[Chrysler300] 1958 Plymouth 318 Idle Problems

[jlsavard@xxxxxxx]

In a message dated 10/16/2008 12:54:39 P.M. Eastern Daylight Time,  
ronbo97@xxxxxxxxxxx writes:

Hi Joe -
 
Glenn Barratt said you'd be the right person to consult for my carb  issues.

 
Any thoughts ?
 
Ron
 

Maybe, maybe not.  I worked exclusively on Chryslers, so have  no direct 
answers regarding Stromberg carbs.  I thought they only used them  on trucks!  I 
can try to help, though.

 
At Chryslers at Carlisle this summer, I bought a nicely rebuilt 2 bbl  
Stromberg 15-28 carb to replace the Stromberg 15-28 that was (so I thought)  giving 
me problems on my 58 Plymouth with a 318. The car runs well  now with the 
exception of the following issues:
 
1. When making a turn and stepping on the gas at the same time, the car  
feels like it's going to stall. I have to feather the gas pedal to keep that  from 
happening.

Does this happen when you are turning both ways, or only left or  right?  The 
only difference when turning would be in the fuel level  "sloshing" one way 
or another.  Is the float level set correctly, and is  the top of the carb 
fastened firmly to the bowl?  Is there  a vacuum port that goes through the seam 
between the carb body and the top, like  up to the choke?  Some of the WCFB 
carbs had a problem when turning left  with the throttle closed.  Fuel would 
slosh up against the seam and get  sucked into the engine, making it stall, which 
stopped the power steering in the  middle of a turn.  Several cars were 
wrecked, and we were quick to fix  that!  We put a little brass tube into the body 
casting to bridge the  seam.

 
2. When adjusting the mixture, if I lean out the car to where it's  idling at 
around 500 rpm when in gear, it runs somewhat rough. If I shut off  the car 
for a few minutes, then try to restart, it takes a while to restart  instead of 
restarting right away. I've also had a couple of stalling problems  at this 
rpm. However, if the slow idle is brought up to around 625, these  problems 
mostly disappear.

Two problems here, maybe.  As to the hard start after shutting  off:  If the 
engine is warm/hot when shut off, I think it is probably the  fuel boiling 
over into the manifold from latent heat.  This might be helped  by putting an 
insulated (Bakelite) spacer between the carb and the manifold, If  you can find 
one.  This is made worse by the modern fuels, I hear.   Mine ('59 Saratoga) 
does it.  I just live with it, by holding the throttle  wide open when starting 
warm, to clear out old fuel.  I also just  remembered that a loose carburetor 
top could provide a path for fuel to go into  the carb throat and thus to the 
manifold, too.  Be sure that your float and  needle assembly are sealing off 
incoming fuel completely.  If the needle  valve leaks, this can cause flooding, 
in various degrees at low engine  speeds. 
 
As to The rough idle, this can be caused by so many things!   Vacuum leaks, 
bad valves (burnt or out-of-adjustment), ignition, etc.  I  think I'd start by 
pulling the carb and looking at the throttle plates and  throttle shaft.  An 
old shaft can be worn and sloppy in the bore, causing  an erratic leak and poor 
idle.  I would also back off the idle  speed screw and be sure that both 
throttle plates seat firmly in the  throttle bores.  It is very easy and quite 
common to set the carb down on  the bench with the blades sticking out and bump 
them out of  alignment.  If they don't close properly and fully, you need to 
(gently!)  loosen the screws and reseat the plates.  When seated, they may want 
to  stick slightly in the bore, but when you set the idle speed up they should 
be  OK.  From fully closed, open the throttle plates 1 1/2 turns for a basic  
setting.
 
Remove each idle mixture screw and check the tapers.  They are  brass, and 
frequently have damage from someone tightening them up too  tight.  If the taper 
is damaged, it makes them hard to adjust.   Sometimes they can be refinished 
by spinning them in a drill press (Vertical  lathe!) and using a fine mill 
file to reshape them.
 
Put them back with the springs, close them gently to seat them, and  back 
them out 1 1/2 turns.
 
Reinstall the carb.  The basic settings should be good to get  the engine 
running and warm it up.  To set the mixture, adjust the throttle  speed screw 
until it is running around 500-600 rpm.  Open both mixture  screws together (1/4 
turn on 1 side, then 1/4 turn on the other side) until the  speed stops 
increasing, or falters.  (This tells you that you have enough  fuel to run the 
engine.)  Then turn them in closed again, 1/4 turn at a  time, together.  The 
engine should continue to run smoothly until it begins  to falter from lack of 
fuel.  This is a critical time.  Pay full  attention to the engine, and if you 
have a vacuum gauge, use it.  The  moment that the engine begins to falter, or 
the vacuum drops, stop closing the  screws and open them up about 1/8 to 1/4 
turn.  This should give you a  firm, steady idle.  You may need to reset the idle 
speed and even may want  to reset the mixture screws to get it just right.
 
If, when you are at this stage of the game you notice that your  vacuum gauge 
is giving a regular, repeating "Bounce", you have been blessed with  a bad 
valve and need further help.....
 
Good Luck, and let us know what you find!
 
Joe  Savard
Lake Orion, Michigan
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