Engine problem - suggestions + support needed

Captain Avgas said:

I suspect that what you are proposing to do will be illegal so it might not be such a good idea to advertise your intentions on a public forum. Nor would it be a good idea for other builders on this forum to encourage you as any subsequent accident resulting from illegal maintenance may reflect unfavorably upon the Experimental Category at large.



I just hope that your learning experience is not an unpleasant one.

Click to expand...

Actually Bob I don?t think anyone is proposing anything. Education and Knowledge is safety. And the knowledge base from this forum is worth is weight in gold.

Hey guys. I was finaly able to go to the hangar today.

I spent the entire afternoon there and came back home at 7pm, with an empty stomach, but with a great deal of knowledge aquired.

I went there with intention of geting rid of the problem... so, a lot of things have been checked meticulously.

-Gascolator (drained)
-Fuel lines
-carb + hardware
-fuel tank cap seals
-Intake hoses + clamps
-primer line
-Carburator rod + butterfly
-Air filter
-air box + support plate / cleaning
-etc.....

Here are the reason why my engine had stumble and hesitation:

#1 - Fuel contamination.
#2 - Debris in carburator

Check picture of the water drainded from the gascolator and the debris picked up in the carb sump during drain.

Put everything back togueter, re-installed both cowlings (alone! ) and did a test run. (temp -4 deg c / dew point -7 deg c / hum. 77%).

Oil temperature came up quickly - as expected with both cowlings in place. Idle, 1700RPM mag check and 2000RPM test went great. Engine now perform as expected.

I'll make an drain extention for my gascolator that I'll poke under the lower cowling - so I can drain it before each flight. If you guys have pictures of a similar setup - I'd like to get inspired!

I didn't had enough time but next time I take off the lower cowling, I'll clean up the screen at the entrance of the carburator - I've been told it would be a good idea to do it once a year... If you guys have instruction on how to do it, I'd like to hear you. I guess with the carburator manual, I should be OK too... we'll see...

There you go, one problem solved, for now!

Good news indeed

Glad to hear you found the problem.

Thanks for reporting back.

Make the next flight close to the airport for a half hour or so....

I'm very hesitant to believe that was your problem. The gascolator can be nearly full of water and the engine will still run correctly. The junk you found in the screen is minimal.

rocketbob said:

I'm very hesitant to believe that was your problem. The gascolator can be nearly full of water and the engine will still run correctly. The junk you found in the screen is minimal.

Click to expand...

Well, the engine ran beautifuly... and didn't show any signs of hesitation.

I also think there might be other factors - but for now, I checked all main "problem sources" and this is what I found.

I still haven't heard back from Van's about the 10-4164 carb settings. I'll wait untill I have more info on this before doing anything as my engine/carb were performing flawlessly before. I'd be stupid to change something that works great.

We'll see.

10-3878

For what it is worth, I have an O-360-A1A off a 1958 Mooney M20A and it has a 10-3878 Carb.

Thx for the info Robert. I guess you're not the only one too?

Just wanted to post a quick update on the engine. Went for a flight yesterday afternoon. Engine performed great, no hiccups at all.

Not to rain on RocketBob's parade, but I've been flying my RV8 with an O-360 and 3878 carb for close to 400 hours now without any hesitation problems. The RV6A I built and sold a few years ago also had the same engine and carb(3878) and also never stumbled!
Just my experience.

was it a straight up 3878 or 3878 "M"? 3878M is the same as 10-4164-1.

Two summers ago a friend of mine brought his Cherokee 180 over to see if adjusting the idle mixture would cure the stumble on a freshly overhauled engine. It had the 3878. We fooled with it for an hour or so and couldn't get it to run any better, so I told him to send the carb back. He did and a few days later reported that the carb shop fixed it. Was it modified to the M? Have no idea. It could be as simple as setting the economizer.

rocketbob said:

was it a straight up 3878 or 3878 "M"? 3878M is the same as 10-4164-1.

Two summers ago a friend of mine brought his Cherokee 180 over to see if adjusting the idle mixture would cure the stumble on a freshly overhauled engine. It had the 3878. We fooled with it for an hour or so and couldn't get it to run any better, so I told him to send the carb back. He did and a few days later reported that the carb shop fixed it. Was it modified to the M? Have no idea. It could be as simple as setting the economizer.

Click to expand...

Ok Ok I'll look to see if it's an "M"!

rocketbob said:

was it a straight up 3878 or 3878 "M"? 3878M is the same as 10-4164-1.

Two summers ago a friend of mine brought his Cherokee 180 over to see if adjusting the idle mixture would cure the stumble on a freshly overhauled engine. It had the 3878. We fooled with it for an hour or so and couldn't get it to run any better, so I told him to send the carb back. He did and a few days later reported that the carb shop fixed it. Was it modified to the M? Have no idea. It could be as simple as setting the economizer.

