Off Topic Tech: fuel vs spark

[Reaper]

alrighty

i have a 79 chebby 3/4 ton 4wd truck 355 sbc, runs perdy good. but my one stumbling block at the moment is at about 1/4 throttle the truck stumbes and picks back up then is fine through the rest of the powerband.

my question is it fuel or spark?

i have a GM dist with recurved weights, and springs. the cap rotor look in good to great shape, plugs are new wires are in great shape.

as for timing i cant remmber what its set at. to be honest i kinda fine tune it by ear. i had a light on it once then just move it left and right till the idle smooths out and then take it for a spin and see what happens. (prolly not the best way but its how i was taught)

as for fuel it has a 600 cfm carter AFB on it with edelbrock metering rods set at one step lean. i looked online and cant find the part numbers for the kit i used. ( i willl look later)

but for now the generic question is would this be fuel or spark?


man i hope i make sense.

thanks
Dathan

 

[myclone]

When it stumbles are you accellerating or holding the throttle steady? If you are accellerating my guess would be youve got yourself a lean condition (fuel issue). If it was me Id richen it up slightly and see if it improved.

If you dont wanna mess with the carb then double check your vacuum advace operation and for proper connection to the carb. There may be an issue with the advance doing the wrong thing at the wrong time (1/4 throttle vacuum level=stumble).

Least thats where Id start.

 

[Reaper]

Originally posted by myclone
When it stumbles are you accellerating or holding the throttle steady? If you are accellerating my guess would be youve got yourself a lean condition (fuel issue). If it was me Id richen it up slightly and see if it improved.

so would i have to go back to the stock jets and springs then or can i just do a lean roll with the mixture screws? the reason i ask that is with the jetting i have the truck makes the most power its just recently that this stumble has occured.

Originally posted by myclone
If you dont wanna mess with the carb then double check your vacuum advace operation and for proper connection to the carb. There may be an issue with the advance doing the wrong thing at the wrong time (1/4 throttle vacuum level=stumble).

Least thats where Id start. [/B]

i will look at the vaccum lines and also verify that the advance is working.

thanks for the advice.

Dathan

 

[scottyb]

Vac leak.