ORIGINAL: Konrad
You have a small cased series V Compact 40 with small bodied Mk X carb (0.290 choke area).
The Fox carb is rather small for a 6.5 cc engine (good fuel draw).
The tank centerline should be with in 5 mm (1/4'') of the carb's spray bar in the vertical plane. Fuel load should be no more that 230cc (8 oz).
Prop should be a 9x7 to 10x6 glow plug Fox long reach (non idle bar)
Seal the carb to crank case with silicon RTV (as was done at the factory). The back cover plate should have a paper gasket and no sealant applied. The head should have on head gasket to seal against the cylinder flange. There should be no need for fuel tubing on the carb needle threads if using fuel with the proper viscosity ( 20 to 25% castor oil) fuel, nitro should be 5 to 10%.
First off, thanks for the reply. Second, I have the tank set properly (on my test stand, its a LST1 Monster Truck fuel tank - 170CC) and am using a balanced 10x6 prop. Carb and setscrew is already sealed, new paper gasket on backplate with a thin film of silicone - reason is one of the screw bosses was busted off so I made a new one with JB Weld. I put fuel tubing on the High speed needle because I had fuel leaking out - many others I found have had to do this for the same reason - I cannot source any all-castor fuel locally and its too expensive to have shipped - what should I do?
ORIGINAL: Konrad
As you have disassembled the engine take a look to make sure that the cylinder sleeve port that is pointed towards the exhaust stack opens first as the piston comes down. With the carb fully open and the high speed needle open 2 to 3 turns apply glow to the glow plug and spin in a clockwise direction as viewed from the cockpit (behind the engine). She should come to life. Run the engine very rich for the first 5 minutes (even with this well worn engine, as you have disturbed the bedded surfaces of the piston and liner) now set the high speed mixture to be on the rich side of peak RPM by 500 RPM. Close the carb so that there is only a 0.5mm (0,020) gap (opening) use the idle adjustment screw on top of the carb for this. Bottom the idle mixture needle gently then open up about 2 turns. Start the engine and try to idle the engine with the glow plug lit from the driver. Set the mixture so that when you pinch the fuel line to the carb the engine stops in 2 to 3 seconds. Now tune the engine with 1/6 to 1/8 turns of the needles to get the best transition from idle to full power. Once you have this back off the idle speed screw (the thing on top of the carb, so that the carb just closes).
FYI. Some folks think there is a need to seal the needles to stop air from being drawn into the carb. Please note this is not to stop a fuel leak but rather an air leak. Air is around 6 times easier to draw (suck) than fuel. This is why it is so important to make sure you have no air leaks in the fuel system. The need to use muffler pressure has more to do with fine tuning the midrange that to help with fuel draw on this carb with its small choke area. If you need a leaner mid range use muffler pressure (this forces one to use a leaner high speed mixture hence leaning the mid range).
This is good to know. The guy at Fox gave me a more basic run-down. I set the carb at about 1/2 turn low-end and 3 turns high-end. I could not get the engine to run to full RPM with the pressure tap connected. Transition was rough and smokey with it connected or not. Had a few stalls throttling up - touch to restart because it was so loaded up. I was going to try a idlebar plug (this is an R/C engine) per Fox's recommendation and check to ensure the carb needles and/or orifices aren't fouled up.
ORIGINAL: Konrad
And last think about posting in the Fox club thread as there are a lot of folks that know how to set up these fine non asian engines! This is not an OS engine and does not tune like an OS! This is a good thing!!!
Friends don't let friends fly nickel,
Konrad.
P.S.
Not that there is anything wrong with an OS, yeah right! They flooded the US market and now all we have left is Fox in the sport arena. I'm happy to see you try to bring back this old Fox, even if it was only Duke's answer to the OS FP. At least it has an auto mixture carb! You won't find an air bleed type carb on a Fox. All Fox carbs since the mid 60s are auto mixture carbs of some type!
I will check out the Fox forum.
I will also say that A) I have never ran an OS and B) I dont plan to ever run an OS, either. If it says "Made in USA" then I'm happy. I survived a K&B Sportster break-in, so I figured I could handle a used Fox. It was free, and from what many say will run 13000-14000rpms. I (some may frown upon this) have the K&B on a flat-bottomed airboat and I was going to build another airboat to put the Fox on.. I am afraid to fly - I'm somewhat crash prone with my R/C Cars, don't want to change destroying a plane. The boat is more appealing to me.
If I can get out of work early enough to have some daylight left, I will make a few modifications to the setup and verify the sleeve is in the right way. (I checked when I assembled it and the exhaust port lined up.)
The closest I can get to full castor fuel is SIG Champion 20% oil (10% castor 10% synthetic) I would rather run full castor in all of my airplane engines but nobody will get it for me and I cant afford a whole case. I'm not sure what I should do.. I think I can get FAI fuel - all castor but I kinda like the idea of having some nitro in it..