Engine bog when power applied.

itsjames2011

itsjames2011

Pre-takeoff checklist
Joined
Jul 21, 2014
Messages
165
Location
Chicopee MA
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Display name:
James
I'm having an acceleration problem in my airplane(1964 cherokee 140 with 160hp o320-d2a) When I'm advancing the throttle from idle and the tach hits 1400 rpm it hesitates and boggs down to about 1250 or 1300 then shoots up to 1500 and onwards. The airplane came out of the annual last month got two new cylinders, a new muffler, and had the carb heat box welded. Also I have checked that the primer is in and locked. For what it's worth, it seems to be more pronounced when the engine is fully warmed up.
 
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Same thing used to happen in my O320. I was told it is normal.
I mitigated that by applying throttle over a 3-5 count.
 
SixPapaCharlie said:
Same thing used to happen in my O320. I was told it is normal.
I mitigated that by applying throttle over a 3-5 count.
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It tends to become really noticeable during throttle adjustments in the traffic pattern as well.
 
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itsjames2011 said:
It tends to become really noticeable during throttle adjustments in the traffic pattern as well.
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Get thee to an AMT.

Unlikely to get a diagnosis from a distance - "could" be trouble when bog becomes engine failure.
 
wrbix said:
Get thee to an AMT.

Unlikely to get a diagnosis from a distance - "could" be trouble when bog becomes engine failure.
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It's sitting in an airport with an a&up who is going to look at it this week. I'm certainly not going to take advice over the Internet when it comes to safety. Just a) trying to get an education so that a I learn something and b) so I know if this mechanic is full of crap or not :)
 
It seems every engine is different.

My O-200 in the Ercoupe used to do this. There was like a dead spot that it would be fine above and below.
My O-320 in my Warrior did not.
My O-360 in my RV-8 HATES to be at idle in the pattern. It pops and snarls, and bogs if you leave it at idle and full rich too long.
My O-540 in my Pathfinder was easy to foul the plugs, when burning avgas.
 
It means the accelerator pump seal in your carb is starting to get weak most likely, or you have some other induction leak getting you a lean spot in the acceleration.
 
Jay Honeck said:
It seems every engine is different.

My O-200 in the Ercoupe used to do this. There was like a dead spot that it would be fine above and below.
My O-320 in my Warrior did not.
My O-360 in my RV-8 HATES to be at idle in the pattern. It pops and snarls, and bogs if you leave it at idle and full rich too long.
My O-540 in my Pathfinder was easy to foul the plugs, when burning avgas.
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Lean your idle in the pattern then, but it really shouldn't be tuned that way.
 
So if it is the Accellerator pump am I looking at replacing the carburetor or just Sending it to a shop? My engine is an O320-D2A and the carb part no is 10-3878-2. My mechanic who is on vacation said I should replace it with a 10-5217 because it will be richer on takeoff and have better Atomization. If I do have to replace the carb any idea on a realistic cost with my core? Also what is the carburetor exchange I've heard about?
 
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itsjames2011 said:
So if it is the Accellerator pump am I looking at replacing the carburetor or just Sending it to a shop? Brand-new carburetor seem extremely expensive but it seems like you can buy an overhauled carb for a little under $1000 with a core.
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That is just insane.......:yikes::mad2::mad2::mad2::mad2:....:redface:
 
Send to a shop. If they can't repair it with bench stock they'll overhaul it cheaper than a factory OH.
 
Some A and D models have that flat spot in the acceleration. Something to do with the shape of the intake plenum and turbulence therein. That said, fuel issues are unfairly and futilely blamed for many perfomance issues when the real problem is weak spark from one or both mags. Cylinder pressures are quite high during acceleration and spark can be quenched at some plugs. How many hours since the mags were last inspected internally?
 
Dan Thomas said:
Some A and D models have that flat spot in the acceleration. Something to do with the shape of the intake plenum and turbulence therein. That said, fuel issues are unfairly and futilely blamed for many perfomance issues when the real problem is weak spark from one or both mags. Cylinder pressures are quite high during acceleration and spark can be quenched at some plugs. How many hours since the mags were last inspected internally?
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Good point Dan......:yes:.....:thumbsup:
 
itsjames2011 said:
...When I'm advancing the throttle from idle and the tach hits 1400 rpm it hesitates and boggs down to about 1250 or 1300 then shoots up to 1500 and onwards...
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This could very well be a problem with your carburetor. The "bogg" happens when it is transitioning from the idle circuit to the main jet. I had the same problem with a newly overhauled carburetor on a PA-12. I tried everything to fix it then finally called the shop that we got the carb from. They said there was definitely something wrong, to send it back and they'd ship another one. The replacement came and worked fine right out of the box.
 
Dan Thomas said:
Some A and D models have that flat spot in the acceleration. Something to do with the shape of the intake plenum and turbulence therein. That said, fuel issues are unfairly and futilely blamed for many perfomance issues when the real problem is weak spark from one or both mags. Cylinder pressures are quite high during acceleration and spark can be quenched at some plugs. How many hours since the mags were last inspected internally?
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The mags were pulled and inspected during the annual last month. I replaced cylinders 1 & 3 and all has been well. I have about 20 hours on them and this was not occurring before 2 days ago.
 
