I've been helping a new club member with an evolution 46 engine in an Avistar trainer. The engine ran -OK- in the summer, but won't run at high RPM in temperatures less than 20 degrees F.

I know it sounds crazy, but what we've discovered is the oil from the muffler appears to be plugging the pressure line.

Symptoms:
1) Engine initially tuned rich--leans itself to max rpm and then quits (in about 10-20 seconds)
2) Fuel quickly pulls back from the carburator as engine quits (indicating possible tank vacuum)
3) Disconnecting the lines from the carb and the muffler and blowing revealed a definite "plug" in the system.
--Blowing into the carb line (back into tank) would produce audible bubbles and an inflate fuel tank--(with fuel squirting out of the fuel (carb) line when mouth is removed)
--Blowing into the pressure line (from the muffler back into the tank) allows no air to pass
4) Blowing hard enough, you can clear the lines again. Nothing is visible except oil in the pressure line from the muffler.
5) The problem gets worse as the ambient temperature gets lower

Things we've checked:
--We've had the fuel tank apart at least three times. Replaced "smaller" ID aluminum tubes with "standard" brass tubing for the fuel and pressure lines going through the tank stopper and into the tank. Eveything else deemed OK by three experienced modelers.
--No obstructions in the tank--blowing hard enough will push the oil through the pressure line and allow smooth flow
--Reconnecting and running the engine redevelops the plugged condition again
--Ran three different fuels with the same problem (2xWildcat 15% from different batches and 1 Omega 15%)
--Had muffler apart--didn't see anything unusual
--Flushed the muffler and pressure & carb lines with fresh fuel

Has anyone else ever experienced this before? Could others with undiagnosed Evolution engine problems (in the cold) check and see if this might be happening?

Any advice is most welcome!

Thanks,
Doug

What temp are you storing your fuel?

Running engines below 20 degrees can be a challenge.

Sounds like (not sure) the castor is just too cold and thickening due to the chill. Then with the pressure line being exposed to propwash and flight airflow makes it even colder/thicker in the pressure line.

Not familiar with that muffler but if it resembles the standard 2-stroke mufflers on other engines it would sure make a great refrigerator in those temperatures. That cast aluminum will chill right through in a heartbeat and freeze anything on the inside.

I can see how this could occur. I have flown in all sorts of temps over the years and I have had the oil residue get real thick in the pressure feed into the tank, but I cannot remember it being so bad that the engine quit running. I would think that putting the pressure fitting on your muffler out of the direct exhaust port of the engine might help. Just a thought. Good Luck, Dave

Hi dwoolridge
On two or more occasions I have seen the small hole in the muffler plugged with carbon deposits. If yours is nearly plugged ypur condition could occure. Use a needle to clear out the hole. Let me know how it works out. These were not Evolution engines.

Is it possible to have the pressure outlet on the upper side of the muffler so not as much oil gets into the pressure line?

This is particularly endemic to the new engine.

It's not a fuel issue usually. I've seen it on practically ALL of the Evolution engines I've owned.

The new engine builds up a "sludge" from the metal bits coating the interior walls.

You see this as a greyish sludge in the exhaust ( everyone complains about this in the Evolution threads ) that disppears once the engine has had several gallons run through it.

That "sludge" in turn builds up exactly as you said, in the pressure fitting.

You could re-tap the muffler to install a larger fitting and pressure tube...

You can also just run it for a while, cleaning the fitting out after each flight until it stops happening with such frequency ( I check mine every trip out to the field ).

As stated, you can try to adjust the muffler so that the fitting is on top, to lessen the build up.

You could use a different muffler...

Anyone else have any ideas?

I don't have a great idea but an idea none-the-less.
Ditch the pressure line until the engine is ran in (or warmer weather comes) and use a fuel pump for now.(you can re-use the fuel pump in another model in the future if needed.)
http://www3.towerhobbies.com/cgi-bin...&I=LXDG61&P=ML

Thanks everyone for the replies. I really do appreciate ALL the thoughts and suggestions.

Just a couple of quick clarifications...
--Fuel Temp/cold muffler--We're flying other airplanes at the same time, same fuel storage conditions, etc, and no one has experienced this with other engines (interesting note... we don't have any other evolution 46 winter flyers for direct comparison)
--The blockage is occurring in the pressure line, not the pressure fitting screwed into the muffler
--We tried running it with the pressure line disconnected and it DID run consistently (too lean though). It didn't have enough draw, so the fuel pump idea sounds feasible
--The muffler's pressure tap is already on the upper side

I'm going to talk to the owner about a couple of the suggestions you've posted for me:
1) Disconnecting the pressure line and running a pump
2) Moving the pressure tap on the muffler closer to the engine exhaust (theoretically hotter & less viscous oil in the pressure line)

opjose: It is an engine with very little time on it. That makes me wonder if metal "sludge" could provide additional structure to the viscous (cold) oil, and be the root cause of the problem. I'll have to take a close look at the "exhaust oil" next time to see if there's evidence of metallic coloring.

