Continental engine stumble

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Lawson Laslo

Pre-takeoff checklist
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Hello
Had some stumbles this morning
IMPORTANT INFO
Continental O200
Temperature spread was only 3 degrees with temps around 30f

engine was heated for 2 hours before start

it was a very humid day and fog just cleared

so first we did the run up (1700rpm), all was good normal mag drop (100rpm)
Once oil temp was 100f we went to takeoff, applying full power. At 1600rpm the engine hesitated and stumbled for about 2 seconds so I aborted takeoff. Did run up again with no issue so decided to stop engine and check for anything obvious, couldn’t find anything

so went to do some high speed taxi test and was presented with the same issue when going to full power, sometimes stumble wasn’t as long but still noticeable

the only way to have no stumble is if I very slowly add the power
(About 7 seconds Idle to Full power)

Any suggestions?
Thanks
 
My O-200 used to do that. Idle mixture ok? Water in the carb bowl? How long were you taxiiing for? They ice up fast.
 
GeorgeC said:
My O-200 used to do that. Idle mixture ok? Water in the carb bowl? How long were you taxiiing for? They ice up fast.
Click to expand...

Overhauled carb last July and idle mixture set then

No water in fuel

taxied for about 7-10 minutes but wasn’t rough at low RPM only at 1600 so probably not carb Ice?
 
Did you try pulling the carb heat on for a minute or so, then closing it before opening the throttle for takeoff? You were in serious carb ice terrritory. O-200s are famous for it. Taxiing (idle or low RPM) will offer the best ice-formation conditions. Oil temperature doesn't help it at all. Carb ice causes a huge percentage of power-failure accidents. There just isn't enough training and understanding of it.

Besides that, did anyone do work on the carb or intake spider recently? Here's an excerpt from one of the many posts I've made on this over the years:

The Continental O-200 has a carb "spider" intake manifold. The carb bolts to it and it, in turn, is bolted to the crankcase. The O-200 is different from its older A-and C-series granddaddy engines in that the spider is mounted loosely on the case studs, with special "Lock-O-Seal" washers on the studs between the case and spider and between the spider and castellated retaining nuts. These washers are metal with a rubber insert molded into them, like an O-ring. The overhaul manual says that those castellated nuts are to be turned only finger tight and the cotter pin installed. The reason is that the MSA carbs don't like being shaken, or they'll spill fuel out of the bowl vent and into the carb throat and the engine will run rich and really rough. The old Strombergs weren't nearly so prissy, and those old A- and C-series engines had much stiffer rubber engine mounts so the engine couldn't move around so much. With the carb spider a little flexible on the studs, and the rubber hose connections on the intake tubes, the engine can torque-vibrate around the crank while the carb will stay relatively still. I have smoothed out O-200s doing exatcly as yours is just by installing the proper washers and doing up the nuts exactly as the manual says. It's an obscure paragraph in the manual and gets overlooked or ignored.

I also found that the engine would do it in the takeoff roll much more readily than with the brakes locked. I believe that ANY nosewheel shimmy can start it, since the nosegear (in a 150) is attached to the engine mount and can shake the engine somewhat. If the spider is properly mounted with the Lock-O-Seals and the nuts finger-tightened, the shimmy will have much less effect on it.

Aside from that, ignition problems cause about 90% of performance problems.
 
Ice during taxiing is IMO not something a lot of ppl think about but can certainly happen in the conditions you are talking about.
 
Dan Thomas said:
Did you try pulling the carb heat on for a minute or so, then closing it before opening the throttle for takeoff? You were in serious carb ice terrritory. O-200s are famous for it. Taxiing (idle or low RPM) will offer the best ice-formation conditions. Oil temperature doesn't help it at all. Carb ice causes a huge percentage of power-failure accidents. There just isn't enough training and understanding of it.

