Ive been having this issue for a while now and havent been able to figure it out yet. My 235 run great, sounds good, abit smokey but other than that its good until I try to accelerate from idle quickly. As soon as I push the pedal down faster than normal, it wants to cut out It only cuts out when its going from idle or low speeds quickly. If i accelerate easy/normal, it does great and is smooth. The carb has been rebuilt, new gas tank(old lines though), new fuel pump, new plugs, wires, cap, rotor, coil, valves adjusted properly. Does the vacuum advance have anything to do with this? I dont know if this is just a fault of the rochester carb or if this is something Im adjusting wrong? Thanks for all the help guys, Cody.
I don't remember the details about the internals of the carb, but it sounds like an accelerator pump problem to me. When you first step down on the gas, it causes a big drop in engine vaccuum, and the normal fuel/air flow is temporarily interrupted. To compensate for this, the carb is supposed to give a little squirt of gasoline directly into the throat of the carb to get past that dead spot. With the engine and air cleaner off, look down into the carb throat, and manually 'pump' the throttle. See if you observe a squirt of gas. If not, you may just need to adjust a linkage, or maybe the check in the pump assembly isn't seating properly so it can't pick up fuel to pump. (This thing basically works like a squirt gun). Maybe Ken50 or Nate can be a little more certain of how this carb works, but that is generally what is happening with almost all the cars that I've seen this problem with. Hope this helps. Bill
Flat Spot Is what this is called and yes , often it's the acelerator pump isn't beginning to squirt the *instant* the throttle is opened . Also , this is what " ported vacuum " is all about ~ @ idle , there's not supposed to be any vacuum to the dizzy , as soon as the throttle opens , a vacuum signal goes to the dizzy & advances the timing a few degrees , this helps prevent the flat spot . Sadly , many Hot Rodders don't take the time to learn so they think Ported vacuum is a new thing and instead want to run manifold vacuum to the carby all the time... Go back and re check your timing to be spot on ball & pointer @ 600 RPM's or less ,then work forward from there .
Check the Vacuum advance and see if it is working, you can do this by just cracking the throttle by hand and watching the distributor. If the distributor moves when you crack the throttle then it works, if not then it doesn't. Like Nate says your vacuum advance needs to be connected to ported vacuum source cause a manifold or constant vacuum source can make it work backwards....When you accelerate hard your advance kicks in if it doesn't it can make the engine sound a little rough or make you think it is missing a little....Big Tim
Thanks for all the tips guys. I checked my vac advance today and the distributor doesnt move at all when the engine is accelerated. So I guess I need to look into getting another one put on there and see if it'll help.
Dist. Vacuum Advance Can O.K. , looking in my vintage Standard Ignition catalog it says # VC-24A or maybe VC-150 . Lots of partshaus' carry Standard Ignition / Blue Streak products , they'll prolly have to order it in though .