Click to expand...

I'm not sure if this is relevant yet, but here goes. When I started building my -6 in 2000, I came across a good deal on a rebuilt 0-360 from Bart that was a first time overhaul, so I bought it. After I had flown my -6 for a while, I decided I could afford a new roller tappet engine so I ordered one from Bart. Yup, I kept the old carb which was a 10-3878. Even with the old engine, I noticed on occasion a slight stumble when reducing power from T.O. to climb or shortly after. Well, sure enough, the stumble transferred to the new engine, but only on occasion. I wasn't sure at first that it wasn't an ignition issue, but over time I eliminated that possibility. Finally I got fed up with the stumble and called Bart. He said, send me the carb I'll bring it up to a -M status. I noticed, too, that all the newer engines coming out of Bart's place around here were of the 10-4164-1 variety. What the -M does is change out the nozzle assembly and increases the economizer output a little, same as the 10-4164-1. The result is a richer mixture in the economizer range, i.e., when not at WOT. As Bob J. said, this is the correct carb for the O-360 engine. By the way, Bart said the parts retail around $200 to get this done. I'm sure he'll do better than that, though.

Right now I'm waiting to get my carb back from Bart and when I do I'll report and changes.

Pat, go ahead and report back any difference.

Thx

Got my MA4-5 carb back from Bart LaLonde today. He brought my 10-3878 p/n up to a -M status and installed the new float kit, p/n 666-1002-F. Turns out I had the old white plastic floats which definitely needed to be changed. I guess if you have the brass floats you can carry on, but the latest floats are the composite (blue) ones. Also known as "foam floats."

Went flying late today and all I can say is that I did not get a stumble at all, felt very solid, but only time will really tell if this fixed the problem. I suspect that it has.

Just updating this post today (6-25-14): I have had no stumbles since upgrading my 10-3878 carb to the -M mod status over two years ago.

Just an FYI... brass floats can be repaired easily.

If I'm counting right, Marvel has had 4 float changes since 1964.

Epoxy Floats

This video covers the history of the float progression in Marvel-Schebler carburetors and why they got to the current epoxy floats. Interesting...

http://www.youtube.com/watch?feature=player_embedded&v=2RCcgwXsMG8

P.S. What is confusing the issue, I think, is that sometimes the new epoxy floats are referred to as "foam floats" when they are really not. The following Marvel Service Bulletin covers all of the different hollow and foam floats that are not approved and have been replaced with the blue epoxy floats.

http://www.msacarbs.com/pdf/SB-2_B_RPLmnt_of_Foam_and_Hollow_Floats_062209.pdf

Scroll down to the bottom of the SB and you'll see pictures of each kind.

Interesting info on those floats, Thx for sharing.

Now, since I never actualy removed the carb on my plane, is there a way to quickly check the type of float we have in our carbs if we're unsure?

Or we have to take off the lower bowl section to get access to it?

Any hints would be apreciated.

lockeed said:

Interesting info on those floats, Thx for sharing.

Now, since I never actualy removed the carb on my plane, is there a way to quickly check the type of float we have in our carbs if we're unsure?

Or we have to take off the lower bowl section to get access to it?

Any hints would be apreciated.

Click to expand...

There may be a couple of ways to check without tearing into the carb. Look on the nameplate and see if you have an I.C. number of 15 or higher or if the letters "FF" appear. This would indicate you have the new epoxy float, p/n 30-862. These floats have been in production since 11/2005 so if your carb is older than that, you probably have the old floats. See Precision Airmotive Mandatory S.B. # MSA-13:

http://www.msacarbs.com/pdf/MSA-13.pdf

More than likely you have an older float, however I don't think this is your problem. But it certainly is something you can do to bring your carb up to date.

If your part number is 10-3878, I would have it modified to the -M status, see Marvel-Schebler Service Bulletin #A-11. This can be done in the field by an A&P with kit # A666-660, according to the service bulletin.

Here's a quick picture of the carb tag.



As for the engine/carb, everything is working perfectly now. No more hesitation. Not a single hiccup since inspection and gascolator/carb drainned.

I'm still very hesitant to switch my carb to an "M".... as it just performs flawlessly now, as it always did before. I feel like I'm trying to fix something that isn't broken...

I'd love to be given hard facts about why the "M" is supposed to be better for RV's. I know it's richer, but why being richer would equal "better" most of the time?

Data Tag

Its been a while but I believe the MF = metal float and the V= one piece venturi.

I agree, if you don't have any further issues, you could just wait until the next time the carb is in for maintenance and get the two S.B.'s done then. You might check to see if you have any paperwork from the overhaul done in Alabama or give them a call, if you haven't already.