Besides that, did anyone do work on the carb or intake spider recently? Here's an excerpt from one of the many posts I've made on this over the years:

The Continental O-200 has a carb "spider" intake manifold. The carb bolts to it and it, in turn, is bolted to the crankcase. The O-200 is different from its older A-and C-series granddaddy engines in that the spider is mounted loosely on the case studs, with special "Lock-O-Seal" washers on the studs between the case and spider and between the spider and castellated retaining nuts. These washers are metal with a rubber insert molded into them, like an O-ring. The overhaul manual says that those castellated nuts are to be turned only finger tight and the cotter pin installed. The reason is that the MSA carbs don't like being shaken, or they'll spill fuel out of the bowl vent and into the carb throat and the engine will run rich and really rough. The old Strombergs weren't nearly so prissy, and those old A- and C-series engines had much stiffer rubber engine mounts so the engine couldn't move around so much. With the carb spider a little flexible on the studs, and the rubber hose connections on the intake tubes, the engine can torque-vibrate around the crank while the carb will stay relatively still. I have smoothed out O-200s doing exatcly as yours is just by installing the proper washers and doing up the nuts exactly as the manual says. It's an obscure paragraph in the manual and gets overlooked or ignored.

I also found that the engine would do it in the takeoff roll much more readily than with the brakes locked. I believe that ANY nosewheel shimmy can start it, since the nosegear (in a 150) is attached to the engine mount and can shake the engine somewhat. If the spider is properly mounted with the Lock-O-Seals and the nuts finger-tightened, the shimmy will have much less effect on it.

Aside from that, ignition problems cause about 90% of performance problems.
Click to expand...

thanks for info
Replaced carb last july
It is an o-200A though
 
Dan Thomas said:
Did you try pulling the carb heat on for a minute or so, then closing it before opening the throttle for takeoff? You were in serious carb ice terrritory. O-200s are famous for it. Taxiing (idle or low RPM) will offer the best ice-formation conditions. Oil temperature doesn't help it at all. Carb ice causes a huge percentage of power-failure accidents. There just isn't enough training and understanding of it.

Besides that, did anyone do work on the carb or intake spider recently? Here's an excerpt from one of the many posts I've made on this over the years:

The Continental O-200 has a carb "spider" intake manifold. The carb bolts to it and it, in turn, is bolted to the crankcase. The O-200 is different from its older A-and C-series granddaddy engines in that the spider is mounted loosely on the case studs, with special "Lock-O-Seal" washers on the studs between the case and spider and between the spider and castellated retaining nuts. These washers are metal with a rubber insert molded into them, like an O-ring. The overhaul manual says that those castellated nuts are to be turned only finger tight and the cotter pin installed. The reason is that the MSA carbs don't like being shaken, or they'll spill fuel out of the bowl vent and into the carb throat and the engine will run rich and really rough. The old Strombergs weren't nearly so prissy, and those old A- and C-series engines had much stiffer rubber engine mounts so the engine couldn't move around so much. With the carb spider a little flexible on the studs, and the rubber hose connections on the intake tubes, the engine can torque-vibrate around the crank while the carb will stay relatively still. I have smoothed out O-200s doing exatcly as yours is just by installing the proper washers and doing up the nuts exactly as the manual says. It's an obscure paragraph in the manual and gets overlooked or ignored.

I also found that the engine would do it in the takeoff roll much more readily than with the brakes locked. I believe that ANY nosewheel shimmy can start it, since the nosegear (in a 150) is attached to the engine mount and can shake the engine somewhat. If the spider is properly mounted with the Lock-O-Seals and the nuts finger-tightened, the shimmy will have much less effect on it.

Aside from that, ignition problems cause about 90% of performance problems.
Click to expand...

I am going to go out and try having carb heat on and turning it off as I apply takeoff power and see if that solves the issue
Will let you guys know the results
Thanks
 
100 degrees is barely warmed up IMO, and that's after the runup. I'd warm it up more.
 
The 0-200 will do that when the accelerator pump is set to rich. -- or Lean. See which hole is being used, and adjust accordantly.
Cold air will need a little more fuel to get the RPM going quickly.
and vice verse
 
Besides the carb ice suggestions, how's your fuel tank vent? Any chance a little water dripped on it and partially iced over?

Ron Wanttaja
 
I agree with Tom.

The 10-4894 Carb has an external bell crank with3 holes to adjust the length

of the Accelerator Pump stroke.

Common in cold weather to need the longest stroke.

If stumble goes away with Carb Heat ON then you are too lean.
 
Magman said:
I agree with Tom.

The 10-4894 Carb has an external bell crank with3 holes to adjust the length

of the Accelerator Pump stroke.

Common in cold weather to need the longest stroke.

If stumble goes away with Carb Heat ON then you are too lean.
Click to expand...
Plus.. the A&P should do a idle mixture check..
 
