New Zenoah 38cc

[Brian Dorricott]

I am new to bigger petrol engines and have bought a Zenoah 38cc to eventually put in a follow on trainer or similar . I always like to learn my engines before committing to an air frame so have mounted it on a frame with a servo/receiver combo to keep my fingers away . It started ok and ticks over nicely without touching any needles but when I open the throttle it initially speeds up to about 4500rpm then starts to die , I richened it a little and can now exceed 5400rpm before any more throttle makes it start to die again . Is this normal is it just tight ? It's on a 18x10 wooden propeller and running a mix of about 35:1 petrol mix . I know it says in the instructions fit and run but I like to get acquainted first and haven't got anything to put it in yet . Any thoughts anyone ? New to forum hope it's in right category.

[Alan Cantwell 1131]

Check your fuel line, 3 mm bore Tygon, check the needles,
Low Speed Needle: 11/8 plus/minus 1/4
High Speed Needle: 13/8 plus/minus 1/4
There is a pulse hole for the pump diaphragm, make sure this is in line with the hole in the carb,
Check the mag gap to the flywheel, loosen the mag, trap a piece of notepaper between the flywheel magnetos& the mag, tighten it up, and remove the paper,
Check for any air leaks from the crankcase halves,

[arthur barlow]

38cc are not not high revving engines Prop should be be a 19x10 or a 20x8 and it sounds too lean on the top end

[Cary Bailey]

Also run her in using Mineral 2 stroke oil for about 1 gallon before changing over to synthetic (unless you want to keep it on mineral oil). The engine static should easily pull 55-5750 rpm using a 19x10 prop. It will rev more by about 400-500 rpm when in flight.
Run her rich on the bench for a few minutes at a time and then let it cool. Running on the bench does not cool the motor adequately therefore they will start to get hot quickly, don't worry about that but don't run her for long periods. Once you have decent throttle response settings, but keeping her a little rich, get her in the plane and fly her.
Cary

[DAVE JOHNSON]

Brian---if the test stand will fit in your car--why not bring it along when you visit the LMA site---and i will set it up for you?? i can also advise you on suitable airframe and any available secondhand airframes for sale----DAVE

[Brian Dorricott]

Thanks Dave it's currently bolted to a garden table but if I can find a portable solution may take you up on that .

[Bob Thompson1894]

One point- 19x10 props (the ideal size) can vary quite a lot. Make sure you use a decent make, Xoar, Menz etc. I have some 19x10 ones that have no pull at all.

[Brian Dorricott]

Got another question regarding the Z38 when fitted in an airframe , how do you operate the throttle with its sideways style ? I'm guessing something like a bellcrank but can't visualise it , anyone got a diagram or picture they could share ? Just a thinking a bellcrank would require some space under a cowl or is there a better way ?

[Peter Siggins]

Hi Brian a bell crank is the way to go I use the red control arm that is supplied by Hitech 645 servos - just trim two ‘arms’ of to leave a 90 deg bellcrank .Make a small suitable 90 deg bracket out of strip steel (sold at B&Q:) then find a bolt on the engine itself to undo and set it up from there.Some small washers and a 3mm bolt and lock washer completes the job
Unfortunately got no pics but hope the explanation helps - probably as clear as mud!

Pete