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Jan 10, 2020, 12:16 PM
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OS Max 61 fx


I have a 61 fx that I picked up somewhere and am just now trying to get started.It will start and idle and go to full throttle and after a moment stop running.I turned the idle mixture screw and then all my trouble started. Now it will not even start. If I turn the idle screw all the way in and then back it out a 1/2 turn should this be close to the correct point for running?I could go from there. The only other problem is it seems to not have much compression at all. Turning the prop by hand it has very little compression. It all but turns free with no resistance at all.It all but turns free.Any advice?
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Jan 10, 2020, 12:37 PM
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Pix would help. Did you open the head and the back plate to check the internals?
Jan 10, 2020, 01:23 PM
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I opened the head and all seems to be in order. What pictures would help?
Jan 10, 2020, 01:24 PM
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What would I look for behind backplate?
Jan 10, 2020, 01:25 PM
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I didn't see a ring. Did I miss something?
Jan 10, 2020, 03:53 PM
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The 61 FXs are not ringed engines. If you still have the head off remove the cylinder liner. Check for peeling of the plating from the liner.
Jan 10, 2020, 04:51 PM
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Glow plug tight mounted?

TF
Jan 10, 2020, 05:10 PM
A man with too many toys
Could just need cleaning and new gaskets.

Bast to disassemble everything, clean, inspect, maybe replace bearings maybe replace gaskets, and reassemble. If the carb has o-rings replace them.

When you first run it again use high oil fuel with 50% or more of the oil castor. Castor oil helps restore compression in old engines.

.
Jan 10, 2020, 06:04 PM
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Quote:
Originally Posted by RC Man
Could just need cleaning and new gaskets.

Bast to disassemble everything, clean, inspect, maybe replace bearings maybe replace gaskets, and reassemble. If the carb has o-rings replace them.

When you first run it again use high oil fuel with 50% or more of the oil castor. Castor oil helps restore compression in old engines.

.
A non ringed engine will not improve in compression by cleaning it. A stuck ringed engine will improve in compression once the ring is freed. Maybe the engine is tired and the only work around is a new piston and sleeve besides new bearings and gaskets.
Jan 10, 2020, 06:26 PM
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Have attention for this post of me, also this OS Max can been over heated in the past. Problem was solved by a modification of the backplate assy/ needle valve.
Can you show a photograph of your engine?
https://www.rcgroups.com/forums/show...4&postcount=39

This was a result of measuring and data logging of the CHT of this engine

TF
Jan 10, 2020, 07:35 PM
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The problem may be that I am not used to non ringed engines. It has compression but not quite the pop I am used to. After replacing the head it seems to have more compression. I will try to start it again tomorrow and post the results. Thanks for all the input.
Jan 10, 2020, 07:38 PM
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Non ringed engines must have much more "pop" than ringed!!!
That's why these easely can be started by back flip.
Be carefull not overtighten the head bolts. When it was a matter of over heating the fit between head and cilinder sometimes can give problems as result of metal deformation of the surfaces.

TF
Last edited by Taurus Flyer; Jan 10, 2020 at 07:44 PM.
Jan 14, 2020, 10:17 PM
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Today I started the engine on a test stand. It started and ran. The top end was not as high as it should have been. Also the idle was not consistent. The engine when not running has very little compression.It turns over almost with no compression at all. Just turns and turns. What is the" most" likely problem?
Jan 14, 2020, 11:33 PM
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Quote:
Originally Posted by Mash P39
Today I started the engine on a test stand. It started and ran. The top end was not as high as it should have been. Also the idle was not consistent. The engine when not running has very little compression.It turns over almost with no compression at all. Just turns and turns. What is the" most" likely problem?
Lacking compression is the problem. Probably an old and tired engine that has a worn out piston and/or sleeve. A 2 stroke engine is not a super complicated machine. You need a good seal between the piston and the sleeve to have good compression. Without compression your engine will never run properly.
Jan 15, 2020, 04:47 AM
Still gassin' it.
Running all castor lube in your fuel or at least a 50/50 castor/synth package) might restore that compression back to usable values (where is my compression gauge when I need it?).

It did for an old Fuji outboard that I received maybe 20 years ago from somebody from Hawaii. Engine was very low on compression, hard to start (needed extensive use of an electric starter), did not idle well etc etc.

After putting through maybe 2 litres of fuel 50/50, 10% Nitro, compression was more or less back, and the engine could fairly easily be rope-started again.


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