I just installed a moosecan muffler on my OS 40FP. I all I did so far for tuning was cut the back 1.5" of the header and then build me a moosecan for it. I am using an 11x3APC prop. OS "3" plug, and byron 15/16 fuel. I am peaking out in RPM range in the low 12's. I have it set to fly at 12,000 RPM.

I don't remember what was tacking w/ the stock muffler because it has been a while since I ran it. Are my RPMs close to what everybody else is getting or am I was off. i was hoping to get around 14,000.

I don't know the demision of the can. But it's pretty small. I will get them this afternoon.

But I did fly it on my 3.5lb menace. And it had a good pull out of a hover, But I am looking for it to shoot out of a hover. But it was windy, and I did't get to hover much with it.

Can you tell me how my 40fp is compairing to yours w/ the moosecan.

I am not familiar with the 40 FP and the MCM but on my Thunder Tiger 36, Thunder Tiger 46, and O.S. 32 I am using a White Rain 5 oz. Mouse can. Most engine in this size range pick up about 1,500 rpm over the stock muffler and the midrange will rival a 4 cycle for being linear.

the moosecan that I was using was 6 1/2"length by 1 1/2" diameter. I tried using a can that was 6 1/2" length by 1 3/4" and I would have to lean it out completely to get it to run. So I swapped to the 6 1/2" by 1 1/2 diamter, to get 12,000 RPM/

The White Rain Mouse cans I use are 1 3/4 x 6 1/2" long. Did you just cut the 1 1/2 " a quarter inch at a time or did you whack it all off at once. I tuned an O.S. 32 to a MCM this week and I only took of 3/4 " in 1/4" incriments and it turned 15,000 rpm with an APC 10-4 prop. If you cut it all at once you might have cut off too much and went past the sweet spot. If you did you have ruined the header for tuning that engine. You can salvage the header by making another MCM and making the big end that goes into the header about an inch longer than it is supposed to be and then when you tune it cut the MCM instead of the header. Also I didn't have much luck with the A3 glow plug. Iwent to the#8 O.S. and the low and midrange was much better.

My 40FP turns an APC 11x4 at 12,500 with an open exhaust. I can't find my data sheet right now, but I'm thinking with a 1.75"x6.5" can, and a 1/4" outlet hole it turned a shade over 13,000. I would think your 40FP with an 11x3 would turn even faster.

When I tried the 1.5"x5.5" can on the 40FP, I got similar RPMs, but the needle valve setting was really sensitive, and the throttle response was really screwed up.

If your 1.75"x6.5" can didn't work great, check to make sure the outlet hole isn't partialy blocked with JB Weld. This would explain having to lean out the engine so much, and the lack of RPM gain.

I also agree with bbjoe about having low end and mid range running problems with the A3 plug. The OS #8 cured that completely.

I checked the outlet hole, and it is completely clear.

As for cutting the header. I didn't. All I did was cut 1 1/2" off the back, and then JB welded it, into the moosecan. All I did was just cut the header, then put that piece in the moosecan. So really I didn't shorten it.

On the 6 1/2" by 1 3/4" can. I would have to completely shut the high speed needle vavle to get it to lean out. (Bad) I though Dave McD was getting about 2K more than I was so I just swapped cans, to the 6 1/2 by 1 1/2 can, and that is when My motor ran good. But is was only at 12,000.

I am glad you thought of that. I remember drilling out my exhaust hole, on the outside of my can. So maybe the inside of the can that hole is clogged to.

I remember that I tried using this exact same can, onmy 40FP, and it didn't work, I had to lean it out until the needle was almost shut. I tried it on my ST45, I had to lean it out until the needle was almost shut, and on my St90, and I had to lean it out until my needle was almost shut. So maybe the exhaust hole is only partially open.

I build 2 of these can on the same day. I am using 1 on a TT46 and it worked great. But one that I am messing with, I have never got it to work. So maybe there is a problem with the can.

I take the 1 off of my TT46, and try it. that might solve my problem.

If you cut 1 1/2 off the header to go inside the MCM then you did cut the header. The header length and the MCM big end tube are two different things. Get the brass tubing and use that on the MCM big end. A 1 1/2 cut off a header is a big big cut and would cause it to go lean. Whoever is telling you guys how to tune a pipe or MCM is uninformed. You are not tuning anything. You are mixing and matching mufflers and pipes and sometimes you luck out and sometimes you don't. A properly tuned MCM will make a 2 cycle engine run about 1,500 rpm faster and the midrange will be better than most 4 cycles and it will idle so low and so quiet you can't hardly hear it run. Also they will hold a needle valve setting forever or until there is a radical change in the weather. The time you are spending mixing and matching these headers and MCM could be spent flying instead of messing around with your engines.

1500 RPM and better throtle and idle?

Sounds worth the effort to me.

Bigjoe,
Here is a picture I for my moosecan setup on my St90. On this header, I didn't cut any at all at first. I used the full 6" of the header, then my moosecan shown has a 1 1/2" piece on it. I was worried about the header being to short anyway, so I didn't cut off any of the header. But this is for my ST90.

On my 40FP, and other 40size motors,
I take the stock header, and cut 1 1/2 off the back. Then install that 1 1/2" piece into the moosecan. I don't cut and throw away the 1 1/2" piece. So techinally I am not shorting the length of header at all. My lenghts are the same. Maybe I am doing it all wrong. I will go and pick me up some 3/4" pipe this week, and try it your way, because, what I am doing isn't working out the way I want it.


As for the motors going lean, I don't think they are. I think its just the opposite. their going to rich. Because, I am having to lean out the motor untill I almost shut off the high speed needle valve.

By lean I don't mean needle valve lean. When a header and pipe are tuned to the correct size there is a ramming affect that causes the header and muffler or pipe to actually suck the exaust gas out of the exaust port. That is why you will get more rpm and throttler responce. It is similar to supercharging a four cycle engine. The overall volume of the header and pipe together are what is important. Imagine if you plugged up the end of a MCM and header and held it straight up and then filled it up with water. This is the volume I am talking about. You can see that if you cut a piece of the header off 1 1/2 inches you would have less volume. If you used a bigger Mouse can you would have more volume. So if you use an appropriate size Mouse can and you make sure the header is extra long or the big end pipe of the MCM is extra long you then are set what is called rich for the ramming affect. Not needle valve rich. Then when you start cutting the header or big end pipe of the MCM about a 1/4 " at a time you are gradually going LEANER.You keep cutting a little at a time until you QUIT gaining rpm. Then stop right there. Don't make another cut or you will loose the sweet spot where the header and pipe are working great.

Well, I drilled out and straighten the bend on the 6.5 x 1.75" moosecan's stinger. installed it on my 40FP. And I was turning 12,200peak on 11x3APC prop. I then I installed a 10x4APC. I went to 14,100peak. I know have my it set to fly at 13,700. So it looks like my stinger was stopped up.

14,100 on on a 10x4APC insn't bad. Since my OS32Sx on a moosecan only does 15,200. And I can buy two 40FP's for the price of 1 OS32SX. It they still made the 40FP. And the 40FP is lighter to. So if I need another I will go with a TT42.

I probably going to put this motor on a pizzabox. Right now I have it installed on a MS Menace. I need a little more noseweight on the menace, and my OS32SX will do the job.

I will post some pictures of this sometime some.