Stuart Turner R3M

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seagull1

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Recently de-coked the engine and had the magneto serviced.
Timing is accurate. Engine runs, but will not tick over, it runs down and stops when the throttle lever is put to idle position. Engine speed decreases when the boat is heeled to Port and increases when heeled to Starb'd. All jets in Amal Carb' clean and in good condition.
Anyone got any ideas as to what the problem is please?
 
[ QUOTE ]
Recently de-coked the engine and had the magneto serviced.
Timing is accurate. Engine runs, but will not tick over, it runs down and stops when the throttle lever is put to idle position. Engine speed decreases when the boat is heeled to Port and increases when heeled to Starb'd. All jets in Amal Carb' clean and in good condition.
Anyone got any ideas as to what the problem is please?

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Float needle valve need adjusting?
 
What kind of adjustments are there on the carb for slow running? A air by pass screw or a stop to lift the slide?

Try the float as mentioned.

Also, user of these forums MTB deals in old carbs and knows his stuff.
 
Sounds as though air is being sucked in, somewhere after the carb. It may be that
worn valve guides are letting air in... the carbon build up disguised the problem until the decoke.
It doesn't explain the behaviour on different heel but it was the cause of tickover problems on an old Jap V-twin I had.
 
The air slide on the carb should have about 1/4" to 3/8" of thread showing. Don't screw it in all the way. It's the only adjustment I know of which alters tickover. Too far out and it'll backfire (weak mixture), too far in and it'll stop.

You can't really motorsail with a carburated engine. When the boat heels the float sticks and the carb starves or floods (usually floods in my experience).

Don't forget. To stop the engine, shut off the fuel and let the carb run dry. This prevents a gummy residue from building up as the fuel evaporates.

Hold on a minute. You mentioned Amal carb. My 1/4" to 3/8" refers to the ST carb.
 
Thanks for all your ideas and tips. The carb' has an air by pass screw, it has no slide. I thought a float chamber problem might explain the "heeling" symptom. The float chamber appears fo be full to an adequate level when I have removed it. There is no adjustment for float level other than to bend the tab that controls the inlet valve. Is that standard practice?
The engine is two stroke and has no valves to leak air.
Thanks again to all.
 
Just a few ideas...

On any float chamber carb the float chamber and the carb itself should be in line fore and aft. If the float chamber is off to one side then you will definitely get a change in mixture as it heels.
But you've probably no control over this anyway.

Have you considered low sparks?
On starting there's (usually) a spring loaded gadget that not only gives a big spark at cranking speed, but delays the spark so it doesn't fire before TDC.
But when it's running, maybe the mag isn't giving all it should.
You might try closing the plug gap down a bit to see what happens.

All the best with it.

Ron
 
Two things to look at: is the fuel tank outlet at one end of a transversely-mounted tank, so that the pressure on one heel is greater than the pressure on the other heel? Aso check the spark plug leads. These are rarly given the importance which they require. If the leads are the old copper-cored ones, the may be sufficient corrosion at the ends to prevent the spark from getting to the plugs. This corrosion can be so slight as to be invisible, but it also wicks along the cable from the ends toward the middle. Replace the cables with carbon-impregnated plastic cored leads.
Peter.
 
Stuarts always keep you guessing. The best use I have found for them is on the end of 60 metres of chain. /forums/images/graemlins/grin.gif
 
If your going to make jokes about a Stuart Turner the least you can do is make them original! /forums/images/graemlins/tongue.gif
 
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Stuarts always keep you guessing. The best use I have found for them is on the end of 60 metres of chain. /forums/images/graemlins/grin.gif

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... thats almost as quick a way of sending your boat up the bank as trying to use one to power it /forums/images/graemlins/laugh.gif

This may not be a carb problem as such: When the engine was decoked, you presumably left the barrel in place? Did the head gasket separate easily? Or did it stick, as they so often do? If so, theres a good chance you have cracked the barrel to crankcase gasket, and it is leaking. Any leak into the crankcase will upset carburation, and cause at best the tickover problem you describe, and often make it difficult or impossible to start the engine at all. I have a theory that much of the ST's poor reputation was down to poor sealing of the crankcases either at manufacture, or in subsequent rebuilding. I believe the quality of the crankshaft seals was pretty poor, also compounding the starting and running problems that beset these engines.

The problem with crankcase sealing is that it is virtually impossible to diagnose it, even on strip down. As a result it is often virtually impossible to identify and seal the leak at rebuild, and it is only too easy to build it and other leaks back in on rebuild.

As to heeling, as has been said the ST carbs did not like being tipped over and could easily alter the carburation as the angle of heel increased, particularly when fitted with the older style brass carbs.
 
I agree on the crankcase sealing issue. Also probably explains why they were so often difficult after an overhaul. I certainly did not pay sufficient attention to the crankcase seal after rebuild as I did not fully appreciate the significance at the time - it was only later that it dawned on me but by then I had taken to diesels.
 
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