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HotRod6A

Member
Recently my O-360 starting running very rough between 800-1200rpm, engine ran like clockwork prior to this issue developing.

Mag check is perfect, idles well, starts well, compressions all over 70/80, 300hrs smoh. No apparent Intake/Exhaust leaks - gaskets are relatively fresh, again engine runs well at higher rpms and making full pwr.

Idle mixture screw doesn't make any notable changes in performance or changes in engine roughness, no change in performance with boost pump on or off. 3psi boost pump off - 5-6psi on, fuel pressure is pulled from top of carburetor, no apparent changes when cycling the mixture.

MA-4-5 10-3878 overhauled in 2018

Thinking is a carb issue or sticky valves.

Does sticky valves plague the entire rpm range or can be isolated to a particular rpm like Im experiencing?

Thanks!
Rodney
 
Do you have a 4 point engine monitor? If so are the CHTs and EGTs similar across all cylinders in the 800-1200 rpm speed?
Have a MAP gauge? What does that read at 800-1200 rpm?

Mags? Last overhaul on them?

I think intake leaks will be more apparent at lower throttle openings as you'll have more vacuum (hence more leak). How about checking the intake tube hoses?
 
HotRod6A said:
Recently my O-360 starting running very rough between 800-1200rpm, engine ran like clockwork prior to this issue developing.

Mag check is perfect, idles well, starts well, compressions all over 70/80, 300hrs smoh. No apparent Intake/Exhaust leaks - gaskets are relatively fresh, again engine runs well at higher rpms and making full pwr.

Idle mixture screw doesn't make any notable changes in performance or changes in engine roughness, no change in performance with boost pump on or off. 3psi boost pump off - 5-6psi on, fuel pressure is pulled from top of carburetor, no apparent changes when cycling the mixture.

MA-4-5 10-3878 overhauled in 2018

Thinking is a carb issue or sticky valves.

Does sticky valves plague the entire rpm range or can be isolated to a particular rpm like Im experiencing?

Thanks!
Rodney
Click to expand...
Yes, an intake leak is my guess to. Look for a loose intake in the oil pan. (64781 Swaging Tool, Intake pipe).
This tool, if required, is expensive. Suggest you can borrow one.

Good luck
 
Make sure the carb isn't loose either the split seam for the bowl or the 4 mount bolts to the sump. It may not be obvious, but grasp the FAB snorkel and see if it moves side to side..mine did it, and so have others. Also, I've had 2 spark plugs at 2 different times that had an insulator crack and initiate a slight oil fowling which caused similar roughness.
 
Avanza said:
Yes, an intake leak is my guess to. Look for a loose intake in the oil pan. (64781 Swaging Tool, Intake pipe
Avanza said:
Yes, an intake leak is my guess to. Look for a loose intake in the oil pan. (64781 Swaging Tool, Intake pipe).
This tool, if required, is expensive. Suggest you can borrow one.

Good luck
Click to expand...
No leaks on the intake runners/tubes, new gaskets well placed, and new rubber couplers.
Click to expand...
whats the swaging tool do?
Avanza said:
).
This tool, if required, is expensive. Suggest you can borrow one.

Good luck
Click to expand...
 
fixnflyguy said:
Make sure the carb isn't loose either the split seam for the bowl or the 4 mount bolts to the sump. It may not be obvious, but grasp the FAB snorkel and see if it moves side to side..mine did it, and so have others. Also, I've had 2 spark plugs at 2 different times that had an insulator crack and initiate a slight oil fowling which caused similar roughness.
Click to expand...
wouldnt this show in a mag drop? and threw out the rpm range, this sounds much different. Float bowl is tight and carb is tight with good gasket to oil sump
 
blaplante said:
Do you have a 4 point engine monitor? If so are the CHTs and EGTs similar across all cylinders in the 800-1200 rpm speed?
Have a MAP gauge? What does that read at 800-1200 rpm?

Mags? Last overhaul on them?

