The Stovebolt Site Forums The Shop Area Engine Shop Carter stumbles on acceleration

Greetings,
I have a curious carburetor issue: (1955 235 with a Carter 2100 carb, standard points and distributor, 6 volt system)
When the truck is cold and I attempt to start, it will usually start after approximately 15 seconds or so of cranking, so long as my foot is OFF the gas pedal. It will start up and idle slow, but as soon as I touch the accelerator the engine will die. If I give it a minute or two to warm up at low idle, the problem disappears. Accelerator pump seems to be good, as it does squirt gas; I found it will flood if I pump the pedal a couple times before starting. Truck will not start if choke is used. When driving everything seems to function fine. What ideas have ye?
-Curtis

Make sure your timing is set correctly and that all the usual ignition components are in perfect order.

Was the truck running and driving properly until now? Did this problem develop out of the blue? Has the carburetor ever been rebuilt?

Your carburetor may be leaking fuel down into the intake manifold while it sits. Next time it's cold, open the throttle and look down the throat and see if there is fuel pooled on the intake runner.

I'll give it a check. Everything was running normally until this past week, but the change coincides with the coming of cold weather, so I'm not sure but that the cold is making the problem apparrent. Carburetor was recently rebuilt, in September of this year. I'll give a check to the things you mention tomorrow, thanks!
-Curtis

"It's never the carburetor."
Say that three times so that it sticks in your head.
It is much easier to check just about everything else which makes an engine run right than tearing apart a carburetor where you can't visually see anything wrong.
Save the carburetor for last.
When was the last time the engine ran right?
I'll wait for your response before I give you anymore advice.

Vacuum leak to the vacuum advance? I had that happen to an old flat head just recently.
It was acting the same way.

Don

Ran fine till about a week ago, when the weather started getting cold. Seems like a nice cold morning brings out this issue.

I did read your first post, but try using the choke maybe half way.

Don't know what you consider "cold", but chokes were placed on carburetors to be used.

It sounds like the carb is way too rich, not needing choke prior to the weather changing.

Jon

Jon, everybody knows a choke knob is there to be a hanger for a lady driver's purse! Cranking for 15 seconds? Is the choke being used at all?

Jon, check your private messages, please.
Jerry

Sooooo.... I'm trying to understand this, now, too. My '49 3804 with a Rochester B has the same issue (maybe not as bad)

Having just gone through JonG's (not to be confused with JonH or even JohnM ... ) *excellent* new tech tip on Rochester B-Series carburetors (which none of you have seen yet because it's still in the final editing phase ...) ... I now consider myself to be a newly self-ordained minor authority in training on the Rochester B series carburetors

Are all these one-lunger (single barrel) carbs similar to the B in that running too rich is a sign that there might be a vacuum leak somewhere/multiple places, or a stuck open power valve?

Are the Carters as susceptible as the Rottenchesters apparently are to bad joints in the idle circuit and the Air Horn to Fuel Bowl seam?

Or could it be as simple as a float adjustment, or stuck power piston/power valve? (Does the Carter even have issues with these things?)

Not trying to be the teacher, just a student trying to wrap my head around carburetors ....

But it seems to me that to get to the bottom of this for a "good" fix, the OP needs to pull the carb and do some forensics.... Ja?

As a self-ordained even minor-er authority (I have rebuilt and run both the Carter and the B) on the Carter YF᠁

Carters have many more screws securing the air horn to the float bowl. I am not aware of leakage there being an issue. Certainly not for me and I don’t recall it ever coming up in a post here on the YF.

The power enrichment system is just a totally different animal. I kinda understand how the Carter works in that regard, but have never wrapped my mind around how the B is “supposed” to work. A higher authority would have to weigh in.

I will say that the ease of starting, smoothness of running, throttle response, etc. was SO much better when I made the switch. And I say that as a natural skeptic. I thought it would be a slight upgrade.

I have no idea how pristine was the condition of my B. Perhaps a pristine B runs just as well. I wasn’t willing to do the work to find out.

(1) (vacuum leak) - no
(2) (bad joints) - no
(3a) (float adjustment) - possible, an incorrect fuel valve is more likely, but it: Quote "When driving everything seems to function fine". End quote.
(3b) (stuck power piston) - it is possible for the accelerator pump shaft to "freeze" in its housing if the carb were stored in a humid climate for a few years.
(5) (pull the carb) - John - I don't think the OP should do this without some testing.

I think the choke here may be the issue.

