by Alex Varv
I have read and also spoken with different pilots a few times about difficulties in removing the external vacuum operated decompressor on the Cors-Air M25Y/Black Devil.
The difficulties consist in the very small clearance between the cooling fins and the decompressor body itself.
Sometimes decompressors get stuck and the way to get rid of this issue was posted by other pilots so I will make it short:
1)DO NOT remove the decompressor in order to free it if it gets stuck.
2) Remove only the vacuum hose and spray a small amount of WD 40 or light engine oil in the opening. This should take care of the problem.
Since last November in over 150 engines sold in the US, we replaced 4 decompressors because one was really stuck and three others because the pilots wanted to remove them from the cylinder head trying to unscrew the nipple since they had easy access to it. The nipples broke and we replaced these three decompressors.
One pilot from Indiana received a free nipple from me because he was able to remove the broken threads from the decompressor body.
3) As you see, a very small percentage of decompressors were replaced in so many engines.
4) After several discussions on the phone with JPX Italia and explaining that there is NO such tool available in the US and that the clearance between the decompressor body and the cooling fins should be bigger, the factory categorically stated that this may affect the cylinder head cooling.
5) Since I have seen this small tool last December during my business trip at JPX Italia and I tried different tool stores to find something similar, I gave up.
Today,June 29 2005, I was forced to go to the local hardware store in order to purchase some parts for my old lawn mower.
On the display I saw a two headed tubular-thin-walled spark plug wrench.
The smallest opening was very close to the diameter of the decompressor on the Black Devil.
Since this tool cost me about 2 dollars, without hesitation, I bought it along with the lawn mower parts.
Well, it did NOT fit because the wrench was still too large!
But the difference was very small.
I immediately saw a solution: I started to squeeze all six walls of the wrench in a vise.
In a few minutes, there was just a little clearance between the decompressor and the six walls of the wrench. I took a small hammer and I knocked on the very edge of all six walls of the wrench.
The decompressor fits perfectly!
It took me about 10 minutes to do this operation.
6) Again, please do NOT grind the fins on the cylinder head in order to insert a standard wrench to remove the decompressor.
7) And again, please do NOT remove the decompressor in order to clean it.
There is a small copper washer under it and also the threads are treated with a compound to seal it and keep it firmly in place.
If you remove the decompressor it may start leaking.
8) Oil will deposit around the decompressor in time but if you did NOT remove it, the oil is coming through the small external vents. It will suffice to clean the head from time to time with carburetor cleaner. The oil deposits will be more significant during the run-in period when there is more oil in the gas.
I have received a few letters from pilots with the same question: "why does JPX Italia not use the old mushroom shaped decompressor that has only one opening and ends with a small nipple?"
The answer is simple: the old mushroom shaped external vacuum operated decompressor being much longer is more difficult to protect from damage. Also, having a longer stem, it is known that because of the vibrations on a longer arm, these decompressors used to break off.
Some other questions expressed the desire that JPX Italia makes an internal decompression release orifice, just like the good old SOLO 210 uses.
Our philosophy is different. Why remove the cylinder head and replace the head gasket in order to clean this hole?
We strongly believe it is better to leave the head in place and clean or free the decompressor from the outside. This operation is much simpler, faster and less expensive.
I hope, I answered all these private letters and questions over the phone and posting them here, all Black Devil owners will learn about it.
In the end, I would like to present two pictures of the decompressor wrench used tha the JPX Italia factory. It is a regular 15 mm socket that was "turned". In othre words, the wall of the socket is very thin and this can be achieved by a carefull grinding as well.