The Stovebolt Site Forums The Shop Area Engine Shop 1955 first series running rich

Hello Bolters.

I finally got my 55 first series together enough to fire up the engine...

The backstory is I bought the truck in Arizona three years ago. Nice body but no drivetrain. I got the correct transmission from fellow bolter Lederman and bought the correct engine from a guy in Virginia.

Anyway the engine fires right up and sounds pretty good. I am only running it on idle because my vacuum advance is shot. At low speeds the engine is running rich, I can smell the gas fumes and the new exhaust and plugs got pretty sooty. I adjusted air mixture screw and the timing. The carburetor is a Rochester model C with a manual choke and a 56 main jet (I am sure the main jet isn't active at idle speeds).

The carburetor is pretty clean, do any of you have any ideas on what to try?

pic of the carb

[URL=http://s1035.photobucket.com/user/mendonjo/media/image_zpsc8b19fd4.jpg.html]carburetor[/url]

99 percent of the time a Rochester is running rich it is because the wrong base gasket was used. This blocks the power valve port on the base.

Thanks Dave!

I took the carb off the base and this is what I found

Real thick gasket (insulator?)

[URL=http://s1035.photobucket.com/user/mendonjo/media/image_zps68465d81.jpg.html]Gasket[/url]

I bet this is the passage that is not supposed to be blocked

[URL=http://s1035.photobucket.com/user/mendonjo/media/image_zps87d66656.jpg.html]Bottom side of carb[/url]

Yes, I can see the impression on the gasket where it was blocking the power valve vacuum port.
Vacuum needs to get to that port or the power valve will stay open all the time dumping way too much gas.

The truck sucks a LOT less gas at idle now. Thanks again Dave for answering my post. Without you I would have never found the problem (I would have just assumed it was a gas sucker).

Joe

Glad I could help.
This is such a common problem with Rochesters.
I would say that close to 90% of the vehicles that come through my shop have the wrong base gasket.

Does this blockage cause the hesitation/stall on accelleration? I have found this problem on Rochesters and never figured out how to solve it. I usually just switch to a Carter.

No, the blockage makes it run richer masking hesitation problems.
For hesitation problems it is almost always the poorly assembled recharge check valve in the accelerator pump.
At the very bottom of the accelerator pump assembly there is a small brass insert with a ball bearing above it. As the pump is moving down on the pump stroke gas flowing up around the ball sucks it up against it's seat causing the gas to be forced out the discharge path in the bottom of the carb.
The problem is that the replacement pumps do not have the brass insert pressed in far enough. This leaves too much clearance between the ball above it and the ball seat. With too much clearance the gas flowing by can not lift the ball up against it's seat. (I know, funky design)
If you hold the pump upright and look between the four slots between the ears that hold the insert in, you will see the ball.
I see them with as much as 1/16" clearance between the ball and seat. I put the pump in my vice and press the insert in so there is about .015" clearance.
This is the most common problem but not the only one you could have. In some cases the leather hangs up in the bore stopping it from moving and pumping.
Sometimes the link between the pump and throttle arm is mis-adjusted.

Thanks, I am going to dig out a rochester and check this out.

That 'Rochester-B' hesitation has been the subject of many, many
discussions here Dave. I finally gave up on them after
meticulously rebuilding and adjusting a half dozen over a
couple of year period. Went as far as switching to very hard to
find, leaded, alcohol free fuel for a while to see if the
alcoholic petrol was causing the lean mixture, dint help any at all.
They all ran great and the engine pulled super strong with
the choke cracked just a smidgen. I run the correct stock
timing on my engine, I figure the engineers knew what
they were doing to get peak performance from these stock engines.

In frustration I finally went back to a W-1, which was a
little better but still seems a bit lean starting out.

This is the first time anyone has mentioned the ball check as
being the culprit. I'm bout 2/3 of the way finished with the
organization and set up from my move to the new place and
hopefully will get back to wrench twisting and a chance to
give your suggestion some attention come spring or early summer.
Thanks for the suggestion, hope that will prove to be a
solution for this all to common problem.