Jon

i will reinforce the idea of checking for vacuum leaks. My example is after Hot Rod Lincoln and I performed a head gasket turned valve job, I thought it prudent to perform some good old fashioned preventative maintenance. Of new fluids, cooling system hoses, spark plugs and ignition...the one thing I have overlooked for 50 years of ownership was the vacuum hose from the intake manifold routed through the firewall, up through the A pillar and supplying vacuum to the wiper blades which had ceased working. Talk about 77 year old hard fossilized rubber!!!

I agree with Jon/CarbKing. It sounds like it is running rich. Over the past 5 or 6 years I've posted some reasons why a Carter YF might be doing this. Some are rather obvious (improper float setting, cracked or split diaphragm, orifice of the fuel inlet seat too large, improper fuel pump pressure, and others). I mentioned one reason that people tend not to see nor think about...even though it is just as important as the rest of them and in some cases maybe more so. The bonnet that holds the diaphragm to the float bowl can be warped. It suffers the same problem as the Rochester B...4 screws hold it in place (at the corners) and it can be warped by improper tightening. Basic message is you don't have to torque these screws down. Some cheap rebuild kits include a gasket for correcting this...Jon knows about it and who created it. This was designed to solve the warping problem, but I think it makes it worse and for that reason I'd never use that gasket. Essentially the important thing to understand is there is always vacuum present below the diaphragm (the square-ish rubber piece that also operates as your accelerator pump). The design of the YF is that this vacuum will help regulate the position of the metering rod in the main jet...and when things are right it does that very well. Throttle position will also help regulate the position of the metering rod. Here's how the vacuum portion works: manifold vacuum is present under the diaphragm and that vacuum changes depending on the needs of the engine. If the engine is laboring and needs an extra bit of fuel, manifold vacuum will drop. The large spring on the diaphragm rod is then free to lift the metering rod up a bit. The linkage is designed to let this happen. This means the thinner part of the rod will then be in the jet and that means more fuel will be sucked into the manifold. If the engine isn't laboring but is just running along normally, vacuum is higher and that means the thicker part of the metering rod will be pulled into the jet and that means less fuel will be fed to the engine. In this way, manifold vacuum and the pressure of the spring will work together to regulate the air/fuel ratio of your engine. Marvelous design, but if your diaphragm does not seal correctly manifold vacuum will suck fuel right past your diaphragm and into your manifold all the time. How to fix this? I got a piece of flat wood...think it may have been a small piece of poplar and drilled a 1.25" hole in it about 1/2" deep using a forstner bit. Then I cut circles into a couple of pieces of sandpaper...one was 180 grit and one was 320 grit. Then I placed those on the piece of wood, put the bonnet on top and rotated until it looked like it had been machined smooth. In one there was quite a bit of warpage. I've found this problem to be present in about 6 or 7 YF models I've bought. Please look at the images below. The first shows the bonnet piece. The second and third show the vacuum passage leading to the recessed area in your float bowl that should be sealed by your diaphragm. The fourth shows the bonnet with the diaphragm and spring mounted. The fifth shows the bottom side of the diaphragm. The sixth shows the now-smoothed bonnet surface. The seventh and eighth show the little tool I made. A couple of folks have asked "will this affect the a/f ratio at all speeds?" The answer is yes and especially at idle, when the engine should be running at its most efficient mode and on deceleration (when the vacuum is higher). At those times, more raw fuel will be sucked into the recessed area and passed straight into the intake manifold. Just a thought and a bit of explanation of how the power circuit works on the Carter YF. Good luck!

To add a bit to this, below is an older YF bonnet. It looked flat visually but it wasn't. Actually it was out by .006" on one side and .008" on another side causing it to sit slightly crooked and to leak between the corner screws. The sitting slightly crooked part wasn't a problem nearly as much as the fact the diaphragm didn't seal on 2 sides. Once that was fixed, all was Jake. There's also a cutaway view showing the metering rod & jet plus the diaphragm scheme.

Fascinating. Thanks Jon(s).

Sounds like another Tech Tip ...?

I used Jon’s technique a few months ago to get a Carter YF straightened out. The genius truing tool for the accelerator pump bonnet was the secret to getting the old carb in proper tune.

The search function does work, Jon shared his how-to before.

RonR

Sorry for my delay in replying, have not been near a computer for awhile. Update: I have checked for external vacuum leaks, and I have thoroughly checked ignition system, which is in tip top order now, though it did suffer from a squirrelly condenser and a weak (incorrect?) coil both of whom were exasperating my problems. Now it fires virtually instantly the moment I pull the choke.

BUT it still will only run at low idle when the engine is cold (i.e. after sitting overnight on a cold morning) and will stumble or stall as soon as I touch the throttle, until it has had time to warm up. Once it has warmed up this issue goes away and runs fine whether at idle or driving. Thanks very much for the tip Jon, I am percolating on this wisdom presently.
-Curtis