Model B

[Keystoner]

I'm trying to determine if I have the correct throttle body for my 235 engine. The throttle body casting is # 4522.

Not counting the mounting holes, the top and bottom have two holes.

My concern is that the carb. insulator only has one "hole" that lines up with one throttle body hole. Is that correct or do I have the wrong throttle body or wrong insulator?

Also is a gasket used between the throttle body and the insulator?

Any help would be appreciated.

Tom

 

[vwnate1]

RE: Rochester Model B

Tom ;

This is correct , the one vacuum port on the bottom of the carby should be lined up with the one depression in the insulator , this is the the vacuum signal that operats the power valve and it's important

The vacuum causes the valve to remain closed @ idle and trailing throttle but when you step on the gas , the vacuum signal drops and the valve opens gradually as the vacuum goes down .

Ideally , there is NO GASKET between the insulator and the intake manifold . if it leaks (sucks air) use the thinnest gasket you can find .

I hope this helps ,

-Nate

 

[Keystoner]

RE: Running rich

Thanks for your response Nate. I was happy to hear it was correct.

My problem is all 6 plugs, are showing signs of running very rich. I thought maybe is was a vacuum problem with the insulator.

I have rebuilt and tried three different Rochester Model B, and makes no difference. The main jet is a #58.

The engine, 235, is almost brand new. Cylinders bored, new pistons and rings, head redone, new lifters (hydraulic), bearings, oil pump, coil, and so on. I rebuilt this engine in my living room and it was a joy to do. It ran like a watch.

But, after only 1000 miles it started to pop and backfire. After adjusting the valves five times, checking timing, it continued. So I pulled the head and back to the machine shop I went. The head checked out fine. The shop said to check for manifold leaks.

Little did I know there was supposed to be sleeves between the intake manifold and the head. So I ordered them from CD and they fit in the head but not in the manifold. I then found out the intake and exhaust manifolds were for a 216. Changed to the correct 235 manifolds, installed sleeves, changed throttle body, and ~ bingo ~ backfiring stopped. Oh, and by the way, thank you Nate for your correct valve adjustment information, because I had been using the 1 1/2 turn. A 1/4 turn makes a big difference especially when starting.

Had to buy a 2nd new (6 volt) coil because the first one leaked ~ oil. The negative side of coil goes to the dizzy. I am going to replace this wire using 18ga., just to be sure. The spark plugs are a #43. Exhaust manifold heat riser works properly.

Engine runs fine, has quick response and good power.

Now that you know the rest of the story, any guess on how to fix the "burning rich" problem.

Tom

 

[mikesters1950]

RE: Running rich

Tom, when you say the plugs show signs of running rich, what are you seeing? Are they fouling out to where there is a misfire? You said the engine runs fine, with good power. The plugs should ideally be a tannish color. More than likely they will be darker. It is possible that the idle mixture adjustment may be too rich. Have you tried playing around with it? How does it idle? It might be as simple as a minor idle mixture adjustment is needed. Let us know....Mike

 

[Keystoner]

RE: Running rich

Mike,

The plugs, all 6 are very dark and dry. New plugs turn that color in about 10 minutes. There is no misfire.

I have tried the idle mixture screw, but I'm not sure what is correct. Some say the best setting is when you get the highest vacuum, while others say the best idle. If I set it at 1 1/2 to start, the only thing I notice is when turned in a 1/2 to 1 turn the rpm's increase. So I'm not really sure where to set it. Maybe this is the problem. Where would you set the mixture screw? Any suggestions?

Today, I installed the rebuilt carb with new filter, and new plugs.
Tomorrow I fire it up and adjust the mixture screw and see what happens.

Thanks - Tom

 

[mikesters1950]

RE: Running rich

Tom, you are correct, there are a lot of different opinions on how to set the idle mixture. An exhaust gas analyzer would be best, but not many people have access to one. Sounds to me like it might be a little rich at idle, based on the idle increasing when leaned out by turning the mixture screws in. Seems to me, on mine, there was a fine line between best idle, and too lean to where it misfires. I set mine to best idle, then 1/4 to 1/2 turn out (richer), and left it. It runs and starts fine. I don't really care if the plugs are a little dark, as long as they are fouling out. I am sure you will get other procedures and opinions too. Just make sure the valves are adjusted good, and the engine is plenty warmed up before starting adjustments. Good luck....Mike

 

[vwnate1]

RE: Running rich

O.K. Tom ;

start by checking the spark plug gaps to .035" , NEVER trust them to be pre gapped .

I'd say use AC # 45's as # 43 is too cold , that's a commercial plug , designed for heavy load , high speed highway driving .

I don't have the P/N right now but when I cannot find the correct AC # 45 plugs , I use NGK's , with the copper cores , platinum plugs are crap in older engines , they run way too cold and foul easily .

I'd go buy a nice Bosch (brand) BLUE coil for a 1965 VW Beetle , that'll toss some serious sparks and once you remove the decals and invert it in the plastic cap from a Foo-Foo can and paint it black , no one will ever know why your truck idles so smoothly and starts instantly , cold or hot . =

If the vacuum signal to the base of the carby is blocked , the power valve will remain open and cause too rich running at all times...

Remove the power valve and polish it with metal polish until it slides
in and out of it's hole super smoothly and ensure the tip isn't bent
as that needs to go through the tiny hole and depress the little ball bearing . the spring should be fairly weak too and the little ball bearing needs to have a spring underneath it , just under the brass cap , to hold it up and closed when the power valve piston is retracted by the engine's idle vacuum .

As far as carby idle adjustments go , make sure the ignition timing is spot on before you begine and then the vacuum gauge method is thus :

Turn the screw _clockwise_ and watch the gauges needle climb , it will begin to twitch as it goes higher , you want it to be the highest _STEADY_ vacuum reading , this is very different from the highest vacuum reading .

Generally the best position is to set the highest steady vacuum reading and then turn the screw 1/8 ~ 1/4 turn _counterclockwise_ but NO MORE as carby adjustments are very sensative .

I hope this helps..


-Nate

 

[Bossman]

RE: Running rich

A fundamental question... where do you hook the vacuum gauge? At the carburetor port or the vacuum tap for the windshield wiper/brake Hydrovac line?

 

[Keystoner]

RE: Power piston & small ball

Mike:

Thanks for the info. I'll adjust the valves and then I will set the mixture screw for the best idle, with the 1/4 to 1/2 turn and see if that helps.

Nate:

The only sparks plugs the parts store (advance auto) had were autolite 303. I checked the gap and all were preset at .035. My next set will be the -NGK B4- plug.

If the negative wire (18ga.) from coil to the distributor is the incorrect gauge is that a problem?

As far as the power piston...... tomorrow the air horn is coming off and the main well support removed and the power piston will be polished. Will also make sure small ball bearing was used.
Then I'll check timing and try the vacuum gauge method. Thanks for your help.

Bossman:

I'm not sure but my guess would be the carburetor port where the vacuum advance is connected.

Thanks to all for your support.

Here's a good site for Rochester info.
http://www.tocmp.com/manuals/Carbs/Rochester/B/index.htm
This is their index page for other info. http://www.oldcarmanual.com/

Tom

 

[vwnate1]

RE: Vacuum Gauge Connection

You'd be connecting it to the manifold port , where the wiper motor connection is so it gets full , unmetered engine vacuum .

You have Hydrovac ? you lucky dog you ! .

BTW : a tip : the vaccum advance on _ANY_ engine should NEVER have vacuum @ idle ! . I find some later versions of Rochester B's have more than one connection point for the vacuum advance line .


-Nate