VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 hesitation upon giving throttle, need help

i have stock 48 216 chevy. when you accelerate the car bogs down and sometimes backfires through carburetor. i have replaced fuel pump, plugs, points and condenser, distributor cap and rotor. i also put on a rebuilt carburetor last summer. i set distributor dwell at 35 and gapped plugs according to specs. accelerator pump on carb seems to be working fine by shooting gas upon pumping throttle. vacuum advance appears to be working properly. last year i drove the car in a parade and it got hot idling. i need help with diagnosis. could a blown head gasket cause this problem? would a compression check detect that? dave

The two most frequent causes are: Vacuum advance not working & accelerator pump not working in the carburetor.

Backfiring indicates a lean fuel mixture or weak spark or late timing or a couple of other conditions. Are you sure you have the correct rebuilt carburetor? Was it rebuilt by a quality rebuilder? or just a mechanic? If using a Carter W-1 are you sure that the throttle plate and metering rod are properly coordinated? It is critical to produce the correct mixture. Is condensor and coil up to snuff? Do you get a strong blue spark? Yellow?

i am more a tinkerer than a mechanic so will you give me some instructions on how to check timing with timing light. also how do you loosen distributor to change timing?

Welcome to Chevy Chatter II. Glad to have you aboard.

If you don't already have one, you might want to order a shop manual for your '48. The shop manual contains a world of information that you will find useful, including checking timing, carburetor repair and other cool stuff.

:) :grin:

48 Aero, I went through the same thing this last summer. Mine ended up being the carb. But check the timing, and vac. advance for sure! If you have a modern day timing light hook the power leads to a 12V batt. so the light will be bright enough, and then hook the the inductor lead to #1 plug wire of your 48. The timing mark is in a small hole just behind the starter. The mark is a small BB embedded in the flywheel. It should line up with the pointer in the hole when viewing it with the timing light at idle. If it doesnt. Loosen the screw on the vac advance collar, and rotate Dist. till it lines up. If Vac. advance is working you should be able to see the dist. advance when you snap the throttle.

thanks for timing info. i would have looked for timing mark on crankshaft pulley. david

i bought a rebuilt carburetor from kanter. i am not sure of quality. i note that chevs of the 40s also sells a rebuilt carburetor. i dont know how to check out carburetor to see if it is the problem. if you know of good rebuilder i would be willing to send mine to be checked out. david

If you are a VCCA member, check an issue of the Generator & Distributor under "Services Offered" for several quality carburetor rebuilders.

:) :grin:

David,

"DO NOT" get a Carb. from Chevs of the 40s. I made that mistake this summer. I ordered a W-1 from them for a pretty penny PLUS a ridiculous core charge. What they sent me was beautiful on the outside, but wouldnt hold an idle due to the throttle plate not even being close to the size of the carb. bore. The replacement one they sent (which they charged my account for AGAIN) had a non-functioning accelerator pump. There response was do ya want to try a third? I got one from NAPA. It was perfect right out of the box. Quality rebuilders are in the G&D.

i have a canadian shop manual but i didnt see anything about timing in it. also if you are carburetor rebuilder mentioned in g & d let me know because i would like to have some tips on checking out accelerator pump. david+

To test the accelerator pump remove the air cleaner. Using a flash light look down into the carburetor throat. When you open the throttle you shoud see a stream of gas coming out of the pump at the front of the throat aimed towards the center. This should occur with the engine stopped or running but will happen only about three times with the engine not running. I assume that you have a Carter W-1 Cast iron carb. If so you can remove the single screw that holds the little black tin cover in place on to of the bowl - top front of carb. The link and lever that actuates the acc. pump can be see there. Make sure the link is connected to the lever on one end and to the acc. pump stem on the other.
The timing is set with the engine at a slow idle. Time off of #1 cylinder. The steel ball in the flywheel should line uo with the pointer that is in the opening on the right side of the flywheel housing facing forward. Just behind /to left of the starter. The timing can be advanced another 8 degress or so beyond the ball for best performance.
The shop manual has less info. than the above and no picture.

i looked at flywheel through hole in cover today. i saw the pointer but i didnt see a hole or bb or ball in the flywheel. how big is it and is it raised on the flywheel or recessed. david

Probably you should remove the flywheel cover under the clutch and find the BB sized ball. Then mark it with a dab of white paint. You'll find that using a timing light is a lot easier with the dot..And, by turning the flywheel by hand, you can clean the front surface of the flywheel and dab or read the other marks...