Denny Graham
Sandwich, IL

I am probably the only one here that likes Rochesters.
I have worked with them for years and can get most to work correctly.
I have not posted much about them because it is a little hard to explain some if the info. I always plan on doing a photo shoot, which would help, but have not made the time.

Really like to see that happen Dave, they really belong on these
trucks but are very often replace because of the problems. They
are extremely simple in design, which leads to a lot of the
problems with them. The warping of the air horn is a major
headache. I made a 1" thick plate up that I could mount the air
horn to and tried baking them in the oven thinking I might be
able to stress relieve them and flatten them out again. It
worked a little, but still not enough to get a good seal on the
gasket. I got that idea from Jon, you know what his opinion is
of the Rochester 'B'.

Denny Graham
Sandwich, IL

There is at least 2 of us Dave!
I'm got a 'B' from a '67 C50 on my '60 235 C10, runs strong & smooth. As far as fuel leaks I've had good results using very light film of loc-tite Pipe sealant w/ teflon on either side of the air horn to fuel bowl gasket. Can't be too badly warped and only a very light film of sealant on gasket. Advised one guy to try this & he brought it to me with sealant in passages, little thinner next time!

A little sealer goes a long way.

What warps the Rochester airhorn?

Intergranular Corrosion (IGC) in the zinc die casting alloy.
Early zinc die castings, i.e., in the 20's-30's had so many
problems that many of the castings made back then will literally
crumble in your hands today. Zinc castings were often made from
recycled alloys and poor control over what went into the
melting pot created problems in many products.
Aluminum die castings are much more stable over time than
zinc castings.
One of the major problems with the 'B' was the fact that the air
horn used only 4 screws to hold it down to the main body. Had
they used a few extra fasteners it would have helped stabilize
the die casting and many of those badly warped early 'B's would
still be usable today. Adjustments to the alloy in later
Rochester 'B' versions is the reason they faired better than
the ones made in the early 50's.
Lots of information on the web pertaining to the IGC problem.
Denny Graham
Sandwich, IL

Theres atleast 3
I must have a later model "B" as it works very well. No hesitation, no warpage, starts good when cold, operates good when warmed up and was somewhat easy to rebuild.
Knock on wood

Dave

Most of the 'B's had problems the first few years after
they were introduced. I've seen very few of the early,
'50 thru '53 'B's that were not warped, you see one every
once in a while. They kept making improvements in them
and by the end of the run it was a pretty good trouble
free carburetor. I've seen very little warpage in the
later ones, don't know for sure but somewhere about
midway along they must have changed the alloy which seems
to cure the curled up edge problem. It's clear that they
were having leakage problems early on because the first
air horns had a very thin edged and soon after they went
to the thicker 1/2" edge on them. They also changed the
ball check in the well several times. I can't remember
which documents I saw this in but the hesitation was
addressed a couple of times, I think it was in the
service bulletins.
The Carters didn't have problems with edge warpage. Apparently
the use of more hold down screws helped, and/or maybe they had
tighter control of the zinc alloy they were using also in their
castings. It's a shame when you have to use a bead of silicone
rubber to seal up the seam on a carburetor. I've seen a few
with that blue goop bulging out from between the air horn and
main body and it taint pretty.
Denny G

On occasion I use "Seal All" on the gasket, but it is clear.

I've had early 'B' air horns that were warped up nearly an 1/8"
Dave, don't think any sealer would help them. I've never found
a way to fix them. I even thought about machining them flat but
that isn't practical cuz you'd loose the raised bead that
creates the seal. Wish we could talk the Chinese into casting
some Rochester 'B' air horns in aluminum to repair these. It's
really a pretty simple casting. Must be tens of thousands of
them that could stand to be replaced. The main body or bowl
doesn't seem to be subject to as much distortion, probably just
because it's more massive.

DG

Loc-tite pipe sealalant with PTFE isn't blue or silicone. It is white in color and I use such a light film that it an issue. BTW G.M. part # is 12346004.