Glow Engines Discuss RC glow engines

ST 3000, 2500 won't idle

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Old 03-29-2013, 07:40 AM
  #1
308jockey
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Default ST 3000, 2500 won't idle

Morning all,

I've seen this problem many times over the years but don't know what to do about it. I'm running, or trying to run, an ST3000 in an Ikon Fairchild 24. A bit much engine but it's what I had available. It runs fine at high end but with the ST carb, as soon as I start to pull power back it just shuts off. No sputtering, it's as though I threw a switch. No matter how I adjusted high or low end, no matter what plug I tried or fuel (even Morgan's ST blend) it just won't stay running. If I go quickly down to low throttle it may run for 15-20 second before it dies. I changed to an OS 7M carb and the results are as bad. It almost sounds as if it is sucking air somewhere but I can't find any leaks between the carb and engine. I have a similar problem with a 2500 in a clipwing Monocoupe. It idles a little better but won't run at all in the mid range. I'm fed up with both motors. I'm sure there is a solution but it has eluded me. Any ideas are appreciated. Right now I'm planning on pulling the 3000 in favor of an OS 120 which will be plenty. As for the 2500 well, that's a scary airplane on it's best day anyway. Thanks.

Rick H.
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Old 03-29-2013, 08:25 AM
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tschuy
 
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Default RE: ST 3000, 2500 won't idle

what glow plug are you using? I've read that the OS #8 works best.


A search for the ST3000 manual didn't yield any positive results. But I did find one for the ST3250: http://manuals.hobbico.com/sup/supg0268-manual-v1_1.pdf

Go back to square one and reset everything to factor settings. Fuel tank placement could be sensitive. I had a ST3000 in a giant ugly stick many years ago and it was a good running engine for me....

Befor you decide to toss it let me know.... I'd like to take a swing at it and see if I can fix it...


Cheers,

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Old 03-29-2013, 09:11 AM
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Default RE: ST 3000, 2500 won't idle

OS 8 plugs are med/hot. IMHO, ST engines should get a hot plug. McCoy mc59 & mc4c, fox miracle, and Enya 3 plugs are what I use. The mc59 works well in all three of my ST engines on just 5% nitro. I'd start with the glow plug. Readjust the carb as needed and off you go. This is all assuming the fuel tank/system is in good condition and leak free.
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Old 03-29-2013, 10:15 AM
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Default RE: ST 3000, 2500 won't idle

Adjusting the carb is where most make mistakes. The ST carb idle needle needs only very minute adjustments once you find the needle position where a slight hiss comes from the carb that is closed to the size of a pin (0.8mm) (fit a piece of fuel line and blow on it.
Having had ST engines as my favorites for a long time. OS-F plugs were the best to use. I would slowly close throttle. If the engine cuts suddenly, idle is too lean. Adjust until idle is rich at 1/3rd throttle. very slowly lean the idle from there, using a blade width at a time.
One series of ST carbs had the reversed dogleg idle correction groove in the rotating drum. These engines would die at mid range, but have good idle and full throttle. Best advice is to replace the carb, unless you are handy with tools to reverse the dogleg.
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Old 03-29-2013, 07:04 PM
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Default RE: ST 3000, 2500 won't idle

I have run a gazillion of those old Tigres. Great engines. There's good advice already in the thread.

They need a HOT plug, like a 4-cycle plug.

The low oil fuel works best. I always used Morgan's Omega ST blend. 10% max on the nitro. 5% is just as good. On higher nitro, the engines will detonate in the hot summers in the US.

12%-14% oil content.

The way back original carbs that came off a .91 worked fine. When they started enlarging the carb throat diameter to get more power, they screwed it up. I found that the OS 7D from the OS 1.08 was great, but expensive. The carbs from the ASP 1.08 or the Magnum 1.08 were what I mostly used. You will need the sleeve from the older STs to make these fit. The opening in the crankcase is too large for them. This sleeve used to come in all the STs up to the 3000K.

The pin in the carb method works great.
a. Trap a pin in the carb by closing it on the pin. This leaves a small slit. You'll have to have the radio on or use a rubber band to hold pressure on the carb arm.
b. Close the idle needle all the way.
c. Get about a foot long piece of fuel tubing and hook it to the carb.
d. Hold your ear down next to the carb throat.
e. Blow into the tubing and slowly, click-by-click open the idle needle.
f. As soon as you hear a hiss, stop. This is your idle mixture setting. You may need to tweak it, but not too much.

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