Forgive my ignorance please and don't beat me up because I have a STOCK 1954 4 barrel T-Pot on top of a stock 256 coupled to a stock 3 speed with overdrive.

I have read countless time on forums that the power valve in the carb can be damaged from backfires thru the carb.  During initial timing and start-up I experienced many backfires, eventually getting it to run reasonably well.  The carb has been rebuilt and the idle mixture screws have been adjusted by using a vacuum gauge.  The float level is properly set and the auto choke appears to be working properly.  The main jets are appropriate for the local elevation.

Now, the problem.  Under load (pulling my 2,000 lb. vintage trailer up a grade) the engine coughs with too much throttle in third, I back off and shift into second with less throttle and it smooths out quite a lot but not completely.  The coughing begins immediately if I give it more throttle.  Could this issue be related to a failure of the power valve?

Now the ignorance!  I have not opened the carb up to inspect the power valve but, when I do, is it glaringly obvious that a backfire ruined it or is the damage more subtle?  How can I tell if it needs to be replaced?

The power valve on the model 2140 4V Holley (Teapot by another name) is the slotted brass fixture in the bottom of the fuel bowl between the two jets.  The actuator for that is the long stemmed piece with a spring around the stem and that whole assembly is fastened to the fuel bowl cover with three screws.  It hangs down into the fuel bowl and with the engine off or at full throttle, the stem is in the fully down position which is the enrichment mode for the power valve.  When there is sufficient vacuum, the stem is pulled up thus allowing the power valve to be in the closed position for economy purposes.  If the actuator fails, it typically does so in the down position which is ‘enrichment’ thus keeping the small stem on the brass power valve depressed and open.  Your coughing or backfiring under full throttle indicates a lean condition or an ignition break down.  The power valve would not be the problem in this case.  A stopped up passage in the carb and possibly on the secondary side is a likely candidate.  Likewise a breakdown in carbon core spark plug wires or other ignition component could be the culprit.  That valve that's on the outside of the carburetor is very often mistaken for the power valve but is a spark control or advance valve for the distributor vacuum.  I trust all that made sense.

Lorena, Texas (South of Waco)

Thanks, Ted.  I do have an ignition problem as well.  I will be meeting a carb/electric guy tomorrow for a diagnosis but wanted to know more about the power valve before hand.  I have Merc manuals available to cover carb issues - crossing my fingers.  More later!

Ted, I have other questions.  If the power valve has been damaged due to the previous backfiring, would it cause it to be lean or rich?  If I have to have further carb work, as stated in my previous question, what do I look for to determine whether or not the valve has been damaged?

Nobody on here will "beat You up" for having a Stock Setup. There are as many Guy's here with Stock or near Stock Vehicles as non Originals  That's what is great about this Site. Everyone Respects all Types of Y-Blocks.

  

One method that should work, turning the idle mixture screws in fully clockwise will cause the engine to stall out. If not, this points to a defective power valve. It's normally held closed by engine manifold vacuum, opening only when engine load demands extra fuel as when accelerating. A defective power valve, one that is open constantly, will waste lots of fuel. Selecting the correct # power valve is important too for the same reason.

y blocks like lots of advance.

Your carb was calibrated originally for leaded, non-alcohol gasoline.  When the country went to unleaded, I found some carbs needed bigger jets to run properly.  Alcohol produces less heat, so required more fuel to run properly.  In our area, we get a winter mixture of 15% alcohol instead of 10%.  The winter blend starts in Sept. and ends in June.  If you get 15% and haven't filled up yet this year, you are running lousy gas.  You may have to increase your jet sizes a couple of numbers to get rid of your popping.

John - "The Hoosier Hurricane"

The power valves in the Holley model 2140 and 4000 4V carbs (Teapots) are not easily damaged by backfiring through the carb.  They are brass in construction and the spring within them is more easily damaged from age rather than from outside mechanical means.  Those power valves are also sized for the particular application and they will have a number stamped on them.  That number typically indicates the size of the drilled orifice within the power valve.

The ‘economizer’ or the actuator for the power valve does have a rubber diaphragm that can have its seal to the fuel cover broken in the case of a backfire.  In this case, the economizer is unable to retract its stem when vacuum is present and the power valve is simply open all the time or in the enrichment mode.  When rebuilding those carbs, care must be taken when installing the economizer to insure it is indeed working and not leaking air at the diaphragm.  I coat both sides of the diaphragm with white grease which helps.  The economizer is affected by age in that the rubber diaphram becomes stiff thereby not working and/or sealing properly.

John brings up a good point about the ethanol in the gasoline.  Even at 10% levels, I’ve found the need to up the primary jetting at least two numbers to compensate for the lean conditions created by the added ethanol.  15% ethanol just compounds the problem.

While the primary jets in the model 2140 carbs (yours) are the same as the later model Holley carbs, the secondary jets are unique.  1954 was the last year for that style of jet and finding a pair of larger sized jets for the secondary sides is going to be near impossible.  The secondary jets are made in such a manner that makes them difficult to modify easily.  It’s potentially possible to redrill the end of the jet with the appropriate number drill and at least enlarge the opening but there's not much material to work with there.  Downsizing those 1953-1954 secondary jets would take a bit of thought.  The ’55-’57 Teapot carbs (model 4000) have a different style of secondary jet and are subsequently easier to modify.

Here is a picture of the power valve.


Here are pictures of the actuator or ‘economizer’.
 

 

Lorena, Texas (South of Waco)

Thank you all for your comments.  I run non-ethanol fuel primarily but when it is unavailable (seldom) I add Star-Tron so it probably is not related to ethanol in the gasoline.  I will check the mixture screws, as suggested, to see if there is adequate fuel to keep it running when closed.  The carb was completely rebuilt about 2000 miles ago so the problems of age probably don't apply, but the power valve diaphragm seal may be a contributing factor.  That can be determined if the carb has to be disassembled again.

More later after the carb/electric guy does his magic!