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New carburetor Carter RBS for 250ci 6cyl.


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Hey,

 

It's been a while since I've posted something. I had some issues with my carburetor on my 1972 250ci fastback. He really hesitated a lot when accelerating and almost no throttle response. It was a bit like driving an old tractor. I really had to balance the clutch to drive it somewhat smoothly.

 

My mechanic stated it was the carburetor that was worn out someplace. (when I pulled him of I heard a rattling sound in the choke control) I looked a lot on Ebay to find an identical carburetor (Carter RBS) and repair kit for the old one. (Since I live in Belgium, sending this overseas costs quite a lot.) When it came I pulled the old one of and replaced him with the new one. (the thread on the fuel line connection was worn, so it wasn't a "never been used" like the stated). But it worked like a charm! He started right away. The throttle response was immediate and so light, I was happy as a child.

 

I thought i could tweak it a bit better to get a 100% smooth ride and idle with the mixture screws. But I couldn't seem to get it right. So I remembered I forgot to adjust the float prior to installing the carb. I thought the fuel bowl was a bit too full. So I checked the old carb and adjusted the new one like the old one (the float in the new carb was set about 1,5mm higher than the old one). But it didn't make any difference.

 

So when I drive it now the throttle response is awesome but I can feel that he hesitates while accelerating and maintaining speed. And when I brake on the engine, I hear popping from the exhaust (sounds great but I know it isn't supposed to be like that, so I think he is running rich). When idling he runs a bit rough. Where the old carb did run a smooth idle.

 

I hope I've been clear with my explanation since english isn't my native language.

 

Would there be things I should try before pulling it of again? I'm a bit afraid that worn thread will become useless. All other systems were checked by a classic mustang mechanic locally.

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I would check the timing and make sure the vacuum advance is working properly. Popping on deceleration can mean the timing is not advanced enough. Timing and vacuum advance will also affect acceleration and cruising operations.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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My 73 convert has the 250 with the RBS carburetor too. I agree with Don C that the popping may be from the timing or vacuum issues. The biggest improvement I achieved was deleting the points from the distributor and using the Petronix Electronic Ignition. The 250 idles and runs a lot smoother with the Petronix. It's an easy install and is not visible in the engine compartment unless you look under the distributor cap.

Mike AKA Ole Pony & Rare Pony
Our current Mustang garage/driveway
1973 Mustang Convert - Bought in 1974 - Still have it!
2004 Mach 1 Oxford White Auto, Bought Sept 06

20180127_082009.jpg

 

 

 

 

 

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The fuel lines have been replaced 2 years ago. The fuel pump and filter have been replaced a few months ago when I thought that would fix that first problem I had with the first carburetor. I am not sure about the fuel tank if its ok or not.

 

I have done a bit more tweeking this afternoon with the idle-screw and the fuel mixture screw. I believe it idles really smooth right now with a nice steady 6cyl pur, but I don't know if the mixture is good though, the mixture screw is almost completely out of the carb. I have read it should be the other way around? (I could be mistaking, it is now as it was like with the previous carb and the spark plugs seemed to be ok after 2 years) The popping has been reduced a lot too. But There is still the hesitation under load and when I maintain speed. Maybe I should indeed check vacuum and timing. When I removed the old carb there were 2 gaskets on top of each other. So I did the same, but is that the right way?

 

Good tip on the Ignition, I will put it on my to do list. It is hard to find easy install improvements for the 250. Most improvements would cost me a lot since I need to ship it to Europe. I looked for an aftermarket 2V carb. But that meant a bigger investment, a manual choke and adjusting the throttle arm and cables and more room for error. Since its my daily driver I need to be sure it works properly.

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If the idle mixture screw is all the way out, and you're having the same issues as with the old carburetor I would check the intake manifold for leaks, as well as all other potential sources of vacuum leaks, such as the vacuum advance and the pcv valve and hose.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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I don't have the same issues, sorry if i wasn't too clear on that (Me being Belgian and all) :). The settings are the same. It works fine now except for the hesitation and powerloss under load. I will check vacuum issues for sure now. Thanks

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If your idle mixture screw is all the way out, it is way too far. Should be around 1 1/2 full turns out from a gentle bottom out(close).

So that would be all the way in, then back it out 1 1/2 turns. That should get the idle set pretty close. Then you can make small 1/4 turns from there to dial it in.

+1 on the Petronics ignition module..tha is a must and I would say that should move to the top of your list, next to things that are free of course. Not sure what they run in Belgiun, but US they are like $90.00.

One thing to check is your idle mixture screw. If it bottoms out, and the car still runs, you have a problem with your idle circuit. Check the manifcold and gasket to make sure that your idle needle is peeking through into the manifold circuit(channel). If not, that is a problem.

I have seen more then a few incorrect manifolds installed with mix matched carbs that cancel out the idle circuit altogether. So you may want to check all of those things for compatibility and make sure that everything lines up and is operational.

#DontMachMe making the rounds and being abused all the way

 

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  • 9 months later...

Its been a while since I went online to this forum. So I'll have you know I adjusted the float in the fuelbowl and now I can push the pedal to the metal without any hesitation. That is when he is warm enough.

 

I will look into the petronics ignition module for sure. Thanks for the advice! Some friend of mine also bought a mustang so we wil be grouping our purchases and ship them overseas.

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Its been a while since I went online to this forum. So I'll have you know I adjusted the float in the fuelbowl and now I can push the pedal to the metal without any hesitation. That is when he is warm enough.

 

I will look into the petronics ignition module for sure. Thanks for the advice! Some friend of mine also bought a mustang so we wil be grouping our purchases and ship them overseas.

 

Thanks for the update.

Doc

Project started 8-7-10

Completed: All new suspension, rebuilt 351C H Code bored .030 over with mild cam and intake, new 3.50 TracLok, custom exhaust system

Current "mini-project": interior upgrade :-/

[button=http://www.7173mustangs.com/forum-garage?filterxt_uid=76]Doc's Garage[/button][button=http://www.7173mustangs.com/thread-1973-mustang-convertible-restoration-and-modification]Doc's Wiki[/button]

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Glad to hear the 250 is running great. Let us know when you install the Petronix and how it works for you.

Mike AKA Ole Pony & Rare Pony
Our current Mustang garage/driveway
1973 Mustang Convert - Bought in 1974 - Still have it!
2004 Mach 1 Oxford White Auto, Bought Sept 06

20180127_082009.jpg

 

 

 

 

 

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