Engine stumble when applying power for takeoff around 2200rpm

[1964-M20E]

When adding power for take off my IO360A1A has developed a stumble.   This is as going from idle to full throttle and happens around 2200rpm but clears up as the engine gets to 2500 with or without the boost pump.  During the engine run up there no issues.  I have cleaned the injectors, intake screen on the fuel servo and the collator is clean.  All intake tubes seem to be good.

It sounds almost like it's lacking fuel during that throttle phase similar to advancing the throttle when leaned on the ground.

 

Any ideas?

[Rwsavory]

Do you have engine analysis data to share?

[Jsno]

Could be your engine driven fuel pump.

[PeytonM]

You might want to clean/check spark plugs. This happened to me a couple times during takeoff roll; very disquieting! Cleaning plugs resolved it. (Fine wires at that!)

[M20F]

Check all the nuts on the spider are tight.  

[PT20J]

Does it only do this during acceleration or will it do it if you run it up at a steady rpm in the 2200 rpm range?

If it does it only during acceleration, it sounds like it is momentarily running out of fuel. The RSA fuel servo does not have an accelerator pump or economizer valve. It simply meters fuel according to airflow. There isn't enough airflow below about 1500 rpm for accurate metering and so mixture is controlled manually by a valve connected to the throttle. So, the first thing to do is set the idle mixture for a 25-50 rpm rise during shut down and then set the idle speed for about 650 rpm. If it still has a problem, I would look to see that the servo is receiving adequate fuel pressure. There are no other field adjustments on the servo.

[skykrawler]

On 2/20/2025 at 12:29 AM, Jsno said:

Could be your engine driven fuel pump.

Maybe not.  OP says it clears up by 2500.  Does with or without boost pump.

 

........  Check all the nuts on the spider are tight.  

Maybe not. Probably would have blue fuel stains for leaks at the spider.   The spiders are very simple - piston with a spring that meters fuel at very low pressures (idle) and also closes off at mixture cutoff to prevent sucking fuel at shutdown.  

 

..... Spark plugs / ignition..

Maybe.   Mag check both mags through that 2200 rpm range up to full power.   Also in air mag check on a full power climb.  How many hours on those mags?

What are the plug gaps?