carb question on 68 olds 350

[lightemup2]

hey guys im having trouble with my carb on my 68 olds 350... it has #5 heads, .30 over, mild cam, edelbrock performer intake ect... I have a holley 715cfm on there right now vac secondary's and the secondary's are not opening up, ive changed the spring out and everything a couple times and still nothing... im thinking its dumping to much fuel in... and also it bought it used and it was rebuilt... so im looking to buy brand new... ive done my research and still cant really find what im looking for.... I had a 600 on the car before and it kinda hesitated before it would take off when I got on it..

so the question is, what size of a carb should I go with? and what kind?

also is has a th350 trans with shift kit and 2100 stall, and a 8.5 rear with 3:73's

 

[Rktpwrd]

hey guys im having trouble with my carb on my 68 olds 350... it has #5 heads, .30 over, mild cam, edelbrock performer intake ect... I have a holley 715cfm on there right now vac secondary's and the secondary's are not opening up, ive changed the spring out and everything a couple times and still nothing... im thinking its dumping to much fuel in... and also it bought it used and it was rebuilt... so im looking to buy brand new... ive done my research and still cant really find what im looking for.... I had a 600 on the car before and it kinda hesitated before it would take off when I got on it..

so the question is, what size of a carb should I go with? and what kind?

also is has a th350 trans with shift kit and 2100 stall, and a 8.5 rear with 3:73's

Before you go swapping out a potentially perfectly good carb, Holleys have an o-ring that seals the cover to the vac secondary body and a diaphragm below the spring. Make sure both of those are present and in good condition (no holes or tears in the diaphragm). Even a pinhole in it will keep the secondaries from opening.

 

[HAFROD]

Holley recommends a 650 for a 350 cubic inch. If you do not have a vacuum gauge, you cannot properly tune a Holley. Gauges are cheap. (around $15). You set the air bleeds to the highest reading on the gauge. After car is warmed up, put it in gear, gauge on manifold vacuum, whatever your reading is, split the number in half and that's the proper power valve size for your engine. To check primary jet size you must be driving normal above 35mph on a less populated side road and kill the engine, check the plug, and jet up or down depending on how they look. Only go 2 sizes at a time on jet size. You cannot just bolt on a new carb and expect it to perform at its best. Every engine is different and you have to tailor it. All the above tuning info depends on your timing being set correctly first. If the timings was incorrect, the carb tune will be too. To drain your carb float bowl on the car, I like to use a spray paint cap. Hold the cap under one of the bottom float bowl bolts and loosen the bolt and unthread it a bit. The gas runs into the cup and not all over the engine. The hesitation can be a couple different things but the above info will cure it

 

[lightemup2]

thanks for all the help and info, I have checked the diaphragm and that o-ring, and both seem to be in great shape!, i'm in a hold right now as I have the rear end pulled out, because i'm throwing in a 8.5... I don't know what else to try, im pulling plenty of vacuum, and everything seems to be functioning as should...

 

[olds307 and 403]

I say a carb like Street Demon 625 or 750 should be considered.

 

[lightemup2]

thanks everyone I ended up buying a new carb holley 600 double pumper, manual secondary's and choke and im very pleased with it!