Futurase

My Feedback: (10)

I have a used MVVS 2.15 gas engine and I have the stock weedeater exhaust that came with it and it runs fine, but is very loud. I bought a new Bisson Pitts Style muffler and the engine runs like crap wtih it. You can not lean out the top end enough. You can screw the top end needle until it starts sagging, but the engine does not run clean at all. It still is very rich. It runs fine with the stock little muffler.

What gives??? This muffler is brand new and bolts up tight and straight. I am clueless. It is not the engine as it runs fine with stock weedeater muffler. Who is running this combo together successfully and Morris sells this muffler. This is not a new red head as no part is anodised. Probally about 2-3 years old. Looks good otherwise. Has only a gallon or two through it. Looks new and has great compression. I have a 18x8 Pro Zinger on it turning it at right at 8K.

The throttle stick does nothing above half stick in the air. Runs rich on the ground too. Swap muffs and all your problems go away.

Ideas???

Norman Ross Jr.

H. Wayne S

My Feedback: (18)

Run the stock muffler !?

Does the Bisson have one or two pipes? If it has two, try stopping one up to produce more back pressure. If it has one, try plugging it with a cork with a hole drilled in it or add a couple if inches to the pipe with a rubber hose and a clamp. . Just to see what happens.
A two stroke depends on a certain amount of back pressure to clean the chamber.
This is a test, just a test. A stab in the dark.

Futurase

My Feedback: (10)

A friend had a chicken stick in his flight box and it was the perfect size to stop up one pipe on the Bisson and yes it has two. So does the stock muffler. The RPM's would sag when stopped up. Of course it probally needed to be reneedled. I have two Bisson mufflers and I am not impressed wtih them at all. I have a Slimline on my DA and it runs like a Swiss watch. Best engine I have ever owned hands down and I have been flying for over 21 years.

The stock muffler has less volume by a 1/3 at least and the engine will turn the prop higher RPM than the larger volume Bisson which makes no sense. It has to be more restrictive, but the stupid thing works fine.

The stock muffler is a two piece that leaks like a piece of crap. I can take it to a welding shop and have them lay a bead around it to seal it for good and then paint it with some high heat engine paint. BBQ grill paint works great. Worst part is a NEW $60 piece of junk!!!!!

My experience with gas has been mufflers make little difference. I cut the exhaust pipes on my Slimlin on my DA by several inches so as not to have to cut my cowel a lot and it did nothing. Didn't even touch the needles. Glow it matters as they use backpressure for getting fuel to the carb, but gas does not. The bisson is stock. I did nothing but bolt it on.

I am at a loss with it.

Norman Ross Jr.

rmh

The Bisson has rolled tips on pipes ? yes?
these are restrictive -to lessen sound
open ends by sawing neatly.
as for mufflers on gas engines -they make huge difference in performance .
the little in cowl things commonly used , simply kill performance in many cases as much as 2000 rpm --- documented .
If you remove the "muffler" -then adjust needle at full throttle --you will get maximum power --except for a tuned header and can device .
In cowl devices (mufflers), will all reduce rpm .
The back pressure needed in two strokes is for low speed operation -ditto on glow -or any two cycle engine.

Futurase

My Feedback: (10)

Thaks for the help Dick. I spoke to Morris. They described the problem to me perfectly before I even told them what it was doing. I just told them what I had. They told me to cut the pipes off quite a bit and it would solve my problem. They told me the rolled pipes and muffler design is just way too restrictive. I have yet to run it and try it, but I have modified the muffler.

The pipes had rolled end are were about 6 inches long each. I cut the pipes to 3/4 of an inch both. That is quite a bit so we wil see. I will definetly let you know how it goes.

Norman Ross Jr.

martyg

My Feedback: (42)

What RPM are you getting with the modified muffler? On what prop?
Do you have a sound meter available to get a reading with?

Mine gets 7100 on a Bambula 20x8, 99dBA (Slow scale) at 10ft over pavement.
Using the MVVS quiet pipe and header over here.

RysiuM

My Feedback: (1)

I have Bisson muffler on MVVS 1.6 The rolled tubes made the exhaust area around 150 mm2. The exhaust port is twice bigger. so I cut both rolled tips so the exhaust area were about 300 mm2. Just from that engine got 5% rpm more. I didn't notice more noise.

RysiuM