I think intake leaks will be more apparent at lower throttle openings as you'll have more vacuum (hence more leak). How about checking the intake tube hoses?
Click to expand...
I do not have a engine monitor, only mechanical gauge CHts on all four and they were very even during this event, one egt which wont tell me much.

Mags are slicks and 200hrs since new.

I didnt cross reference the MAP gauge, what would that tell me in this particular case?
 
HotRod6A said:
wouldnt this show in a mag drop? and threw out the rpm range, this sounds much different. Float bowl is tight and carb is tight with good gasket to oil sump
Click to expand...
When my carb got loose it did not show mag drop. It flew fine at cruise, got rough during midrange mostly notable when reducing power for landing. The plug issue was intermittent and dud show at mag drop, but cleared after a lean and clean. It was hard one to pinpoint. Plugs were 200ish hrs from new, never dropped or mishandled.
 
HotRod6A said:
I do not have a engine monitor, only mechanical gauge CHts on all four and they were very even during this event, one egt which wont tell me much.

Mags are slicks and 200hrs since new.

I didnt cross reference the MAP gauge, what would that tell me in this particular case?
Click to expand...
If there's enough intake leak the MAP will read higher than normal.
A reading at 800 rpm might help us diagnose.
 
HotRod6A said:
wouldnt this show in a mag drop? and threw out the rpm range, this sounds much different. Float bowl is tight and carb is tight with good gasket to oil sump
Click to expand...
Mixture will burn or not regardless of which magneto is firing, if both magnetos and plugs are good.
So a mixture issue won't show as an unusual mag drop.
 
You say movement of the idle mixture screw makes no difference, correct?

warm it up good, set RPM at 800 and move the mixture needle from full in to full out with the engine running. If you have no change in RPM, then something is going on inside the carb. Sticking valves create symptoms across the full RPM spectrum.

Larry
 
Swaging tool reseats the steel tube into the aluminum sump. Probably need to remove the intake tubes and then GENTLY try to wiggle the short steel tubes in the sump. If this is the problem the easiest solution is to send the sump to someone like Divco in Tulsa.
 
Where does this occur. There is a known problem that occurs on 320's but I don't know if it applies to 360. On the 320's it occurs at the transition from idle configuration to higher power. i had this on my non RV 0 320. It only occurred on descent and at low power setting. Maybe I just began reducing power more slowly or maybe it just went away. Hasn't occurred for several years. My recollection from the Lycoming forums years ago that the only fix was to change carbs.
 
I have had two problems over the years that *might* cause what the OP describes.

1) Looseness between the bowl and body of the carb. Rectified by replacing the bend-over tabs between the carb and bowl and re-tightening the screws. Probably caused by an insufficient gap between the fiberglass intake and the carb, resulting in too much vibration/movement between the carb and cowl. Which "worked" the FAB until it loosened the carb bowl. This manifested itself as a hiccup transitioning from idle to >1500 rpm.

2) A leak where the intake tube joins the sump. Rectified by renting the swaging tool for Zephyr Engines in Florida and re-swaging the intake tube to the sump. That was done without removing the sump and wasn't a difficult task at all. I don't remember how I discovered the leaky intake tube/sump join or what the symptoms were...
 
Check for lead fouling in the plugs, too. Little balls of lead grow in there over time and will degrade the spark enough that it's noticeable at low RPM. I clean out a small pile of them at each annual. Hopefully new fuels with less (no?) lead will fix that.
 
jrs14855 said:
Swaging tool reseats the steel tube into the aluminum sump. Probably need to remove the intake tubes and then GENTLY try to wiggle the short steel tubes in the sump. If this is the problem the easiest solution is to send the sump to someone like Divco in Tulsa.
Click to expand...
gotcha, didnt check the sump intake tubes, so this I will check.
 
