Fine Tuning a 360 Magnum with a Brawler "Double Pumper"
Yeah I’ve just been poking around with random things to see if I can get it dialed in again.
I'll say the same as three other guys said. Stop. Write everything down and approach this systematically.
These carbs (I'm including carters, Rochesters and most of the downdraft 4bbls we deal with) have a low speed circuit that is feed from the main or high speed circuit. Get the low speed established first, beginning with idle. The low speed or idle circuit works off of the pressure difference (vacuum) below the throttle plates. It is most effective with high vaccum in providing good distribution. It is by its nature somewhat slow to respond to changes. Get the idle and then off idle established so it works with slow throttle opening. Then use the accelerator pump tuning to assist with fast opening.
You can 'get away' with being off a bit more with a manual transmission because you control the clutch directly.
Anyway. Timing is first. Then carb. With carb, start with fuel level, then initial throttle position. Adjust fuel mixture next. This is all an iterative procseess - hence the need for written notes and one change at a time. Use small adjustments in timing to adjust rpm as needed to keep the primary throttles in their operating range at idle. Then work on off-idle.
Holley (and their variants) say to set the pump arm with a .010" gap. I've never done that. I set it at what I call a "light zero". In other words, I make sure the pump arm isn't depressing the pump diaphragm arm at all, but there's no clearance, either. This way, the pump starts to work as soon as the throttle is moved.
Yep yep yep.
I think its in one of Urich's books he mentions the 0.010" is the check at wide open thottle; and its not free play but that a feeler gage can be forced in between and the spring will compress (insuring the lever won't bottom out and damage something with our foot to the floor).
Jmanhoff. Sorry i thought it was this thread I mentioned that, but it was actually this one
https://www.forabodiesonly.com/mopar/threads/holley-750-stumbles-on-wot.575305/post-1974937100
Is there any good write ups or maybe videos that go into detail about all the little parts of a carb that would be a good place to start looking? It seems like YouTube is flooded with the basic stuff and not the internals as much.
IMO youtube is flooded by self proclaimed experts in many fields but carb science and mechanical stuff in general suffer so badly I don't bother looking there. Sure its fine if you want to find a video of things like a restored up-down vertical saw mill in operation - especially if you know the name of the place, but otherwise there is a lot of chaff for the amount of wheat.
Basics: Used copy of Urich and Fisher for a good explanation of the carb circuits.
Alternatively (or additionally): Chrysler's Master Tech series as several books about Carb fundementals.
look 'em up here
Master Technician Service Conference - Chrysler's Training for Mechanics
and if you prefer pdf format go to the
www.mymopar.com to download and/or watch.
As far as understanding and mapping out the idle restritions, air bleeds, etc, yea sure do a search here.
A lot of what I posted will have links back to posts or threads by "Tuner" and "jmarkaudio" and "Shrinker" on other boards like racingfuelsystems. Those guys got their info through years of experience as well as reading real books on the subject - the type of books and papers engineers learned from and referenced when carbs were king and fuel injection was mechanical.