Momentary Hick-up

WB0TMC · #1 08-20-2008, 08:20 PM

Hey guy's, I'm fairly new to this, but I fly a RV6a, been flying it for about 1 year, did not build it, but love it just the same.
My question is: Has anyone else heard of this?

My engine has a very fast hick-up when I pull the power back going from cruise to landing . If I am in cruise say 2450 RPM, when I pull back on the power to about 2150 or so it sounds like it is running out of fuel, but it happens so fast, by the time I hear it it's over with, I can leave it at that power setting and it don't do it again, JUST COUGHS, LIKE FUEL STARVATION . I first thought it was the power setting but I have found out it will also do it at other power settings, for instance, If I am decending and pulling back on the power, it does it, say when I pull back on the throttle maybe 1 inch or so, So its not a rpm setting it seems to be a throttle setting.... It will do this almost ever time. I can avoid it by pulling back on the power to about 1200 RPM quickly.

I am puzzled????

CraigC · #2 08-20-2008, 08:44 PM

Do you know what your setup is?

Carb
FI

What engine?

airguy · #3 08-20-2008, 08:47 PM

Does your mixture (lean/rich) affect this behavior?

WB0TMC · #4 08-21-2008, 09:01 PM

My lean mixture does not effect this action....

The set up is a rV6A 160 hp with a marble schrader carb, Engine was just 0 timed 6 months ago, it done this before overhaul also,,, Carb heat or mixture has no effect on it,,, it always does it when I slowly pull back power, at level flight it happens at 2150 PPM, at decent it happens when I pull back throttle about 2 inches on the throttle knob.

?????

dhammer · #5 08-21-2008, 09:28 PM

When the engine was overhauled was the carb at the same time by a good carb shop? Something to check is the jetting of the carb. If someone drilled it they could have screwed up its shape.

Per http://www.kellyaerospace.com/articl...essory_AMT.pdf not all jets are straight, but may be stepped or tapered to give a proper fuel balance across the full range of throttle openings. If someone drilled it, the mixture could be wrong at that throttle position.
Just something to think about.
Don

WB0TMC · #6 08-24-2008, 06:30 AM

Thanks Don:

I wondered about that, to answer your question, NO, the carb was not overhauled, I think that will be the next thing I have done, I will try that...

Thanks
James

Kyle Boatright · #7 08-24-2008, 06:46 AM

I've seen that with an induction leak around the carb. In my case, the bolts that attach the carb had worked slightly loose (or were not adequately torqued in the first place).

The way to check for this is to try and wiggle the airbox. If the carb moves relative to the sump, you may need to tighten the carb bolts. Which, of course, requires replacing the 4 little $0.25 safety tabs.