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Engine stumble

As everyone has said before, gotta love this website for its valuable database of information. My O-320-E series (160hp, higher compression pistons, now an experimental), also seems to suffer from the "Grumman Stumble". Very glad to learn that it's not just my airplane.

I'm interested in finding the pepperbox kit. Does any one have a link or information on where to buy the parts to convert my 5009 to and "N"? After a few hours of searching, I'm coming up fruitless.
 
Kit Info

I purchased P/N 666-813F from Marvel Schebler direct online. Total $150.00 but it turns out I had the pepperbox fuel nozzle. I am planning to return the nozzle and hopefully they won't charge a restock fee.

BUT what did I do and what was the result? This all started with a rebuild of the carb. Upon return of the carb I had the stumble and it would not lean - no temp rise at altitude. This forum had me go the pepperbox route. I choose to buy a new nozzle because the old nozzle did not have a PN on it so I did not know what I really had.

Once I rec'd the new nozzle I physically compared them as well as measured the fuel inlet and outlet. Results: OUTLET (old/new): .1265/.129, INLET (old/new) .094/.093. Reamed values of old: .128/.096. Test flight resulted in little change. Maybe a touch less stumble but still unable to get temp rise on lean. Leaning goes direct to rough running after a few turns.

Next move: I read where someone opened the INLET to a #38 (.1015) hole. Can anyone confirm this and the results? I was considering "sneaking" up on #38 one size at a time but that it too many carb removals for me.

Details on operation are here on Google drive, 2 pictures and pdf:
https://drive.google.com/drive/folders/1vlBDGropWMGFkVjShXNqUXAnWFUuFSSY?usp=sharing

Looking forward to comments.
 
More equal fuel distribution??

My O-320 E2D doesn?t exhibit the stumble described by the OP, but it won?t tolerate running much LOP at all (just gets rough, presumably as a result of unequal fuel distribution/mixture/power in the cylinders). Any reason to believe this pepperbox mod/upgrade will improve this situation?

Especially for those with experience with and without ? any benefits for LOP operation?

Peter

You can buy the pepperbox jets for around $150 and they're relatively easy to replace. There is a part # for a good replacement from Marvel, but I don't have it off hand. I wasn't having your specific problem, but did experience atrocious distribution problems and this replacement helped quite a bit.

Larry
 
Pepperbox mod

Pepperbox mod is PN: 666-813-F from Marvel. Includes the lockwashers, washers, etc. to replace the fuel nozzle.

Re: intake tubes... I did check for intake leaks and found one at the intake to head gasket. Repaired. I also have some RTV around the intake to sump connection and re RTV them as well. The did not bubble when testing for leaks. I did not thoroughly examine each intake, guess that will be next.
 
Mark,
I had a Grumman with the E2G engine that exhibited the same occasional stumble. I found 2 of the aluminum intake tubes cracked at the flanges that mate to the cylinders. I replaced them with the new style tubes that have reinforced flanges. Each cylinder has a different part #. Good luck.
 
High EGT

I bet it's a bad plug. High EGT is one plug not firing. The 'bump' is when it starts to fire and then the EGT drops to normal.

Randy, I found your post about a bad plug causing high EGT interesting. I've just started Phase I testing, 3 hours so far. #3 EGT runs 200F higher than the others. CHTs are all fine. At 3,000 OAT=55F, 23x23 cruise all EGTs run around 1165 except #3 runs 1432. It displays about 200F higher than the others. I don't detect any other issues and thought I placed the probe at a different distance from the head or have a bad probe.

But are you saying, I may have a spark plug not firing? Are there other symptoms of a bad plug?

I will check this.
 
I purchased P/N 666-813F from Marvel Schebler direct online. Total $150.00 but it turns out I had the pepperbox fuel nozzle. I am planning to return the nozzle and hopefully they won't charge a restock fee.

BUT what did I do and what was the result? This all started with a rebuild of the carb. Upon return of the carb I had the stumble and it would not lean - no temp rise at altitude. This forum had me go the pepperbox route. I choose to buy a new nozzle because the old nozzle did not have a PN on it so I did not know what I really had.

Once I rec'd the new nozzle I physically compared them as well as measured the fuel inlet and outlet. Results: OUTLET (old/new): .1265/.129, INLET (old/new) .094/.093. Reamed values of old: .128/.096. Test flight resulted in little change. Maybe a touch less stumble but still unable to get temp rise on lean. Leaning goes direct to rough running after a few turns.

