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How to Convert an your R/C 20 or 25 to C/L

If you have a OSFP .20 or.25 for R/C (Radio Control) you can easily convert them to use for Control Line.  Just simply orderf the parts from Towerhobbies.

Why use an OS .25 instead of .35 or .40.  For most control-line models that were originally designed for a Fox .35, the OS .25 is a better replacement.  If fit closer to the same engine mount spacing, has roughly the same weight and is more powerful.  Instead of running and big 10 X 6 propeller at 8700 to 9200 rpm, you can run a 9 X 4 or 10 X 4 at ~1100+ on the OS .25    I've use this engine with a APC 10 X 3 on an over weight Banshee (42 oz) and it pulls is a lot better that my previously installed Fox .35.

Option 1: If you already have an OS 25 LA RC Engine:

Tower Part #OS Stock No.DescriptionPrice
OSMG925222312000Venture 20-25FP $8.99
LXMU3021381980 Remote Nozzle $5.79

Option 2: Standard Needle Valve with the metal FP cover plate

Tower Part #OS Stock No.DescriptionPrice
LXCF8922307000O.S. Cover Plate .20-.25 FP$3.89
OSMG868422613006OS Screw Set .20-.28$5.79
LXW9922312000Venture 20-25FP $8.99
LXCR4922311000 Needle Valve Assembly $13.49

Six head bolts 2.5 x 10mm caphead bolts
Four backplate bolts 2.5 x 7mm caphead bolts


Remove the original R/C carburetor.  I'm sure you can sell it to an R/C person to recover some of your cost.  A new R/C carburetor retail for about $25.


Insert the new C/L venturi (OSMG9252).  This venturi can also be used in OS .35 or .40 engine.  Using this venturi and lower pitch propellers in these larger engine will cure the "Run-Away" problem.

Insert the Remote Needle Nozzle.  On older O.S R/C engine with out the remote needle valve, you can replace this with a ST Needle Valve assembly.  It require a slight over bore, but it work very well for C/L.

Now you have a OS .25LA Control Line Engine!