Great Power 38

Phil Ford wrote:

Not fuel lines Brian. Carburetor issue or pulse issue. ie; flappers or there is a blockage in the carb body or I have overlooked something obvious.

Ignition !

No fuel John. Dry spark plug. Squirt some down the carb mouth and it will fire straight away.

Went over to Kevin's on Sunday for some testing Carb is fine. The HDA 246A carb appears to be designed especially for GP engines with an extra high jet for for fast opening of throttle. Crankcase has no air leaks. Reed block and reeds look a bit suspect. Two out of four are not fully closing. Have asked for advice on latter from Clive McInness at AerobatX. They keep GP engine spares unlike some others I won't mention.

Monday 4th - Check if fuel pump is actually working. Reassembled the carb and reed blocks and mounted on the engine. Clamped engine into my work bench. Removed spark plug, fit prop and spinner. Spin engine over and watch fuel moving up the line. Remove regulator cover and whilst spinning motor over depress needle valve. Fuel appears! :huh: That's a good sign.If weather holds off today I will refit the engine to the Extra and see what happens..........Images not necessarily in right order.. Kevin cleans up reeds and checks them with suck n blow. A cut down credit card bolted to reed block with an fuel line adaptor.

Engine refitted to airframe. Fueled up. Flick it over and fuel pulling in to engine. Choke on. Flipped a few times and no kick? Choke off, throttle a little open, flick and nothing. Remove plug. Flooded. Dry plug. Try again this time just throttle. KIcked once or twice and bouncing back on compression and then nothing.

I am at a loss here. I have had enough of this crap. I have spent around 8 hours over the past weeks on this. Take the flipping thing out and send it back under warranty. Should not be fannying about like this in the amount of runtime this engine has had.

Before you give up completely Phil, have you tried a different spark plug? I read somewhere that a plug may spark OK in the open air, but fails under pressure.

Done that Brian a while ago. Two things that have not been tested. 1. Kill switch 2. Try another ignition unit. Later today if weather holds off will bypass kill switch. Next swap the ignition unit with a DLE spare one and see if it fires up. (Note it may not perform the same as the ignition advance curve probably is not the same). I have now realised that although these GP engines are well made in Taiwan the back up of spares and knowledge is minimal except for two companies in the UK.

Definitely a fuel issue. All other items checked.

I can stick it onto my test bed and have a tinka if you like?!!

Hi Chris - As you will have read ive also looked at Phils motor so your fresh view might be a good idea. Phil is in two minds as to put the motor with Probuild or let the AerobatX look at it.

Just to review what i have done.
Leak tested crankcase (for bearing seal leak)
verified the pump works (by removing the fuel chamber cover and releasing the regulator plunger) which Phil has also carried out on his bench.
The reed block is quite a lightweight plastic structure and the reed petal mount screws had distorted the mounting point. Ive tried the flatten that distortion. The petals don't close absolutely but I dont think sufficient to prevent running.
Using a pippet ended tube, I've blown thru the idle and main jets feeds and verified the flow changes with needle adjustment.

This carb has a sprung ball valve preceding the main jet outlet which i assume opens to release a pulse neat fuel when the butterfly is opened rapidly. I know it opens because I've trickled neat fuel on the inside. when I pushed the ball with a needle point the fuel runs into the venturi. HOWEVER, IF THIS DOES NOT CLOSE IN REVERSE IT WILL ALLOW AIR TO FLOW BACK INTO THE FUEL CHAMBER AND VENT ALL THE FUEL.

C.Morris wrote:

I can stick it onto my test bed and have a tinka if you like?!!

Hi Chris. another set of eyes over it would be great. Nearly two months now since it stopped running. I will email you to arrange. Thanks. An update today 5th October. Neat fuel down carb mouth and it fires up momentarily.