I am running an RCS 1.80 in a 1/4 scale cap with a 18x8 prop. The engines is running great until the nose is pointed downward. The best way to explain it is to say it sounds like it is missing. Level flight and nose up are fine. The engine doesn't quit but it sputters. I have richened the mixture and increased airflow with no change. I am stumped!!

I have a Brison that does this at a particular power settings. I have changed propellers and throttle curves to that I never have to fly at that setting. Since yours is at idle, if there are no other issues why change it?

CHECK TO MAKE SURE THE FUEL TANK CLUNK HAS'NT LODGED ITSELF FORWARD. COMPLETELY EMPTY THE TANK.WITH THE NOSE POINTING UP SHAKE THE PLANE. MAKE SURE YOU HERE THE CLUNK RATTLING AROUND. MAKE SURE THE CLUNK PICKUP TUBE IS'NT TO LONG AND GETTING JAMMED AT THE BACK OF THE TANK. I HAVE SEEN THIS SYMPTOM BEFORE.

I took all that apart today just to be sure and everything was fine.

Geistware - Mine is not doing this at idle ... it does it when the nose if pointed downward

Call Mike at RCShowcase, he has been very helpful to me. I called and left a message and he called me back at work the next day.

Great personal service. This alone will keep me their customer.

Andy

GOFLYIN,
SO when flying on 45 or 90 degree downlines the engine sputters? Does it do it on inverted 45 degree downlines? Do you have unburned fuel residue on your plane?

I take it if you hold your plane inverted, that it does sputter as well?

I have experienced this problem on the downline when flying large motors. I first installed a velocity stack to help the motor get more air. My problem came on the downwind line. It was apparent that the velocity stack was forcing too much air into the intake. I turned it 45 degrees down and that really helped. The motor quit sagging untill I made a hard downline and pulled up abruptly. It seemed to be happening all over again. I tuned and tuned. I checked with the guys at
http://webpages.charter.net/rsengineconversions/

We talked and tried the motor with and without the veloicty stack. What we finally ended up doing was turn the stack UP about 45 degrees. It appears that what was happening was when I pulled up abruptly the slippage of the plane towards the ground was putting the plane in such a situation that I was again forcing too much air into the intake. Now my motor runs like a scalded dog no matter what attitude. It runs as well inverted as it does uprightand straight up or down it really scoots. Those guys really know their GASSERS ! It's pulling my Hangar Nine Ultra Stick like a dream and for pennies a day.

Big Al

Big Al, I appreciate the info but unfortunately my carb is in the rear of the engine. I don't know that a velocity stack would help me.

GoFlyin,

You're correct. I didn't think of that. My homelite has the standard side mount carb on it. Even with this in mind, it still sounds exactly like my problem. Keep looking Once it's right it's AWESOME !!

Big Al