Kolm Engine Tuning Made Simple...
I know that there are a lot of modelers out there with a lot of experience and some of this information may be redundant.
I have four Kolm engines and they all run flawlessly. For those struggling with Kolm engine tuning I hope this will help.
Kolm Engine Tuning Made Simple
The first thing to check after your engine install is for all of your carburetors to be in line via the linkage as it comes from the factory. This is a very important step that will save you a lot of time and frustration later. The carburetors being off can, and will, cause problems during the tuning process. Each carburetor should match from closed all the way to full throttle.
On your first attempt at starting the engine you want your needle settings to be L1 H1.5 (low needle setting) 1 turn out from the stop and the H (high needle setting) 1 ½ turns out from stop. When setting your needles back to the stop position be careful not to tighten them too tight at the closed position as you can damage the needle valve and seat on the Walbro carburetor. Just lightly closed is good. Remember counter clockwise richens / opens and clockwise leans / closes.
Tuning
If you open the throttle fairly quickly and the engine dies, the Low (L) mixture is too lean. To richen it, turn the (L) needles counter clockwise about 1/8th of a turn on all carburetors and try again. This may take several attempts: turn the low (L) mixture screw counter clockwise 1/8th turn each time.
If you go past the ideal setting when richening the Low (L) mixture when you increase the throttle smoothly the engine will not die but start to sound dirty or slightly rough running on the way up. If this is the case lean the low (L) needle ever so slightly ( 1/32nd or 1/16th ) until the engine performs as you want it.
The Kolm engine, like any engine, will be tuning upwards of 1000 rpm’s faster while flying and will be under less of a load. If at full throttle while flying, the engine sounds slightly dirty land and richen the (H) high needle valve by turning counter clockwise about 1/16th of a turn until the dirty sound stops. You should never have to richen the high (H) side more than 1 3/4 turns out.
Safety check. Some people are and some are not comfortable with this, but before you fly you should have two or three people lift the aircraft off the ground while running. You should then transition from idle to full throttle and have the people tilt the aircraft almost vertical to ensure that the engine maintains constant a PRM. If the engine dies this means that the high (H) side is definitely too lean and you need to richen the high (H) side. Start with 1 /16th of a turn.
*Remember when you take your aircraft to different parts of the country atmospheric conditions and altitude may have changed and you may have to re- tune*