91 c spec and MP2 trouble

[rambo]

Hi All

I have been having this problem with my OS 91 c spec, with an MP2 pipe on it.....

Every time I come to start the engine it is locked up (full of fuel or oil), and it is so locked up that I need to undo the glow plug and start it with the plug half out. After a few mins the engine will start fine again, it is just that initial start.

Now you wont believe what I have tried in order to fix this...I have a fuel clamp before the carb, I suck the fuel form the engine as well as letting the engine run out of fuel, I have also left it on the silencer so that any oil runs out of the engine. And yet it is still locked up again next time I start it!!!

The bearings and conrod are new, so nothing to do with them, everything else in the engine looks fine, so prob isn't the engine...

all I can think of is that it could be the MP2 pipe blowing oil back into the engine...

is this possible and has anyone experienced this before????

[Raptorite]

Yes this is common, especially with new engines which have needle settings on the rich side. Once the engine has been run in for a couple of gallons you can if you wish lean it a couple of clicks to optimum running settings.

Even then I suspect that the first start of the day you will need to take the plug out to flush any congieled oil out, then it should be fine for the rest of the day. I have to do this with mine still now and its done god knows how many gallons, it does get easier as the engine loosens up though.

Cheers,
Pete.

[Biggles]

WHat fuel and plug do you have?

[rambo]

Well the engine aint new, I bought the whole heli second hand and by the looks of it the engine has had lots of use!

This doesnt just go away after the first part of the day, I have to do it before every flight, which you can imagine is VERY annoying!

Its an OS 8 plug, and im using Bekra 16 (tut, am I allowed to say that round here?? )

[jimbob]

One think I've tried is clamping the exhaust pressure pipe during start to reduce the pressure a little. It soon locks up if you dont get a quick start.

I also try and clamp the carb line as soon as I can when i shut down. Seems to lessen to 'extra' fuel a little....

[rambo]

I always clamp the main feed line, but i havent tried clamping the pressure pipe.

This seems more like it is coming from the silencer direct to the engine....are MP2's renound for this???

[jimbob]

You mean its floooding into the exhaust port from the pipe?
Is it burnt fuel that floods it or fresh fuel from the tank. That would point you in the right direction.

[rambo]

I dont really know, but it cant be fresh fuel because I never fill the tank fully, so it doesnt go down the pressure pipe.

It must be burnt fuel, and in that case the silencer must be chucking it back at the engine, but doesnt make sense!! Thats the only thing I can think of, but there is no way of stopping it except changing the silencer!

[Steve]

Exactly the same with my 91 C Spec and MP. Mine's a pumped version as well.

To get around it - I always clamp the fuel line between the header tank and the pump inlet when not in use, so that's from the minute I've finished flying until the glow-stick is on and the starter motor is connected for the next flight, be that 5 minutes or 7 days.

<- You can see the pump sticking out of the bottom of this heli!

Secondly, with that heli, I always run the tank bone-dry at the end of each flight.

When I first had this problem, I studied it closely, and immediately after flying I could see fuel syphoning into the fuel pump and the carb, so the next time I wanted to start, even if it was just five minutes or so, th eengine would be flooded and locked up. Using the clamp religously and running the engine dry stops this from happening. Even now though, If I take the clamp off any more than about a minute before I'm ready to start the engine, it's too late, it's flooded again. So, leave it right until the last second.

Works for me.

[rambo]

Ok, I will try that....I have run the tank dry and clamped the fuel line, but i wasnt as strict as you...so perhaps if I do what you do I might be ok!

cheers for the help guys, at least I know I am not alone...

does anyone know why this happens???

[colin n]

just check

which way around have u got the header on the muffler . cos u can flip it to make the muffler lower than the exhaust port. However, i also have the same problem with OS and YS all i do is tip the heli up on one skid ( exhaust side down ) and crank it over by hand untill it frees up.

[rambo]

The header is angled so that the muffler is lower! Also I have left it on its side for a while, but never done this whilst turning the engine!!

Will give it a try, but still none the wiser to the cause!

[colin n]

the cause.

well u know, i rekon that all that oil and fuel that is left in the engine when it stops just pools in the bottom of the crank case . there aint no way ur gonna get it all out. also nitro attracts water vapour so ur gonna get some of that in there as well. Rusty bearings aint caused by nitro but by the water it attracts. add to that the odd smartie that the 3 year old stuffs in and its just one big shit sandwhich that we all take a bite from.
well thats my theory.

[colin n]

also.

if u ever look inside a muffler like the mp2 there is a cone in there that the gasses hits then does some magic stuff. this is just like putting ur hand behind the exhaust . its gonna get covered in oil . so for the last min or so of the engine run this oil will collect and because the motor is at idle there is not enough blow to clear it out.

back in the day when i had a 2 stroke bike we had to rev the nuts off them to try and stop them getting coked up.

anyhow back to the gin..

[rambo]

lol

it must be something to do with the muscle pipe because the engine is fine.....it doesnt collect a lot in the crankcase, 1. because I have checked it, and 2. because it is the first engine I have had that does this.....

all I can think of is that the muscle pipe collects the oil and then somehow spits it back into the engine....how it does this I dont know but its all I can think off!