Recently i got a irshad's low winger with OS fl70 installed on it. I m totally new to 4 stroke engines.
We tried flying it last sunday,but the plane wouldnt take off . The engine goes down right after the launch (oh yes we hand launched a 46 size plane   coz the land is hoskote is bad).
Though the engine behaved perfectly when we had the ground tests,it turns into a dead stick the moment we launch it.
we checked the tubes,and the glow, everything seems to be fine. If there is any special care to taken with this engine please let me know ppl.

Have you tried tilting the plane nose up and in other orientations on the ground with different throttle ranges ?  Have you tried sudden acceleration (throttle input) etc also on the ground ?

Check the "klunk" inside the tank. Looks it's come off the tubing.

4C engines have very good suction and are less critical of plumbing. No special precautions needed.

Try richening the HSN 1/4 turn and go through the motion of launching (do not release the model) if the engine behaves you are good to go.
From what you describe, it looks like you are at dead peak and the accelaration and unloading of prop combined further lean it out leading the engine to quit.
Since this is your first 4 stroke, do not try to tune for screaming 2T sound, the best way to tune  a 4T is with a tacho in the best power band for the particular engine.
Also what fuel are you using? I had the very same engine where I saw a sea change between castor based fuel and synth. Ever since I have never used castor mix on my 4T.
To add on to what Sushil says, even though the clunk may not be coming off, you need to check for following if the step at the begining of my post does not work
1. Does the clunk have a slot cut at the end apart from the hole? If not replace the clunk with a proper one.
2. Your clunk should be free in the tank, about 5-6 mm away from the end wall of the tank, this ensures that the slight elongation of tube while accelartion of the model does not lead to the clunk touching the tank end wall and stopping the fuel feed. For this very reason the slot in required at the clunk end.
Do let us know if you are able to solve your problems  

Please also check RX Battery. Futaba and some other brand do have a safety feature that shuts the throttle if the Rx battery is not performing. you will get a ded engine almost 30 to 40 seconds after launch.

The suggestion from Manoj makes sense if you have enabled the throttle failsafe on your radio

thanks for the response ppl... we will do a proper scrutiny of the engine tomorrow.. we are using synthetic oil 20% with 10 nitro% on this engine.. i think i m doing justice to the machine... not using gummy castor.....   we are even planning to use a t-nipple in the pressure feed to the fuel tank..to boost the fuel pressure..  i will let you know how it turns out..

regards
shadman

I have been using ONLY 4C engines for over 20 years and would like to repeat what I said earlier. They have very good suction and are fairly uncritical of feed. In fact, Laser Engines advise AGAINST use of pressure! And they have a logical explanation for that.

BTW, how do use a T nipple for additional pressure?

Sushil,
The FL 70 has two nipples on the muffler, may be Shadman was planning to use the other one as well to add third line for pressure to the tank .

Shadman,
Please refer the manual for FL 70 you do not need additional pressure .
I have posted the link, please refer to page 19 for correct plumbing
 http://manuals.hobbico.com/osm/fl-70-manual.pdf

The second one is used to connect to the crankcase breather. I have added one to most of my engine mufflers - but at the exhaust end - as it keeps the oil out of the way.

To repeat, I have NEVER felt the need for any additional pressure when flying in any attitude.

the muffler of OS fl70 has only one nipple.. so i m planning to connect one end of t-tube to the muffler and both the other ends to the fuel tank .. i m not using the crank pressure at all.. the configuration look similar to this ..

If it looks similar to the picture above then your muffler should have two nipples.  Or it could be that the muffler supplied to you is not the original FL 70 muffler.
On other hand what are you planning to do with the third end of the tube? If you are just going to balnk it off, why use a T at all? Connect the pressure tap on muffler direct to the pressure feed of the tank and have the third line blanked off for filling.
Anyway before doing all this, just try richening the HSN 1/4 turn and check that should solve your problem. Since you are new to 4T, my guess is you have tuned it by the ear similar to a 2T engine which means it is at the peak on ground and the launch/unloading of prop is taking the engine over the peak
 

k.. i try tuning it with a tacho .. i ll keep u updated ..

we tried the process again yesterday... it dint work out again... engine shuts down when nose is down.... 

What did you mean by "the process" ?  Did you do step by step investigations, including checking the clunk line ?

I am redying one small Tank for my AMP Master. Bring it to my place some time and we would try it (I also bought a 7Ah Lead Acid (SLA) battery for my NAS, which I can use for the starter.

Earlier it was shutting down when launched i.e when climbing. Now it shuts down when nose is dipped. If you just richened the HSN the sweet point is somewhere in between your two settings. This is provided you have not fiddleed with anything else.
As indicated by Anwar, what did you do ? In order to trouble shoot you will have to eleminate each suspect one by one, if you do too many changes all at once you would not know what is wrong or what was correct 

Hi Shadman,
                  I found these PDF files on OS site for this engine.

http://www.os-engines.co.jp/english/2004autumn/2004spring/pdf/mfl70_e.pdf

http://www.os-engines.co.jp/english/2004autumn/2004spring/pdf/evfl70_e.pdf

Hope this will help you.

Akshay, the manual's link was already posted at  #8 . But good to see your eagerness to help.  

Ok I didn't see that, any ways, one more link for blown engine parts.

Thanks for pointing out.

Also, Akshay, it doesn't appear to be a faulty engine but a fuel feed problem.

Shadman, have you checked the clunk as yet?

That's true Sushil_Anand , I have seen this engine and with my little experience with Automobiles. I  also suggested him to check his fuel supply. As engine is starting fine, but running is a trouble.

ok initially there was no compression seen while rotating the prop.. so we opened the head.. we found the exhaust valve was too tight.. so we did a half turn on the exhaust valve nut to achieve perfect compression... now the main problems are:
1) the engine isnt tuning properly at the low end.. (shuts down if throttle is down)
2) engine shuts down when we launch the plane..
3) the latest problem ,the engine shuts down when nose is down

we have scrutinized the clunk and the pressure feed properly.. still cant figure what to with this..
i m planning to take to adarsh.. lets see..

We would love to find out what was the problem!

Alam

My 4S fuel config, you could try, rarely this config has given me problem. 70 meth 15 Synth 10 nitro 05 castor. try it