Magman said:
I agree with Tom.

The 10-4894 Carb has an external bell crank with3 holes to adjust the length

of the Accelerator Pump stroke.

Common in cold weather to need the longest stroke.

If stumble goes away with Carb Heat ON then you are too lean.
Click to expand...
Tom-D said:
Plus.. the A&P should do a idle mixture check..
Click to expand...

after doing test here are results
Full power no carb heat still stumbles
Carb heat on while taxi then off to apply full power still stumbles
Carb heat on while adding full power no stumble!

so it’s running to lean
Do you recommend we adjust idle mixture or the accelerator pump first?
 
CEA6DF2B-DB82-45F9-82EF-FBA906F9969D.png is this the accelerator pump arm?
 

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Put the link in the center hole. try it.

don't touch the throttle linkage
 
7CFAFAFD-76B9-4829-84F3-E0F480F4B184.jpeg
Magman said:
I agree with Tom.

The 10-4894 Carb has an external bell crank with3 holes to adjust the length

of the Accelerator Pump stroke.

Common in cold weather to need the longest stroke.

If stumble goes away with Carb Heat ON then you are too lean.
Click to expand...
Tom-D said:
Put the link in the center hole. try it.

don't touch the throttle linkage
Click to expand...
Thanks Tom
Just to confirm this hole
 
Magman said:
The 10-4894 Carb has an external bell crank with3 holes to adjust the length of the Accelerator Pump stroke.
Click to expand...
I was not aware of that, thank you.
 
Tom-D said:
yep,, that will shorting the effective stroke of the pump.

this is where most of the pumps are. the medium stoke.
Click to expand...
Looks like it is set on the longest stroke hole which puts out the most fuel, do you think by chance it is received to much due on acceleration ?
 
To answer that you must know whether you are Lean or Rich.

Check Idle Mixture for 25 RPM rise.

If more = Rich Less =. Lean

Carb Heat will richer Mix.
 
Magman said:
To answer that you must know whether you are Lean or Rich.

Check Idle Mixture for 25 RPM rise.

If more = Rich Less =. Lean

Carb Heat will richer Mix.
Click to expand...
Idle mixture doesn't effect how much fuel is expelled by the accelerator pump.
Set the RPM at 500-600, let it idle for 1 minute, pull the mixture to stop the engine, watch the rise as the engine quits, it should be set to 10 to 50 RPM.

If the RPM rises over 50 than it should be corrected by the turning the mixture screw.
If the RPM doesn't rise any, it should be adjusted with the mixture screw.
Never adjust the mixture screw more than 5 clicks at a Time.
 
Lawson Laslo said:
Looks like it is set on the longest stroke hole which puts out the most fuel, do you think by chance it is received to much due on acceleration ?
Click to expand...
If the accelerator pump is out of adjustment it may give the same symptoms as lean or rich.
it may be starving, or it may be getting too fuel.
When it is starving, it will most likely quit.
 
Magman said:
To answer that you must know whether you are Lean or Rich.

Check Idle Mixture for 25 RPM rise.

If more = Rich Less =. Lean

Carb Heat will richer Mix.
Click to expand...
I agree that carb heat richers mixture, when I shutoff engine I get about 75rpm, which would mean I am to rich, but the stumble goes away when I have carb heat on (richer)
 
Tom-D said:
If the accelerator pump is out of adjustment it may give the same symptoms as lean or rich.
it may be starving, or it may be getting too fuel.
When it is starving, it will most likely quit.
Click to expand...
Ok so maybe it’s getting to much fuel, but how would carb heat make problem go away?
 
Lawson Laslo said:
Ok so maybe it’s getting to much fuel, but how would carb heat make problem go away?
Click to expand...

This sounds like a pretty common issue I see with these engines. When accelerating from a full Idle (throttle all the way back and minimum RPM on the ground ) it will stumble unless you crack the throttle let it gain a 100 rpm or so and then it will accelerate normally. One of my theory’s for this is that it the Accelerator pump is giving it to much fuel. The RPM is so low that it can’t pull enough air in to provide a useable fuel mixture.

If the engine has a bit of RPM like on short final, power off it has enough to RPM and will always accelerate normally if a go around is initiated.

I am curious as to how adjusting the accelerator pump, effects your issue?

