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OS 140RX pump problems? (long)

Old 07-31-2002, 02:54 PM
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Default OS 140RX pump problems? (long)

Hi -
I have a 140RX in my Elan pattern plane. I think I may have fuel feed problems --- possible gummed-up pump (??)

Bought the engine used. I've put 125 flights on the engine after 1/2 gallon of rich run-in on a bench mount.

Mac header, Bolly 480R muffler, APC 15x11 4 blade or APC 17x10N 2 blade prop. OS-F plug.
Replaced the bearings after 40 flights - saw bearing corrosion in the engine that made me think it had sat awhile before I bought it.



I run 15-25% (20-25% in the current hot weather) nitro fuel / 17%syn oil, 2% Castor. I double filter the fuel into the tank; there's an in-line fuel filter between the tank and pump.

I run the fuel out of the engine and put after-run oil into the venturi after each day's flying.

When first flying it I'd occasionally blow a glow plug after 2-5 flights - (lean run I assume) though the engine was set 100-150 rpm rich from peak (by tach) when launched, and the idle was set for 30-45 seconds of steady idle at 1850-1950 rpm.

Now I usually launch 200 or so RPM off peak and have had no glow plug problems for about 30 flights.

Heard possible pinging /rattling at part throttle in flight (hot weather) and added a second head gasket- no more pinging.

Recently when spinning the prop I sometimes *don't* see fuel moving thru the line into the pump.

About one time in 5 the engine will go hard/lean on run-up; to get it rich I have to back the needle out 1/2 turn or more before the RPM comes down - then it drops fast to blubbery rich and I can set it from there.

Twice I've pulled the needle valve and plug and spun the engine w/ a starter -- run an ounce or so of fuel thru the pump and out the needle valve hole -- hoping to clear the lines and pump of any foreign matter - seems to help some, but then the needle setting problems return shortly.


1. Any thoughts on what to do to fix this apparent fuel feed problem?

2. Shouldn't the engine be OK set 100 off peak?

3. Is there any way for a semi-skilled user (I can replace bearings and other engine parts) to further fault -isolate /flush/fix pump problems?

Thanks in advance

Rick
Old 07-31-2002, 07:05 PM
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Default OS 140RX pump problems? (long)

There are several things you brought up. One of the things that 'jumped' out at me was the reference to the fact that it will go hard lean and take a lot of needle to richen, where the engine will drop into blubbery-rich running.

This indicates that you are getting air agitated into the fuel inside the tank...also known as "fuel foaming". Engine vibration causes this. You'll have to either add more foam rubber around the fuel tank or take some out. If not enough rubber, the tank's not insulated against the vibration, and if too much, the foam is compressed so much it's not working.

If you go with higher nitro, you'll have to add oil to help cool the engine. Nitro acts as a oxidizer in the fuel and adds power. More power means more heat. Unburned fuel and oil thrown out the exhaust take heat with them. If you're running 20% nitro, you should add oil to bring the oil content percentage to 20%. 25% nitro would need some more.

With a pump, you can usually set the engine right at peak RPM and fly it that way. The pump should prevent leaning as the fuel level in the tank goes down.

If you disconnect the pump from the carb and spin the engine, you should get a good stream of fuel. That tells you the pump's working nicely.

If your pump needs repair, send it in. We can't repair the pump, but we can do an exchange if under warranty, or offer a discount on a new one.

We hope you find this information helpful. Should you have any further questions or concerns, please do not hesitate to contact us at this email address. (Please be sure to copy all previous emails into any future questions.)

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Bill Baxter, Manager
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Old 08-01-2002, 01:35 AM
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Default 140RX problems... DUH!!!

Thanks for the quick, solid answer.

fuel foaming.... DUHHH!!!

Put more padding around the tank, and got three solid, dependable flights today!

Needle seems very nice again too. !

Thanks again!

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