lousy mileage and power

Check valve clearance.

Are the exhaust systems of the same make and model? Idle jet the same? The engines being rebuilt, are the heads the same(valve sizes)? Camshaft the same? Heatriser on manifold unclogged on both engines? The vacuum diaphragms intact on bot distributors? No vacuum leaks on the manifold to endpieces rubber grommets?

J.

I used to build Chevy small block V8's and drag race 55-57 chevys.

I would build identical engines.

One was a rocket, the other a sled.

Never knew why. Clearances maybe?

Verifying that the vacuum diaphragm is intact on the vacuum advance on the distributor is a good place to start as Berg suggested. Checking how the timing advance changes with throttle position/rpms is another thing to do. General tuning state of the carb would be the next place to look. Dirty jets will sometimes do what you describe.

Both carbs are used german originals? could be throttle shaft bushings too... one may be worn more than the other and sucking a slight bit more air than the other is and causing your air/fuel mixture to lean out.

compression might be slightly different on the two engines what about plugs? both the same brand and gapped the same? tire size the same on both cars? it does make a little bit of difference.

all the small differences add up and can give you lousy milage.

First check that all cylinders are firing.

With a fully warmed up engine do the following tests: Measure the idle advance with a timing light, with the vacuum hose disconnected. You should have around 7.5 degrees advance. Then connect the vacuum hose (engine running) and see what happens to the advance. It should stay the same (7.5). If it increases, then the throttle butterfly is not correctly adjusted on the carb, or the throttle positioning screw is resting on the fast idle position. Rotate the fast-idle cam so that the throttle butterfly closes all the way.

Every carb adjustment starts by setting the throttle butterfly closed position. This is critical so that the idle can be set later and so that the vacuum advance works correctly. To do the adjustment, the fast-idle cam must be at the "hot" position, where the chock plate is fully opened. Then unscrew the adjusting screw on the throttle lever, until it no longer contacts the fast-idle cam. In this position the butterfly is completely closed. Now you must tighten (turn in) again the screw until it just gets in contact with the fast-idle cam, and then tighten it 1/4 turn more. The butterfly must be just a bit open, so that it doesn't bind on the throttle body and wear it.

Now you can set the idle from the two screws on the left (as described many times in the past), and set the advance.

If this doesn't cure your problem, then swap the carbs. This would easily tell you if it's a carb tuning problem or not. The fact that both carbs have the same main jet (130) doesn't mean that they are jetted the same. You have to compare the idle jet, which is responsible for engine operation up to 2000 rpm. Also compare the emulsion tube/jet (the one under the carb cover, which looks like a tube with small holes on it's sides).

Check the float valve in the carb cover. It might be defective, allowing fuel to overflow in the carb and leak in the throttle bore.

Other reasons for excessive fuel consumption and poor low end performance would be valve train related: wrong valve adjustment, burned or bent valves. After adjusting the valves do a compression test (engine must be warmed up for a compression test).

Bill Spiliotopoulos, '67 Bug.

try spraying a tiny puff of either (engine starting fluid) at the outside hinge of the carb pivot points for the butterfly when the car is running. It may be that there is an air leak due to worn bushing. Also, in the carb, have you adjust the (air) bypass? The 34 pict 3 has that, as I recall. The diaphram in the distributor sounds like a possibility since it runs well at higher RPM... but not at low... maybe it is sticking closer to the higher timing? That is abysmal gas mileage to be sure! Good luck! KWW