RE: [Chrysler300] Questions about understanding advance in 57 WCFB . .. and WCFB itself . Spark porting ...

["'Henry Schleimer' henry.schleimer@xxxxxxxxxxxxxxx [Chrysler300]" <Chrysler300-noreply@xxxxxxxxxxxxxxx>]

Hi John

 

All the “special” settings for the 300C are covered in the Chrysler Corporation Service Bulletin No.1002-CH March 1 1957.  It goes into detail about distributor and carburettor settings.

 

Timing is set by getting a smooth idle at 650 rpm, disconnecting vacuum advance, set ignition to 4 degrees BTDC and resetting idle to 650 rpm.

 

I had a look at my rear carb which is off the car.  The primary throttle valves are stamped 15 degrees opposed to the secondaries stamped 10 degrees.  When closed, the vacuum port always has vacuum because this port can’t be closed with the 15 degree valve.  Idle speed is set with the by-pass air screws, not the throttle valve.  From this I assume Chrysler wanted vacuum advance at idle since the idle speed is significantly higher than standard cars.  Those would probably get a vacuum signal at 650 rpm from the throttle valve opening so there is nothing really different happening here.  Never set idle timing with vacuum line connected to distributor unless specifically instructed.

 

300D carbs don’t use by-pass air screws to set the idle but use the front carb primary to bleed idle air.  This wouldn’t affect the rear carb’s vacuum signal to the distributor.  300D’s are set at 6 degrees BTDC.

 

There is another Chrysler bulletin about converting 300C carbs to 300D specs if customers complain about hesitation and stumble but it involves a fair amount of careful modifications and parts.  My car came to me with unmodified carbs and it had gone round the clock twice so it can’t have been a consistent problem.

 

Despite your carbs being rebuilt by pros, did they use the above bulletins to set them up?  Can’t use the FSM for this.  Incorrect float level (and many other carbs issues) could also give stumbling problems, probably more than timing, and would be something I would double check.  May be as simple as a vacuum leak at the manifold...

 

I could scan the bulletin for you if you want.  I forgot where I got it from.  Probably on the net somewhere.

 

Regards

 

Henry

 

From: Chrysler300@xxxxxxxxxxxxxxx [mailto:Chrysler300@xxxxxxxxxxxxxxx] On Behalf Of John Grady jkg@xxxxxxxxxxxxxxxxx [Chrysler300]
Sent: Thursday, 29 August 2019 7:42 AM
To: chrysler300@xxxxxxxxxxxxxxx
Subject: [Chrysler300] Questions about understanding advance in 57 WCFB . ... and WCFB itself . Spark porting ...

 

  

I touched on this once before , and 57 FSM is sorely lacking on any info . I was using Dodge 57 FSM , believe Chrysler same — in ignition section . It says set idle ignition timing static at about 8 btc for this motor (325 poly power pack) ( must be crank degrees although all specs( in back) are in distributor degrees ) crank = 2x distributor .( nice touch) 
It makes no mention whatsoever of vacuum line during setting — or disconnecting it . It does explain ( paraphrasing )” after throttle is opened and vacuum exists, vacuum will advance more “ . This description is absolutely wrong info in 57 FSM . The port is for sure physically below the closed throttle edge In 57 WCFB ( not above as in later cars ) , so full vacuum is in the advance line at idle before throttle opens ( how the hell can that work* ?) . However — it also describes setting timing with a 12 v test light ( engine not running) at same 8 . So from that .. I set at 8 static btdc with line off . OK . — But the minute you connect line it jumps maybe 6-8 degrees , how it works — for sure.. . I inquired of Daytona carb , * who rebuilt carb, they did not understand the issue. Frustrating .. like talking to a brick. They said “ do whatever book says “Well book says two opposite things “ — only one can be correct . 

! Well — with no mention of disconnecting line if you set 8 idle while running, timing checked with 12 v point light would be way retarded ,that 6/8 + degrees , as would the whole car ignition curve . 
So in past have ignored all that anyway .. instability of idle “ zero” timing always an issue with higher idle rpm typical of a 300, and so set I had max advance point at say 3k at say 28-30 degrees no vacuum .. What matters most. Need tape .. but crazy not to have a timing tape. Dial back lights , especially new snap on a joke . Jumps all over the place . Cannot see advance work . Back to old sears with solid connection to #1 . The 57 distributor seems to only have 20 crank centrifugal degrees in it ( low) , specs in back of FSM are useless,— as In FSM it only gives you two data points at low rpms , like 1200 or something . No max advance spec in FSM . Usually is at 2500-3000. Similarly , off topic, you buy mopar electronic conversion , no advance curve at all is given . Nice ! 

On this , light seemed to confirm only 20 — that was all It moved ... That is good actually — allows more initial . 
So left it as if set by a 12v light ( why I said static above) , would be about 28 max . Seems not crazy ... close to right? Other way IS crazy . But now idle with it connected must be 15 or more . Way it is. 
Must have been designed to instantly retard idle timing at initial opening ,( or something?) then come back in like ported Vacuum at cruise ? 

Why all this , you say ? And maybe carb , or maybe due to this, it has a slight lean stumble off idle , worse when cold. Can get in accident if it goes 20 feet , and then stalls just off idle in first 5 minutes . Heat riser , choke , accell pump all perfect . Suspect low float levels or rods/ jetting now . But “suspect “ is not enough to tear into something ( carb) supposedly rebuilt by pros to stock . 400$ ago . With stock correct carb list parts. And this ignition BS might play a role. . While on this I have found 4-5 errors in FSM in 57 , at best many sections are very poorly written .poor English , wrong or no drawings. Try to find simple thing like firing order and where# 1 wire goes in cap . Or this whole timing thing .. 
Maybe someone else has chased stumble off idle with WCFB ? I opened “gas level check ports” , gas is not there; but how can those work with varying float settings ? Unless all settings end with gas at the port ? Even bought chev and Cadillac / Buick WCFB books. Even Carter rebuild book covering WCFB . No info of any value on this — just specs . 
Car runs superbly except for this ... hope someone out there gets all this ..... very easy to end up timing your car retarded significantly ...by following FSM .. 
and that stumble is dangerous ... also stumbles if accelerating from stop while cornering . If that helps . Straight line warm it is perfect. 
55-56 300 had to have this perfect .. to race . not really familiar with those ..
Thanks , comments welcome ,understanding this matters .. 
John 

Sent from my iPhone not by choice 





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Posted by: "Henry Schleimer" <henry.schleimer@xxxxxxxxxxxxxxx>
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