I purchased a 10 year old but brand new as in un run engine. Starts good right from the beginning but would not idle below 3400 even after the break in run which was done as per instructions.I am using 12X6 prop and 20/20 all synth oil and F4 Plug. After some 10 flights it started to come out with a hoarse sound which turned out to be due to a failed back bearing !. I replaced the two bearings back and front. The problem with high idle is still there. I am familiar with tuning engines like Saitos ,OS,ENYA 4 s,Ys 4s and am aware of issues like problems due to leaky fuel lines and tank position. Am I missing anything here? I am not sure what to do next and would really appreciate receiving any leads and suggestions .Thanks.

Try using a more hot heat range glow plug. Also try using a higher percentage nitro glow fuel with a 4 stroke plug in the engine.
I had the same problems with some rotary valve engines like the Webra T4 series, where they didn't want to run well or idle with my regular 5% glow fiuel, but they ran great with 15% nitro glow fuel. A hotter heat range glow plug might do the same thing as running a higher nitro-percentage in the glow fuel too. The T4 engines idled a lot better with more nitro in the glow fuel. A couple of ASP .61 four stroke engines also behaved the same way too. RCV suggests using a 10% nitro glow fuel with a synthetic/castor oil blend for the oil. All castor might gum up the engine too much but a little castor helps a lot with lubrication and preventing corrosion. I normally use Omega fuels in all my engines or Powermaster, where the oil is a blend of synthetic and castor oil. I have some all castor oil fuels but I use that in lapped piston plain bearing engines though.

I have two RCV .58CD engines myself, but I haven't much of done anything with them yet. I am planning on a twin of some sort to put them on.

yeah pretty much any engine that might have sat unused for many years is at risk of having bad bearings in it. I have had that happen to a number of engines over the years too.

Thanks a lot for the suggestions.I am running this engine with 20% nitro.I will try to mix some 5 % caster in the oil part and see if things improved.Any suggestions on what would be a hotter G.plug to use?I am not sure of the OS numbers,going up numbers are hotter?Thanks.

One thing you're doing wrong is running too much oil, cut it back to 16% and run a Fox Miracle plug, a Saito SS plug or an OS-f. Cut the nitro back to 10% max, early on when yours was mfgd the recommended fuel was WildCat 10% fuel with 16% 80/20 syn castor blend. Even 18% lube will make the engine run wet and smoky in the midrange.

Die Cast
Engine Type 4-stroke - Glow ignition
Displacement 0.58 cu inch 9.5 cc
Max Power (approx.) 0.85 bhp 0.64 kw
Weight (exc. silencer) 17.6 oz 500 g
Length 4.01 inch 104 mm
Height - centre line axis 2.64 inch 67 mm
Cowling Radius R70
Propeller shaft diameter 1/4" UNF
Practical RPM range @ prop 2,400 - 12,000 rpm

Example prop sizes (2-blade) 10x6, 11x6, 12x6, 13x6
Recommended Fuel 10% Nitro / 15% Oil including max 6% Castor
Here are the current recommendations, the oil recommendation has been reduced to 15%.

Thanks Hobbsy,ah well, that’s new news to me .I will try this fuel combo which shouldn’t be a hard to get as I mix my own fuel. I do use os f plugs on all 4s motors that I have. I will report back once I am able to run the engine when the weather permits. Cheers.