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'52 carb hesitation


Erik

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Hi All

I rebuilt my stromberg 4a and now experience a lag or hesitation just above idle when adding power.

Most driving seems to be around idle (ca 450 rpm) and when slightly depressing the pedal the car stumbles or hesitates.

Depressing the pedal more the accelerator pump kicks in and all is well.

The needle valves are adjusted at 1-1/8 as specs for initial setting.

Floats are set so fuel just covers the threads i the tell-tale holes.

So what's wrong???

Suggestions are welcome:D

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Generic response: What changes did you make on adjustments internally? Be sure idle quality responds when you turn each idle screw in to seat and back out, if not, blow some compressed air thru the screw hole (engine shut down). Butterfly idle position internally set by idle screw has an effect on proper "tip in" fueling also. Try readjusting idle mixture screws idividually for smoothest idle, if no better, turn both 1/4 turn in first then out to assess the effect. .....Don't discount base timing and advance function as they can cause same issues. Carb settings before rebuild may have been masking advance issues. Again, just generic, I am not a Stromberg expert.(not sure I even spelled it right) TJ55

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Check the ignition system first, as others have mentioned.

IF the ignition system is in good working order:

Check the idle mixture setting. The idle mixture control screws (the two pointed screws with the spring retainer) should be set from 1/4 turn to an ABSOLUTE MAXIMUM of 1 1/4 turn from lightly bottomed. If the engine is in really good condition and well broken in, I would suggest from 1/2 to 3/4 turn. Run the engine until it reaches normal operating temperature, and then try 3/4 turn. Set the actual idle RPM with the throttle positioner screw. Many enthusiasts set the carburetor to give the best idle, which is virtually always TOO rich. This can create "puddling" in the intake manifold. When the throttle is lightly opened, the onrush of air will sweep the droplets of fuel or "puddles" adhering to the intake manifold runners into the engine creating an instantaneous RICH condition and a momentary bog.

Jon.

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Aaron - each carburetor has a manufacturer recommended range for the idle mixture control screws.

The method I personally use (others will differ) is as follows:

(A) determine the range for the specific carburetor

(B) divide the range into 3 parts, and set as follows:

© for engines which are new to roughly 1000 miles go 2/3 of the distance from the minimum setting

(D) for engines which have a 1000 miles (broken in, and still have acceptable compression - good running engines) go 1/3 of the distance from minimum setting

(E) for engines which you are just trying to get through the summer before complete rebuild, go to the maximum setting

And of course, the obligatory example:

Assume the manufacturer's range to be 1/2 turn to 2 turns, then 1/3 of the range would be 1/2 turn.

Thus for the fresh engine 2/3 added to the minimum would be 2 times 1/2 turn or 1 turn added to the minimum or a total of 1 1/2 turns

For the good running engine 1/3 of the range would be 1/2 turn added to the minimum of 1/2 would be a total of 1 turn.

And of course the worn out engine would go to the maximum of 2 turns.

REMEMBER, these calculations are done with a "dreamed-up" range of 1/2 to 2 turns. Check the original manufacturer's specification for your carburetor.

This only works for a modern "in to lean, out to richen" idle circuit, many early carburetors have inverse circuits that go in to richen.

As a general rule IF YOU CANNOT FIND THE EXACT SPECIFICATIONS, a good starting range for carburetors produced before 1968 (smog emission) will be 1/2 to 1 1/2 turns.

When smog emission became a reality, it was necessary for more precise idle mixture adjustments. Thus the angle of the point on the idle mixture control screw was changed (the taper became longer). Generally, the range on these longer taper screws would be maybe 1 1/2 turns to 3 1/2 turns.

Jon.

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Well.... remember that ethanol has a completely different molecular makeup than real gas. Your original carburetor was designed with inner air and fuel flow channels that "governed" the molecular mass of fuel to air ratios when utilizing real gas. When you put gas-a-ol into the equation, then the parameters and dynamics change. The initial throttle stall response is on one of many symptoms which do occur. In some cases recurving the distributor along with enlarging idle circuits diameters to accommodate the gas-a-ol via it's heavier mass when compared to real gas is the key fix. These are not the same fuels and you cannot expect the same operational and performance characteristics. The float may need to be adjusted as well in this re-vamping of things. If you do a wide enough search parameter on the net you will discover many of this topics and issues.

Hope this helps to get you onto the right track.

Edit: Just for kicks. As always I tell everyone, Before you do anything else go buy if you can at your gas stations Real non alcohol laced fuel if it is available, If not and the gas nazi's have taken your state over like out here in California forcing one to purchase corn gas, then a can of leaded or unleaded NON OXYGENATED ( Equals NO Alcohol ) racing fuel is your next option. Try and buy the lowest octane rating like 95 or so. VP racing has C-10 which is a stable unleaded non oxygenated fuel. Sunco has a Non Oxygenated unleaded one as well. They both also offer leaded non oxygenated real gas as well. Either way, this approach will give you a "real gas" calibrator to work off of. You may be surprised how things work. Then go back to your alcohol laced fuel and report back to us with the results.

Good luck.

Edited by buick man (see edit history)
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Thanks for all the suggestions.

Of course I will recheck the vacuum advance and timing, but...

Jon: Yes, your description of "puddling" fits the bill, but if "puddling" occurs when mixture is to rich and my needle valves are at 1,1/8 out, wouldn't it get worse if I screw the valves in to 3/4 out? Shouldn't it be out by 1½ to get the mixture leaner?

David: I'm running on 95 octane 5% ethanol with added lead additive, which is what I can get here. I can get 92 octane, too.

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Guest shadetree77

This sounds similar to a problem I had. What kind of fuel pump set up are you running? Original or electric? If electric, what PSI is it rated for and where did you put it on the car?

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Guest shadetree77

Ok, nevermind then.:) My problem was with an electric pump. Hope you can find your problem soon. Good luck.

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Thanks for all the suggestions.

Of course I will recheck the vacuum advance and timing, but...

Jon: Yes, your description of "puddling" fits the bill, but if "puddling" occurs when mixture is to rich and my needle valves are at 1,1/8 out, wouldn't it get worse if I screw the valves in to 3/4 out? Shouldn't it be out by 1½ to get the mixture leaner?

David: I'm running on 95 octane 5% ethanol with added lead additive, which is what I can get here. I can get 92 octane, too.

On this carburetor, turn in (clockwise) to lean; out (counterclockwise) to richen.

Jon.

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