I finally got my rebuilt motor (351c) up and running. The only problem I have is the vacuum secondary’s on the Holley 600 are not working. When I step on the accelerator to max it doesn’t have the power it should. I put a paper clip on the plunger for the the secondary’s. Took it for a test drive and checked the paper clip. It did not move. I checked my vacuum and it’s a little low around 15. When I add a little throttle it’s around 21-25. I’m not sure if the cam is stock or is a very mild cam. I have it set up for 850-880 rpm’s.
I was reading about changing the spring for the secondary’s. Maybe someone knows a way I can test the secondary’s another way.
One more thing! When I was setting up the motor after Rebuiling it the carb back fired a few times. Could that damage the diaframe for the secondary’s?
Hi Superbond, how sure are you about the ignition timing? The vacuum sounds ok.
It was set up at 12 deg and total timing 36. It seemed like it was sluggish so I weekend it by ear. Turned the distributor maybe 1/8th of an inch clock wise which gave it way more power. Before I did that when I floored the gas petal it would have a hesitate small backfire then speed up. After I changed the timing the still is a tiny hesitate but no back fire. She takes off pretty good but my passing gear is not working so if I won’t some real power like if the 4 barrels had kicked in I have to slip the tranny into 2nd. But even when I do that I checked the paper clip and it still hasn’t moved
Not sure of this but I think that you can’t get the secondaries to open in the driveway. It needs to be accelerating under load. Just bringing it up to keep you thinking of all the possibilities. You say your passing gear isn’t working, so its an automatic tranny? Is your carb linkage and kickdown cable setup right?
No
It’s hooked up but may have been bent while putting in the motor. And I know the secondary’s only work while under a load ( driving)
Changed the secondary housing top to a quick change housing for changing spring strength. Checked to see if diaframe was ok. Turns out it wasn’t. Change that and put the carb back together then put the paper clip back on the secondary shaft. Took it for a drive. I could tell right away the 4 barrels were working. When I got home I check the paper clip and it was knocked off the
Shaft. Perfect! The only thing I have to correct is there is a stumble when I step on the gas. Maybe i have to adjust the automatic choke
stumble might be to weak of secondary spring.
https://www.holley.com/blog/post/how_to_adjust_holley_carburetor_vacuum_secondary_springs_/
It’s the stock spring which is supposed to be the heaviest one. Thinking accelerator pump needs adjustment. Not a fan of that
Try advancing the timing a couple degrees.
I could try I guess.
Advanced it a few degrees like you said. Runs good. Hard on gas guess that’s to be expected. Thank all you guys for the advice
So
After driving for a few days with no issues well maybe one. I smell gas quit often. Strong smell. There are no leaks and it’s seems to be only while accelerating on the hwy. is there anything I should check? How do I check to see if the machanical fuel pump is pumping too much fuel. It’s relatively new
I advanced the timing. It’s at 14-15 degrees. Runs good. But isn’t that to high for timing. I read no more then 12 degrees. I’m still having overheat issues if I sit at long red lights temp climes fast. Start driving and come down fast.
A larger accelerator pump squirter will often help with hesitation/stumble.
Is the gas smell coming from underhood or from the exhaust? Absent a visible leak/flooding, I can’t think of any good reason for a strong underhood gas smell.
- Missing hood to cowl seal
- Hood not adjusted properly so there is a gap between the hood and the hood to cowl seal