Need Carb Help!!

Hey everyone,

I'm new to the board but not new to Fords or working on anything. Just new to the Sixes. I have a '73 Comet with a 250. It has the engineering marvel RBS carb on it. I guess I should start by saying that the car has 8300 miles on it and that's original. So needless to say it sat for a long time. I rebuilt the carb and it seemed to run much bettter. I can't get the thing to idle smoothly. I timed it and ended up with 12 degrees which took away the hesitiation it had on initial accelelration. The idle is still rough. So my questions are;

Was there ever a 1v Holley direct replacement?

What can I do to the carb on it to make it idle/run better?

Is there an "easy" 2 v conversion? I have looked into this a bit and I get conflicting stories about fitment, linkage issues, and on the Mavericks/Comets there is a height issue with the curent adapters available. Any way around all of his? I really want some thing easy and effective that fits.

Any and all help will be great!

Jon

the owner of this forum sales an adapter to mount a holley or ford two barrel.

The fox bodies mustangs and fairmonts that were equipped with the 200 came with a 1V holley, I think it was model number 1101, and have read it is angular discharge, but I doubt it will improve the idle characteristics vs. your RBS. Your RBS outflows the Holley too, If I rememeber correctly, the RBS was the largest 1V that came on our motors. There is no direct bolt on 2V that works with our integral manifold, and the adapters limit the performance gain of the 2v, as well as cause hood interference with our comets/mavericks. I blame the engine roughness on lean #1 and #6 cylinders and rich center cylinders due to the single center mounted carb of the integral manifold, but it should not be that rough at idle.
In your case, since it has sat a long time, maybe you have some valves sticking? I would hook up a vacuum gauge to verify the condition of your valvetrain and aid in setting your air mixture and initial mechanical advance, you should be able to go more than 12 BTDC, mine is at 16. You can also try to move your vacuum advance from ported to manifold, this also usually helps. Welcome!

Can I assume this engine has DS2?
If you feel confident about your carb rebuilding and adjusting, then maybe it's a vacuum leak, or electrical.
There are, however, passages in the carb that are very difficult to get clean, especially if it sat for so long with GAS in it, That gas turns to a sludge and could be clogging up a circuit.
On the electrical, I'd start by checking the plugs, and work my way back from there.
You should be able to get the engine to run very smoothly and adjust the carb at a lower timing, and I suggest backing it off to 8 or 10 degrees until you figure out the problem.

I was assuming you had verified the ignition system, and ruled out vacuum leaks. If not, look into it first as Jackfish has suggested. My '73 250 was a DS1 unit.

Welcome to the forum!

I'll bet that you are running on "Ported" vacuum advance. I don't recall when the attempt to improve emissions through the use of "Ported" rather than "Manifold" vacuum began. A ported advance turns off the manifold vacuum to the advance pot at idle. The added advance you would get at idle by using manifold vacuum would smooth out the idle and the engine will run cooler as well.

Let us know what you find, Ric.

HOwdy Jon:

And welcome to the FORUM. Yes, it is that good. Your quest of a smooth idle is likely in the basic tune-up world. Your brief description of what you've done, so far, leaves alot of questions.

The Carter RBS is about as large a one barrel as you'll find for your engine/car. It is rated at 215 cfm. It is also one of the shortest carbs around. The Holley 1vs are either the side bowls from the 50's and 60's ranging from 135 to 170 cfm. All are the earlier SCV type vacuum signal for a Load-O-Matic type distributor. The Fox bodied holley 1vs that came on 200s were a #1946. They are taller then an RBS and not user friendly.

Your RBS maybe one of the simplist and easiest carbs to work on and to rebuild. It has a ported vacuum source for your distributor. Does your distributor have points? As part of your tune-up make sure the inside of the distributor is clean and that all parts are able to move freely. Make sure the vacuum diaphram is working and able to move the advance plate. Your distributor has both mechanical and vacuum advance. Neither of these will effect the idle quality. The initial advance setting will effect idle. Be sure to disconnect and plug the vacuum from the carb when setting the initial advance.

A Carter YF from a early 80s pickup with a 300 six may be an option, but I don't know what they are rated at. I can tell you that they are taller.

As far as tune-up goes start with the ignition. Most carb problems are ignition related.

As for a 2v conversion- the only option is to modify the intake log to directly mount the carb. All other options (adapters) would create hood clearance problems with your car.

Keep the info coming.

