[rb69]

I have tried a used-new to me 4777-7 650 on my 355 sbc. I also have swapped over to a 850dp w/ 750 base from another of my cars & it runs as it should. I have new MSD dist.,coil,plug wires & 6AL box.

I taken the 650 apart & blown things out & all checks out ok.
It runs, but doesn't idle very well & has a lag @ the hit of the throttle, even @ a slow rate. It sometimes pops . I have replaced the pv w/ another 6.5.
It did have a electric choke & I replaced it w/ a manual & did cover the vacuum source that the electric used.
It seems to have a vacuum leak & I have used carb. cleaner around the base & at the sides of the carb. w/ no change in idle speed. I have all the vacuum ports plugged on the carb.

Thanks for any ideas!!

[cobalt327]

I would start by using a straight edge to check both metering blocks for warpage, as well as the main body.

Many times, a used carb will have been "modified" by some ham-fisted PO, who did more harm than good. So, what I will always suggest, is baseline it back to stock, and work forward from there.

Jets, Primary- 67
Jets, Secondary-73

Power valve- 65

Primary accelerator pump shooter- 0.028"
Secondary accelerator pump shooter- 0.028"

Accelerator pump cam- white (IIRC)

There are subtle differences in the base gaskets, be sure the one you're using is correct.

Be sure you're using the correct power valve gasket (shouldn't have any "fingers" to locate the valve- just a simple ring shaped gasket), and that it's not too thin, allowing the PV to seat before it is sealed fully.

The off idle stumble could be related to the accelerator pump adjustment. Be sure the throttle linkage moves the pump arm the instant that it moves, and that there's fuel discharged from the nozzles, also instantly. There should be at least 0.015" clearance between the arm and linkage at WOT. If there isn't the pump diaphragm can be damaged.

There are two check valves for the accelerator pump one under the nozzles (will be a long needle)- and one under the diaphragm (will be a red rubber "umbrella"). They all must be there, and sealing, or the fuel will leak back into the bowl and this causes a lag in the fuel delivery through the nozzles.

Good luck and ask if there's anything else that you think of.

[rb69]

I pulled it back off to go over it .
I changed meter block gaskets, inlet needle & seats.
I checked the base for straightness & where the metering block sit on the carb., also the base plate.
I reset secondary's to set the transfer slots. I check vacuum @ the large port of the carb.. It measured 8. I had a 6.5 pv in the front & changed over to a 3.5. It had 28 squirters, now has 31's in it. Still has 67 jets in front & 73 in the rear.
It does run better than it had, but still sounds like it's missing down low. Seems to run better when it's up in the rpm range, but still not crisp.

Pulled off & swapped back the other carb & it's running as it should