The Stovebolt Site Forums The Shop Area Engine Shop Rochester B woes..

Have a bit of a dilemma here — thinking that my old fuel pump could no longer hold pressure (clear inline filter at carb was always appearing empty, along with a lot of cranking before startup) I did some research and installed a check valve just before the filter. The pressure now maintained but the original problem remained.
So I bit the bullet and ordered a new fuel pump and put that in. Voila! Now lotsa volume and pressure.

But upon startup the carb started hemorrhaging fuel at the main gasket including down the accelerator pump rod and onto the manifold. A pressure test was done again (just after the check valve) and it showed like 8+ lbs and climbing with every crank of the engine. Fearing that the carb might be rupturing with the accumulated pressure I quickly removed the check valve and re-ran the engine just with the new pump. The filter now stayed at least half-full but the carb still flooded as before.

I yanked the carb and disassembled it. It was cleaned, float checked to factory specs and needle and seat checked for wear (none).
I also replaced the main bowl gasket with a new one.

It still does the same thing — leaking everywhere.

The appearance of the carb was tight before the pressure surge — no flooding.

Other than buying another carb, what should I be looking for in this carb to solve this problem?
Will lowering the float level help?

Is the new fuel pump stock mechanical type or electric?

Dennis

It is an Airtex 4149 mechanical fuel pump.

According to info at RockAuto, that pump should put out 5# max. Since you are seeing 8+ I'd say it is the culprit. Is there a part # on the pump? If not, maybe someone mis-boxed it.

Dennis

It is measuring well below the 5#. The attached tag shows part number 4149 -- which is spec'd for this engine.
When the check valve was in place my gauge showed pressure advancing with each engine crank. So it seemed that the pump just kept loading the line and the check valve kept holding it (and passing it along). The gauge ended up pinning itself before I disconnected everything! And I don't think any mechanical pump could manage those kinds of pressures

When I took away the check valve, the pump showed about 3# on its own -- but enough to load the carb ok.
And the carb has continued to leak since the pump/check valve was introduced and then removed.

I wonder what that over-pressure has done to the carb, and what the solution will be?? I mean I replaced the main gasket (which I meticulously hand-cut) which seems the only thing that could easily damage.
And I don't suspect warpage as the (newly rebuilt) carb didn't leak before getting the new fuel pump.

FWIW, today I yanked the pump and through an online suggestion, I married the new bottom half of the Airtex pump to the existing OEM glass dome half (c/w check valves).
This was to keep some semblance of authenticity ..besides I like the look of the old style.
Pressure is still about 3# with good volume.
But after running the engine for a minute the carb begins to leak again like a sieve!

OK, I understand what you're saying now. Makes sense. I'm sure someone else will come by that knows that carb with good advice. Maybe the high pressure upset the needle such that it can't stop the fuel flow.

Dennis

And that made sense too until I checked it. Such a simple ensemble (including the little gasket) -- nothing much there to look at.

Since you like taking the carb apart(yea right) double/triple check your float for leakage and make sure it is set to the proper height. Take the top off the carb and lay it on a piece of glass and see if you can slide a piece of paper between the top and the glass then do the same to the body. Just some suggestions to help you along your journey.

As 1/32" seems to make so much of a difference with the factory specs; when I go to re-check the float height, is it measured down to the to edge of the actual float body or at its standing solder seam?

The measurement is to the top of the float body. Needles and seats can look great and still malfunction. Also when the pressure changes with a new pump, it sometimes requires a tweak of the float adjustment. Sometimes the new float height is slightly different than the that in the manual. Leaking down the pump arm means that the level in the float chamber is above where it should be.

Thanks.
I put the float pontoon in a pot of hot water and no bubbles. So far as leaking goes I'm assuming it is ok.


Without drilling out the (very smooth) quartz countertop base it is very difficult to do as complete units as there are numerous protrusions on the horn and one on the bowl.
But after moving both parts around on that surface (with the protrusions over the edge of the quartz) I did notice that both pieces seemed to rock at various points. Those rocking points were noticed at the screw eyelets -- on both the horn and the bowl! I imagine that it may be from over-tightening.

I wonder if taking those eyelets down with a file might help level the surfaces?

How important are the raised gasket lines on the castings -- If not too much then maybe also a light grinding with some valve compound will work, or even using a flat sander?? ..but then there are those annoying protrusions .

Thanks -- this time around I'm gonna make up a stiff cardboard bridge gauge for both float measurements. Then perhaps drop the specified float level by 1/32" (to account for ethanol) -- just a thought after reading comments elsewhere.

Here's a thought. Not saying it's a good one though. Disconnect the fuel line somewhere before where it attaches to the carb and blow into it to make sure the needle seats.

Dennis

What carb do you have?
Regardless whether it is a Carter or a Rochester, you won't have massive leaking from a bad gasket seal between the horn and the bowl halves of the carburetor. You may well have drivability issues from internal air or fuel going in the wrong places internally, but not externally.
You need to make sure that the float does not contact the the sides of the wells once assembled.

That'll definitely be on my agenda

Ok, so I've taken all the screw ears down a tad with a file. Both halves of the carb now mate much better than before. However, the end of the horn where the fuel comes in there's still a small gap. But I think the gasket may fill that void. If not, then I'll double up on the gaskets that I cut (1/32").

