[jselvatici]

Hello folks from VAF.
Looking for some brainstorm in here.
Yesterday went for a flight after couple of weeks of not flying the plane. Did the pre-flight, engine run, and on the takeoff roll, RPM didn't raise as expected, so engine not making full power I would say.
I downloaded the data from JPI EDM-900 and plotted some items (huge thanks to Savvy platform), and noticed my FF on yesterday's takeoff was low (around 7) compared to a previous flight takeoff (almost 12).
It worth say that after the rejected takeoff, with power all the way to idle, the RPM dropped below of what I checked during runnap pre-flight.
Does this indicate it's time to service the Marvel Schebler carburetor?
I was going to check on spark plugs and so on, but after looking at the data, seems like spark plugs are out of the equation.
Engine is Lycoming O-320 (carbureted) with MS MA-4SPA (PN: 10-5217).
Thank you for reading this and appreciate some insights.

 

[D-Dubya]

I'd check the easy and cheap stuff first. Fuel filters, gascolators, etc...are they clean and clear? Any kinks or restrictions in the fuel lines or vents?

 

[Sam Buchanan]

Something else that is easy to check.....make sure the carb heat flap is functioning as it should, the air filter is in good condition and there are no uninvited guests in the airbox.

 

[Tailwind/RVGuy]

X2 on the above two posts. Eliminate the simple stuff first. I am leaning a little toward some "breathing restriction". Is it possible you had a build up of carb ice before takeoff? Was run up good?

 

[lr172]

Hello folks from VAF.
Looking for some brainstorm in here.
Yesterday went for a flight after couple of weeks of not flying the plane. Did the pre-flight, engine run, and on the takeoff roll, RPM didn't raise as expected, so engine not making full power I would say.
I downloaded the data from JPI EDM-900 and plotted some items (huge thanks to Savvy platform), and noticed my FF on yesterday's takeoff was low (around 7) compared to a previous flight takeoff (almost 12).
It worth say that after the rejected takeoff, with power all the way to idle, the RPM dropped below of what I checked during runnap pre-flight.
Does this indicate it's time to service the Marvel Schebler carburetor?
I was going to check on spark plugs and so on, but after looking at the data, seems like spark plugs are out of the equation.
Engine is Lycoming O-320 (carbureted) with MS MA-4SPA (PN: 10-5217).
Thank you for reading this and appreciate some insights.

Tough to say with the limited data. However, at first glance it appears that something was preventing the correct fuel flow. That could be in the carb, in the pump, in the filter, in the lines, in the tank, etc. You need a seasoned hand to help with more troubleshooting steps to identify the source.

Larry

 

[664781]

Tough to say with the limited data. However, at first glance it appears that something was preventing the correct fuel flow. That could be in the carb, in the pump, in the filter, in the lines, in the tank, etc. You need a seasoned hand to help with more troubleshooting steps to identify the source.

Larry

Switch fuel tanks and run it up again to see if anything changed.

 

[jselvatici]

Thank you all that replied. I will take a look on easy stuff first for sure. I did check for water in the tank on the pre-flight, no water.
Will check the gascolator tonight. I did condition inspection on the airplane not too long ago and gascolator / air filter was checked / cleaned, but worth checking it again.
Vents, very good question. Will check that.
Carb heat door was solid closed.
Carb ice. That's a interesting one. Never had that. Ground run was good, with normal RPM and FF. Outside temp yesterday at the time was around 74F.
I did switch fuel tanks during a later runnap, and static run does not show anything out of normal. Was just that only one takeoff roll.

I will check some other points tonight. Then plan for another takeoff roll during daytime. Will post the results here. Appreciate everyone's expertise.

 

[gsxphil]

What fuel are you running? 100LL or maybe an ethanol free?

 

[Sam Buchanan]

Carb ice. That's a interesting one. Never had that. Ground run was good, with normal RPM and FF. Outside temp yesterday at the time was around 74F.

Just as a datapoint, 74F with Florida humidity is prime icing conditions especially if you have a lengthy taxi to the runway. Not a bad idea to check carb heat just prior to takeoff.

 

[Ironflight]

Gotta say - when I read the original post, my first thought was carb ice…. You might just try another start/run-up and even a full-power take-off acceleration/stoop to see if the problem is still there. You can spend a LOT of timing chasing a problem that has gone away….

 

[Robin8er]

Could have also possibly been vapor lock. Running the Axillary fuel pump helps mitigate that a bit.

 

[georgemohr]

Thank you all that replied. I will take a look on easy stuff first for sure. I did check for water in the tank on the pre-flight, no water.
Will check the gascolator tonight. I did condition inspection on the airplane not too long ago and gascolator / air filter was checked / cleaned, but worth checking it again.
Vents, very good question. Will check that.
Carb heat door was solid closed.
Carb ice. That's a interesting one. Never had that. Ground run was good, with normal RPM and FF. Outside temp yesterday at the time was around 74F.
I did switch fuel tanks during a later runnap, and static run does not show anything out of normal. Was just that only one takeoff roll.

I will check some other points tonight. Then plan for another takeoff roll during daytime. Will post the results here. Appreciate everyone's expertise.

I had carb ice once on departure. What was the relative humidity that day, any idea?

 

[jselvatici]

Gotta say - when I read the original post, my first thought was carb ice…. You might just try another start/run-up and even a full-power take-off acceleration/stoop to see if the problem is still there. You can spend a LOT of timing chasing a problem that has gone away….

As Sam and Paul said, it could have been carb ice.
The conditions at the moment of flight attempt were:

Wind	Vis.	Weather	Sky Cond.	Air	Dwpt	Relative	altimeter	sea level
(mph)	(mi.)	Humidity	(in.)	(mb)
S 7	10	Fair	CLR	72	66	82%	29.92	1013.1

But, following everybody suggestion, I took the time to check fuel tank vent, gascolator, air filter, all being no problems noticed.

Today, I went for a runnap, all good, then flight. Take off all okay. Conditions today were:

Wind	Vis.	Weather	Sky Cond.	Air	Dwpt	Relative	altimeter	sea level
(mph)	(mi.)	Humidity	(in.)	(mb)
NE 10	10	Fair	CLR	75	44	33%	30.08	1018.5

I can notice a difference there.

I'm comfortable now with this data. My only point to chase now is that during pre-flight runnap, idle looks good, but for some reason after landing, the RPM drops to a point where the engine "wants to die".



I've adjusted he needles before... Since I don't know the total time on this carb, right now it's just passed 300h, will consider rebuild to have a fresh start.

Appreciate everyone's time to write or read this post. Thank you.

 

[Taltruda]

Glad it seems to be working for you.. as for after landing and the engine wanting to die, does leaning out seem to help raise the idle? After landing is the time to set the idle mixture..