bsteckler

Neophyte questions to be sure. While flying yesterday, I noticed that the exhaust residue was darker that it had been previously. It seems that the engine has now completed the break-in phase as it can now be leaned and hold its setting. The power increase was also impressive. The question is whether this exhaust color is indicative of an over compressed engine, or if this is just about right. The engine did not sound labored.

Also, when I was attempting to remove the anodized portioned of the head (where the compression screw is located) the entire cylinder came off. No big worries there, but looking at the piston, I noticed a fair amount of carbon build up. Is this normal? Like the above question, does this indicate an over compressed engine, or is it a byproduct of burning kerosene?

Thanks - as always - for your time.

Jim Thomerson

I run commercial fuel, and expect a clear to honey colored exhaust. I suspect you were slightly overcompressed, but your engine is well run in and can take it. On my Cheetah 2.5, I start it by cranking the contrapiston in a half turn. then I open it a half turn and go fly. The exhaust is clear. One time I forgot to back it off, and could not tell anything different about how the engine ran, but it came down with fairly dark exhaust.

I started having carbon build up problems and broke some engines. I changed fuel brands and have not had any more problems. I had run the other fuel for years with good results.

gkamysz

My Feedback: (19)

The question burning in all of our minds now is: What fuel were you using and what did you switch to?

Jim Thomerson

I was running Davis fuels, I am now running Eric Clutton fuel and am on my fourth gallon.

eroc144

My Feedback: (1)

This is interesting. The exhaust from my previously owned PAW .09 and my converted Norvel .061 is almost always dark brown using the "other" fuel. These are my only diesels so this is what I've come to expect. Should I be expecting something else? I can't imagine backing off the contra piston a 1/2 turn - my RPMs would drop significantly.

EG

Jim Thomerson

My mention of 1/2 turn is engine specific. Other engines start OK at running setting. Still others need a slight tweak. I consider how the engine ran, as well as the color of the exhaust, when thinking about adjustment changes.

Hobbsy

My Feedback: (102)

Steck, the carbon is soft and migrates, it will have the same amount a year or two years from now.

AMB

It will clean out the excess buildup as Hobbsy stated its is softt not like burned hard castor you may get in a glow engine I would guess a little overcompressed and running a little rich
to compensate, my ivrine 40s with the factory or Davis head run very clean very little smoke or oil on davis ABC as a matter of fact I richened up a little because the exhaust had almost no oil comming out martin

gcb

EG,

It is a good idea, for the first flight of the day, to establish the running compression by letting it run for a couple of minutes to fully heat up, then adjust compression by backing off, then increase to peak. That should get you set for the prop, fuel, and atmospheric conditions of the day.

Of course this is just one way, and one opinion. [8D]

George

gkamysz

My Feedback: (19)

I think exhaust color is specific to the engine and even prop on a given engine. I ran an MVVS 1.5D recently and exhaust residue was very dark. The engine had a certain bark to it. This is the second one I've had. I had one 12 years ago which ran the same and had the same dark exhaust. The MVVS 2.5D was similar. I just ran a Norvel .074 conversion and the exhaust was was virtually clear. It probably needs some more run in time, but I don't expect much change.