SixPapaCharlie said:
Same thing used to happen in my O320. I was told it is normal.
I mitigated that by applying throttle over a 3-5 count.
Click to expand...
It is absolutely NOT normal. My Tampico absolutely does not do that. (For those keeping up at home, 6PC flew a Tampico also. We both had/have O-320-D2A engines.)

Henning said:
It means the accelerator pump seal in your carb is starting to get weak most likely, or you have some other induction leak getting you a lean spot in the acceleration.
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Henning nailed it. I would be looking at the accelerator pump.
 
Comanche flyer said:
some times primer leak cause those symptoms.
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Too much fuel, as with a primer leak, will typically sputter, while too little fuel from a bad accelerator pump or induction leak will cause the power to just sigh away then pick up as vacuum decreases again.
 
So if it is the Accellerator pump am I looking at replacing the carburetor or just Sending it to a shop? Brand-new carburetor seem extremely expensive but it seems like you can buy an overhauled carb for a little under $1000 with a core.
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N801BH said:
That is just insane.......:yikes::mad2::mad2::mad2::mad2:....:redface:
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$945 rebuilt, $600 refundable core charge
$945 overhauled, $600 refundable core charge
$2100 new

Not really sure what the difference is between rebuilt & overhauled...

http://msacarbs.com/10-59959.html

QAA
$835 overhauled, $600 refundable core charge

http://www.qualityaircraftaccessori...rburetor-marvel-schebler/carburetor-ma-4spa-1
 
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Kiddo's Driver said:
$945 rebuilt, $600 refundable core charge
$945 overhauled, $600 refundable core charge
$2100 new

Not really sure what the difference is between rebuilt & overhauled...

http://msacarbs.com/10-59959.html

QAA
$835 overhauled, $600 refundable core charge

http://www.qualityaircraftaccessori...rburetor-marvel-schebler/carburetor-ma-4spa-1
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QAA Seems like the best deal. They bill your card $1435.00 and refund $600.00 upon receipt of the core. I can't win with this airplane. I've had it 3 months, done $11,000 worth of work and I've flown it 30 hours ><
 
Henning said:
Too much fuel, as with a primer leak, will typically sputter, while too little fuel from a bad accelerator pump or induction leak will cause the power to just sigh away then pick up as vacuum decreases again.
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Actually no....

Too much fuel OK, but it is because the primer pump is in the wrong hole, and pumping too much fuel. Remember the two new cylinders? and the other maintenance. The Accelerator pump needs to be adjusted to a leaner setting.
 
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If it's the same problem I experienced it has nothing to do with the accelerator pump. The "bog" or stumble would occur right at the transition point between 1200 and 1400 rpm no matter how slowly you advanced the throttle.
 
I've seen this problem when the carb was very slightly loose on the 4 studs where it mounts to the sump. Once you started inspecting things down there, you could detect a very slight wiggle if you applied a little force to the carb.
 
If this was asked I missed it. Did it do this before the Cylinders were replaced?
 
WingNut42 said:
If this was asked I missed it. Did it do this before the Cylinders were replaced?
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I did not happen before the cylinders we're replaced and it did not happen for the first 18 hours after they were replaced either.
 
itsjames2011 said:
I did not happen before the cylinders we're replaced and it did not happen for the first 18 hours after they were replaced either.
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Check security of intake runners on the new cylinders.
 
After throwing some money at it, it turns out the airplane needs a new carburetor. My engine is a O-320-D2A and has a 10-3678-32 and we have decided to replace it with the 10-5217 that way it will run a bit richer on takeoff and it will have better atomization all around. Apparently the 10-5217 is what they're putting on almost all of the new O-320s. I will have her back on Monday and hopefully I'll get a little reprieve on the maintenance issues.
 
itsjames2011 said:
After throwing some money at it, it turns out the airplane needs a new carburetor. My engine is a O-320-D2A and has a 10-3678-32 and we have decided to replace it with the 10-5217 that way it will run a bit richer on takeoff and it will have better atomization all around. Apparently the 10-5217 is what they're putting on almost all of the new O-320s. I will have her back on Monday and hopefully I'll get a little reprieve on the maintenance issues.
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Since bog= lack of fuel. the "new " carb should fix the issue....
 
something was "un-fixed".....time to have the mechanic look it over again, he did something to it....specially if it didn't do that before he touched it.
 
My 0-360 does the same thing on my Cherokee, around 1300 ro 1500 rpm it hesitates. I've read from its normal to no its not. Even read a guy on another forum who put a new carb on it and...it still did it. Who knows...I'm told on mine its when the idle circuit switches over to the main jet(which happens in that RPM range). I have all new plugs, rebuilt mags, no induction leaks and the carb was over hauled in 06 and it still does it. Doesn't matter if I lean or apply carb heat either. So I take what my mechanic says and what Ive read just switching circuits. Hopefully your carb fixes the issue.
 
Ever since I posted this thread a couple weeks ago I've been told everything from its normal and safe to I wouldn't fly it at all. For what it's worth, here are the results of replacing my old 10-3678-32 with a brand new billet machined 10-5217 from AvStarDirect.

I've had the plane back since Sat and have logged 9.3 hours on the new carb. Not only did the problem go away but it's like a completely new engine. The throttle response is way better, the idle is better, pulling the mixture to shutdown is a nice quick spin up and then it powers off, and she seems to burn less fuel. I know it hasn't been the same situation for everybody but my issue is completely solved.
 
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