Interesting - during this process of filing there was a flashback to my days as a kid with my first ratrod. I seemed to remember going through the same thing with warped Rochesters and filing them down. But it's been so long that I can't remember how well it worked.

Let you know how it works out when it's back together..

You have likely just ruined your Rochester B beyond repair by filing on it where the gasket goes. But don't sweat that too much because that kind of gap is caused by warpage which is difficult to fix permanently.
Regardless of any of that, your leakage problem has nothing to do with that gasket. Gas cannot reach that high if the float needle//seat is functioning properly.
I suggest that you buy another carb, and if you have more trouble, report back and then wait for responses, then actually read them.
Carl

As promised here are my findings for the repair of this Rochester B carb.

After very carefully filing just the outside screw 'ears' on both the horn and bowl (no, I didn't touch the mating surfaces (raised-lines)) and cutting new main gaskets, the two halves fitted back together almost perfectly -- no leaks.

To take care of the flooding I first inserted a vacuum pump/gauge into the inlet of the horn and determined that there was a small leak at the base of the needle valve combo.
A sanding dowel fixed the casting seat. And metal polish smoothed the brass needle and seat assembly to almost mirror finish.
After installing a new round gasket on the valve it was then installed.
The vacuum pump/gauge showed that it now held vacuum well.

The float pontoons were again tested for leaks and readjusted exactly as per specs and everything was put back together and installed on the truck.

I also reinstalled the OEM glass-dome fuel pump (after a good cleaning and set-up) and it tested at 4.5 lbs. with good volume.

The truck started up right away and ran well with no leaks or flooding.
The test drive also went ok as I ran the carb through its stages from around the block to advancing onto the highway.

The only (minor) question I now have is regarding the idle mixture screw (in the throttle base).
Before the carb problem I normally had the screw at about 1.5 turns which was about right for smooth running.
With this rebuild, the turns are now at 2.5 in order to maintain its highest vacuum (at 19.5").
While it does run well, it's this little detail that bugs me.
I can still learn to live with it though as it's just great to finally be on to another project.

Thanks all for your input

Maybe your polishing refined the settings a bit?

The 1 1/2 turn initial setting is a beginning point to allow the engine to idle on startup after a rebuild. Use the vacuum gauge to fine tune the mixture, unless you're willing to invest a few thousand dollars in a 4-gas exhaust analyzer for a really high tech way to determine the ideal mixture setting.
Jerry

Nice save on the model B.

It's quite precise at 2.5 turns -- can't go much on either side before it affects max vacuum. I'll still have to monitor it for potential vac leaks as I have modified the base attachments to the intake manifold: an assembly of gaskets, thick heat spacer and custom 1/8" aluminum plate (heat dissipation/sink).

To that point today I noticed just the tiniest bit of hesitation/stumbling when punching the pedal from 1/2 throttle.

But for the moment it is acceptable considering all that I've been through with this carb.
Maybe think differently as I get used to the feel.

Thanks.
Should have mentioned that I did use some (new tech) Permashield sealer on the gaskets -- didn't want to take any chances of leaks.
Stuff is advertised as ethanol fuel resistant. If it proves gummy then I'll re-clean the carb and go without it.

Hah... hard to fathom that those items were polished that much.
But it could be interesting to find out just why the discrepancy.

Any sort of sealer on a gasket where vacuum is present is a pretty risky procedure. Try advancing the ignition timing a couple of degrees to deal with the hesitation, but that might also have an effect on the vacuum and the idle mixture and idle speed.
Jerry

Good suggestion. My timing was originally set to compliment the carb before rebuild.
Can't recall offhand what it is currently set at. But there's gotta be room for more adjustment, and without pinging.
I'll get on that soon and let you all know

"tiniest bit of hesitation/stumbling when punching the pedal from 1/2 throttle."
Don't touch a thing. That "quality" seems to be in every Model B.
That is why Carters were such a popular replacement. That dude made a fortune selling replacements for ADs. They do not hesitate.

Well, I can always dial the timing back if it doesn't play nice.

I can recall running with twin AFB's in one of my cars ('59 Ford s/wagon w/full race cam) back in the day.
Sticks in my mind that they were a challenge to rebuild and set up ..especially when syncing them.
But a lot of fun to cruise the strip with on a Sat night ;-)

"That is why Carters were such a popular replacement. That dude made a fortune selling replacements for ADs. They do not hesitate."

I'm supposing that the Rochester replacement was eventually a YF..?

Thought I'd get back to this thread with my findings.

Truck runs well now -- strong acceleration and good road power.
I advanced the timing +5 deg. with nary a ping or knock. The slight hesitation at 1/4-1/2 throttle has almost left the scene.
This, still with E-10 fuel.
Can't help but think that any carb make would be better than this one. But again I have to use ethanol gas ..if I wanna stay within budget.
When I put the truck under cover in the Fall, the tank will be re-filled with Premium (non-ethanol) gas with an ethanol-compatible storage treatment (like Sta-bil 360 or StarTron).
Next year it may find itself with a new owner...