So I fired up the 160 4-stroke twin today, the old dirty greasy methanol variety, the motor idles like a swiss watch transitions beutifully like a singer sewing maching to a sewing machine on steriods till I hit top end...... then it farts and carries on and starts pulsing and hunting for top end. I'm running 20% nitro full synthetic and the motor has only done 1 hours running.

Any one have any clues??, i've tried leaning it out like a 2 stroke till it dies and ritchening it up till it nearly drown without success. Could it just be that the motor is still seating??

Could be that the valve/seats have rusted from just sitting, or that things are "gummy", and need more time. Toss your coin, and take your pick. I was once told that, idle, "something will rust".

Les

Per the OS instructions, I'm estimating that you break it in for two hours before you can run full lean. Also, have you checked your valve clearances? And you might be using the wrong fuel. OS recommends 5-15% nitro and at least 10% oil. Some 4 stroke fuels (Saito) are 20% nitro, 20% oil which may have an effect on your engines performance.

As an example how fuels can effect performance on large engines: I have a couple of Super Tigre 2500's and they run like crap on 15% nitro, 18% oil. ST recommends 5%, 12%. Some fuel makers do make specific fuel for big ST's but my LHS doesn't carry those brands. So I take a gallon of 10%, 18% and add a half gallon of methanol from a motorcycle shop to it and the engines run perfectly.

I do prefer some castor content in my fuels rather than all synthetic.

Ok good suggestion will give a go and let you know, the motor I am running here is the magnum copy throwing a 3 blade 14x 7 master airscrew.

This is not a high speed engine. Depending on prop 8000 rpm is about max; 7500-7800 about normal. Dont run it too fast and dont run it too lean. Also make sure you are getting enough fuel to the carb.

Ok well it's definately not the exhaust extensions, I had a good look at either exhaust stub and noticed what looks like white puffs of vapour on the left hand bank when just above half throttle and makes me wonder if it could be Unburnt fuel because if I leave it at that throttle setting the motor stops with hydraulic lock from excessive fuel..... I'll buy a couple of new plugs tomorrow.

After posting the same question on three separate threads we find out it is not a OS engine ....but a Magnum? Goodness only knows what that problem could be.

Originally Posted by Jim409

After posting the same question on three separate threads we find out it is not a OS engine ....but a Magnum? Goodness only knows what that problem could be.

So Jim in the other thread where I posted this (not everyone reads all the forums, many minds and all that) the suggestion has been made that there could well be a sticky valve going buy the white puffs of smoke out the left Han bank after half throttle finishing with hydraulic lock. This is why I poste in three diffrent forums on two diffrent web sites...... Someone will have an answer out there,
Now how do I fix a sticky valve.......?

".but a Magnum? Goodness only knows what that problem could be."

Absolutely correct. Magnum did a GREAT Chinese copy of the APPEARANCE of OS. There, the resemblance ends. Some the the engines were just great, the others were garbage. It was a total crap shoot. When you opened the box, you never knew what you were going to find.

Les

I have and you may find as OS book on 4 stroke engines. In it you will find part numbers and all kinds of information. Disassembly and reassembly.......
Your engine need be disassembled to repair. First pull off the rocker covers. Turn the engine over to see if all the valves are working or stuck.
If stuck open further dissassemble to repair. If stuck closed, tap it until it unseats.

You may need to send the engine for repair. My OS ran like a champion with an 18X6 Zinger wood prop. I ran 10% Wildcat......also use OS ""F" plugs.