Please help, ASP 75 cutting out.
 

My ASP75 is fitted with one of the new series ST 75 carb for fuel economy, and the combo has always performed well. After recently replacing a split fuel tank and doing a carb strip down, I am having a problem keeping the engine running at idle.

The top end is fine, with a reasonable midrange which is typical of the ST carb, but is not a major problem.

The engine idles normally on an OS #8 plug with the starting battery connected, but as soon as the battery is removed the engine quits, yet it idles well with a Fox miracle plug when the battery is removed.

I have tried several new #8's with no change, what could be wrong. I would like to continue using the OS plug as it gives a good midrange response. I have checked all fuel lines for leaks and pressured the system, and used high temp RTV silicone to help seal the carb neck / engine to guard against a possible air leak.

What am I missing here ??

RE: Please help, ASP 75 cutting out.
 

Your fuel might be getting stale....if the engine dies out when you remove
the glow it is usually bad fuel.

The Miracle plug is a hot plug, and works great in two cycles....why not
continue to use it ? ;)

FBD. :D

RE: Please help, ASP 75 cutting out.
 

Is it an inverted application?

RE: Please help, ASP 75 cutting out.
 

No it is not an inverted installation, the engine is mounted sideways. I had never thought that the fuel might be stale as all my other engines run well on it, just as the ASP used to.

As Flyboy Dave suggested, I will stick with the Fox miracle plug, and as soon as I get a new bottle of fuel I will change back to the OS #8 plug and see if it makes a difference.

RE: Please help, ASP 75 cutting out.
 

Hey, I'm having a problem with my new st-75. Do you by chance know what a good starting point for the idle adjuster screw. Maybe 3.5 turns out? I just can't keep it running for longer than about 45 sec.

The manual recommends a high end starting point but no idle adj. starting point.

Thanks,
Chuck

RE: Please help, ASP 75 cutting out.
 

Chuck, my ST 75 engine's idle needle is set at approx 3.25 turns out, and will idle all day at 2,800 rpm on a 12x6 MA prop.

I would suggest that you start with the needle set at 4 turns out and work from there. HTH

RE: Please help, ASP 75 cutting out.
 

thank you, I'll give that a shot!