When doing ground run testing, if I slide the trottle in swiftly, like you might to when arreting a descent, it stumbles. I'm running the HA-6 carb. Unknown when ti was last overhauled.

New mags, new fine wire plugs, even new plugwires. Primper recently rebuilt too.

I have no history with this plane - restoring it back to top shape, so i've never even flown it yet.

One symptom: The Accelerator pump DOES work, but i notice if I pump it even just ONE time, fuel comes running out the airbox drain tube. Not sure if this is excessive?

I'd really like to rule out the accelerator pump.It seems like a lot of fuel, but I've never owned an O-360 I had only injected engines prior... how much fuel should come out the overflow on each pump of the accelerator pump?

I've noticed there is NO RPM rise when I lean the engine at idle cutoff as it should. This MAY mean the idle mixture is too lean - anyone know if this itself might cause it to stumble?

Any insights so i can work on it in the next day or two would be great!

-Brendan

you have an updraft carb and if you make quick adjustments you will get a cough hesitation apon acceleration if you do it to fast especially from idle. smooth application will prove usefull

It's enough of a stumble that I'm afraid the engine could die - it's not insignificant. the HA6 is a sidedraft, not sure it matters tho. I have reasonable expectations of the carb like my 36 Ford's slight hesitation, but its dangerous on goaround the way it is, so I have to do something.

Sounds like too much fuel from the accelerator pump to me. Possibly combined with either a partially blocked idle air tube and/or the idle mixture set too rich.

If the engine was really cold and not allowed to warm up completely it can also cause this stumble on swift acceleration. Or if it was really high elevations and hot it could be too rich already with the accelerator pump making matters worse.

Here’s a pretty good document that might help. If you’re not completely familiar with carbs I suggest an overhaul especially if it is not documented how long it has been installed. There could be other ADs not addressed.

http://www.insightavionics.com/pdf%20fi ... Manual.pdf

Check out https://msacarbs.com/carburetor-troubleshooting

Crazed my M5 180-C does the same thing. It is unnerving when you apply power to arrest the decent. I keep the throttle a bit above idle cut off on decent. The M5 has a high sink rate. Keeping the throttle in a little bit makes the approach a bit shallower and if you need to descend you can further reduce power. That throttle hesitation is a heart stopper and made me cautious about flaring late and/or made me approach at a higher airspeed. Altering my technique leaving in a bit of throttle improved my landings.

Yes I’ve read those guides. It still comes down to a few key observations:

1. Accelerator pump is working, shoots are least a few tablespoons per press
2. I cannot get an RPM RISE at Idle Cut Off/Leaning.

So I would lean towards the pump being ok, I have the following specific questions I think I need answers to:

1. Where, on the HA-6 sidedraft can I adjust the accelerator pump linkage to adjust the pump volume (can’t find any diagram showing this) and
2. Shouldn’t I get an RPM RISE even when the engine is cold at Idle Cut Off/Leaning?

Applying throttle too quickly will often cause an engine to stumble. If it's too lean, it could also make it stop. Even in a go-around, the throttle should be applied smoothly with the mixture full-rich.

I don't let my RPM drop below 1400 in a descent since the air flow will turn the prop faster than the power setting. Sometimes that causes small backfires or sputtering. Idle power can be applied when you slow down before flaring. At that point there's not enough air flow to turn the prop.

It's possible that your carburetor isn't set properly. The absence of an increase in RPM at 1,000 RPM during leaning on the ground is troubling. You should get around 100 RPM increase at peak lean. Makes me think the mixture setting on the carb is wrong. If an aircraft is routinely operated at higher elevations, sometimes owners will set the carburetor mixture for more power. If you're now operating at lower density altitude, then the engine could be running too lean. You might just need to reset the carburetor mixture.

My plan is a thorough induction leak test then adjust mixture. I doubt the gaskets or hoses have been checked thoroughly in years.

It moved from Texas to Oregon so maybe mixture will help, we’ll see !

Normal O360 behavior. I attribute it to momentary over rich mixture due to accelerator pump.

If you're not getting an rpm rise at idle cut off you're most likely set too lean. Assuming your mags and plugs are good and timing is correct. Turn the idle mixture screw out to richen the mixture then at idle speed pull the mixture, it might take a few attempts to set up for a 50rpm rise, clear the throttle between settings and check for proper idle speed once you have it set. I normally adjust the mixture seasonaly on mine.

I agree with bobguhr. I think its to lean.

i enrichened the idle and i get the RPM drop now.... still seems to hesitate slightly hwen i stuff in the throttle but it's probably due for carb overhaul one day maybe that would perfect it.

Yes ALL new ignition... ALL.

-Brendan

Did this new to you airplane fly regularly before you bought it or had it set for weeks or months between flights.
Did it stumble on acceleration when you first got it? Or did it take 10-15 hours to show up and seems to be getting worse?
If ether and more likely both of conditions apply you could be another victim of the dreaded Lycoming cam& tappet rust . I hope I'am wrong but a new stumble after just a few hours is quite often the initial symptom.
Change the oil and inspect sump screen & filter for metal and recheck the new filter after 3-5 hours if there were any magnetic flakes in the current filter

CRAZEDpilot wrote:i enrichened the idle and i get the RPM drop now.... still seems to hesitate slightly hwen i stuff in the throttle but it's probably due for carb overhaul one day maybe that would perfect it.

Sounds better then it was. Good job!