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Power Interuptus

jetjok

jetjok

Well Known Member
I have been chasing a problem with my RV-6 that has me about ready to wish that Wilbur and Orville would have stuck to bicycles.
My plane has developed an intermittant power interuption that I believe is fuel related. I have diassembled the carburetor and found no obvious problems. The fuel system seems to be plumbed properly and fuel pressure is good with the engine driven pump. Keeping in mind the SB on the fuel pick-ups, but this problem occurs irrespective of the tanks being topped or at half capacity. I did check the tank vents and they are clear
I have pretty much ruled out ignition, as there is no improvement by switching mags. However, just to make sure I have checked the P-leads, and switch finding no anomolies.
My RV-6 was certified in 93' with a new O-360 and Hartzell C/S prop. All accessories were also new at the time. This plane has less than 100 TT, but all components seem to have weathered the long periods of inactivity.
The problem seems to be exacerbated once the engine has come up to operating temperature, and is most noticable if the engine has only been shutdown for a few minutes. Additionally, pre-takeoff run-up is fine, and it only happens under flight conditions.
One of the members of my RVators group advised me that Vans was familiar with this problem, and recommended a "Mooney Mod" to the carburetor, which fixed the problem. He did not elaborate on what the mod entails, and I was wondering if anyone here had some ideas, or experieince with a problem such as this?
 
100 hours total time since factory new engine?

OAT when this is going on? Any variations with OAT?

Fresh 100LL or a tank of gas from 93? or MOGAS ? :eek:

Where is your fuel pressure gauge tap from? Rock solid all the time?

Does it on either L/R tank?

Does it with the electric boost pump on or off?

Just a cough or momentary stumble or more?

Could be sucking air into the fuel line from a location after the tank but before the electric boost pump. Probably not after because you would find a leak. Not for sure on that because it is possible to suck in but not blow out.

If you can recreate the situation in flight on demand try leaning and see if that makes it go away or makes it worse.

Do you have 4 CH cht / EGT ?
 
93? Did you slosh the tanks? There has been more than one plane have problems from that stuff coming loose.

Edit... I was thinking more about your problem and can't get the slosh thing out of my mind. You are in the right era for that stuff and it just makes sense to look further if you have it in your tanks. After a quick google search it is obvious that there is a lot of info out there to read on this problem. Here is a link to on site that I found that shows the stuff peeling, and it also links a Van's article regarding peeling slosh. Have you seen any small white particles in your fuel drains or gascolator?

http://www.evansaviationproducts.com/Slosh.htm
 
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I incorporated the "Mooney" Mod

I was fighting a Lycoming timing problem on LASAR equipped new engine drop shipped direct from Lycoming with Test Cell run sheet and I was working with Lycoming (WORTHLESS FACTORY support)- GREAT WEST COAST field representative support), Unison (GREAT tech support engineer then) and Precision Airmotive. In the process the man I talked to at Precision said Van specified the lean version of their carburetor at the time you and I bought our engines. Since that time Van has changed to the rich carb that Precision had recommended in the first place. I bought the mod kit and installed it. It had nothing to do with my problem of course but it has not hurt anything as far as operation is concerned. I bought the manual from Precision Airmotive for overhauling the carburators with all the variations and part lists for several hundred dollars to be sure I set everything correctly as I completed the mod. The situation is very foggy as far as I can see with respect to Precision Airmotive. They were stoping the manufacture of carburetors and after some panic in media I heard another company was taking over manufacture and support of them. Good luck with your search - I know how frusrtrating it can be. All I can say in support is there is no down side of the "Mooney Mod" that I am aware of.

Bob Axsom
 
Old Hoses?

Mark, did this problem exist when new, or start several years later? If later, I'd replace all flexible fuel hoses, as they do deteriorate with age. Best wishes.
 
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Mark, I completed 2 RV-6s in '93 and I would have to agree with the 2 posts that mention slosh compound and fuel hoses. Back then almost every RV had slosh in the tanks and the fuel pickup was made by cutting slots in the pickup tube with a hack saw. If the slosh comes loose, which it commonly does, it can easily wrap around the tube and cut off the fuel supply. Typically fuel hoses have a 5 year life whether in use or not. If these are original, get them changed. I would also remove the pickup tubes and inspect them. While that plate is off, check out the interior of the tank for loose slosh.
 
