Distributor Springs - When do they need to be changed or flawed logic.

[74 challenge]

When it comes to carb I have tried jetting, accelerator pump, choke, air fuel, transition slot/ idle screw... What else could it be? I could buy a new power valve but that would mean the one from proform that came in the car was a dud.

I absolutely hate this carburetor.

[Chryco Psycho]

Ok what is the carb exactly ?
 new or used
 Why not try changing springs in the dist it could help too

[74 challenge]

Ok what is the carb exactly ?
 new or used
 Why not try changing springs in the dist it could help too

Proform 650 Vacuum secondary. Bought it new from summit. Has ~500-600 miles on it now? Never had a backfire.

If I swapped the springs I go to lighter ones right? it seems that this is everything that is available. Seems a lot of people swap to one stock one and one lighter one but I run a summit distributor that was built after 2001 so it's likely that it already has lighter springs?  I have a totally stock mopar distributor - I am tempted to throw it back in just to see if it makes a difference.

I will be completely honest this is my first "old" car I have ever decided swapped a cam into and never realised all the timing implications and minor things that needed to be done by hand. All those Nissan 240's I built all you had to do was throw in some numbers, get a flash and swap the ECU.  Building a 400 hp SR20det engine seems like a cakewalk compared to building a mild '72 360!

So the more laymans we can get here the better, I feel like this is setting my skills back years lol.

[73_Cuda_4_Me]

Before throwing anything at it, throw some $$ into adjustable timing light if you don't have one yet...

It would be best to baseline and report what timing curve you have before veteran gurus - Chrycho comes to mind here ; )  - can suggest which way to go...

You need to map where timing is at idle, at what RPM it starts to advance, how far it advances, and RPM it reaches full advance... even rough 500 RPM timing increment readings would be a great help! (i.e.- what timing you have at idle, 1500, 2000, 2500, 3000, 3500 RPM)

Spring recommendations would follow those results to get you better in the ball park

 

[Chryco Psycho]

Swap the dist & see what changes , if nothing we are back to carb tuning

[74 challenge]

Swap the dist & see what changes , if nothing we are back to carb tuning

I will give this a try early next week. I need to have the car in to an exhaust shop on Tuesday so running poorly is better than not running at all!

[Chryco Psycho]

Did you go through my tuning guide in the archives on tuning Holleys , you need to work through a process as every change can affect the other circuits unless you change in the right order . Here is the link http://www.cuda-challenger.com/cc/index.php?topic=822.0
 A stumble when cruising with slight throttle movement could be check ball or pin missing so fuel is not immediatly there with throttle movement or wrong pump cam profile not moving the lever enough with the throttle 7-10% open where you may be in cruise mode or you might need a slightly larger squirter to deliver the fule faster as the throttle is moved although this is unlikely as there should be very little fuel added at that point , raising the float level might eliminate the stumble as it is easier for the vacuum to pull fuel into the booster  . The power valve may be the wrong rating it might be too low & waiting to long to open .

[74 challenge]

Did you go through my tuning guide in the archives on tuning Holleys , you need to work through a process as every change can affect the other circuits unless you change in the right order . Here is the link http://www.cuda-challenger.com/cc/index.php?topic=822.0
 A stumble when cruising with slight throttle movement could be check ball or pin missing so fuel is not immediatly there with throttle movement or wrong pump cam profile not moving the lever enough with the throttle 7-10% open where you may be in cruise mode or you might need a slightly larger squirter to deliver the fule faster as the throttle is moved although this is unlikely as there should be very little fuel added at that point , raising the float level might eliminate the stumble as it is easier for the vacuum to pull fuel into the booster  . The power valve may be the wrong rating it might be too low & waiting to long to open .

I had to lower the float level to stop it from putting fuel into the engine on anything that wasn't 100% level ground. I did follow this manual a couple of times too to make sure it was running well.

I will admit I have not checked for missing parts as it was a brand new carb so Missing check ball or pin were never verified.

The power valve is already the correct one according to the stats on the little paper that came with the carb at 6.5. I had ~15hg of vacuum. The number is at home while I am at work currently.

https://www.proformparts.com/common/instructions/67207_specs.jpg