What Am I Missing?
 

Did some work yesterday on the 235 in my 57 Chev truck:
-rebuilt the rochester b
-cleaned and regapped the plugs
-new fuel filter
Tried to start it up and it almost fires up, but it pops back through the carb. What did I miss or mess up?? Puzzled in Wisconsin

Re: What Am I Missing?
 

when you removed the plugs are you sure you got the correct wires on the correct plugs?
I re check that.

Re: What Am I Missing?
 

did you fill the carb before starting? are you getting fuel to it? have you pulled a plug and checked for wet fouled plug from overfuelling and also for spark? are all the plug wires attached all the way and placed back on the right plugs? what is the condition of the points, rotor cap? have you checked inside the distributor cap for missing/broken parts? checked the points wire to ensure it isn't intermittently gounding? checked the distributor shaft for wear and slop? check vac advance for sticking? mechanical advance for sticking? is the fuel fresh or does it have an odd odor if it is old? have you drained some into a clear vessel of some sort so you can check for clarity, color and contamination? what brought on the need to redo the carb?when you say cleaned and regapped the plugs, what was their condition, gap and color when you took them out? did you check for cracked insulators on the plugs?
wait for night and have a friend crank it while you look into the dark engine bay, do you see any cross fire "sparks" jumping from coil tower to ground or between spark plug wires or jumping spark to ground around the outside of a spark plug?


then consider below. not that you need a tune up but sometimes tracing through the steps you can find a problem.

tune up: assuming each step passes

check condition of valvetrain, including pushrods for bend, rockers and shafts for wear and ends of valve stems for wear
adjust valves
do compression test, dry and wet, and also cylinder leak down check
check ballast resistor and all wiring connections
check coil visually including pull coil high tension lead and check down inside the coil tower
perform spark check testing for color and gap spark will jump
replace plugs, cap rotor, wires, points, condensor, fuel filter, check condition of wire connection on points to ensure it is not grounding at insulator
check carb condition and adjust fuel accelerator pump nozzle to hit edge of butterfly valve
check all fuel hoses and fuel tank cap/vent
check fuel pump flow output and pressure and condition of fuel.
check vac hoses
check manifold gaskets for condition.possible vacuum leak
check heat riser valve
check exhaust system
start engine, allow to warm to operating temp
perform dwell adjustment
perform timing adjustment

of course that start up assumes you figure out what was wrong

just some thoughts

Re: What Am I Missing?
 

Did it run and drive before you did this? If so go back over the things you changed to see if you got something out of how it should be.
If it ran ok before it is going to be something that you changed during the tune up or didn't adjust right.

Firing order 1-5-3-6-2-4 and pretty hard to get out of order.

Most of the carb kits you get at the parts house these days have an assortment of gaskets for certain spots to fit specific applications and the holes are punched to fit the holes in the body for that application but if you compare gaskets the other ones will have holes in different places or no hole. I found out the hard way years ago that you have match new gaskets to old gaskets to make sure that you have the correct one.

If you changed and set the points did you have the rubbing block on the tip of one of the lobes of the distributor cam when you set the gap. I have no ideal of your skill level or experience but I've probably looked at 40 did a tune up an it won't start or run right rigs in the last 50 something years that the guy who set the points didn't set them right or got the gap wrong. Had a guy once who talked a good game but when he helped me do a quick tune up at the drags before I raced he set the points at .035 same as the plugs. That didn't take long to fix but sure cost him a bunch of car guy credibility.

Re: What Am I Missing?
 

Thanks everybody! I'll follow through with these recommendations. You guys rock!:metal: