I have an old JMI 82 " P51D. this is the lineage that teh CJM P51 was developed from and dates back to late 80s or early 90s.It's a good flyer and I have it well decked out with scale goodies.

Last few years I have had nothing but engine woes, rebuilt the ST2500 once and have had multiple rough arrivals as a result or dead sticks on climb out.

Of note is that the model has a Cline regulator fitted which takes crankcase pressure via a one way valve to pressurise the tank to about 10psi and the regulator has the diaphram section from a walbro carb that allow suction from the carby to open the needle via the diaphram.

I've been experencing a huge dead band that I could not tune out, starts and idles up to fast idle fine but will not transition to full rpm. I had read these engine can glaze up and overheat causing the same symptoms so managed to track down a new in box engine as well as all the parts to rebuild, cylinder and liner.

So I fitted the new donk and fired it up on the bench. Ran like a dog with the ST carb and put the OS 7D on with just normal tank suction. Seems to be ok upright. Inverted though it played up. Tried a range of plugs and was out of the Mccoy MC-8 which this engine likes for inverted running for some reason.

So packed it away and forgot about it for nearly year, finally got some more MC-8 plugs and pulled it out again on Saturday.

Engine ran but very rich transition and kept quiting. Suspect the regulator supplying too much fuel as I could not tune it out. Also was not sure about my old OS 7D carb so fitted antother I have that has remote mixture control via a servo control. By this stage it was late afternoon and had had enough of it as I'm sure the neighbours were sick of hearing the engine and me swearing at it [img][/img] [img][/img]

Sunday after copius quantity of coffee I tried again but this time I got out my old cline regulator and inspected it. Had antoher diaphram and fitted that. Tried it and seemed to run quite well though could still be rich. I

Interestingly by pulling on the edge of the regulator it would lean out and go on song. Hmmmm suspect needle sticking open or possibly diaphram a bit stiff.

I'll get a new diaphram an needle from mower shop during the week but as it is now I could fly it. When it comes on song it is pulling like a horse.

You tube clip of it running.
fun and games!

cheers

P