Rough running...hot gasoline? Vapor lock?

[bvolcko38]

My past few flights, few and far between lately due to poor weather, I get very rough running after initial climb 3000' agl 3800' msl. I attributed it to hot gas, 90 octane non ethanol. This is because if I put the nose down and dove somewhat the roughness would go away until I leveled off again. Egts and Chts were good.
Now here is the puzzler. Yesterday I climber to 4000' and throttled back to 1500 rpm to thermal, engine rough. Lift was good so I shut off the fuel them the ignitions, then thermaled up to 5000'. Life was good. Then the clouds and the lift departed to the south. I'm still in phase I testing so I didn't follow the lift. I glided back to the airport and at 500' above pattern alt I did a restart. By this time the chts and egts were off the scale low. Engine ran very rough like the gas was hot. I leaned it, I richened it to no avail. Landed and taxied back to the hangar all the while engine was very rough. Its been getting worse. Last week I retorqued the heads and adjusted the valves. Today I am going to do a compression check. I am stumped.

BV

[Sonex1517]

Bill

I had a very similar issue with my AeroVee and AeroInjector. I had to re-tune my AeroInjector to resolve it, and slightly peen the threads on the adjustment for the needle to prevent it from moving.

You may have a different issue, not sure.

[tx_swordguy]

pull plugs and see what it looks like (rich,lean) It may be ignition related, timing. Or as said above you might need to retune the carb. One thing you might try is lean it as far as possible for idle and slowly bring in trottle until it stumbles. If it stumbles immediatly you are as lean as you can get. If it takes most of the throttle range to get it to stumble or it never does and possibly runs better as you throttle up than it may be too rich and you have to either lean the needle or switch to a leaner needle

[bvolcko38]

Something is going on with my engine. Ever since my first flight, which
>>>> lasted for 1 hr and flew up to over 7000', my engine has become less
>>>> reliable with every flight. Yesterday I got in a 9 minute powered
>>>> flight when the engine quit at 2000'. Fortunately I landed uneventfully
>>>> on the runway. I could not restart the engine after getting down and
>>>> stopped, I tried to restart about 5 times. The engine would start then
>>>> immediately die After about a 20 minute interval of me walking to the
>>>> hangar and enlisting help and a tow vehicle, it resorted and I taxied
>>>> back to my hangar. At that point I would have sold it very cheap.
>>>>
>>>> Using fresh 92 non-ethanol. I have been playing with needles and
>>>> settings to try to solve this but its not working.
>>>>
>>>> Ideas?
>>>>

[tx_swordguy]

did you ever look at your plugs to see what they look like?

[bvolcko38]

Yes. Front cylinders are black and sooty, rears are grey.

[tx_swordguy]

its a really rich mixture. it can't burn all the gas that is dumping into the cylinders and is bogging down. drop the needle by half a turn (which is quite a bit) clean the plugs and try that. That is just a starting point. You may have to keep going or drop to a smaller needle. look up spark plug colors and it will give you a better idea of what to look for than anything I could write here. You will need to clean the plugs or use new ones until you get it close and then you can dial it in by how you feel it is running.


ps in an earlier post you mentioned dropping the nose and it ran better until you leveled off. I think that was because you unloaded the prop and since it was not working nearly as hard the rpms came up using more of the gas in the cylinder thus running better. Still think it is running excessively rich

[Rynoth]

Which needle are you using? Also, mark the needle when it's in place after you do find a good spot for it, and if you run into trouble again look for the mark to see if it has moved on you prior to removing/adjusting it. My needle wasn't always locking in place before i peened the threads a bit, there are a few ways to make it more secure, sometimes the lock nut alone isn't enough. When removing and re-inserting the needle, don't rely on number of turns, better to make a mark of some sort as a reference line.

Glad you were able to get down safely when it did quit on you! If it is indeed due to being too rich, it will likely run progressively worse as the engine and days get hotter, and/or (density) altitude gets higher.

[dirkverdonck]

Hi Bill,

My personal experience after 80 hrs on the Aerovee: Inititally I had the needle set as per manual but EGT and CHT were on the high side during climb. This got worse as the needle must have moved the wrong, lean, direction after I tried to enrichen. Peening the thread solved this and I now can block the needle in position without changing the setting.
I now run 3/4 turn rich of the setting advised in the manual and climb without overheating and lean in cruise flight to have EGT's around 580°C and CHT's around 165°C.
(I have added a little device called 'Lambda probe' into my exhaust from the start to help me set the correct mixture. I use it as follows: in cruise I slowly pull the mixture lever until I see an increase in the number shown on the stecheometric instrument, wait for a minute to check the EGT climbing and after another two minutes the CHT also starts climbing slowly. I continue to lean until I get to the numbers giving earlier)
On short final I again push the mixture needle fully forward to prepare for a possible go-around.

This is what I do and others may have better solutions....

[Onex107]

Sounds to me like you have two problems. One, the needle adjustment in the AeroInjector is too rich and second there are vapor bubbles in your fuel line. Your plugs should be almost white inside.
I don't know what # needle you are using and I don't know how you adjusted it. In my case, after doing a lot of research on needle design, I have ended up using needle # 3. I marked it with a file, on the under side, where the taper begins, to give me an accurate starting spot I call "0". I screw the needle in until I see the "0" mark and then go 2 1/2 turns further (leaner). At this setting I get good WOT and it will idle without making a mixture adjustment. I don't adjust the mixture from one flight to the next. Only when climbing out and #1 starts to get hot do I go a little richer to cool it off. Then back to 12-1300 EGT's.

The fuel vaporization, especially with car gas, which I use, will cause the engine to die for a second, at cruise speed, every 10 seconds with small bubbles and quit at taxi speeds. There are several ways to prevent that but the simplest is "INSULATE" and it has to be better than just Fire Sleeve. I removed the gascolator because it was too difficult to insulate and it's not necessary in the Onex fuel system as per Sonex. My fuel line is covered with foam pipe insulation and wrapped with alum. tape to keep the oil away. I also wrapped the exhaust pipes to reduce the temp under the cowling. In my area, central Illinois, there are two versions of car gas, winter and summer. The winter gas has a higher vapor pressure, that is it vaporizes at a lower temp and causes a higher pressure in the vapor test, and it doesn't change until April-May. Mixing 100 LL with it in the spring may help.
Start with the AeroInjector instructions and set your needle for a good WOT with good EGT temps. From there you can tweak it until your mixture has effect from full rich to full lean.
Don't give up on the Aerovee. It's a great little engine when you dial it in to the optimum.