69 350sb (380hp) original engine

I have a Edelbrock 750 cfm carburator and experience hesitation at the low rpm and high rpm has a miss. I have bought the jet and metering rod kit and switched out some of those and it has helped, but not cured the condition. I think it's carburation. Any tips? Float bowls are empty after three days of sitting.

 

Do you have any fuel moisture on the outside of the carb? near any linkages. The hessitations could be from a slight vacume leak, which would explain the fuel dissipating after a few days as well.

 

[X(] to say the least its over carbed which may explain both problems. a 750 carb on a 350 motor is too much and will not provide a good vacuum signal to this big a carb resulting in some of the conditions you describe. a 550 or 600 are perfect carbs for stock or mildly built 350's. get the correct carb and i think youll find it works better and youll be happier with it kurt

 

This is absolutely untrue. That Edelbrock Carb has vacuum secondaries. It behaves like a 300CFM carb until you ask more of it. Thats why we saw 750/780 Vacuum secondary carbs on all of the small block HiPo 1st generation Camaros (and others).

Vacuum signal is not generated by that carb. Vacuum signal is generated by the pistons and valve timing events. That's why a larger cam has less vacuum than a smaller cam. Regardless of carb size. If your case were true, we would need to run smaller carbs on our monster cammed engines.

ANY vacuum secondary carb CAN BE tuned to work on ANY mild to wild engine.

You need to go the route that clp stated. Check for vacuum leaks and the like. Often a low RPM hesitation (not bog) is attributed to not enough fuel when you step on the gas. Your high end miss can be much tougher to figure out. Is it steady at a certain RPM? Does it jump around?

Most (not all) of high end misses are a result of an ignition problem not the carburetor. Especially if they are at a steady RPM.

RM

 

Checking for vacuum leaks? ether? High RPM miss, what do yo umean about jumping around at different rpm's or not being consistent? Not certain my timing is correct, if I put more advance in it the hesitation goes away, but a few guys told me it won't run as well and shouldn't need that much advance. 22 degrees is what one guy's timing light sais, so I backed it down to about 1 degree before the timing tab. I have a 270-470 comp cam, which has 4 degrees built into it.

 

Yes, you could use ether to find a vacume leak, just spray it near the vacume line connectors at the manufold and car, dont forget the one to the power brake booster. If the engine surges from the ether spray you have a vacume leak. When I get home I will check out my chiltons manual (unless someone else has one and beats me to it) and tell you what your timing should be set at. Fear not, we will figure this out.