100 hours total time since factory new engine? Yes

OAT when this is going on? Any variations with OAT? - Seems to be worse when the engine is hot. The worst "burp" so far has occured about 3 minutes after T/O (24"/2500) when the aircraft had sat with a hot engine for about 10 minutes

Fresh 100LL or a tank of gas from 93? or MOGAS ? :eek: Ahh...Yeah, fresh gas. 100LL. No MoGas in this plane!

Where is your fuel pressure gauge tap from? Rock solid all the time? - Fuel pressure remains steady, and it is tapped from the inlet of the carb.

Does it on either L/R tank? - Yep

Does it with the electric boost pump on or off? - Yep

Just a cough or momentary stumble or more? - Momentary

Could be sucking air into the fuel line from a location after the tank but before the electric boost pump. Probably not after because you would find a leak. Not for sure on that because it is possible to suck in but not blow out. - I agree with you that I should see a leak, but will check fittings anyway

If you can recreate the situation in flight on demand try leaning and see if that makes it go away or makes it worse. - It did it a couple of times with the engine leaned out at about 21.5/2300, enrichening the mixture did not help.

Do you have 4 CH cht / EGT ? - Yes, but I have not be able to see a difference as it is just so momentary. Additionally, I have to admit that I have found it hard to continue a normal scan with the cold trickle of sweat running down my back and the wool of the seat firmly clenched, well you get the idea!

Thanks for the ideas and I will continue to search. I hope to **** it is not the sloshing compound as suggested in the other messages!
 
Mel, Thanks for the additional information. When I got the plane last year, it had a very rudimentary gascolator that really did not provide any filtering of the fuel. I have changed that to the newer Vans gascolator, and will open that up today to check things out.
Additionally, it is almost time for the conditional inspection, so I would be opening up the wing roots anyway. You are right that pulling and inspecting the pick-up tubes should be accomplished.

I have long range tanks in my RV (28 ea side) and you can't really see much from the filler.

Thanks!


Mel said:
Mark, I completed 2 RV-6s in '93 and I would have to agree with the 2 posts that mention slosh compound and fuel hoses. Back then almost every RV had slosh in the tanks and the fuel pickup was made by cutting slots in the pickup tube with a hack saw. If the slosh comes loose, which it commonly does, it can easily wrap around the tube and cut off the fuel supply. Typically fuel hoses have a 5 year life whether in use or not. If these are original, get them changed. I would also remove the pickup tubes and inspect them. While that plate is off, check out the interior of the tank for loose slosh.
Click to expand...
 
Had a similar problem recently although with different equipment - see http://www.vansairforce.com/community/showthread.php?t=27669

I can relate with your level of frustration. I am still not sure if I have cured my problem, as I have only now just started to fly again after meticulously going through my fuel system and having my ignition system gone over by the manufacturer - but so far, so good.

I can say that I found a very small leak in my fuel system between the fuel tank selector lever and the exit hole to the wing tank that may have been sucking air into the system when operating. The leak was high enough up and/or small enough that I never saw a single drop of fuel from it inside the fuselage. I suspected it was there becauase when I left the canopy closed for a significant period of time, I typically smelled fuel when I first opened the canopy, but it quickly dissipated. Anyway, I found the tiny leak by making sure the fuel tank caps were sealed, then pressurizing the tanks slightly through the fuel tank vent lines using a bit of tubing, a bicycle pump and the valve cut from a bicycle tire innertube. Pressurizing the tanks forced the fuel through the supply lines into the cabin, pushing a bit of fuel out the leak area so I could finally see it. This didnt happen when the engien driven pump and/or boost pump were operating, because they were SUCKING the fuel from the tank rather than pushing it. FIxed the tiny leak, and at the very least, no more fuel smell. Im no expert, but it seems possible that previously I was sucking a small amount of air into the system and perhaps at some point a bubble went through causing my hickup. Something to consider anyway.

Hang in there

erich
 
I'm no expert here so feel free to shoot me down, but the fact that this happens more with a hot engine and the mention of a "rudimentary gascolator" sounds like vapor lock could be involved. Have you investigated that possibility?
 
