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My engine hesitates -- need ideas

D

dwilson

Well Known Member
I have a carburated O-320 B2C in my 9A. I have nearly 300 hours on it and it works great except that when I advance the throttle it "hesitates" or "stutters" between 1150 and 1200 RPM. If I advance real slow I don't notice it.

Using one mag and one LightSpeed electronic ignition.

We have checked the accelerator pump and the intake manifold and they seem to be fine.

One other symptom: When leaned out at 8000 feet WOT runs great, but if I pull the throttle back engine stumbles noticeably for a second.

Does this sound familiar to anyone?

Thanks,
Duane
 
dwilson said:
I have a carburated O-320 B2C in my 9A. I have nearly 300 hours on it and it works great except that when I advance the throttle it "hesitates" or "stutters" between 1150 and 1200 RPM...
Click to expand...
My O-360 has always done this (9 years). I swapped carburators early on but it did it with the new carb also.

Strange thing is that it actually doesn't do it anymore because I have adapted. I no longer advance the throttle fast enough in the relevant RPM area to get the behavior. I'm sure it is still there if I look for it though. It has never been an actual problem.
 
1 piece venturi carbs started doing this, it's nothing to be alarmed about. Our brand new Precision carb doesn it on the O-360.
 
My 0-235 does thisl

My O235 in my Lancair does this. Lots of work including new mags and rebuilt carb did not help. I've come to think of it as normal.
 
engine burp

My -3 has done it for 20 years. I've re-built the carb 2 times, it still does it. :eek: My engine came out of a Tri-Pacer, and I talked to a RV owner who had the same type engine also from a Pacer, and he has the same problem. Now I just take it as normal operation. :D Where did your engine come from?:rolleyes:

Mike Bauer
RV-3 N87LB flying
RV-4 N742MC on the gear!!!!
 
Engine from AeroSport Power

Where did the engine come from?

I bought it from Bart as a rebuild of one that came out of a Robinson helicopter. It has been flawless for nearly 300 hours, except for this one little thing.

Yes, I did check the accelerator pump.

Thanks for all the input. I really appreciate it.

Duane
 
My O-360 did this and I finally diagnosed it, !

A while ago, I posted the same problem. Mine would stumble and miss a few cycles. It would usually do it only on take off at high RPM. After having our ace A & P go through the entire engine, we traced it down to the mechanical fuel pump. Even with the boost pump on, I would see 5 PSI of fuel pressure, so I thought things were getting into the carb. I guess not. Here is what I found when I tore down the engine.

1. The fuel pump was old and came with the engine when I got it. The mechanical arm on it would press about 1/3 to 1/2 way through its stroke before it would actually do any pumping. When the new fuel pump arrived from ASSCO, it would pump at the top of the stroke.
2. When I pulled off the pump, I noticed there was no rod in the back cover to press down the arm. Some idiot who rebuilt the engine at the overhaul, put the rod in upside down-- probably too lazy to remove the rear cover after it was already on, and he just installed it with the ball on the bottom side. Of course this meant pulling the pan, removing all of the accessories, and pulling the back cover. A good time to check everything anyway. All checked out OK and I installed the rod correctly.
3. This led us to surmise that the pump at a 1/2 stroke was blocking the fuel from the electrical boost pump from getting through. Not sure if this is the exact answer, but after buttoning everything back up and retiming the mags, it doesn't do it anymore. Maybe this helps. Might be worth to pull the fuel pump and checking it out. Just a thought. Roger.
 
Revive this thread

All,
This thread came up when I did a search on a problem I am having with my newly flying 0360-A3A. Since the thread is 3 years old and has some conflicting posts, I thought I would ask for some updated replies.

Just like the original post, my engine hesitates when I add power for the take off roll. I also noticed it once at 3000 ft (D.A probably 5300') when I was adding power. When it happened at altitude I also noticed the fuel pressure down in the 3.2 range (on the ground at idle my fuel pressure is around 6.0). In the air, after I added power (and turned on the electric fuel pump) the pressure slowly (over a minute) built back up to the upper 5.x range.

Some additional (maybe unrelated) info... The engine was built about 3 years ago by Penn Yann Aero and now has about 3 hours of flight time and an accumulated ground run of an additional 1 - 2 hours. I am not using any oil to speak of. But, I am also not convinced I am developing full power. I have a Catto 3 blade 76" pitch prop and only get around 2120 on take off roll. I have had it up to about 2450 rpm at a D.A. around 5300'. I checked the throttle control and it is throwing the carb lever full up against the stop. The aircraft is an RV8A with no wheel pants or gear leg fairings.