Snowflake said:
Check for lead fouling in the plugs, too. Little balls of lead grow in there over time and will degrade the spark enough that it's noticeable at low RPM. I clean out a small pile of them at each annual. Hopefully new fuels with less (no?) lead will fix that.
Click to expand...
Plugs just cleaned and tested 2hrs prior to this issue, not ruling this completely out, but you would think that bad plug(s) would cause roughness across the entire rpm range and not isolated to particular rpm range
 
Kyle Boatright said:
I have had two problems over the years that *might* cause what the OP describes.

1) Looseness between the bowl and body of the carb. Rectified by replacing the bend-over tabs between the carb and bowl and re-tightening the screws. Probably caused by an insufficient gap between the fiberglass intake and the carb, resulting in too much vibration/movement between the carb and cowl. Which "worked" the FAB until it loosened the carb bowl. This manifested itself as a hiccup transitioning from idle to >1500 rpm.

2) A leak where the intake tube joins the sump. Rectified by renting the swaging tool for Zephyr Engines in Florida and re-swaging the intake tube to the sump. That was done without removing the sump and wasn't a difficult task at all. I don't remember how I discovered the leaky intake tube/sump join or what the symptoms were...
Click to expand...
carb bowl is def tight, will check oil sump intake tubes.
 
jrs14855 said:
Where does this occur. There is a known problem that occurs on 320's but I don't know if it applies to 360. On the 320's it occurs at the transition from idle configuration to higher power. i had this on my non RV 0 320. It only occurred on descent and at low power setting. Maybe I just began reducing power more slowly or maybe it just went away. Hasn't occurred for several years. My recollection from the Lycoming forums years ago that the only fix was to change carbs.
Click to expand...
I understand the bog or slight hesitation when the carb transistions from idle circuit to the mid/main circuit, but this is not that, typically Ive seen this stumble between circuits is around 1100rpm on this engine. This is moderate roughness offidle around 800-1200rpm, idle (650) runs smooth, over 1200 runs great.
I sent the carb to D&G to get the mooney mod done to help with wide open throttle fuel flow to help mitigate cht temps on take off, its not bad on this particular plane but I have 2ea cylinders that hit 420f on take off with a very shallow 130mph accent, not bad but I figured I have an expert overhaul the carb and make the mods so I know its right going back on the acft.

thx
Rodney
 
lr172 said:
You say movement of the idle mixture screw makes no difference, correct?

warm it up good, set RPM at 800 and move the mixture needle from full in to full out with the engine running. If you have no change in RPM, then something is going on inside the carb. Sticking valves create symptoms across the full RPM spectrum.

Larry
Click to expand...
I did do this, from 1 turn out to 3 turns out, no change between 800-1200rpm, carb has been sent off to D&G Supply for the mooney mod and overhaul
 
HotRod6A said:
I did do this, from 1 turn out to 3 turns out, no change between 800-1200rpm, carb has been sent off to D&G Supply for the mooney mod and overhaul
Click to expand...
good call on the overhaul. The marvel carbs use a liquid metering valve for the idle circuit, as opposed to an air bleed. Therefore, if you can go from 1 turn out to three turns out with no change in RPM, there must either be a clog or leak in the liquid metering circuit or a leak in the air balancing circuit.

Just confirming that you did this with the engine running and a fixed throttle position, Your wording did not necessarily imply that.
 
So got my carb back , group did the "mooney mod" essentially making it a 10-4164, and recommended "replace/repair as necessary" since the overhaul was done in 2018.
All I can say the problem went away, the slight hesitation at aprox 1100rpm is gone, the engine significant roughness 800-1200 is completely gone, and my CHT's are considerably lower, I can climb at 105-110mph without #3 going over 400f. Happy Camper!

All I can think of is some idle circuit or air leak in the carb was causing this problem.

thanks for all your input!
Cheers
Rodney
 
Glad to hear that the carb overhaul/mod did the trick! Can you share the cost and turnaround time on getting your carb done at D&G? I'm running an O-360-A1D with a 10-3878 carb, has been running fine since overhaul in 2006, but the discussion I've seen lately of the 4164 Mooney Mod has me wondering if I should get send mine in for IRAN and the mod...
 
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