RE: [Chrysler300] C hemi dual quad idle
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RE: [Chrysler300] C hemi dual quad idle



A further complication on air cleaner contact is we put the rare 4 bolt “truck” exhaust manifolds on this car, which almost forces some jacking up of drivers side…( how they did it, per reports /recommendations of the day) ---the manifolds hit the large 57 steering box, and inner part of upper control arm parts  . If anyone else goes this way, some pretty aggressive grinding of back of suspension parts should be done to get 3/8” or so there. Looking at it installed , the parts of suspension that interfere do not look structurally important  to me. Your opinion may vary. Some of these big flange manifolds have flats cast there . I researched that pretty well at the time, how to get those in a 300C, and no where was the air cleaner issue at the hood mentioned. I wanted 2.25 exhausts,  and if you look at pretty bad stock 300 “log” exhaust manifolds and tiny exhaust pipes on converts, a lot of what the hemi is all about is very obviously lost in the overall 57 exhaust design. We opened the frame cutouts in the X too.

 

On the carburetors, we ground off that fast idle cam end so throttle plates are now sitting as closed as they get. However a new and unexpected complication arose; the front carb idle air screw has no real impact on the idle; we think the carbs may have been apart at the throttle plates /shafts, (extremely tight tolerance fit at manufacture to throttle bore) and although now closed mechanically till they touch, air is still getting by front carb, more air than is allowed in by the screw , in the first few turns  . So adjusting the screws(air screws) to same turns out per  300C dual quad set up instruction gets you nowhere. Both idle stop screws on the linkage are now not touching, (correct) both air screws were initially 4 turns out  to get reasonable idle speed,--but after figuring out front one is not working right, it was turned in 2 turns , then went for vacuum readings on 4 mixture screws.   The front mixture screws do impact idle vacuum, so front cab is contributing OK, irrespective of air screw setting . The factory setup suggests 1 turn out on air screws, it would not idle there at all. Rear one acts normal. This experience and thoughts about it might help someone else…

 

Someone mentioned using a carb air flow balancer /unisyn on this . This really makes sense to me now… (I did not have one) ---you cannot depend on counting turns on the air screw to sync carb air flow ..too many mechanical fit variables in that.

 

It seems happy now, stable idle and no bang engaging torque flight, no stalling. Not real happy with what I know now, one carb not closing 100% right, but it is information. But take away is probably best to NEVER  take off staked screws holding throttle discs on throttle shafts. ..ever …even if shafts are a little loose.  Note that on single quads with throttle linkage stop screws  holding the carb open for idle, all this is no problem/does not matter....

 

On to next problem….

 

john

 

From: Keith Boonstra [mailto:kboonstra.zeegroup@xxxxxxxxx] 
Sent: Friday, November 06, 2015 6:20 PM
To: John Grady
Cc: chrysler300@xxxxxxxxxxxxxxx; Chouinard JY
Subject: Re: [Chrysler300] C hemi dual quad idle

 

The drivers side air cleaner on my C also rubbed a groove in the hood pad that another owner had installed. Maybe that's why Chrysler didn't put a pad on the '57 hoods out of the factory. 

 

Without the pad there now there's no rub, but it's really close (about 1/4"); and I know if I ever snap the left side engine mount, I'll have a pretty big zit on my hood.

 

Keith Boonstra

 

On Fri, Nov 6, 2015 at 5:16 PM, John Grady jkg@xxxxxxxxxxxxxxxxx [Chrysler300] <Chrysler300-noreply@xxxxxxxxxxxxxxx> wrote:

  

More info after previous post on this issue of setting idle correctly -- or understanding intent . 
It turns out that although both idle screws are obviously there on the 2 carbs and linkage ... They are NOT to be used to set idle . The factory supplement image is marked "do not adjust" at each screw . It should say screw should not touch anything .. Or be removed . 
On these setups,only ( and not on WCFB in general ), there are two air bleed screws for idle air, like the large ones on ram cars , but these look like large mixture screws. They are on drivers side of each carb, to rear of secondary throttle shaft .The back one is hidden behind the vacuum fitting/ neutral switch . A few guys emailed me,suggestions about this setup , unaware of this idle air screw deal .. as I was too . So setting idle by front carb idle stop screw is wrong idea . But that screw will change idle . 
Further the carbs have to close 100 % or air will go by throttle plates like a normal carb at idle . On my car the fast idle cam tang when off the cam (warm engine ) was hooking under the cam end ---holding the carb from closing 100 % . I am going to add clearance there by bending or grinding end of cam disc . Then carb will close 100 % . Then air is set by bypass air screw . There is no fast idle adjustment except bending that same tab, which would hold carb open resting on cam until choke pulls off . Supposed to be about 1350 rpm. Once all this is working , balancing 2 air screws and 4 mixture screws ( count turns to start ) ought to have it idling as designed . It uses both carbs at idle . They suggest one turn open on 4 mixture screws to start . The 300 supplement explains all this , but to me anyway , is not specific about the idle screws . I have learned something here.. Want to share it . The idle screws are not idle screws . A new issue , my air cleaners are rubbing on underhood pad . That is close !! 
More later , ! Progress!! 
John
Sent from my iPhone



 



[Non-text portions of this message have been removed]



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Posted by: "John Grady" <jkg@xxxxxxxxxxxxxxxxx>
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