Brian
CFIIG/ASEL
 
Lawson Laslo said:
I agree that carb heat richers mixture, when I shutoff engine I get about 75rpm, which would mean I am to rich, but the stumble goes away when I have carb heat on (richer)
Click to expand...
That implies weak ignition. When was the last time the mags were off for internal inspection? The last time the plugs were spark tested under pressure? The last time the ignition harness was tested?
 
What carb is installed? If a Marvel, what venturi does it have? The one piece venturi modified carbs have been known to exhibit a stumble due to the way the air and fuel flows and mixes. There is an updated nozzle that is supposed to help. Look back in the paperwork to see what was installed and where it came from.

The use of carb heat might be changing the airflow enough so that the stumble is gone. If the idle mixture in winter is rich, it must have been really rich in the summer. Set it for conditions now and if the stumble is still there, move on to the other items.
 
Dan Thomas said:
That implies weak ignition. When was the last time the mags were off for internal inspection? The last time the plugs were spark tested under pressure? The last time the ignition harness was tested?
Click to expand...
Mag inspected and points replaced last July
Brand new leads and harness in august
 
JAWS said:
What carb is installed? If a Marvel, what venturi does it have? The one piece venturi modified carbs have been known to exhibit a stumble due to the way the air and fuel flows and mixes. There is an updated nozzle that is supposed to help. Look back in the paperwork to see what was installed and where it came from.

The use of carb heat might be changing the airflow enough so that the stumble is gone. If the idle mixture in winter is rich, it must have been really rich in the summer. Set it for conditions now and if the stumble is still there, move on to the other items.
Click to expand...
Got an overhauled carb from aircraft spruce last july
It marvel ma3spa
 
Av-gas or Mo-gas?

If Mo; could it still be summer blend? ( Lower Vapor Pressure - RVP )
 
Always always run some carb heat before take off...

Similar ice maker tendencies to my c85... when I bought my c140 I put ntsb accident database in excel and studied it. Many of the power loss after take off accidents found the engine ran fine post accident. Now maybe not all are carb ice but it’s a reasonable assumption at least some or many may be...

I run my carb heat minimally all through the run up and just check it’s functionality by seeing if I get an rpm rise by turning it off a second- turning it off-off is my last checklist item before take off.
 
Huckster79 said:
Always always run some carb heat before take off...

Similar ice maker tendencies to my c85... when I bought my c140 I put ntsb accident database in excel and studied it. Many of the power loss after take off accidents found the engine ran fine post accident. Now maybe not all are carb ice but it’s a reasonable assumption at least some or many may be...

I run my carb heat minimally all through the run up and just check it’s functionality by seeing if I get an rpm rise by turning it off a second- turning it off-off is my last checklist item before take off.
Click to expand...
Been flying behind a C85 since ~1987. Still running the way I was taught, in a C-150 with on O-200. The carb heat is on for all ground operations prior to takeoff, unless there's visible dust in the air. Turn it off during runup for the mag check, then cycle the carb heat and note the effect. Leave it on, only turning it off once the throttle is full forward for takeoff. Comes back on abeam the numbers for landing.

I do turn it off for the taxi back to the hangar.....

Ron Wanttaja
 
What do the symptoms mean if the engine isn't warmed up?
 
wanttaja said:
Been flying behind a C85 since ~1987. Still running the way I was taught, in a C-150 with on O-200. The carb heat is on for all ground operations prior to takeoff, unless there's visible dust in the air. Turn it off during runup for the mag check, then cycle the carb heat and note the effect. Leave it on, only turning it off once the throttle is full forward for takeoff. Comes back on abeam the numbers for landing.

I do turn it off for the taxi back to the hangar.....

Ron Wanttaja
Click to expand...

same here- I just usually omit that I turn it on for all of taxi to avoid the “you’ll ruin your engine” lecture ;) I put mine on as I get to the pattern so it gets a blast of good hot air a bit before pulling the throttle back- so sounds like we run the same program basically :)

what you flying with a c85?
 
Huckster79 said:
same here- I just usually omit that I turn it on for all of taxi to avoid the “you’ll ruin your engine” lecture ;) I put mine on as I get to the pattern so it gets a blast of good hot air a bit before pulling the throttle back- so sounds like we run the same program basically :)

what you flying with a c85?
Click to expand...
Bowers Fly Baby homebuilt.
upload_2021-1-11_16-11-39.png

Ron Wanttaja
 
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