Thanks for any comments.
 
The stumble you describe around 1200 is pretty normal - it's where the transition takes place from the idle circuit.

The stumble at altitude is a little different. From the message, I can't tell if you throttled back then up through the 1200 range or if you had a stumble at a higher RPM. The fuel pressure you're getting on the mechanical pump is probably sufficient. (The TCDS for an O-320 is a minimum of .5 PSI.) So, if you're getting a stumble at higher RPM, it may very well be the two observations are not related.

As you describe the power issues - first thing I would probably do is to check the Tach at low and high RPM.

You could call Penn Yan - I've had pretty good luck when I've worked with them.

Dan
 
hesitation issues

1st let me say that in spite of it being a common squawk that lots of folks have had to learn to live with hesitation, stumble, bogging ect is not normal. The reason a lot of people live with it is that it can be very tough(read expensive) to isolate and fix. The previously posted link to Sac.sky-ranch covers the possabilties quite well. In my experiance the no.1 most likely cause is a fuel issue. This is were I would start. Make sure you have proper pressure and flow to the carb, make sure the part number (not model number)carb installed is correct for the engine, make sure the finger screen in fuel inlet is clean and in good condition, check for any leakage as indicated by stains, check idle mixture setting, at 800ish RPM a slow (3 sec.)pull to idle cut-off should produce a 50-75 RPM increase folowed by shut-down, and finally check for correct carb float and float setting. If all checks out ok and you still have a problem check and see if the one piece venturi AD has been performed on that carb. If so borrow a carb that it has not(still two piece venturi or manufactured new), install and test. If this fixes your problem either have your carb rebuilt with a new tempest venturi and main jet installed, or buy a new tempest carb. I have found this squawk is commonly caused by a low quality one piece venturi and/or mismatched venturi/main jet in rebuilt carbs. Some engines will require a richer main jet when using the one piece venturi. Lots of good info relating to carbs @ www.msacarbs.com Good luck, Russ
 
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apatti said:
When it happened at altitude I also noticed the fuel pressure down in the 3.2 range (on the ground at idle my fuel pressure is around 6.0). In the air, after I added power (and turned on the electric fuel pump) the pressure slowly (over a minute) built back up to the upper 5.x range.
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My O-360 carbed engine and fixed pitch prop 6A will have the fuel pressure perhaps below 1 often. Noticed that today at 11,500' in the mountains. I don't worry about it anymore

But, I am also not convinced I am developing full power. I have a Catto 3 blade 76" pitch prop and only get around 2120 on take off roll. I have had it up to about 2450 rpm at a D.A. around 5300'. I checked the throttle control and it is throwing the carb lever full up against the stop. The aircraft is an RV8A with no wheel pants or gear leg fairings.
Click to expand...

Add wheel pants and fairings
 
AK4x4 said:
....., make sure the part number (not model number)carb installed is correct for the engine, ...., Russ
Click to expand...

But Russel, the Lycoming manual shows multiple carbs for several engine models.

As an example, the O-360-A1A shows both a 10-3878 and a 10-4164-1 carb. as acceptable.

The MSA carb link you show adds a 10-5193 and doesn't mention the 10-4164-1. Lycoming says this is OK on an -A4M, but my catalog may not be up to date.

I's sure the major differences are in the jet sizes and they have been optimized for different airframes. How do we really know which one is best for RVs, remembering that the carb. part number should match Lycomings documents if you want the 25 hr Phase I time?
 
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The same engine is in the Cherokee I rent. It's placarded against opening the throttle too quickly -- no quicker than 2 seconds between idle and WOT. Believe me, you will learn the need for this if you have to do a go around. :D
 
carb

For the 0 320 carbs the higher the part number the later the model of the carb. The single piece venturi is a known problem, so instead of tearing the fuel system apart, why not start with a known problem. The single piece venturis have manufacturing flaws that cause many of the problems mentioned above. Instead of spending $100 or more on a new venturi, the roughness, etc in the bore of the venturi can be polished out. If you don't want to do this yourself contact TerriLee Bell at Aircraft Fuel Specialists in Hagerstown MD. You can also find a lot of information on the yahoo Lycoming forum
 
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