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Old 10-25-2005, 09:28 PM   #1
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gold head OS

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Picked up a used OS 61 with gold head at the sale.
Seems to run okay but I see that this older model carb never had an idle screw .So how did they adjust the idle
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Old 10-25-2005, 10:16 PM   #2
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Maybe it is an airbleed carb?? Is there a tiny hole at the front of the carb?
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Old 10-25-2005, 10:46 PM   #3
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OS Goldhead

If you mean"low speed needle" and if they are like the old (circa) 1970 OS Blackhead, the needle is non adjustable. They came with,I beleive, three different low speed needles and you installed the one to give you the most suitable idle and transition to your likeing..
I had one of the old"Blackheads" with this set-up...
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Old 10-26-2005, 06:45 AM   #4
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Carb Adj.


I have one of these engines and had purchased in around 1970. It is a good reliable engine but can be difficult to adjust. The idle is adjusted by an "air bleed" screw. That is, you adjust the high speed needle and then lower the speed to idle, then adjust the idle mixture by closind the hole just in front/top of the carburettor opening. I did a post here someplace regarding the adjustment. I'll look it up and put below, I don't know where I got it from, but whoever did the original - thanks.

Most of the modelers I knew replaced the carburettor with a Kavan or Perry carb but any good .60 size carb with the correct fit will work well.

The proper name for the engine is:


Wayne Miller

Adjusting Glow Engine Carburetors:

First make sure there is no air leaks in the fuel lines, make sure the fuel lines are not kinked and the fuel tank is not too far from engine. Ideally, the center line of the fuel tank should be in line with the fuel pick up on the carburetor. The tank “klunk” pickup should not block fuel flow, that is, it should never touch the end of the fuel tank when the nose of the tank is pointed straight up (test when tank is out of aircraft). Also if a pressure tap from the muffler is used, make sure the tap is not clogged and the pressure feed to the tank does not have any air leaks, nor is blocked.

With the engine level and running at full throttle lean the mixture (turn the needle towards the closed position, usually to the right) until the engine wants to stop. Then quickly richen the mixture (open the needle valve, turn to the left) until maximum RPM is observed.

At maximum RPM, continue richening the mixture (slowly turn needle to left) until you note a slight drop in rpm. This should be will be the normal operating mixture for the high speed adjustment.

There are two styles of low speed carburetor adjustments, that is, a 2nd low speed needle valve or an air bleed adjusting screw. If it is a low speed needle valve, the needle valves would be in line, and opposite each other. If you have a low speed air bleed screw would be to one side of the carburetor and will open and close an air hole.

These both are low speed, idle, adjustments and such low speed adjusting should be done with them alone, the high speed setting should not be NOT TOUCHED once adjusted as described above.

Low speed idle adjust speed procedure:

Close the throttle to the slowest steady rpm. From that, quickly open the throttle.

TOO RICH (too much fuel in mixture):
Did the engine run rough, burp, want to stop? If it did, the mixture is too rich.

If you have a low speed needle carburetor, this can be leaned by turning the low speed needle in (to the right) about 1/2 revolution at a time.
Repeat (after first opening the throttle to clean out any excess fuel in the crankcase) until the change from low to high is immediate and clean.
If a lower idle speed is desired, close throttle a little and repeat the procedure.

If the engine has an air bleed carburetor and the initial quickly opening the throttle indicates a rich mixture (as described above) the air bleed screw has to be opened a little. This will let more air in, try turning the air bleed screw to the left 1/2 turn at a time. Follow same test procedure as with the needle valve procedure when testing, that is, opening throttle quickly.

TOO LEAN (too much air in mixture):
If the engine ran smoothly during initial quick throttle opening the engine, then slowly quit. The mixture is to lean.

If you have a low speed adjustment needle, turn the low speed needle out (to the left to give more fuel) until the engine does not quit when the throttle is quickly opened,

If the engine has an air bleed carburetor, and the mixture is too lean (too much air) then turn the air bleed screw in, to the right, to limit the air in the fuel mixture.

When proper low speed setting is attained the engine will transverse from low to high smoothly time after time with no tendency to stop. If not increase the low speed rpm very slightly until action is proper.

If when an engine has been set up with this routine and you still see the problem you describe the trouble is probably in the fuel supply system not the engine, see the notes at the beginning.
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Old 10-26-2005, 09:11 AM   #5
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carb adjt

Thanks Wayne for the great info .
I new someone would have the answer.
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Old 11-01-2005, 07:20 PM   #6
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I have the same engine. I put a Perry carb on it. Problem solved.
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