OS 60SF bench run anomalies. - RCCanada - Canada Radio Controlled Hobby Forum
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Old 12-30-2006, 01:09 AM   #1
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OS 60SF bench run anomalies.

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I recently set up my OS 60 on a bench. I run it with a pipe, and I read somewhere that you are to get a benchmark reading without a muffler on it before tuning the pipe.

I run a Perry pump on it, so it is pumped.

All that stuff aside, I noticed something weird.

With the header and pipe on, it runs fine. I removed the pipe, and everything was normal. I had to shut it down right away though, as it was Christmas day, and I live in a Townhouse complex. It did sound cool though.

Next, I removed the header (keeping with the Xmas theme) and started it up. It sounded weird, but ran alright. I decided to stop making noise, and killed the throttle. The engine wouldn't stop. I choked the carb, and it still ran. I finally had to remove the fuel line (Fuel sprayed everywhere, so the pump works very well).

My question is. Why will the engine shut off just with the throttle closed with the header on, but it won't without it. I obviously won't be running it without a header and the pipe, but I still find it odd that it would keep running.

I have thought about the carb seat leaking, but the problem would be there even with the header and pipe on. Wouldn't it?

Could the engine be getting air through the exhaust outlet?

Not a problem, but an observation that I'd like to explain.

Thanks in advance.

oh, and Happy New Year, (even Sammy, John, Ted, Mitch, Billy-bob, and Sally )
Michael Gyger
MAAC 58295
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Old 01-04-2007, 09:41 AM   #2
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with no back pressure and the top of the piston open to atmosphere it has probably enough oxygen to still run with fuel in the base. the pump may be driving fuel past the needles with the throttle closed
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Old 01-04-2007, 01:38 PM   #3
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With no back pressure also see if you carb barrel is partially open. Don't know how to explain it except wihout the back pressure there is less resistance so it will have a tendancy to stay running.
John Davidson
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