All Small Six Learning Continues - carburetor

[John Ha]

I have a 250 engine in my Mustang that I was told came from a 73 Maverick. In chasing my fuel mileage issue I decided to try my spare RBS carb on the engine. It fit fine until I went to hook up the throttle linkage. It was different.

Down the rabbit hole I went and found out that the numbers on the side of the carb (like 0-2044) apparently determine what the thottle linkage looks like on that specific carb. I've found that the carb that came with my engine is actually from a 1970 Mustang or Maverick, which may partially explain why I was able to hook it to the stock 1966 I6 throttle linkage. The spare carb (0-2241) appears to be from a mid-70's Maverick/Mustang and won't hook properly to my throttle linkage. As far as I can tell the 1970 RBS is unique to that year of Ford. I know that AMC and Jeep used RBS carbs as well and have not plumbed those depths yet but it appears to me that the carbs for the 1970 Maverick/Mustang are scarce. I guess that's not too surprising.

Interesting, I thought. Photos below to illustrate.

 

[bubba22349]

Hi John, yes X2, the reason that all those later Carbs have the different throttle linkage hook ups and numbers is because Ford went to a Cable Pull type Throttle Linkage instead of the older Rod type Push Carb Linkage. This is also why most people with the early model cars often switch from Rod type Linkage to the cable Throttle Linkage when going to the newer Carb's. That's what I have done on most all the car builds I have done since 1970's makes for a clean installation too. Best of luck

 

[Just_Fare]

Is it possible to swap out the parts from each carburetor to make it work? I ask for both John and myself. I too, have both kinds of RBS but the 1970 one is not repairable and the other one should work but does not hook up for the same reason. Of all the carbs I've used on my small 6, the RBS offered the best fuel economy and was quite lively to boot.

 

[bubba22349]

Yes if you can Fit / Swap out the complete Throttle shaft or just its Arm (Lever) into that newer Carb to change it from the Pull Cable Type to a Push Rod type.

 

[John Ha]

Is it possible to swap out the parts from each carburetor to make it work? I ask for both John and myself. I too, have both kinds of RBS but the 1970 one is not repairable and the other one should work but does not hook up for the same reason. Of all the carbs I've used on my small 6, the RBS offered the best fuel economy and was quite lively to boot.

Yes if you can Fit / Swap out the complete Throttle shaft or just its Arm (Lever) into that newer Carb to change it from the Pull Cable Type to a Push Rod type.

While you guys were responding (thank you!) I was out in the garage messing around and did exactly that. Just (very carefully) remove the two screws that attach the throttle plate to the shaft on both, remove the tiny clip, then remove the shaft. You can then insert the Mustang shaft into the "other" carb. I had to do just a tiny bit of bending on the Mustang linkage so it would clear the choke linkage on the "other" carb but it did work.

I put the modified carb on and WOW! What a huge difference. The car perked up noticably and I could not be happier. I did notice, though, that adjusting the idle speed is not easy. I'm not sure why - haven't looked at it in detail - but it's either about right or too fast. It should be possible to swap the choke stuff over too but I have not looked at that closely either. There are some differences in the carb body casting that might make it hard.

I also noticed that it won't work the other way - swapping the later throttle shaft into the 70 body. There's a spring on the later throttle shaft that is picked up by the body on the later carb. There's nothing on the earlier body to pick up the end of the spring and the shaft won't go in fully if the spring is not seated properly. I suppose it would be possible to grind away the splurge that attaches the shaft to the linkage and, make adjustments and reweld but I haven't looked at that closely.

I have suspected since I rebuilt it that someone up-jetted the 70 Mustang carb I had on there. That jet is obviously different and appears larger than the one in the "other" carb. I tried to swap them but the one in the "Other" carb was not willing to come out after application of modest force and I didn't want to damage it and have two flakey carbs.

I think that the jet in the 70 carb was over fueling the engine and hurting the performance as well as the being the source of my poor fuel economy. So now I'm in the market for a stock jet for a 70 Mustang RBS carb.

EDIT: After looking at some information, it's the idle circuit jet that's definitely been changed. I'm not sure about the main jet (the one with the rod through it). I don't think that a larger idle circuit jet would have an impact on fuel economy or performance. But there is a big difference between something in the carb body that was on there and the one that's been altered slightly to work with the stock throttle linkage. So now I have to figure out what the issue is.

 

[78_200_C4]

Many people do 90% of their driving on the idle-low speed-transition slot circuits.
A wide band Air Fuel meter will tell you what is going on.
You might be surprised to see the A/F ratio lean out (relatively speaking) when the carb starts operating on the cruise circuit.

 

[78_200_C4]

Carter RBS 1 Barrel Carburetor 1970 Ford 4.1L W/250 $159.00
30 sold

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