I am definitely considering vapor lock! On that note, I have another question:
The builder's manual does not call for or show a cooling shroud on the engine driven fuel pump. I have seen them on other planes using the same type of pumps. Has anyone ever had the need for a cooling shroud, and if so where can they be purchased?
I looked at the Van's site, but the pumps and shrouds seem to be for the injected engines.


jmartinez443 said:
I'm no expert here so feel free to shoot me down, but the fact that this happens more with a hot engine and the mention of a "rudimentary gascolator" sounds like vapor lock could be involved. Have you investigated that possibility?
Click to expand...
 
There's a reason Lycoming says 12 years max between overhauls. This engine has been sitting around for 15 years and stuff is beginning to deteriorate.

I'd be cautious flying this beast.
 
Check your primer?

This probably is not your problem here, but simple to check just in case. In my plane, the gascolator primer top input line is not filtered and some **** entered the lines and got stuck at the primer plunger location. As a result, over time my primer was not closing properly, and the engine was sucking in extra fuel to the cylinders causing an over rich condition at certain times. I checked everything, including the carb and couldn't find a problem. Finally took the primer apart, cleaned it, and the problem was solved.

Walter
 
David,
I totally agree with you that there is a reason that Lycoming is now calling for a 12 year maximum between overhauls. I would bet that if one researched it, you would find that it came from risk management, not the engineers. Probably the same reasoning that forced me to throw a perfectly good set of wing struts for my PA-20 in the trash a few years ago.
Thank you for your admonishment to be cautious with "this beast" and I assure you that I have. Oil change oil at 25 hours,having only burned about1.5 qts in that time. Oil analysis indicates that all is well and compressions are great.
At this point in time I am not concerned about the engine itself, but the accessories attached to it! It is a problem of not getting fuel (possibly ignition, but I think not) that is causing the problem. Tearing the engine down to measure parts is not going to cure this problem.
MarK

There's a reason Lycoming says 12 years max between overhauls. This engine has been sitting around for 15 years and stuff is beginning to deteriorate.

I'd be cautious flying this beast.[/QUOTE]
 
David-aviator said:
There's a reason Lycoming says 12 years max between overhauls. This engine has been sitting around for 15 years and stuff is beginning to deteriorate.

I'd be cautious flying this beast.
Click to expand...

Did you miss the part where he said 100 hours Since Factory New?

This engine was built Pre-Lyc outsource.

http://www.prime-mover.org/Engines/Lstrike/index.html

Barring any "cause", to split that case based only on the "12 year limit" would be insane. Now if you were talking Subie and a "1 year limit" I would agree with you all the way. :D
 
Look at carb...

jetjok said:
.....
At this point in time I am not concerned about the engine itself, but the accessories attached to it! It is a problem of not getting fuel (possibly ignition, but I think not) that is causing the problem. Tearing the engine down to measure parts is not going to cure this problem.
MarK
.....
Click to expand...

Mark... do you have a good carb A&P guy nearby?

Of all of the accessories, this would seem to be the one to go after. If you can speak directly to the "guy", you can ask for an "inspection" rather than a complete overhaul. I think having an expert look inside it would be useful.

Something flaky in the needle valve assembly or accelerator pump could cause the symptoms you describe.

Having two magnetos should rule out ignition problems...

gil A
 
asav8tor said:
Did you miss the part where he said 100 hours Since Factory New?

This engine was built Pre-Lyc outsource.

http://www.prime-mover.org/Engines/Lstrike/index.html

Barring any "cause", to split that case based only on the "12 year limit" would be insane. Now if you were talking Subie and a "1 year limit" I would agree with you all the way. :D
Click to expand...

No, I did not miss that part. I was referring to the accessories and should have said so.

I know of one 0-320 that is beyond 20 years since OH and running fine. But carb seals, intake pipe connectors, mags, fuel lines, primer o rings - all have a life span. Fuel line rubber in particular can be a real head ache.

