richrd

Last weekends at the Toledo show I picked up a Royal 28 (BTW for $20. ) cleaned it up an put new O rings in carb. It started right up but can’t seem to get the mid range transition the way I want it either great high end and idle but then stumbles and rich mid or great mid but too lean on both ends.

So question is this typical Royal 28 or is something wrong with this carb ?

Setup is tank rubber banded bottom with base mount and fuel is wildcat premium 15%.
Try different glow plugs from 4 stroke too A3, A8 etc only change minor things but A8 seem to be it’s favorite.
Rich

RaceCity

Richrd...you've just described the vast majority of 2C engines on the planet. Lots of engines are grossly over-carbureted to help allow them to run at insane rpms, (and produce the impractical HP ratings that the marketing folks like) but unfortunately the rest of the speed range suffers from really poor performance.

You might continue to fiddle with the needles to arrive at some happy compromise, or you could run a slightly smaller prop which can partially alleviate the problems you describe. Other things might be to try a few different fuels (just to be sure), or a carburetor with a smaller bore venturi. A .28 doesn't need a canyon-esque carb bore to run well...or run fast.

Just some thoughts...

loughbd

Royal engines were made on the same assembly line as Hobby Shack's original Magnums and had all the same problems. Number one being lousy carburettors. Jerry Toppel was the west coast rep for Royal while I was working as Hobby Shack's engine tech in San Diego. We both agreed that quality control and both lines was spotty at best. The biggest dofference was Royal knew the problem and made sure the engines they sold worked reasonably well. Hobby Shack just sold them all and then took them back under warranty.

OS did not "overcarburate" their engines to run at "insane" rpm. The average 40/45 ran at about 13,500 which was about normal for a 10x6 11x5 prop. Nothing spectacular but good. The max rated HP was 17,500 for anOS45FSRABC but the torgue curve was highest at the 13,000rpm level where most were going to be used.

Most GOOD two cycle engines don't have that problem. The OS 28 FSR transitions beautifully as do 99% of OS carbs. Same with Enya and other Japanese engines. The 4B, 4BK, 4D 7M 7L, 2D and most of the OS carbs have excellent transition.

richrd

Prop did'nt think, but could be only had this 9-7 pattern to try and it turned about 11,600 so was'nt thinkin it was over proped, I'll try to get a lower one see if it spools better. Thanks Rich

RaceCity

I guess it depends on the engine, but a 9-7 might be a tad steep for an old clone to manage. Most small 2Cs need to be allowed to spool up a bit to run their best.

An inexpensive experiement would be to try a 9-6 or perhaps a 9-5 and see if the motor doesn't perform a little more to your liking.

loughbd

A 9x7 is equivalent to a 10x6 and that was the prop used on old 29's in the 60's and 70's. A modern 28 should turn one with no problem

NM2K

My Feedback: (14)

-------------------


Drop down to a 9x4 or 9x5 prop. A 9x7 is causing you to tune the high speed needle way to rich. The midrange metering is fixed, but associated with the high speed needle. By tuning way rich to compensate for too much prop, the midrange becomes way too rich for good running.

piper_chuck

My Feedback: (12)

Yet another one for dropping the prop size down. I run 9x7s on my OS .32 FSR and it's really happy with that size.

richrd

Ok got some on order to try, Also couple quarts of lower Nitro, ya know it's spring I just gotta play.

BUT !! help me on this new problem if I under prop it where is the danger rpm, 11600 on pattern 9-7 now can this old boy ROYAL 28 take high 13,000 15,000 or OMG 18,000 or will I just ruin this engine.

I don't know if royal is a classic or not just hate to take it out trying to do something it's never done or will do but once.[]

BTW putting it on our club racer to practice on then switch over to Tunder Tiger 25 the legal one. Royal was the motor until discontinued, they then went to TT but now it's dissappearing wow what a sport.
Rich

loughbd

A Royal can take 13K easy. Classic?? Nope and never will be. It's a Taiwan clone of an OS. The weakest link in thse is the rod lower end. Use it just like any other OS clone.

Tennis and football are sports. This is a hobby.

jaka

Hi!
Don't be afraid to rew the engine...16000-18000 is perfectly OK ...but it is certainly not what you should aim for.
Try a 9x5 -10x5 APC instead of the 9x7 (which in my opinion is too big for most airplanes I can think of).

Regards!
Jan K
Sweden

loughbd

Go ahead and run it at 18,000. You can get new rods from RPM or Tower. The OS 28 uses the same rod. So did the magnum 28. The 25's used the same rod. Of course when it goes it will probably take the piston with it

loughbd

Go ahead and run it at 18,000. You can get new rods from RPM or Tower. The OS 28 uses the same rod. So did the magnum 28. The 25's used the same rod. Of course when it goes it will probably take the piston with it

RaceCity

Cool prop is the APC 9.5x4.5. Those things really howl on a .25.