If anyone has experienced this (especially with a new evolution engine), please let me know.

Thanks again and keep the ideas coming!
--Doug

Have you tried running some LARGE ID fuel tubing? could help and is (very) cheap...


Steven

If you go to the Evolution threads, you'll see everyone complaining about the "grey goo" that comes out of a new engine.

It's rather viscous. If it does not plug the fitting, it will collect in the pressure line as you've described.

You'll see less and less of it as time goes on.

By the time you have about 3-4 gallons through the engine in flight, you'll only need to periodically check for any gunk.

If you're getting gray goo in the pressure line, it's from the baffle in the muffler "fretting" or vibrating, and the wear particles are mixing with the oil.
One of the best things you can do with the overly restrictive Evo muffler is ditch the baffle. You will get more power, and none of the gray goo...and still have enough muffler pressure to the tank. It's only marginally louder.

I'm releatively new to engines so these are good comments. I have three Eval. engines. Two .46's and one.61. The "grey goo" exhauest has been common in all. The 1st .46 ran very well even with this condition. I checked with the dealer who also is a club pres. and he said it's ok. It eventually "froze" and wouldn't turn over. Disasembled, I found pieces of what looked like ceramic brown pieces...( constantly to lean of an adjustment?). The .61 ran fine on the bench, got it in the air and it surged when full power was applied... I already moved the tank lower than the carb. and it helped so I lowered it some more but was not dependable so now it's retired. I'm looking to put it into another plane...had it in a J-3, way to much power! The present .46 is in a Kadet trainer and I keep th adjustment so it doesn't run to lean like the 1st one may have done...it has less power in cold weather and still has the gray deposits but that has becoming less noticable there is now more of a thick castor oil deposit. I've changed over to O.S's for other projects. The Eval. is good to learn with. This thread doesn't really solve a problem just comments, but I'm picking up a lot of info. Will be checking the Eval. web site.
trumpteb

Eh, I removed the baffles on mine and it is still produced...

Though everyone agrees with you that the wear in particles are to blame.

Oh...that's very different...nevermind (anyone remember Emily Latella/Gilda Radner on SNL?)

If you still have gray gunk comming out of the muffler (w/ the baffles removed ) then it's either the muffler to exh. stack interface chafing, or...something substantially more serious.

Maybe pull the backplate and have a look?

Every Evolution I've had, does this when new.

I've pulled the back plate on each and the only thing I've seen is a bit of wear where the piston rod rubs against the backplate.

All of the Evolutions I've had, do this as those owned by other club members.

Once the engine is broken in this very very slight contact stops.

I'd imagine you could cure this with another back plate washer in place, but it does stop by itself after a few gallons.

I have the evo 46. and 10 years of nitro engine racing ,and repair experiance.
We have about 11 of these evo engines at our club, EVERYONE, of them has had the few tings in cmmon
1. they make ALOT LOT of very thick dark gooey exhaust for a while.
2. They all had to have the pin in the high speed needle removed so that for cold weather or real hot weather, they needed morerange of adjustment, but only about 5-6 clicks past the orriginal stop point.
3. we removed the baffles from most of them to only replace them right away because these engines are much more sensitive to fuel pressure than most engines,.... one would run OK, the rest leaned out alot and died immidiatly, and none of them ran any better, ALL ran worse.

SO i do not recomend removing that baffle, it wont help, not on this engine, and realisticlly, for more power via exhaust, do it right and get a tuned pipe if you gonna mess with it.

my suggestion is try larger fuel line first, if not larger, just replace it andalso check that the holes are VISIBLY clear.
I would try that, if it dont work try removing the stop pin on the high speed needle with a pair of needle nose, but only if you need to go farther and are currently running into the stop.

Seriously try the line first, It may not be a situation of a blockage but a leak?
The best way to see if the pressure is flowing in run it on the plane standing still at wide open, ON ALL of our evos the oil is in that line alot more than that of most engines, but it does visibly move thru that line while running. If it isnt moving that oil or is slows down as it runs then stops as it dies, it may just be a temperature thing. 20* is pretty cold, but i fly in 25-35 so... i dunno. Hope i helped. M

PROBLEM SOLVED!!

Short story...
Removed the muffler baffle and the vent line no longer gets plugged.

Long story...
The engine's owner had sent the engine back to Horizon where they replaced a bearing (inner race spinning) and did something else--a gasket or something. They returned it and said the engine was running fine.

The engine owner came out to fly Sunday (1/27/2008) when it was about 20 degrees F. We made sure the vent line was clear before starting the engine. We started the engine, it ran about 10 seconds at full throttle, leaned out, and stopped. The vent line was now plugged.

We cleared the vent line (blew hard) and removed the muffler baffle. We tuned the engine and got two flights in without a hiccup.

I hope that someone from Horizon reads this and can determine if there is a flaw in the muffler baffle design--especially for cold weather flying.

--Doug

Nope it's not the baffle.

It does the same thing with the baffle removed.

See the "Goo" posts above.

This will stop once the engine wears in, typically after a few gallons of fuel.