I've been having some problems with a mousse can pipe that I built a while back. It's mounted on a Mac's header and is made from a 6oz. can with a 9/32" stinger about 3" long. I built this pipe for an Avistar with an OS 40LA. It did wonders for that humble little engine, increasing rpm by 2200 rpm and giving it improve transition and all around power.

When I put the can on a TT 46 Pro with the appropriate header and an APC 12x4 prop I started having serious problems with flame-outs at full throttle. What happens is that everything is fine (even on the ground) throughout the rpm range and power is a lot stronger everywhere until the engine is run WOT for a few seconds above 12,500 rpm. Then suddenly raw fuel comes spitting out the carb throat, the engine goes into a high rpm 4c/2c kinda burble and dies. During this spitting phase the carb cannot be leaned enough to change at all until the needle valve is completely closed. Then, of course, the engine dies and it won't restart until the needle valve is reset to it's original setting. Then it will run fine until the rpm get too high and the engine breaks into this irreversible decent into Hell.

At frist I thought the needle valve wasn't working right or maybe the engine had an air leak around the carb. After checking these things and calling the TT engine guy back East I finally decided the engine was a lemon and planned to send it back for repairs. However, after I put the stock muffler back on the engine ran fine with no problems whatsoever. I even put the pipe on an OS46FX and although it spit back a little less it did eventually do the same exact thing as the TT.

I'm thinking the pipe is putting to much pressure in the tank and fuel is being forced past the needle valve somehow but I'm not sure. The header, by the way, is 1/2" longer than the recommended length for a Mac's tuned pipe. I know the stock muffler will cure this but I really want the light weight power of the "canned" 46 for a fun fly Edge I have.

I've thought about a bigger I.D. stinger (or maybe two stingers!) or even a Cline regulator but before I go chasing after those birds I like to read some other's thoughts.

After reading the thread about the Webra 120 w/pump going rich while in flight I thought maybe my problems might be similar or in some way related. I don't know. Anyway, I'm hoping someone might have an answer to my problem.

Thanks,
Big Mike

Try tuning your CAN a little different. Increase the volume some.

Enjoy,

Jim

I believe the MCM is creating to much back pressure. What size is the outlet?

The MCP outlet (stinger) is 9/32" which is a little bigger than most use on their cans. I'm pretty sure the problem is excessive pressure in the fuel tank and I even thought about putting a pressure relief valve in the form of a one way valve tee'd off the tank vent with a fine tuned spring in the valve.

The only other thing I can think of as the cause for this spitting would be that the can is somehow sending a "Bad" wave back up through the enigne's intake system. This could be maybe remedied by tuning the can differently as suggested by Jim (thanks, Jim).

Big Mike

The MCP outlet (stinger) is 9/32" which is a little bigger than most use on their cans. I'm pretty sure the problem is excessive pressure in the fuel tank and I even thought about putting a pressure relief valve in the form of a one way valve tee'd off the tank vent with a fine tuned spring in the valve.

The only other thing I can think of as the cause for this spitting would be that the can is somehow sending a "Bad" wave back up through the enigne's intake system. This could be maybe remedied by tuning the can differently as suggested by Jim (thanks, Jim).

Also, I just remembered another key symptom; when the engine starts spitting like this the fuel consumption goes up astronomically, like empty in less than 5 minutes instead of the normal 12-15 minutes.

Big Mike

It would be easy to see if the tank is getting to much pressure. Pull the line off the muffler and see what it does.

IMO, 3" long for a stinger is too long. Look at most tuned pipes and you will see that the stinger is rarely, if ever, over ~ 1 1/2" long. For a MCP I use a stinger that is 1" long

Gene

I think you're right about that and I did consider this as a possible cause. When I had the can on my old Avistar it had a 1 1/2" long stinger that was just barely up inside the can. Unfortunately, that setup was quite loud (102 db measured from 9' off to the side). At our club we have a self imposed limit of 100db so, after reading some threads I found in the forums I decided to try a longer stinger that is stuck up inside the can by 1 1/2 " with another 1 1/2" sticking out. This did make the pipe a little more quiet although I didn't measure it with a db meter. I have a feeling this setup is doing two bad things; adding more restriction and allowing unburnt fuel to build up inside the can.

So, I think I'll switch back to the original configuration just to eliminate the stinger as a possible cause. That'll put me back in the outlaw category however. Any suggestions on how to quite the pipe down? I'm thinking I might have to go to a bigger prop to try to at least cut down prop noise. The last one I was using was an APC 12.25x3.75 (I think)and it was still giving 13,600 rpm.

Big Mike