, Plug Wires, Distribitor Cap, and Rotor these can all be checked out with a simple volt / ohm meter or replaced. Let me know what you find and we will go from there, but don't make too many changes at a time. Good luck in your tuning (y) :nod:
 
Thank you guys for your time and help! I put the remanufactured Carter RBS carburetor that you see in the picture on, so the settings they had on it should have worked. I am going to try the adjustments mentioned to see if I can get it going. But, if that doesn't work it may not be the carburetor. I think what has been said about the ignition system may be the culprit. Although, just this summer (just a few months ago) I had the car tuned and they put new spark plugs, distributor cap, wires, coil, ect and it was working great...and suddenly now it isn't. Besides the cap, I am not sure if they changed the actual distributor. That could be an issue. I may have to take in to a a mechanic that I know can work on these older vehicles. I was hoping that I will let you know how it goes.

Thanks again!
 
Mustang71":3w22748q said:
Thank you guys for your time and help! I put the remanufactured Carter RBS carburetor that you see in the picture on, so the settings they had on it should have worked. I am going to try the adjustments mentioned to see if I can get it going. But, if that doesn't work it may not be the carburetor. I think what has been said about the ignition system may be the culprit. Although, just this summer (just a few months ago) I had the car tuned and they put new spark plugs, distributor cap, wires, coil, ect and it was working great...and suddenly now it isn't. Besides the cap, I am not sure if they changed the actual distributor. That could be an issue. I may have to take in to a a mechanic that I know can work on these older vehicles. I was hoping that I will let you know how it goes.

Thanks again!

That's good the more info on what's been done the better to be able to help you! So with having recent new plugs, cap, rotor, wires, and coil, you can be fairly sure they are still good. If the Distribitor is older it may cause some trouble due to a worn upper shaft bushing that causes the point dwell to be off. You can check this by pushing on the rotor towards the engine block and then pulling back towards you to see if you can feel the bushing ware. Even if the distribitor is in good condistion points rubbing block wears and the gap closes up this can happen in as soon as 5,000 to 10,000 miles. So I would still focus on the distribors points and the condistion of the Distribitor.
Also Substitute these tune up specs for the ones in above post.
Stock base timing for a 1971 Mustang is 6 degrees BTDC, 8 to 10 degrees may still work better though.
Idle RPM for a Manual trans is 750, or for an Auto trans its 600 RPM.

By the way an excellent and easy upgrade for your Mustang is to swap in an electronic kit like Pertonix or better still if your Distribitor is worn out would be to put in the Ford DuraSpark II Distribitor and its control box from a 1976 up Ford Six an easy swap for a big improvement in performance and also better economy. Good luck in the tuning. :nod:
 
:unsure: Before you get wild and crazy with changing a bunch of parts,start with changing the condenser first .The new ones available today are of a very poor quality.China crap.You might also swap to solid state ignition such as the Pertronix unit if you so desire.Or better yet the DS11 ignition system.
Good luck.Have fun.Be safe.
Leo
 
Hi, X2 on the poor quality of replacement parts. A simple spark test is to gently remove the center coil wire out of the distributor and hold it about an inch or less over hole in the cap. Hold the wire from the middle so your fingers are not too close to the distributor cap and have a helper crank the engine. You should see a healthy blue spark jump from the wire to the distributor cap. You can also buy a spark tester at any auto parts store.
If the spark is weak or non existent you have to make sure there is current at the coil, and or suspect the tune up parts. Maybe Pertronix ignition and coil is your best choice.
Concerning the carb and fuel system, are you sure the fuel pump is pumping plenty of fuel to the carb, and that there is no vacuum leaks?
Good luck
 
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