I have an 82 305 auto camaro used for fun/couple of times a week,it is fitted with a holley 650 with vac secondaries,an edelbrock performer inlet,mallory dual point distributor(fitted with electronic ign.),&headers,what I`d like to know is : would there be any gains by changing to a double pumper?if so what size&what mods would be needed.Are there different springs/jets etc available Also i`ve got a flat spot on acceleration,when I floor it there is a hesitation(almost stalling) then it picks up and accelerates well,I suspect the accelerator pump or something related to it any ideas would help,I`m going to try & check tommorrow(british weather permitting!)

 

DP are meant to put more fuel in quicker. This pretty much means if you're going to use an automatic you need to get a high aftermarket stall or you will get a hesitation off the line. There mainly made for drag strip applications.

I would say a DP on a 305 would have to really sized down and would be more a pita than what it's worth. That's just my opinion.

 

replace your powervalve, your probably flooding the motor with fuel from a blown valve, that's more then likely your problem. anyhow, a dp is really not necessary on those little motors. i have a very hot-rodded 305 with a dual feed 600 vs and the car ran high 13's.

 

thanks guy`s for the info, I`ll stick with the vac secondaries!

 

Sorry, but I have to disagree with the blown power valve theory. When a power valve gets a leak, even a pin hole, the carb goes absolutely FILTHY rich. Won't run worth a hoot.

I believe some simple accelerator pump tuning is all that is required. Check your pump nozzle size. Probably around a #25. That is too small. I would recommend a #31 shooter with a Blue accelerator cam in the #2 hole. That is a combo that seems to work very well on just about every SBC. If you're in England and Holley parts are hard to get...use a number drill and drill out the shooter to .031" ( a 1\32" drill will be close enough ).

make sure that you have enough initial timing in the beast as well. Minimum 10 deg BTDC static timing.

Check out some of my posts at this link.

Holley Tuning Tips

 

thanks chickenman! I had a look today & found the earth lead on the electric choke was off,re connected it,the car seemed better (slightly) but still not instant throttle response.Once moving the car seems to really perform well,wondering what engine is really in there! how can you tell 305 from 350? where is the engine no. supposed to be? when I got the car it really "pinked" under acceleration,so I backed off distributor,but sounds as though I could do with as much advance as I can!I tried setting with a timing light but something was definately wrong.Also on close inspection ,when you look into the top of carb.there is fuel slowly dripping into the secondaries from the jet/s,could this be float level? where can I get a detailed drawing of a 650 holley for ref.purposes? ........thanks for the help

 

I belive holleys website has breakdown drawings of the carbs.