Engine Hesitation Lyc. 0-235

A

AlecT

Filing Flight Plan
Joined
Jun 29, 2020
Messages
11
Display Name
Display name:
Alect
Hello all, we’ve noticed that on gradual acceleration my O-235 stumbles around 1300 RPM. Leaning does fix the problem, but not immediately. Normally 20 seconds or so after leaning the stumble seems to smooth out. The odd thing seems to be it only does it when throttle is gradually increased. A quick increase doesn’t yield the stumble, it runs smooth all the way up to the set RPM. We’re just beginning to troubleshoot, has anyone else experienced this?
Thanks in advance.
 
Sounds like it’s just lean for whatever reason. The fact that it does okay when shoving the throttle forward quickly indicates that the accelerator pump is masking the lean condition.
 
The engine runs pretty rich, but my mechanic agrees that it seems like an accelerator pump issue! You think it could be still a pump issue, just on the rich side?
 
There’s a shift in mixture that occurs around 1400-1500rpm on carbureted engines, and it’s normal - the power bump as I like to call it. If it stumbles too aggressively (few hundred rpm drop) you may want to have a look at the accelerator pump, as it’s supposed to squirt additional fuel into the carb so you get a smooth increase / transition in power.
 
Weak spark will also do it.
 
AlecT said:
The engine runs pretty rich, but my mechanic agrees that it seems like an accelerator pump issue! You think it could be still a pump issue, just on the rich side?
Click to expand...

The accelerator pump cannot make the mixture leaner, so if the mixture is already rich the problem is elsewhere.

Increasing power slowly should not add significant fuel to the mixture. So... ????

-Skip
 
Skip Miller said:
The accelerator pump cannot make the mixture leaner, so if the mixture is already rich the problem is elsewhere.

Increasing power slowly should not add significant fuel to the mixture. So... ????

-Skip
Click to expand...

Worn out needle jet in the carburetor? If this was a motorcycle, that's what I'd replace.
Has your carburetor ever been rebuilt?
 
there is a ever so slight tumble in my RPM at 14-1500 range (o-360) , picks right back up after that mark
 
What airplane? We had this exact same issue in our Archer. We replaced the carb thinking that would fix it. Turns out, it was the primer o rings that had worn and needed replaced. Like 6 bucks for the O rings. Try that first if it’s in a Piper.
 
You must log in or register to reply here.
Back
Top