carburetor problems

[skylking]

I need some help/advice on a problem I'm having with my 170A. When the throttle is advanced very rapidly the engine will actually die unless I retard the throttle at which point the engine will catch back up. I don't ordinarily push the throttle in rapidly but by chance I tested it and found this problem. I suspected the accelerator pump and replace that but no improvement. If the throttle is advanced in a normal smooth action it performs perfectly. Any suggestions on what to try next? Thanks in advance for any help.

[GAHorn]

Does this “problem” manifest itself in Flight..? or on ground only..? Is this a “new problem” ?…or has it existed for some time.?

Do you have a record of when the carburetor was last overhauled..? who did it..?

Have you checked the dataplate to determine applicability?

When you replaced the accelerator pump…. did you confirm discharge..? and did you make any changes to the pump-stroke..? (see that there are Three holes in the pump-lever which controls amount of discharge.) Which hole is your pump-lever set?

[n2582d]

If there is no fuel coming out the pump discharge tube, the first thing I would check is the pump inlet screen, p/n 95-54. The associated gasket is p/n 16-A16. If that is clean, I would then check the pump inlet check valve (p/n 36-525) and the pump discharge check valve (p/n 36-540). The associated gaskets with the discharge check valve are p/n 16-A28 and 16-B45. The Marvel-Schebler manual says, “no air flow allowed out of (discharge) check valve holes at 1-2 psi.” Regarding the inlet check valve, the manual says, “the valve ball must be shiny and move freely. If the ball is dull in appearance replace the valve.”

[skylking]

Thanks for the excellent feedback. I am not and A&P so I will pass this information along. George, in answer to some of your questions, we did check the discharge of the pump and there was good discharge. I've had the airplane over 20 years and nothing has ever been done to the carb. I'll have to go back and check the logs . The problem was discovered on the ground while attempting a touch and go by an instructor and I have not been inclined to fly until the problem is resolved.....don't want to be in a position where I might need sudden power and it's not there. As for the other suggestions I appreciate the recommendations and will follow up on each one. Thanks again.

[n2582d]

My previous response was assuming there was insufficient flow from the discharge nozzle. The 100 Series Service manual, in the troubleshooting guide on pg. 12-4, gives three possibilities for “Engine Does Not Accelerate Properly”
1. Idle mixture set too lean
2. Defective or badly adjusted accelerating pump in carburetor.
3. Float level set too low.

[GAHorn]

I’ve sent you two manuals on the Carburetor. Notice that in the troubleshooting chart Items 4 and in the section “hesitation on acceleration” (see pics below) the accelerator pump MAY be injecting TOO MUCH fuel…and that the “test” is made from 1200-1500 RPM…Not “idle”. Under what conditions are You running Your Test?