Hello All,

I took my Giles 202 to the field today. The engine is a Brison 3.2 with electronic ignition. During the initial ground run engine performance was normal (perhaps slightly rich).

Shortly after take off the engine started to burble, and not develope full power.... it sounded like it was way too rich. I returned for landing without undue delay.

I'm familiar the proper technique of adjusting the High and Low needle valves on Walbro carburated engines. The Brison manual states that as a general starting point the Low should be out between 1.5 - 2.5 turns, and the High needles valves should be out between 5/8th and 1 full turn. However with these settings the engine will idle OK, but when I adjust the throttle beyond 1/2 the engine runs extremely rough, and BACKFIRES! (yikes!).

Here is a list of what I've done to try and problem solve....

1. Replace the fuel with completely fresh fuel. No change in performance.
2. Ensured that the ignition battery has a fresh charge... no change in performance.
3. Cleaned the carburator.... no evidence of debris found... no change in performance.
4. Checked the sparkplug connections.... re-tightend, .... no change in performance.
5. Replaced the sparkplug.... no change in performance.
6. Observed the fuel line for bubbles... no air entering the fuel line noted.
7. Adjusted the low and then the high speed needle valves till I'm blue in the face.... even with progressively lean or progressively rich settings the engine performance seems unchanged (i.e. still backfires beyond 1/2 throttle).

The engine has not been in any accidents at all.

What is going on here? I can't understand why it runs really rough and backfires beyond 1/2 throttle.

Help please.[&o]

Cheers,

Marcus

Check the timing

What RCIGN said![sm=idea.gif]

Naw, you have air coming into the engine compartment and changing the pressure around the diaphram. There is a couple of things to do. RCIGN can make you a plate with a nipple on it to run a fuel line back inside the fuselage. You can also make a baffle so that the air around the carb diaphram is still. This will address your problem.

I don't know what your altitude is, but a rich mixture an be part of the problem. Also poor timing. It's also possible that you may need to deflect the air slipstream away from the diaphram opening. Basically, any one of the posts prior to this one, or all of them, could be correct. I'd start by leaning the high end mixture down to somewhere close to 1-1/2 turns with the low at about 1 turn and see what happens. Plan on a little experimentation depending on your altitude.

If you have a Syncrospark ignition I doubt you have a timing issue. Throttle coupled is another story.

Since you have adjusted the needles all over the place with no change the fault is obviously elsewhere..Full advance on a syncro spark igniton is at 4000 rpm..If the static timing is too far over 30 degrees the syncro will advance it too far...
Mechanical advance is more linear, full advance is at WTO...
I stand by my earlier post, check the timing, it should be at 28 to 30 BTDC with either setup..
Mechanical timing is checked with wide open throttle, syncro doesn't matter..
If there's no throttle stop on the carb and the timing is mechanical the carb could be opening too far, further advancing the timing...

Hi All...

Silversurfer & Geistware..... This problem is definetly not as you suggested because this airframe/engine combination have been running very well for several flying seasons. This problem cropped up without any airframe/engine configuration chagnes. So I doubt very much that suddenly I would have a diaphram/cowling/airflow related static pressure problem. I think that inlight of the aircraft/engines previous years very satifsfactory performance, I would be on a Wild Goose Chase if I installed a nibble/pressure line.

RCIGN1 * Bass1.... The timing plate retaining screw was not loose. The timing was checked and found to be pretty close to 4 degrees BTDC. So, according do the instructions from ingnition manufacturer, the timing should be correct. I am having a bit of trouble measuring the timing super accuractely. Hence, how critical is the timing if it is a couple of degrees off? (it has Synchropark ignition). If I were to be a couple of degrees late or early, which direction would be the better of the two?

Other thoughts........ I read on the forum that it might be a loose or poor connection with the hall effect sensor or other parts of the ignition circuits. Aside from checking for loose ignition/hall effect sensor wires what else can I do?

Cheers,

Marcus

P.S. I'm at sea level.

I stand corrected. I was unaware of the length of time the engine has been in service.

Marcus, This is a shot in the dark but a few weeks back at my club field a guy had been flying his Wagstaff Extra with an FPE 3.2. He flew it several times and it ran flawlessly. Then after lunch he went to fire it up for the next flight. It started and idled perfectly but when he went to run it up to full throttle it gurgled and sputtered and would not get close to normal max rpms. When he reduced throttle it smoothed out. Anyway a couple of guys fiddled with the needles for a while and no change. I walked over and started to look things over (the cowl was off) and noticed the ignition battery wires were real close to the muffler. Upon closer inspection we discovered the insulation on the wires had melted through and after wrapping the wires with electrical tape and moving them away from the heat source (muffler) the engine ran flawlessy again. By the way, the melted insulation was almost impossible to see. I guess there was a voltage drop at higher throttle settings from the battery short.....

What condition is the battery in after several flying seasons?

Test the battery with a loaded volt meter, it may be dropping voltage under a load, as a low battery will cause the same problems you have described.

If the ignition is C&H syncrospark the correct setting is 28 to 30 degrees BTDC..Not critical...C&H would not tell anyone to set the static timing at 4 degrees BTDC...Funny it runs at all, set at 4 BTDC, that's all it gets running wide open ..Go to
www.ch-ignitions.com
READ the part about timing

Maybe it is actually a mechanical advance?? Otherwise Ralph is right, no other way around it.

tyrolean_marcus, There are a couple of things which i would check , but first some info is needed .
1) Has the plane/ engine been stored for a while (weeks or months)
2) Has the engine been off the airframe since last flown
3) How did the last flight go ,any sputtering in the air or unusual transition concerns prior to this most recent event.

I would first verify the ground strap is firmly connected to engine or sparkplug
I would also check the screen inside the carb. (these tend to plug up ), at the same time verify that the carb is not loose (but do not overtighten and damage the
gaskets between the carb and insulator and the insulator and cylinder)
also check the gap between the pick up sensor and the magnet ( shouldnt be more than about .020 -.030 )
Make sure your muffler is tight also , these work loose and can cause some performance issues
Good luck , If all else fails call Gary at Brison

I've had that problem with that engine in the same situation. Here is what I found was happening. First I'd crank the engine and it would run OK on the ground at idle until I started to rev it up. Then it would spit, backfire, etc. like you are describing. I went through much of what you going through until I finally found the sensor had a cold solder joint in it. This would allow it to crank, but as soon as it started to heat up the connection would start to go bad, thus spit, sputter, backfire, etc. I could be wrong (it wouldn't be the first time!!) but if you have a spare to change it with or heck...they aren't but about $10, it might be well worth it!
Good Luck,
Jim

Hello All,

The engine mystery was solved today!

The root cause of all problems was simply a very small rip/cut in the spark plug lead insulation. The small cut exposed part of the spark plug lead internal wires, which effectively diminished the strenght of the actual spark. This diminished spark strenght was likely not enough to cause proper combustion at the higher throttle settings.... Hence the backfires.

Moral of the story is to carefully protect all wires related to the ignition system from chaffing and vibration.

RCIGN1... sorry about the confusion with my statements about timing. I simply mis-typed.

RTK... it is definetly a Syncrospark setup. Not a mechanical linkage.

Thank you all for your very helpful suggestions.

Took the Giles to field today... and it ran like a champ.

Now if I could only learn to fly better.

Cheers,

Marcus.