Any tricks to get "too much" carb to work on a motor?

My 235 inline in my 49 Chevy has a Rochester 2 barrel on it off some mid 60's SBC. Driving along is fine, but pulling out from a stock usually ends up with the car stalling, or having to "pump" the gas and feather it to successfully have the car pull out. It seems that the initial transition of the throttle blades is just dumping too much air into the motor. I increased the initial timing, which helps, but it still is pretty crappy.

 

how do the plugs look? my 235 was all stock with a 2 bbl holley/weber and ran like a champ. do you have the correct gasket? there could be a vacuum channel covered.

 

What seems like too much air may actually be a matter of not enough fuel. Make sure it's got a good strong accelerator pump shot that starts as soon as the throttle blades begin to move off idle.

 

x2 on vacuum leak or wrong base gasket. Pumping it is why I say that. Maye close the choke a little to cover up that lean spot off-idle. Any way you slice it, it looks like you'll need to set aside some time to fix the carb or set aside some $$ for a diferent oe, or both.

 

I doubt thats too much carb. My buddy has a 390 4bbl on his and it runs like a champ.

 

Thats what I don't get. When we were working on my buddies slant we couldn't get it to run right with ANY carb but the stock 1 barrel. Any other carb bogged, including a 350CFM demon two barrel and a 390 Holley 4 barrel. For some reason I never have these problems with v8's, only these inline sixes.

One other thing I forgot. During my recent "overheating" issue, if the car was running above 190 degrees, there was NO bogging at all and the carb worked perfect.

 

Plugs are clean, no carbon at all.

I'm using a Vintage speed 2bl to 1bl adapter, and it's the only gasket that fits.

 

I'm with ClayMart on this one. When you crack the throttle open, vacuum goes down quickly and the fuel falls out of suspension. You need a good pump shot to overcome that lean spot. That's what accelerator pumps are for. Good luck.

 

Change the accelerator pump, especially if it still has a leather one. Put a rubber one in it.

 

Your intake may be too cold, leading to the fuel dropping out of suspension. Put in a hotter thermostat (195º), and try it again.

Your clue was the running good while hotter. 195º is not too hot, it's where efficiency starts. Efficiency is using the fuel properly, which you are not right now.

Cosmo

 

The quick remedy but not long term is just run the chock about a third of the way closed.

 

If you really want the two barrel to work, remove the 2->1 adapter; and machine the plenum of the intake to accept the two barrel.

Probably a better solution from the standpoint of power, driveability, and economy is a one barrel.

Jon.

 

So I checked the carb, and to my shock it has NO accelerator pump shot. I took it apart, and the donut had fallen off the end of the shaft. I put it back on, bench tested it, it worked for a shot or two, then stopped. Pulled it apart, same thing. The spring that goes under the accelerator pump assembly is somehow grabbing the donut and pulling it off the accelerator pump. I tried on from another rochester I had laying around, but it was larger and wouldn't fit past half way down the bore.

 

Fixed the accelerator pump, it kind of works now. If you crack the throttle more than 1/4 at idle, the carb just makes a "BWUUUUUUUU" noise and stumbles. When I pulled the carb off, I saw fuel puddling in the intake.

 

Just going from memory here, been a lot time. Is that one of the carbs that is supposed to have a check ball in the bottom of the well under the accelerator pump? If it is you didn't lose it did you?

 

Nah the ball is there. Accelerator pump works fine now.

 

Years ago I put rochesters on several smaller motors, I found that i usually had to increase the jet size. The smaller motor is pulling less air, therefore the vacumn that pulls the fuel through the jets is not as strong, and you need a larger opening.
My 2 Cents.

 

I know this is going to open a can of worms, but could this be because I do not have the intake heated? It has headers on it, and a stock intake, but I am not running either exhaust or coolant to the intake. I have a feeling I know what the answer is going to be, so I'll just duck ahead of time.

 

Thats a good possibility.

Here is a pic of my buddies setup, sorry its such a bad angle, but its the only pic I could find:

 

You might find that there's actually two check balls or valves used in the accelerator pump circuit. When the plunger is depressed, one valve seats to prevent fuel from flowing back into the float bowl and the other valve opens to allow fuel to pass thru the pump discharge nozzle.

When the plunger is raised, one valve closes to prevent air from being drawn thru the pump nozzle and into the accelerator pump well and the other valve opens to allow fuel to be drawn in from the float bowl.

Here's a link to a diagram of a typical accelerator pump circuit. Just scroll down the page a little bit.

http://www.tpub.com/content/automotiveenginemechanics/TM-9-8000/TM-9-80000131.htm

 

I just talked to my buddy. His IS heated.

Hope that helps

 

Do you see any "frost" on the carburetor.

Manifold heat IS desirable on an inline engine; but I still think your major issue is the 2 -> 1 adapter. The air velocity in the carburetor is lower than the carburetor thinks it should be. Thus, insufficient fuel is drawn from the fuel wells at lower RPM.

Jon.

 

Also make sure your idle is not set to high that you are actually idling in the transition circuit of the carburetor and not the idle circuit. If you do have your idle set to high, the engine will stumble until the carburetor catches up to the the engine. the transition circuit is what helps compensate for this along with the accelerator pump.

 

Pour the fuel to it. When you pop open the throttle air moves much faster than fuel can respond, it fills the manifold causing an extreme "lean condition" that won't light. Load that air up with fuel and BANG, you have something that will run. Best thing is to match the induction system with the demand.

 

What about the exhaust heat riser ? We used to block those,...and had stumble on driveaway, until it warmed up quite a bit.

4TTRUK

 

Yes, it does frost up. I posted about that when I first got the engine running years ago and the general agreement was 2GC's just "do that".

 

Nope 2GC's dont 'just do that'. Yep you need a heat riser. The problem you had with the accel pump rubber is due to the fuel we have nowadays. Older rubber pumps dont like methanol. The leather pumps work much better if you can find them. The blue rubber pumps seem to work better. Their make of a different type of rubber, or something besides rubber.

 

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While it is possible for virtually any carburetor to frost under a narrow band of conditions, frosting is EXTREMELY RARE on anything made after about 1930 if the installation is correct. The 2GC's do NOT "just do that".

You need heat. Take a look at some of the mid-1960's Ford trucks and the metal heat stove they used to direct heat into the air cleaner. You can make one of these.

But still think even with the heat, you will not be happy with the 2 ->1 adapter and a two barrel at lower RPM.

Jon.

 

Well now we're gettin' somewhere! I don't know which is better; getting an answer or getting asked the right questions!

 

The reason for the 2 barrel is my wacky throttle setup. I'm using a cable and kickdown for a th350, and the factory 1 barrels have a "pull down" throttle linkage. This was the easiest solution at the time. I may change to one of those progressive weber carbs whenever I can get to the junkyard to acquire one, assuming they have the same bolt pattern.