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HomeRC & PowerAircraftHelicopterEngines Plugs Mufflers Fuel › Sigh, this is a tough one
10-11-2005 11:47 PM  13 years agoPost 1


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Got a used O.S Surpass .70 (1) and it will not run nicely as they usually do. It wont run reliable at idle, no matter what I do. My mates got these engines and they run perfectly well. I run it on 10% Nitro and 18% oil, new O.S "F" plug and I have run both needles until engine cuts with glow current attached, if it is detached, engine quits eventually.

(I have tried all settings that is)

Engine is mounted inverted and a 250 cc fuel tank is mounted with center line 5mm above spray bar measured in level flight attitude. Engine behaves same no matter attitude. It behaves lot better with brand new glow plug but degrades soon in idling charecteristics.

It is usable annyway because it can be kept running by throttle maintanance but its annoying.

On-board glow is a sollution but not wanted, because it should not be needed and adds too much weight and maintenence of another battery cell.

I could scrap it and get a new one but i want to track this down.

"what did this m0ng do to this poor engine ? "

I suspect a damaged carb because it tends to misfire when i open throttle slightly but not fully, also it runs best on 0,8 turns on main needle without muffler pressure.

Thanks for any help.

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10-12-2005 12:48 AM  13 years agoPost 2


Richmond, VA, USA

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I presume you've checked the valves, right? I dislike the OS feeler set with it's "one should fit while the other shouldn't" approach. I prefer to set them at about 2 thou on a cold engine using a set thickness feeler.

Engines can sometimes vary for the strangest reasons. I would try 15% nitro fuel, since 4C's love nitro for best idle performance (and all around performance for that matter).

Maybe try pulling the entire intake manifold w/ carb off of one of your friend's engines and see if the problem persists on yours.

Also, though you typically don't see ring problems with these smaller OS four strokes, a worn ring can cause all sorts of peculiar engine behavior.

Ben Minor

10-12-2005 06:09 AM  13 years agoPost 3

rrElite Veteran

Johnston USA

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Did you check the rear bearing? Chris

10-12-2005 09:44 PM  13 years agoPost 4
rotor- shark



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any engine misbehaviour of type you mention is likely to be some sort of air leak from the carb,i have had this happen on 2 stroke os engines.usually you find the carb is a loose fit in the engine block,before the retainer screw is done up.

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