Next move: I read where someone opened the INLET to a #38 (.1015) hole. Can anyone confirm this and the results? I was considering "sneaking" up on #38 one size at a time but that it too many carb removals for me.

Details on operation are here on Google drive, 2 pictures and pdf:
https://drive.google.com/drive/folders/1vlBDGropWMGFkVjShXNqUXAnWFUuFSSY?usp=sharing

Looking forward to comments.

Not following the thread, so not really a recommendation for your issues. On my 160 HP 320, I believe that I used either a 39 or 40 drill and if anything was a bit richer than necessary. I drilled it out before the first start, so can't say whether that stock jet size would have been adequate. Would not suggest you start at a 38 for 160 HP. This was on a -12 carb. From past research, no one stopped smaller than a 40.

Larry
 
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I had a Lancair with an O-320 that had a similar problem. The engine had been stored for years with preserving oil. It turned out to have a valve hanging up in the guide. I was able to ream the guides without removing the cylinders per a lycoming service bulletin.

The engine also idled much smoother at low rpm afterwards
, which I realized was another symptom. When it was hot I. Had to idle about 900 or above or it would stumble.

I don?t know if I?m helping, but this was my experience.

Tom
 
Randy, I found your post about a bad plug causing high EGT interesting. I've just started Phase I testing, 3 hours so far. #3 EGT runs 200F higher than the others. CHTs are all fine. At 3,000 OAT=55F, 23x23 cruise all EGTs run around 1165 except #3 runs 1432. It displays about 200F higher than the others. I don't detect any other issues and thought I placed the probe at a different distance from the head or have a bad probe.

But are you saying, I may have a spark plug not firing? Are there other symptoms of a bad plug?

I will check this.

When one of two plugs stops firing, it retards the effective timing and produces a resultant high EGT. I had a mag fail and saw my EGT's about 100-125* higher than normal. Best way to check for a dead plug is a mag check. When running on the mag or EI with the bad plug, you should notice roughness due to running on three cylinders and the EGT of the cyl with the dead plug will drop like a rock when you kill the mag with the one good plug. If problems are intermittent, mag checks can be conduct while flying.

Your spread is over 250* and I don't believe that a bad plug could bump the EGT that much. Mixture (i.e. intake leak or plugged injector) is possible depending upon how ROP you were running when observing these readings. Is this cylinder in question running a cooler CHT than the others? I would swap the questionable probe with another one and see if the problem follows it as a first step after confirming that probe is installed at the same distance as others.

Larry
 
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0320/E2G with 30 hrs SMOH. almost every flight it will momentarily stumble for a split second. It can best be described as a (bump). After that it runs fine the rest of the flight. It will only do it once. We changed both mags, wires, and plugs and it still does it. I cant figure out what could be causing this? The plane is going to Sun-N-fun which is 1000 miles one way. I would like to find out if this is a major issue or just an annoyance?

I had the same issue. Just cause I didn't know what else to do, I drained the carb and blew out the carb screen. Then I dropped the exhaust, put in new no-blo gaskets and retorqued. My split second stumble went away. Still not sure what it was....
 
No Blo gaskets?

How would the new gaskets help with this problem? I have been working this issue for 8 months. Last problem was a check of my EGT/CHT gage IAW testing guide from manufacturer and all checked ok. Except, the next flight saw 850F EGT and 275F CHT, both dropped from 1100 EGT and 325 CHT.

I am ready to pay someone to relieve the pain. Engine vibrates from 2100RPM up. More than a stumble now.

Dear supreme IA... send help now.
 
It sounds like

water in the fuel to me. Once the water gets below the pickup tube in the tank the problem goes away. The tanks are left partially filled and condesation forms. then comes the stumble, only one drop of water is all you need. Are your fuel pickup tubes riding on the bottom of the fuel tank? I don't know if it possible to get every drop of water out of a tank and if the tubes are resting on the bottom of the tank they may be vacuuming it up!
 
Perhaps rough running is a better description

This all started after a carb rebuild, 10-5009N (for Now). One the first flight after rebuild I noticed the stumble but now, 8 hours later it just runs rough above 2100RPM. Mag drop seems ok, I found an induction leak, and I doubt there is water in the fuel. 2400 on static run up and 2800 at WOT. Above 2100 the panel and stick start to shake some but seem fine on take off.

Wish I could just click my heels and poof! fixed.
 
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