4 stroke cuts at end of outside loop

I have a 120 4 stroke mounted inverted in a Cyclone 3D Keeps cutting out at the end (top) of an outside loop (bunt) but otherwise runs fine. Doesn't cut with any other aerobatic manoeuvres

I've checked the plumbing, clunk & tank. All seems OK

What could be the problem ?

Thanks

Reply to
fred
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Reply to
2fast

are you sure the clunk is far enough away from the tank end?

Reply to
Kevin

It will fly OK inverted, its just the outside loop that causes the trouble. Might get a perry pump for it, and also the fuel lines could be shortened, they are needlessly too long.

Reply to
fred

Yeah, the clunk does not touch the rear of the tank in any orientation.

Reply to
fred

even under -G and suction from the motor ,it has to be fuel lines or tank I would think

Reply to
Kevin

Reply to
Paul

bottom end to lean? I would have thought you are going to be at somewhere near full throttle at the end of a bunt

Reply to
Kevin

Doesn't it depend which way you do the bunt ? If you start low then roll to inverted and bunt from there then you will finish at low throttle. If you start high and bunt from upright level flight then of course you do end up at full power.

Maybe the OP can tell us which way he does his bunts ?

Reply to
Boo

from the top, flying level, push the nose down.........plane is inverted at lowest point engine doesnt want to get up to full power on the climb out, cuts at the top.

Reply to
fred

Maybe the fuel tank's too high in the fuselage or there's a lean spot in middle of the throttle range ?

Reply to
Boo

Is it a Laser or a Weston engine where the carb is directly behind the top of the cylinder head ? If so then you may need to take special action to ensure the tank mean level is centered on the carb. Usually, engines have the carb mounted nearer to the crank axis and if a plane has been designed with this in mind then the tank position may be wrong.

As an aside, does anyone know why these two engfines have that peculier layout ? Quite apart from the tank position issue there is the problem of ensuring enough room for the engine to breathe between it and the firewall.

Reply to
Boo

I always thought a loop started from inverted was called an inverted loop rather than a bunt

Reply to
Kevin

Try richening your idle.

fred wrote:

Reply to
Robert Reynolds

@Boo: Putting the carb directly behind the jug shortens the intake manifold and helps prevent carburetor icing. Used to run into that with one of the first Saito 80's.

@ Fred: Richen up the low end 1/16 of a turn.

Reply to
Six_O'Clock_High

In article , Six_O'Clock_High

Reply to
Doug McLaren

Thanks for all your comments.

Dug out the instructions and the factory default position for the low end idle is: Unscrew (ccw, richen) low idle until it stops, then screw back in 6 turns.

Mine seem to be screwed in a LOT more than that, which could account for the lean setting.

Got the tank back in, the plane is ready to fly with the cowl off for easy needle access.

Reply to
fred

It also keeps the elephants away. That gets a *real* problem on outside loops.

yup. Elephants LURVE them Saitos.

Reply to
The Natural Philosopher

Fred --

It sounds like the tank might be mounted too high in relation to the carb CL. In this scenario, you would have to run the engine on the lean side to get normal ops; when you go inverted and put some negative G's on it, the engine would really go lean causing your sag.

Cheers -- Lyman

"On so-called global warming or climate change, let us not scare ourselves with catastrophic forecasts, or use them to defend and promote irrational interventions in human lives."

Reply to
Lyman Slack

Reply to
Six_O'Clock_High

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