Author Topic: Magnum .36 burp in transitions. (Read 1938 times)

Stan Tyler · « **on:** July 30, 2007, 11:11:38 AM »

With a Magnum .36 on a profile, I've been getting a burp in the transitions from insides to outsides. Symptoms are similar to what a Fox .35 does.

Running an APC 10.5-4.5 prop at about 10,500 launch RPM on 10% nitro, 22% lube fuel. Consistent run with no run away, just a noticable burp in the inside to outside transitions or on a hard outside corner like in the outside square or the inverted turn in the wingover.

Any Suggestions?

Thanks,
Stan

dennis lipsett · « **Reply #1 on:** July 30, 2007, 01:12:28 PM »

Burp it after filling and before you fly. That motor has gas.

Im sorry!!! the devil made me do it

Dennis

Busby · « **Reply #2 on:** July 30, 2007, 03:23:47 PM »

Generally,with my Aerotigers or PAs it is doing its best to tell me to install a new plug.
Try an idle bar thundertiger.

RandySmith · « **Reply #3 on:** July 30, 2007, 03:55:31 PM »

Quote from: Stan Tyler on July 30, 2007, 11:11:38 AM

With a Magnum .36 on a profile, I've been getting a burp in the transitions from insides to outsides. Symptoms are similar to what a Fox .35 does.

Running an APC 10.5-4.5 prop at about 10,500 launch RPM on 10% nitro, 22% lube fuel. Consistent run with no run away, just a noticable burp in the inside to outside transitions or on a hard outside corner like in the outside square or the inverted turn in the wingover.

Any Suggestions?

Thanks,
Stan

HI Stan

Can you tell u s what type of fuel you are using? all castor? syn.?
What type of glo plugs are you using? is the motor very lean or rich?

Regards
Randy

Stan Tyler · « **Reply #4 on:** July 30, 2007, 04:39:46 PM »

Hi Randy,

The plug I'm using is a new ThunderBolt R/C long. Fuel is a pretty generic stunt mix, 10% nitro, 11% castor/11% synthetic. The gallon can was opened about 2 months ago, and down to almost empty, could be a factor but same fuel runs fine in other motors on same day. I will try new fuel next weekend.

Motor is running with a tongue muffler, could be causing too much back pressure. The motor does not appear to be running too lean or too rich.

Forgot to mention, air temp was mid to high 80s.

Thanks,
Stan

Bill Little · « **Reply #5 on:** July 30, 2007, 06:54:10 PM »

I have had a brand new plug be a "bad" one out of the bag. Marshall (Busby) and Randy (Smith) were both there. Put in another "new" one and it's still in the engine.

Steve Helmick · « **Reply #6 on:** August 19, 2007, 08:20:03 PM »

All else failing, I'd certainly try rotating the spraybar in about 10 degree increments from wherever it is now. It might help...or might not. Be sure to post your results.

Steve

Dick Fowler · « **Reply #7 on:** August 20, 2007, 05:31:12 AM »

Below is Lou Crane's reply to the thread - What is the "Fox burp"? and explains why the "burp" happens even on engines that don't suffer from an oversized case bypass channel as is the current theory for the Fox burping. Makes sense.

Re: What is the "Fox burp"?
« Reply #6 on: August 19, 2007, 05:45:49 PM » Quote

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Perry,

You could try searching (that input box at the top right next to the magnifying glass..) under wig-wag for a post I put in a while back. Helps reduce 'burp' and getting in a first flight w/o starving or richening off the engine.

The reason for the burp may be related to the change of g-loading when the model kicks over from inside g to outside g at the intersection in the figure eights. Why it takes the form of an audible misfire or non-fire for some Fox 35s could be a very complicated combination of many things. If the tank, prop, plug and fuel are all good, and the setting is about right, you may hear a one or two step stutter without losing noticeable power, and without the engine shutting off.

The low round loops in the round Eights require about 10 to 11g for their shape, and the effect of gravity adds 1g at the bottoms and about 3/4 g at the top (trigonometry - at the angle that gravity works on the model at 45° line elevation.) The intersections are supposed to be vertical, so lift and gravity are at right angles - they don't interact at that split second... So the loads on the fuel are from 10-11g toward the wheels (in the inside) to the same range away from the wheels (in the outside) and that's suppossed to happen in a hundredth of a second or less. Quite a change.

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steven yampolsky · « **Reply #8 on:** August 21, 2007, 09:09:04 AM »

Quote from: Stan Tyler on July 30, 2007, 11:11:38 AM

Any Suggestions?

Try less oil, it may be cooling the head too much, especially considering that this is a profile. 18% all synthetic will work just fine.

Dave Adamisin · « **Reply #9 on:** August 21, 2007, 09:17:05 AM »

Stan, are you running muffler pressure? Transition burps can be fixed sometimes by opening the venturi up or lowering the fuel system pressure. If you are running MP, try adding a couple holes in the tongue or opening the venturi about .010".

Stan Tyler · « **Reply #10 on:** August 21, 2007, 02:39:33 PM »

For the time being, I've swapped motors from the Magnum .36 to a Len Neuman modified FP35. Using the same fuel the FP35 doesn't have the burp that the Magnum did.

When time permits, I'll try the Magnum with less oil to see if it's over cooling. I typically don't run muffler pressure, but I did try both the tongue muffler and a Scott Dinger tube muffler, no difference between the mufflers, so I can probably rule out a backpressure issue.

Thanks for all the suggestions, when I have the chance, I'll try less lube in the fuel, a different tank (currently an older GRW hard tank), rotating the spray bar a little, and try another plug, although not all at the same time.

Bradley Walker · « **Reply #11 on:** August 28, 2007, 01:54:08 PM »

Quote from: Stan Tyler on August 21, 2007, 02:39:33 PM

For the time being, I've swapped motors from the Magnum .36 to a Len Neuman modified FP35. Using the same fuel the FP35 doesn't have the burp that the Magnum did.

If I have to guess, I would say it was two words:

BOOST PORT

#1 reason for all misfiring, burping, going cold, etc...

Block the boost port in your Magnum. I have one all done and ready to go.

Bob Kruger · « **Reply #12 on:** August 29, 2007, 08:19:46 AM »

Quote from: Bradley Walker on August 28, 2007, 01:54:08 PM

If I have to guess, I would say it was two words:

BOOST PORT

#1 reason for all misfiring, burping, going cold, etc...

Block the boost port in your Magnum. I have one all done and ready to go.

Brad;

Have you flown it yet? If so, I would be interested in your setup (prop, venturi, fuel, etc).

V/r

Bob

Author Topic: Magnum .36 burp in transitions. (Read 1938 times)

Stan Tyler

Magnum .36 burp in transitions.

dennis lipsett

Re: Magnum .36 burp in transitions.

Busby

Re: Magnum .36 burp in transitions.

RandySmith

Re: Magnum .36 burp in transitions.

Stan Tyler

Re: Magnum .36 burp in transitions.

Bill Little

Re: Magnum .36 burp in transitions.

Steve Helmick

Re: Magnum .36 burp in transitions.

Dick Fowler

Re: Magnum .36 burp in transitions.

steven yampolsky

Re: Magnum .36 burp in transitions.

Dave Adamisin

Re: Magnum .36 burp in transitions.

Stan Tyler

Re: Magnum .36 burp in transitions.

Bradley Walker

Re: Magnum .36 burp in transitions.

Bob Kruger

Re: Magnum .36 burp in transitions.