Adios, David

Check for vacuum leaks and tune the beast up. If that does not cure it you can try a Holly/weber 5200 2V and adapter from langdon stovebolt for around $100. I have two maverick ( same as comet in the mid seventies) 170's that I have converted and it works quite nicely. You have a 250 which is taller and the 5200 might not fit under your hood but will still tell you if your problem is carb related. You can always resell the 5200 and rcoupe some of your money. For somewhat more money you can have your head modified for a dirrect mount 2V.

[A Carter YF from a early 80s pickup with a 300 six may be an option, but I don't know what they are rated at. I can tell you that they are taller.

my 75 250 maverick engine came with the carter yf.[which i would sell]

HOwdy Back All:

EFF- The Carter YF was the factory carb on 200 engines from 1970 to 1979. It is rated at 187 cfm. It is not the same carb that the 300 engines in the pick-ups used. A YF from a 200 would be a downsize in performance. 187 vs 215 cfm. The RBS is actually a simplier and shorter carb too.

What's up Jon? How about some more info on your progress on tune-up details?

Adios, David

I have quite a collection of carbs on my 250 (stuffed in my 63 Comet)...
I have tried the following...
Holley 1940 auto choke- small bore and large bore venturi
Holley 1940 manual choke- large bore venturi
HW 5200 unmodified
HW 5200 heavily modified with various jets and venturis bored out by 2-4 mm
Carter RBS auto choke

All of these have had various results. IMHO the best carb for all around performance and reliability is the Carter RBS.
I think this is what was originally on the motor that it was pulled from!! Go figure!

I have also heard that the 1101 will work nicely- I think those came on some Mustangs with the 250s.

What I Iearned is that the closer to stock it is, the easier it is to get to run right (if you are an amateur like me...)

Hope that helps...

My carb page...
http://homepage.mac.com/jaffes/cometcarb/PhotoAlbum22.html


Marc

Howdy back:

Hey Marc- the 1101 was used on the 1969 Mustangs with the 250 six option. This 1101 is unique in that it does not have a port for a SCV so it will work with non L-O-M distributors. It is rated at 210 cfm as opposed to 215 for the RBS. The RBS is slightly shorter too.

What's up Jon? Have we scared you away? Sorry.

Adios, David

Wow - A ton of info and suggestions.

I have not checked for vac leaks. I have a pertronics ignition on it so no points. I put new plugs/wires, rebuilt the carb (easy), cap and rotor although the rotor may be crap, I'm going to change it again. All of the vac lines are stock so there very well may be a leak. I will check all of that. Everything is stock, everything. Like I said this thing has only 8300 miles on it. There is no weird engine noises so I don't think there and sticking valves, hopefully anyway.

"Ported" and "Manifold" Vacuum?? I need some help on that one and how to change it if needed. DS1/DS2? More help.......

I have also screwed with the vacuum advance screw in the distrbutor as well as the idle/air mixture screw. As far as the advance screw I just back it out until the hesitation went away. I back out the air mixtrue screw until the idle smoothed out a bit then stopped.

I know things arn;t adjusted correctlly but it is better than it was, driveable anyway.

Thanks again for all your help and keep the info comming!!!!!

Jon

Bumpity Bump Bump - Bump Bump!

Howdy Bacck JKC:

Sorry to be so late in response. I've been away a few days and missed you ???? It was good that you bumped it up again.

Q- "Ported" and "Manifold" Vacuum?? I need some help on that one and how to change it if needed.

A- Ported vacuum signal comes from higher on the carb and give a different signal. Manifold vacuum comes from lower on the carb- sometimes from the intake manifold. It give it's strongest signal when the butterfly throttle valve is closed. On some engines/carb combos manifold vacuum works better then ported. FoMoCo carbed engines are designed to work off of a ported vacuum signal. These engines have low compression, mild cam timing and fairly high vacuum. A ported vacuum signal to the distributor allows for a higher initial advance setting, typically 6 degrees with a manual trans, and 12 with an Auto trans. Both can be safely increased by 4 -6 degrees. On an engine with higher compression and a more agressive cam/low vacuum a manifold vacuum signal to the distributor may be best.

Q- DS1/DS2? More help.......

A- FoMoCo went away from a point type distributor to the first version of the Dura Spark ignition system beginning in the 1973 model year. The system included the distributor, coil, high capacity plug wires, and a remote solid state module which is mounted on the inner fender. The system was upgraded to the Dura Spark II during the 1975 model year. They can be distinguished by the module, a larger distributor cap on the DS II. Neither have contact points to wear and adjust. Both utilize vacuum and centrifugal advance and represent a significant improvement in quality of spark and ease of mantainance. THe larger cap on the II reduced the likelyhood of carbon tracking inside the cap and crossfiring. Both versions are designed to use a ported vacuum signal from the carb. Some have an adjustible vacuum canister.

