Hiya,

first post so be gentle

Ive just bought my first petrol plane, a second hand Global Sukhoi which came with a DL50 in it.

It starts really easily but even with the idle screw fully out, and the throttle body 'shut' so the lever wont close it any more it still idles very quickly, to the point its doing nearly 10mph on wet grass and will only land if you cut the ignition.

Also, on full power nose up the engine cuts, as if it is too lean. I richened it out by a quater turn on the high end needle but still exactly the same.

I am wondering if the 2 problems are linked and if there could be air getting in to the engine somewhere else other than the throttle butterflies, or maybe someone has another idea?

I am yet to take the engine out, partly because I'm not sure what I'm looking for but any help would be greatly appreciated.

Thanks in advance,
Martyn

You have a crankcase vacuum leak

Or an intake tract vacuum leak. Hopefully that's true as it's much easier to fix!

AV8TOR

Thanks for the replies guys.

Crankcase vacuum leak sounds terminal? Not good.

What is the intake tract, and would the fix be a new part or adjusting something?

Sorry for the huge noobiness!!

Martyn

A pressure test of the engine is the best way.

All the external orifices are sealed and a pressure/vacuum test is done on the engine.

Typically people use roofing rubber or tire inner tube rubber to seal the exhaust behind the muffler and the intake behind the carb flange.

The crankcase is put under a slight pressure (10 psi) and watched for 1/2 hr as to its ability to hold the pressure. The front seal, the crankcase seams, and all the joints where the read block and intake manifold attach are bubble checked.

The same test is then performed with a vacuum (1 tor) and watched as a front seal integrity check.

The problem could be as simple as a bad gasket where the carb fastens or a leaking impulse line from the reed block to the carb?

10 lbs. pressure might be a touch high. 5 lbs. should tell the story and is less likely to blow out seals and gaskets. You really need to put the pressure to it with a hand pump; it is way too easy with compressed air from a compressor to instantly get way too much pressure.

Sometimes you can spray WD-40 or carb cleaner spray around the shaft seals, the crankcase parting line, the reed valve gasket surfaces and the carb to manifold surfaces, etc. and see if the engine changes tune or speed. That will tell you there is a leak. The "intake tract" is just the carb, manifold, reed valve, and any adapters in between. Be very careful of that spinning prop while doing this!

AV8TOR

This is the tool I use to perform the test. I do it more or less as Aviator1977 described

http://www.harborfreight.com/mityvac...ump-39522.html

Yep, that's the one I have too. Love Harbor Freight!

AV8TOR