Hi is it just me or is everyone else having the same prob.When using a in cowl bisson muffler I can't get enough tank pressure without plugging up one tube .This would be ok except it cuts the RPM down considerably.I have tried to place the pressure tap in different places without any good results .I even contacted bisson there selfs and DID NOT get a reply . leads me to believe they know they have a problem and either can't or don't want to fix it .
Any comments on this would be welcomed.

Just a note here I know about pumps and regulators ,but why should a man have to spend additional money to get a engine to run that should run with the equipment thats already there .

I've had good luck with one on a 91FX and a TT 61. Depends a lot on the engine, I suppose.

Cyberwolf,it's not you; it's all thier big engine mufflers. I got a Moki 1.8/Bisson pitts muffler. Well it was suggested I plug up one the tubes to get more tank pressure. All I can say, I wish RCU was around when I bought 90% of the stuff I got 'cause it would still be on thier shelves due to the aggravation factor.

Yes I have a bisson on a 91 FX and its trouble free ,it works as good as the factory muff does So this tells me if they can make it right for one engine why not another.I guess what aggravates me the most is them not returning my email with some sort of a explanation.
Thanks for sharing .

Bisson used to make a single pipe muffler for the 180 Moki that worked well,But I have only seen one of them a friend has it and says its no longer available .
Thanks for your comments its good to know i'm not alone in this matter.

i switched to a bisson from a slimline on my gms 61 for that reason and it was solved. the exhaust tubes are considerably smaller on the bisson.

it must be a large engine prob like you said cyberwolf.

good luck with it

Just recently ordered a OS 160 FX and Bisson muffler to fit. The Bisson muffler had exhaust tubes with rolled ends at exhaust end that decreased ID by about 50%. Seems like they may have addressed the pressure problem. My 160 runs great with this muffler. I do not know if this change has taken place on all of the Bisson Mufflers.

u can also try crimping one outlet not fully colsed but , maybe start off with half then take it from there until u find a balance that gets u enf tank pressure. the classic sign of not enough pressure is ull find that ull find the high speed needle not sensitive\ rseponsive . ideally u shd figure out at what HS needle setting the motor runs with stock muff(if u have one) then try to replicate that setting with the aftermarket one until she runs fine

Weather its a pinched off tube or rolled over ends ,the end results is still the same, you will lose power and RPMS in either case .I don't feel this is a good fix ,what I think needs to be done is some testing back at the factory and get it to work correct then release it after its a proven working part.
What is bothering me is the fact I can and do build my own mufflers if I have to ,but its time consuming and allot easier to just get one prebuilt .I guess me being lazy on this has cost me more time and trouble than making it to start with would have been .As a rule I won't harp on a item unless its very good ,but this just pisses me off to no end and as long as folks keep buying there products there not going to do anything to correct the issues.

I run a Bisson pitts on my Tower .75 in a Shoestring, with no problems whatsover.

Seems like on the smaller engines they do work ok with the exception of the 52 magnum,MY 91 FX as stated above has no issues either but my larger glow engines are a mess ,due to not enough tank pressure .
Today I made new tube ends and only opened the holes to 5/16 dia this seem to work, I had needle adjustment plus I didn't seem to lose much in RPM's .Its still 4 turns open on the top but it will get rich now ,before I could turn it all the way out with no change to the engine.

My Tower .75 runs about 2 turns out.

I run one on a OS 160FX and closed off one of the tubes permanently. Why??? Read the engine instructions. Most all specifically state that you should not use a muffler with an opening bigger then the stock muffler. The Bisson Pitts muffler openings are twice the size of the stock muffler. I couldn't even get the mixture to adjust without closing one off as there is not enough back pressure for the engine to run properly. I crimped the tube farthest from the port with a pair of vise grips right at the box. You can't see it and there is a big enough opening still in it to let any fuel drain out. Engine runs great now. I found the tip in a RC Universe Review.

Sure you can close one tube off if you had bothered to read this thread you would have seen that has been done ,but at a cost of engine performance .Check it both ways both tubes open versis one and you will see what all the fuss is about .
I have a set of 160 instructs here in front of me and I can't see where it says anyhting about muffler outlet size. Building expansion chambers over the years I do know that is a big factor.You double the outlet hole and 4 times the flow can go thru it.
Muffler back pressure and scavanging is everything on a 2 stroke engine , you loose either one and performance will be lost greatly.
And clamping one tube off is not the right answer ,the muffler should have been built with the correct sized tubes already installed .

I have a 91fx with a bisson pitts muffler in one of my planes. Brand new engine and exhaust, broke it in last week. Took it down to the field this morning to set the idle trim and everything in my radio, only problem was the high speed needle had no effect. So I took a piece of a pencil stuck it up one of the exhaust outlets and ran a screw through the exhaust into the pencil, fire up the engine and everything is just about normal again. So I guess the only fix is crimping one of the outlets? Wish I woulda known this before I just woulda spent the extra money and bought a saito 100. Should I crush just one of them, or both of them evenly?

Chris

On mine, which acted the same way, I simply flattened one pipe with a pair of pliers until it was aprox. 75% closed. At this "setting", the engine ran well and the needle valve worked as it should. I find that this engine likes to be run pretty rich, BTW.

After probably 20 or so flights, I opened the squeezed exhaust pipe a little (to about 50%), and found that I could still adjust the needle valve and the engine made a little more power. I have not done any further experimenting because I am happy with the way it runs now.

Interestingly, when I emailed Bisson about this idea of smashing a pipe, their tech guy said he saw no problem with it! Makes you wonder if they actually test run an engine when they make a pipe for it.

Sandy T

i just got the bisson muffler for my os 1.20 the power is crazzy . but after i run about a half of tank i lose power and have engine truble most the time dead sticking .


it sounds like back pressure. (thanks alot for ripping me off BISSON)

You are experiencing a lack of muffler pressure to your fuel tank.

The engine is going lean

I just made a pitts muffler for my OS 120AX using the dimensions/volume and outlet sizes of the Bisson pitts as advertised on their website and had the same problem,I could wind the high speed needle all the way out and it just wouldn't run rich.I spoke to one of the pattern guys in our club and he suggested putting a check valve in the tank pressure line to stop the tank pressure draining back to the muffler during lower throttle settings(sort of like a non adjustable regulator) I bought a $14AU YS check valve, Installed it and bingo problem solved.Ill try and post some pics later on tonight.

Cheers

Weedy