No, I wouldn't spit that engine either. :)
 
Mooney mod is a modification to a 10-3878 carb to change it to a 10-3878-M. It makes the carb slightly richer and also helps a little bit with fuel distribution. Other O-360 carbs 10-4164-1(exact same thing as a 10-3878M) and 10-5193 already incorporate the mod. So if you have a 10-3878 it is worth doing if you have an intermittent miss. You will have a slightly richer fuel burn at full rich after it is done but the intermittent miss should be eliminated. One of the classic symptoms of needing the mod on a 10-3878 carb is an intermittent miss in cruise that is worse when hot and is also sometimes but not always caused by starting to lean or enrichen the engine or by starting to activate or turn off the carb heat.
If you have one of the other part number crabs, the mod is already incorporated.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Gil,
Yeah, I do have a guy. I am heading to the airport today with a long list of items to accomplish:
1. Remove Carb and take it with me to CA tomorrow for inspection, and possibly incoporate the mods referenced in Mahlon's post.
2. Check fuel flow at the carburetor. (Vans recommendation)
3. Drain fuel. Check interior of tank for loose sloshing compund (please God, no!)
4. Order new style fuel pick-ups and blast tube material (cool fuel pump) from Vans.
Thanks to all who have taken the time to chime in on this! I will post up when I finally get this problem solved.
MarkO

az_gila said:
Mark... do you have a good carb A&P guy nearby?

Of all of the accessories, this would seem to be the one to go after. If you can speak directly to the "guy", you can ask for an "inspection" rather than a complete overhaul. I think having an expert look inside it would be useful.

Something flaky in the needle valve assembly or accelerator pump could cause the symptoms you describe.

Having two magnetos should rule out ignition problems...

gil A
Click to expand...
 
Might also check for a broken or weak valve spring...
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
Update

Thanks again to all who replied on this situation. The carb is off and will be cleaned, inspected and updated as necessary.
The fuel system apears to be clean with no contamination (loose sloshing), and flows good to the carburetor. Fortunately, I have a fiber optic borescope with a 3 ft probe. I was able to inspect the fuel tanks, without pulling the pick-up access panels. The tanks are sloshed, but the sloshing compoound appears to be adhering well. I will certainly make that an inspection item on every conditional inspection. Just to be on the safe side, I have ordered the new pick up tubes with the screens, and replace the old ones. This will also allow me to accomplish the SB on the pick up tubes.
 
May not be applicable, but I'd hate for it to be the problem and me not bring it up! This sounds very familiar to a problem I had with a car years ago. I rebuilt the carb only to find out it did nothing to rectify the problem.

Don't remember why, but I wound up changing the fuel filter and that turned out to be it.

Anyway... for what it's worth. Good luck!
 
Carb Mod

This Carb mod is detailed in Marvel Schebler S/B A11-62, however I'll be darned if I can find it. Using internet search engines only leads me to links that say; if you have a 10-3878 carb and your engine runs like your roto-tiller, accomplish S/B A11-62.
Does anyone have the details on the changes called for in this S/B? I know that it calls for changing the fuel nozzle, but not the parts required to do it.
Most are probably aware, but another company has picked up the Precision product line, and we will soon have parts and information available!
Mark

mahlon_r said:
Mooney mod is a modification to a 10-3878 carb to change it to a 10-3878-M. It makes the carb slightly richer and also helps a little bit with fuel distribution. Other O-360 carbs 10-4164-1(exact same thing as a 10-3878M) and 10-5193 already incorporate the mod. So if you have a 10-3878 it is worth doing if you have an intermittent miss. You will have a slightly richer fuel burn at full rich after it is done but the intermittent miss should be eliminated. One of the classic symptoms of needing the mod on a 10-3878 carb is an intermittent miss in cruise that is worse when hot and is also sometimes but not always caused by starting to lean or enrichen the engine or by starting to activate or turn off the carb heat.
If you have one of the other part number crabs, the mod is already incorporated.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
Click to expand...
 
One last thought if you still have problems...I found a piece of metal grunge in the diaphragm of the engine driven pump that caused fluctuating pressures...leading to engine stoppage unless the boost pump was turned on...this was an intermittent issue that I finally resolved when I tore the fuel pump apart and found the offending piece of metal lodged in it...
 
very old post but I'd be curious to know how it ended? I have a very similar issue going on... and I do have the "original" 10-3878 carb setup. I'm wondering if I should switch to the 10-4164-1 nozzle + economizer setup ??
 
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