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OS 46 AX Starting up proplems

Why do I always have to choke my OS 46 AX to get it started, by opening the throttle full and turn the prop for about 4 times while I block the air vent with my thumb.

I do understand that on the first start of the day this may be necessary due to engine would still be dry from fuel, but not every time I have to start up!! Thanks.

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Many possible reasons.
by: Mike from Oz

G'day. Most modern engines like the AX have carbys that are quite large. They are made like this to make them powerful but the down side is that they don't "suck" fuel all that well when they are not running.

Sometime, have a look at an OS Gemini twin. Is is a 160 size engine (yet it has a carby with a smaller thoat than the AX 46.

Your problem could be any of the following -

1. Tank too far from the engine
2. Tank too low
3. Hose leak
4. Muffler pressure line blocked, leaking. I have even seen a new engine with a completely blocked pressure fitting and another that was full of gunk.
5. Partially blocked filter
6. Simply too long fuel lines (keep as short as possible.

You can also choke the engine by simply putting your finger over the exit of the muffler and turning the engine over by hand. Muffler pressure then pumps fuel to the engine.

Also, if you simply block the carby with a finger and then turn the engine over, the fuel is sucked until the piston goes over Top Dead Centre but it is then blown back as the piston comes down. Best to take your finger off at the top of the stroke if you want to use the block carby method.

And remember, if you have the engine in a cowl, you may not be able to choke the engine this way. This is where the blocked muffler method wins.

Of course, if you have an inverted engine, go easy with choking and priming. After priming, always turn the engine over by hand to make sure you do not damage and engine which has a cylinder full of fuel. Good way to break a con rod.

A final comment. I always prime my engines before trying to start them. First run of the day or last of several. I run mostly four strokes and I find that if I prime them by turning them over a few times with the muffler blocked - then give them a few flicks and then apply the glow driver and check that the engine "bumps" as I turn it over while firmly holding the prop, then it will almost certainly start as soon as I apply the starter or give it a solid flick. If it does not, I repeat the prime and try again.

The only time I have problems is when an engine has not been run for several months. If the engine was not run completely dry and a fuel residue remained in the carby, sometimes (because I use a small amount of castor oil as well as synthetic) I will have a part blocked carby. In the worst case, this requires that I remove the needle and blow fuel through in both directions. After this, my engines always start.

No worries
by: Michael from Oz

Please feel free to post anything you like of mine. So long as it helps, I am happy.


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