Q- I have also screwed with the vacuum advance screw in the distrbutor as well as the idle/air mixture screw. As far as the advance screw I just back it out until the hesitation went away. I back out the air mixtrue screw until the idle smoothed out a bit then stopped.

A- I'm guessing that you're working on tuning the Carter RBS carb????? I'd suggust that you start by adjusting the low speed air screw first, by turning it in until the engine begins to lose rpm and.or stumbles, then slowly back it out until it reachs the highest idle rpm. At some point rpm will not continue to increase. Find that spot. If the rpm goes up too much you may need to reduce it to the 600 - 750 range. Any higher and the vacuum advnace will start to kick in. You may want to disconnect the vacuum advnace and plug the line to the carb while tuning the low speed screw and while setting the initial advance. It is also a good idea to get a vacuum guage to use in adjusting the low speed air screw. If you are using a vacuum guage adjust the screw to achieve the highest vacuum reading. I would not recommend that you change the vacuum advance tension inside the vacuum cannister until you are satisfied that you have achieved the best initial advance setting and the best air screw setting.

Now- some more questions for you. What trans is in this car? Are your spark plugs all looking the same? What color? Since you have a Petronix I'm guessing that you have a pre-DS distributor. Does it have the dual vacuum cannister- a port both on the inside of the diaphram and the outside?

I hope that helps your understanding.

Adios, David

Thanks for the help and response! I'm learning a lot!!!!

On to the questions,

The cars is an automatic. Yes, the carb is an RBS. I haven't looked at the plugs since I installed the Pertronix, I will do that. The plugs are new and I set the gap at whatever the factory setting should be. Should I adjust the gap since i am using the Pertronix?

I want to say it has a single port vacuum advance distributer. I will have to double check that.

Don't forget that this car has only 8300 miles and I replaced cap, wires, plugs, belts, hoses, rebuilt carb and Pertronix ignition. All the vacuum lines are stock and originalso there my be a vacuum leak.

I am in Denver at the moments and the car is at home in Dearborn, MI. I will be home in a week and I will start with all of the suggestions. thank you so much for all the advise and info.

Jon

Hi Jon-
I consider myself an expert on taking a working car, fiddling with the carb, and then getting it to run worse!
I have tried several carbs on my 250 and the most common issues I have encountered after a rebuild are
1) vacuum leaks
2) blocked fuel passages/circuits in the carb itself

Most of my vacuum leaks have been around the carb mounting gaskets- sometimes the rebuild kits have extra holes on the gaskets and sometimes the carb is not mounted tight enough. Sometimes the gasket just doesn't exactly match the base. I use the old "heater hose near one ear" trick and listen with the other end all over the base of the carb and near the lines- if I hear a whistle then that's where the vacuum leak is. This has caused a lot rough idling on my carbs.

Sometimes crud from the gas tank will block a passage such as an idle circuit. I have found this be more of a stumbling problem, but I first pour some Carb Cleaner (from the local auto parts store) into the tank and sometimes that works. If not and no vacuum leaks, then I remove the carb again, disassemble enough to get to all the passages, the blow out all the passages with compressed air.

Again, I am a novice at fixing carbs but an expert on messing them up!

Marc in SF
63 Comet with 250 and RBS Carb
http://mercurycomet.net

One of the thing I know I need to check is vacuum leaks. I'll bet I have them.

The tank has been reconditioned, new fuel line from the tank to the fuel pump (stainless), new fuel pump. All this was needed due to the fact that the gas had turned to dust and clogged up the whole system. I'm surprised it ran at all.

Thanks for all the advise and help!

Jon

OK so this is a bit if a BUMP!!! I know it's been almost a year but believe it or not I'm finally getting back to the car. So if you have the tenacity you can read the history of what I'm working on.

In a nut shell I have a 73 Comet with a 250/automatic. No AC. I ran pretty crappy for a while. I have changed everything in the fuel system. I just adjusted the idle and mixture and idle per the Ford manual. Seems better.

Cold start is not good. I haven't adjusted the choke as the manual is a bit confusing so basiclly the choke isn't working. I still have to check for vacuum leaks.

Someone mentioned changing from "ported" advance to manifold advance. Can someone tell be how to go about this as it was said that it may smooth the idle a bit.

Thanks!!!!!!!

Jon

Jon-
Glad you are getting back to the car!
Can you let us know if the carb runs good once it warms up? And once it is warm, is the choke all the way open (looking at the choke plate butterfly after the car is warm, after removing the air cleaner?
This might help determine if you have a choke problem or a different (perhaps additional!!!) problem.
-Marc in SF
63 Comet w/ 250 I6 and Carter RBS carb