1941 chrysler has a flat spot on acceleration

[normanpitkin]

hi

my 1941 windsor has a flat spot just when one starts to accelerate ,it ticks over and accelerates perfectly once one is past the flat spot.Have recently fitted new mechanical pump and use an electric pump merely to prime and then turn the electric one off.Have rebuilt the card with a NOS kit ,only the dash pot for the fluid drive wasn't renewed .HAve checked the timing and fuel pump ,all perfect .What could it be? Maybe the dash pot for the fluid drive?

[greg g]

Have you tried using a vacuum gauge as a diagnostic tool?  The flat spot might indicate a vacuum leak between the carb and intake ports. The leak would momentarily lean the mixture .  does the flat spot occur at with no load, or just she trying to accelerate from stop?

[normanpitkin]

Flat spot only occurs when quickly accelerating under load ,it doesn't happen if one is slowly revving the car in neutral. I am ashamed to say i haven't got a vacuum gauge!

 

 

[greg g]

Well a gauge is not very expensive but you can search for a vacuum leak with WD40 or similar aresol, by directing the spray at carb to manifold and manifold to head joints.  With the engine at idle spray suspected areas and listen for a brief speed up of idle as the spray will enrich the mix temporarily overcoming the leaning effect of the leak. Don't know if you have vacuum or electric wipers, but if vacuum check the line for leaks also.

You also might want to advance your initial timing 3 to 5 degrees. Today's fuel burns slower than the old formulas, so a slightly earlier light off can be beneficial.

 

Edited January 15, 2017 by greg g

[normanpitkin]

AH ,yes ,already tried this ,no leaks! As i said ,the flat spot has only appeared after fitting a new mechanical fuel pump.

 

[T120]

The flexible fuel line to the fuel pump can be a source of trouble restricting fuel flow.

[Reg Evans]

Have you looked down the throat of the carb while working the accelerator to see if the pump is squirting gas ?

[normanpitkin]

yes ,its working perfectly apart from the transition from idle to accelerate

 

[Plymouthy Adams]

what position is the lever in?   should be default to them middle hole..

[Tom Skinner]

Have you a Vacuum Advance on your Distributor?

Take it off the Distributor and check the diaphram for leaks. It shouldn't leak, if it does replace it.

It can be easily checked by blowing and sucking air into it, when this is done you will know immediately if it works.

Tom

[normanpitkin]

Lever has been tried in every one of the three holes ,seems slightly better on Spring setting but still stumbles.

Will check the vacuum advice first thing!

[normanpitkin]

Checked vacuum advance ,its not that! 

[normanpitkin]

I wonder if there should be a spring under the dash pot? Maybe under both?

[Jerry Roberts]

9 hours ago, Reg Evans said:

Have you looked down the throat of the carb while working the accelerator to see if the pump is squirting gas ?

 

9 hours ago, normanpitkin said:

yes ,its working perfectly apart from the transition from idle to accelerate

 

 Reg is talking about an easy test to do with the engine NOT running .  From your response it is not clear that you understand that . Your answer could be understood ether way . 

[normanpitkin]

Hi

pump is squirting gas with running and also not running engine , pretty sure it's the carb has the problem. , pretty much checked everrrything else !

[1949 Wraith]

21 hours ago, normanpitkin said:

Have rebuilt the card with a NOS kit ,only the dash pot for the fluid drive wasn't renewed .HAve checked the timing and fuel pump ,all perfect .What could it be? Maybe the dash pot for the fluid drive?

My 41 Chrysler with vacamatic had a slight hesitation when starting out and you had to be careful when the engine was cold that you did not stall. I rebuilt the carb doing both the the accelerator and dashpot pump. The dashpot was a bit of a pain since you had to drill it out to replace the new leather plunger. But the car runs very smooth now, with no hesitation.

I talked with some old time Chrysler mechanics that said they used to soak the plungers in oil to soften them up and aid in getting a good seal. You might want to try that is you don't want to change the dashpot.

[normanpitkin]

thank you ,i ordered a new dash pot for the pump from birnbaums ,i will soak it in and let you know!

[normanpitkin]

Am wondering if its the linkage to actuate the second dashpot ,has anyone got photos of the linkages for this 41 carter carb with the emphasis on the linkages?

[1949 Wraith]

3 hours ago, normanpitkin said:

thank you ,i ordered a new dash pot for the pump from birnbaums ,i will soak it in and let you know!

The soaking in oil was to try and improve the sealing of the original dashpot plunger.

Here is a picture of my carb apart, you can just see the external linkage at the bottom, just a U shape rod with 2 clips connecting the dashpot arm and the other linkage.