Hi Dave,

I have a 91fz that I bought new from central hobbies, where I buy all my YS engines. I have several and all run fantastic but this one.
It will load up in the midrange no matter what I do with the regulator. When it starts to load up I can touch the battery back to the glow plug and it will come out of it. Low end is great as is the high end.
I do see a lot of air in the fuel line from the regulator to the needle that go away at wide open. In fact at times it looks like more air than fuel and more than my other engines.
I looked at the diaphragm and I didn't see any pin holes and it will hold pressure in the tank (it wont bleed off).

This engine has been sent to you for the ported piston replacement and I think you put a new plunger in the regulator (warranty)

This is the only YS engine I have had problems with and it hasn't ran right from day one. I'm pretty sure it is out of warranty now but I have only had 15 or so tanks of fuel thru it. Spend most of my time trying to get it to run right. Thought about putting a glow driver in the plane but I feel like that isn't fixing the problem.
Ys engines in my opinion are the best you can buy but I understand every once in a while there is a problem child!

I'm running OS plug (new)
15% fuel- my other engines run good on 15%

Have any suggestions? Sure would appreciate some help with this one.

Thanks for doing a great job on this web site. It is nice having a forum where we can communicate with engine tech's so freely.

I suspect that this is a piston seal problem rather than regulator. In any case, the engine will need to come in for repair. The address is:

YS Service
1295 Industrial Court
Gardnerville, NV 89410

Phone 775-782-4562

We'll get it back to you asap.
Sorry for the headache.

Dave

Ok Dave, I'll take it off the plane and get it in the mail to you.
Thanks