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RV6-A 0-360 stops at less than 1200 rpm

Wiley Price

I'm New Here
I flew into KUDG and landed after a 2.5 hr flight. The engine quit on short final and was a bit hard to restart after roll out. I refueled, ran engine w/boost pump on,tried each mag, carb heat on/off, still stumbled and quit if throttled below 1200. Perhaps foolishly flew home and same thing happened on short final. I pulled cowls off and found gascolator bowl full of water. Installed quick drain, refueled - no water in tanks or gascolator, but same problem of engine stopping at lower than 1200. Boost pump works ok, carb screen clean and gascolator screen clean.
What else could I look at? Needless to say, it is quite unsettling.
 
Did you drain the carb bowl? If you had that much water in the system, you might have water in the bottom of the bowl.
 
Welcome to VAF

Wiley, welcome aboard the good ship VAF:D

Agree with Paul, check carb bowl.
 
Please educate me

I am MS carb challenged. I thought fuel comes from the bottom of the bowl to the main jet and the idle circuit would use a small portion of that capability. If the engine gets fuel to fly, why is the idle function subject to water ? Is the idle supply intake separate and BELOW the main jet orifice in the bowl ?
 
I forgot to mention, carb bowl was drained - no water there. Engine was installed new along w/carb, mags, etc. : has about 900 hrs total. I'm not sure why gascolator was in stalled w/o drain, but I did let water out! What else?
 
I?m still trying to wrap my brain around why anyone would fly an airplane back home after it just quit on short final and wouldn?t run below 1200rpm. I feel like you were awfully close to becoming a statistic.
 
If the water was dirty and contaminated it may have plugged up the idle circuit?? The carb may need to be disassembled and given a good cleaning and a shot of air through the circuits.
 
This is one of the common symptoms of a failing (sinking) float.
It causes the engine to start running overly rich which can be tolerated at higher RPM's but not down near idle.
 
Idle

If the water was dirty and contaminated it may have plugged up the idle circuit?? The carb may need to be disassembled and given a good cleaning and a shot of air through the circuits.
Could also be FOD ingested via carb heat or alternate air. Same result: blockage in idle circuit.
 
Water found in gascolator was clear as spring water. There was no water or debris in carb bowl. Who and how much to overhaul carb?
 
Idle mixture needs adjusting? On the ground, I'd try the idle mixture test if that's possible.

It is not unheard of but it is rare for the idle mixture to just change.

The first order of business would be to inspect to be sure that nothing else happened to make it change.
Carb. float failures are rather common. That is the very first thing (after the other things that have already been done) that i would check.

It doesn't require sending out for overhaul. You just need a new bowl gasket and a set of new screw locking tabs. Any halfway decent mechanic should be able to help you take a look inside.
 
As long as the cowl is off while you look into the float, check that all intake tubes are secure to the cylinders. An intake leak will also manifest itself most at idle but be tolerated at higher power. Free and easy check.
 
Agree

As long as the cowl is off while you look into the float, check that all intake tubes are secure to the cylinders. An intake leak will also manifest itself most at idle but be tolerated at higher power. Free and easy check.

Plus 1 for this.....
Also, I have read many times about Carb bolts/nuts coming loose and causing a bad intake leak as well.

An intake gasket leak usually causes disturbance in one cylinder and therefore a rough ilde or hot cht......but a complete shutdown would most likely mean something worse. But not ruling anything out, it could be several intakes leaking.
Good Luck
 
Idle

I had the same thing happen several years ago at a fuel stop during a cross country flight.
Long story short, the idle adjustment screw had departed during flight.
Rich
 
While you are at it, check your primer circuit/fittings (if you have a primer). Make sure the primer isn't flowing when the boost pump is on.
 
i had a sinking float years ago. no problem with stalling at idle but needed to run a leaner mixture in cruise. :)
 
i had a sinking float years ago. no problem with stalling at idle but needed to run a leaner mixture in cruise. :)

Depends on how bad it sinks.

I have seen them them fail so bad that fuel was running out of the bottom of the air box if the electric pump was turned on during troubleshooting ;)

A little more specifics....
There are a bunch of different float designs in use.

Some are metal some are plastic coated foam.

Some are molded plastic pieces that are ultrasonically welded together to form a hollow air filled space.

The foam examples will generally just slowly gain some weigh by becoming saturated with fuel.

The metal ones would partially fill with fuel because the seam was at the mid point and it would trap an air bubble above.
The welded plastic ones would just about totally fill with fuel because the seam was near the top of the float.
These were the ones designed and used by Precision. I think it was the chronic failure of these floats that pushed them to sell the carb part of their business.
 
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900 hrs?
Spark- How is mag timing? Has the 500 hr mag inspections been performed?

Fuel- Any difference with & without boost pump on? Checked fuel primer lines and connections?

Carb- overhaul cost shouldn't be factored in, get it done!
One rare but possible cause- There is an old AD out on Marvel MA-4 carbs dealing with the lean mixture valve rotating in the bottom of the fuel bowl, although not applying to clone carbs, can happen as it did to me on a O-360. Depending on the valve movement in the fuel bowl housing, would either cause an over lean or over rich condition depending of throttle set & would either starve or flood the engine. The clone carb on my engine was a new AStar unit.
 
Engine Quit Below 1200 RPM

After talking with Marvel, I replaced carb with an overhauled unit through Aircraft Spruce. Engine runs just fine from 600 on up.
Marvel said idle circuit probably was clogged from corrosion inside carb from water getting in it. As with most airplane stuff, money will fix anything!
 
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