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Stromberg Carb adjustment '38 Caddy

Started by Bob Martin, August 30, 2014, 02:20:05 PM

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Bob Martin

 Stromberg Carb adjustment '38 Caddy:

Is there a "correct" adjustment procedure?
Been doing it by "ear", and still doesn't seem to be right for smooth engine run.
Think I have both adjustments off best setting.
Thanks,
Bob Martin
Bob Martin
CLC # 28309
1938 60S, #6273078

Steve Passmore

The only adjustments you have are of coarse is Idle, for that you screw the two screws fully in(without undue pressure), then out 3/4 of a turn. Start the engine and slowly un -screw until the idle becomes lumpy, then back in till smooth, then do the other screw.  If you find one of the screws makes no difference to the running there a blockage somewhere in the idle ports or the end of the screw is badly ridged.
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

Coupe Deville

I have had best luck using a vacuum gauge to set Idle mixture screws. Attach the gauge to manifold vacuum and then turn the screw in until it starts to idle rough then out until you have reached the highest vacuum. Then I usually turn it in a Hair (lean). Then your good to go. Doing it by ear too is fine, but Im not that talented.

-Gavin     
-Gavin Myers CLC Member #27431
"The 59' Cadillac says more about America than a whole trunk full of history books, It was the American Dream"

Bob Martin

Gavin, Foolish question, but where is the actual location for connection for my vacuum gauge.. :-\
Bob
Bob Martin
CLC # 28309
1938 60S, #6273078

joeceretti

#4
It's not an easy thing to connect to on the 38 as there is no vacuum advance. The only vacuum connection is on a line connected with fittings to the fuel pump. You can't really do it easily other than connecting to the side that connects to the wiper motor. Or, you can disconnect the fitting and squeeze the line onto the tubing. Better to do it by ear.

How I do it...

1) Carefully tighten the screws down so they are closed. DO NOT tighten them too much or you will damage the carburetor seats in the screws.

2) Open each one 1 and 1/4 turns.

3) With the engine idling and the throttle screw turned up a bit.... hard to describe how much but it's supposed to be but it's at 8-9mph when running in 3rd gear on flat ground. I turns out to be about 450rpm.

4) Slowly open one screw up until it starts to sound bad. Note the position of the screw slot.

5) Slowly turn the screw back in the other direction until the engine starts to sound bad. Note the position of the slot.

6) Put the screw in the middle of the two... one being too lean, the other being too rich.

7) Do the same with the other screw.

8) You are done.

Look for my post where I describe how to set the timing advance. It's another complicated procedure but very satisfying when you get it right, not to mention you will have more power at throttle AND more importantly much better fuel economy. As a hint, the engineers expected that you should or could have as much as 10 seconds of ping (preignition) under throttle.

If you can't find my post on the subject I will send you the directions. 

Coupe Deville

I had no idea that these older motors did not have many vacuum ports. Some 50s Cadillacs have plenty of places to hook a vacuum gauge too. My apologize. But I did learn something.
-Gavin Myers CLC Member #27431
"The 59' Cadillac says more about America than a whole trunk full of history books, It was the American Dream"

Steve Passmore

The other problem with trying to do this with vacuum equipment is the fitting is not in a position to get separate vacuum readings for each separate venturi.
Steve

Present
1937 60 convertible coupe
1941 62 convertible coupe
1941 62 coupe

Previous
1936 70 Sport coupe
1937 85 series V12 sedan
1938 60 coupe
1938 50 coupe
1939 60S
1940 62 coupe
1941 62 convertible coupe x2
1941 61 coupe
1941 61 sedan x2
1941 62 sedan x2
1947 62 sedan
1959 62 coupe

Bob Martin

Thanks Joe,
will try this weekend. Just finished putting new Voltage Regulator on; old one was overcharging, and I could not adjust it.
Ill look for your post on timing advance.
Bob
Bob Martin
CLC # 28309
1938 60S, #6273078

joeceretti

#8
I know I posted this before but can't find it. I will type it again.

To set the timing to optimal. Start by using a timing light and setting the timing on TDC.

Then...

Advance the timing a touch. Drive around and get the engine nice and warm. Listen to it, pay attention to the knock. The engineers expected that up to 10 seconds of knock was normal on these engines. Once the engine is nice and warm (hot) from a standing start go full throttle and listen for knock. You need to advance the timing just enough so that when you let off of full throttle and then ease back on after 10 seconds the knock goes away. Keep advancing until you get 10 seconds or less. If it knocks all the time under throttle you have too much advance. If it is always quiet you don't have enough. Now, you can leave it with no knock and it is a pleasurable thing to drive, nice and quiet, but you will not get good fuel economy and you will not get the power you can.

Basically, to reiterate, you can advance your timing just the right amount so that you get 10 seconds and no more of engine knock. The engine has to be hot to determine this. If you get more than 10 seconds, retard the timing a bit. If you get less than 10 seconds, advance. If you are driving people around for a wedding and want it to be a quiet and smooth experience then retard the timing to tdc where it will run with just a hint of noise. I prefer the advance, it saves me money on fuel and gives me very good throttle response.

All this depends on how well your centrifugal advance is working. How good your ignition system and all it's connections are. What condition the internals of your carburetor are in. If all these things are not as close to 100% as possible then setting the timing and getting good fuel economy and getting proper power will be difficult or neigh on impossible.

FYI, not sure if you know, and for others reading this thread... advancing timing on these engines means turning the distributor counter clockwise. Retarding the timing is turning the distributor clockwise.

To finish, if anyone else reading this thread has done this, please post your experience.