Re: {Chrysler 300} more , some-results, and thinking / coloring a bit ov

One more note/comment/question on timing/tuning of G ram cars-

In the technical service bulletin I copied in an earlier email, it says to disconnect vacuum advance and set the timing to 5 degrees BTDC with the engine idle speed "below 600 rpm".

The same bulletin lists the following specs for mechanical advance in/on the distributor:

0 degrees @ 324-475 rpm

0 to 4.3 degrees @ 475 rpm (?) seems like quite a spread to me

4.5 to 6.5 degrees @ 640 rpm

9 to 11 degrees @ 2400 rpm

This kind of makes sense to me in that if the engine is idling at less than 600 rpm, the mechanical advance present at that rpm could be reasonably assumed to be on the order of 5 degrees.

I'm pretty sure I never actually set the timing at that low an rpm. I may have checked/re-checked timing after tuning carbs and at curb idle of 725-750 rpm, which means at that speed the mechanical advance present would be somewhere in excess of 6.5 degrees, but less than 9 degrees of advance. Is it safe to assume that a car set at 5 degrees with idle below 600 would/could/should show timing closer to 7 or 7.5 before TDC when idle is brought up to 750 rpm? If you set timing at 5 degrees at 750 rpm, is it actually not advanced as high as it should be based on these numbers?

I decided to double check by going to the 1960 shop manual section on ignition timing and it says to disconnect vacuum advance line, start engine and set idle to 475-500 rpm (doesn't specify single or dual point, non-ram or ram car distributor), so they seem to really want to get as much mechanical advance out of the measurement of timing before going back to curb idle of 750 rpm and before reconnecting vacuum.

I'm thinking maybe I'll put the timing light on at current rpm and see if I can drop the idle down and watch where timing goes. If I can get a 'smooth' idle below 600 rpm, I'll see where timing is at that point, and if it's actually below 5 degrees, I'll bump it up, then increase idle to 750 and note where it winds up before reconnecting the vacuum advance line.

Again, same manual lists the following vacuum advance curve-

0 degrees at 7.2 to 8.9" of vacuum

4.5 to 7.5 degrees at 12"

7.5 to 10.5 degrees at 14.5"

The listing stops at that point, so doesn't give any indication what the advance would be above 14.5" of vacuum (?)

Does it sound reasonable that total timing available is maximum of 11 degrees mechanical plus 14.5 vacuum for a total of 25.5??

Looking at all this makes me not surprised that so many folks set timing and carbs 'by ear' or 'by feel', dialing in more advance and lugging up a slight hill to listen for pre-ignition knock/ping and just backing off a little, and leaving the gauges on the shelf. ;-)

On Thu, Sep 17, 2026 at 12:34 PM John Grady <jkg@xxxxxxxxxxxxxxxxx> wrote:

So went through this , we are all thinking.. understanding
put big vacuum gauge about 4-5" on heater vacuum pin , little ones are useless
Baseline , would start , ok but after 10 -30 sec rpm starts dropping vac too it just stops .
Inspected carbs all re built nice job , -- as we will find out plus some good stuff
1) looking first at vacuum and idle mix , the screws are in different in/ out positions ( not good )but I tuned for highest vacuum --first rpm was too high , justvignore it ;?this adj wont be right at later correct rpm . On each carb, screws were out pretty bad , got vacuum to 20 . was 14, All four screws show about equal impact and smooth action . Tells us thstvall 4 are on board, no adjusting screw issues . Note how much vacuum gauge has already told us .
no more lope or stall at start but way fast .
Started messing with air valves to slow down rpm not acting right , have no idea where they are . Followed FSM , shut off , count turns . found one open 4 turns(!) set both to zero then out 1.5 turns, as past has told me 1 (from fsm ) not enough . Started up , idle IS down (0k!!!) , but vacuum down too .
Went around mix settings again going for vacuum major changes in screws like a turn , back to about 18 ( good);? after hitting peak vacuum opened each ~1/4 turn rich , little impact on vacuum ( down slightly).. thinking being a little rich helps the lean issue at transition, less tendency to lean out / stall .Far better than " little lean" , balky . Setting jt perfect to best place exposes you to lean . This is me -- not fsm . All are same # of turns, air valve still 1.5 . runnin nice x checked rpm 700 , ( Awwright ) way pleasant surprise !!

Looked at carbs more carefully , almost no gas out of squirt at small throttle opening movement . Weird . Linkage tight no lash . Started suspecting kit / new accell pump . Lots of designs for those . Moved plunger down very little , off linkage no gas ... ( hmm) . Although meant to control cc volume , noted the 3 holes in actuator , started thinking . At rest, in most aggressive hole ( it was in middle) gas starts flowing instantly because it puts pump plunger deeper into gas at rest Yow.. !!! instant gas! I am sure this will fix off idle stumble at stop sign . Ymmv , way it was here -- there was pre travel / lash in pump plunger before gas = big lump of air w/o gas , = that oh no , you feel leaving stop sign and then it goes That IS gone

So into gear at 700 no bang idle 600 in gear , steady , vac a little low but keeps running ( yes!!)
Impression very jumpy off line wants to GO !! no bs at all
Choke was /is slow going off , keeps on high idle too long . as John said. Going to weaken that -- not sure you need much fast idle in normal temps with classic car , not going driving in snow . Fast idle can add to bang . Ill walt a few minutes if real cold to avoid bang every time over fast idle too aggressive ., so you get a bang every time from cold
Big big improvement , it is factually near FSM , did not touch ignition .
Carb squirter a big deal , vacuum gauge too . You see impact of adjustments , no way with "set smooth idle " instruction of FSM screws were all over the place
Henry' s point about exhaust gas analyzer being better is true but i don't car about idle AF want it a little rich ( alky gas needs less air st optimal burn than 1960 gas , or other way around more gas ) and a perfect idle AF is on edge of all the problems lean brings . You can richen idle a small bit , wont overdo it w vacuum gauge monitoring . Seat of pants NG
Thanks for interest .
Ps Don V trans 1-2 chirp , love it, even not wide open -- nice fast F no more crossed fingers pulling into traffic
Thanks to all
J

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Re: {Chrysler 300} more , some-results, and thinking / coloring a bit over fsm , which was actually quite close