41 Super stumbels

[Ken Lobsinger -Rejuvenated]

My 41 Super Convertible stumbles every time I get it started and am letting out the clutch in either 1st or reverse.  I am an expericed standard transmission driver, and know I am giving it enough gas without racing the engine.  I am nearly certain I saw a thread about this in "Me and My Buick", but can't find it now.  It did before pulling the oil pan, so I don't think it is something that I did during that process.

 

Your ideas about the problem and any viable solution are welcome.

 

Thanks to all of you.

Edited August 23 by Ken Lobsinger -Rejuvenated
spelling (see edit history)

[EmTee]

Does this problem happen only when engine is cold, hot, or always?

[Matt Harwood]

First, what type of carburetors do you have--Stromberg or Carter? Have you tried adjusting the mixture screws on the forward carburetor? Both too lean and too rich can cause driveability issues, so getting it right is important. Adjust them in 1/4-turn increments (both screws the same amount in the same direction) and see if things improve. Turn the screws clockwise (tighten them) to remove fuel, turn the counter-clockwise (loosen) to enrich the mixture. A good baseline is to turn them all the way in until they just lightly seat (don't crank them tight) and then back them off 2 to 2.5 turns. Then adjust from there.

 

Please report back and we'll see if we can help.

[Pete O]

Another thing that can cause stumble on take-off is an accelerator pump that's gone bad.  The seal on the pump piston could have crumbled from the ethanol in today's gas.

[carbking]

Probable causes:

 

(1) distributor advance mechanism not functioning

(2) vacuum leak

(3) idle mixture control screws set too rich (causes puddling in the intake)

   (3-C) Carter adjustment range 1/4 turn to maximum 1 and 1/4 turns (3/4 turn recommended)

   (3-S) Stromberg adjustment range 3/4 turn (recommended) to maximum 1 and 1/2 turns

 

Possible causes:

 

(1) defective accelerator pump - TEST by starting engine, stopping engine, remove air cleaner, open choke valve, work throttle to WOT while looking down carburetor throat. Two streams of fuel should appear. If yes, pump is good; if no, work the throttle again, sometimes an air lock develops in the pump cylinder. If no fuel after 2 operations replace pump. If pump must be replaced, leather is superior (opinion) to any artificial material).

(2) non-functional choke 

 

Jon

[Ken Lobsinger -Rejuvenated]

Guys... Thanks for the imput.   This stumbling occurs hot and cold.  I bought the car with a Carter Front carb and Stromberg in back (stange, I know).

I had the carbs rebuilt by a local guy, using kits I purchased from Daytona Parts, on recommendations from Automobilia, so I would think that the acclerator pump should be good.

I have not done any adjustments to the carbs yet, but hope to over this weekend.

 

Carbking - I really appreciate the specific instructions you probided.

Thanks to all.

[carbking]

Ken - I am NOT going to categorically state that set-up will not work; but I am going to say it is certainly suspect.

 

Carter carbs are available.

 

Stromberg carbs are available.

 

When I see something like this, I wonder if the carbs would be right for the engine, if both were the same brand; or did someone just install what was on the shelf? What else has been modified?

 

At this point in time, I would forget tuning, and start verifying engine components!

 

If everything else checks out, I would suggest looking to see if the original progressive linkage is being used.

 

Then, I would determine if the front carb is CORRECT for the engine.

 

If it is, I WOULD COMPLETELY REMOVE THE REAR CARBURETOR AND REPLACE WITH A BLOCKOFF PLATE!

 

The engine will run on the front carburetor, and even drive up to ??? MPH, certainly enough to sort the engine.

 

If everything is worth saving, then look for a MATCHING Carter to match the front carb.

 

Jon.