Hi;
Just received this engine back fro m YS sent in for for problem with fuel leaking out of carb.Finally got it in plane and tried it yesterday.Can't get to run consistently.On high end no matter how rich set will run then lean out and quit!On lower end seems to surge or hunt?up and down almost quits then goes again no adjustement on the idle will stop this?Pulled fuel line has ample pressure there!Just can't seem to find a spot it is happy at.Wll rev up good and seem fine then slowly taper off and quit!When inverted will still drip fuel out of carb too,that was intial problem!Using cool power 20% with some caster added,cpou;ldn't get the 20-20 I wuld usually use!Think it is cool power it is the green stuff.Any hints?

Surging is a sign of being lean. Try to richen the regulator.

Lean could also be from an air leak as well.

I don't recommend using fuels with Castor added. This seems to be an old habit to break. When you do this it does a couple things. First it introduces more volume to the mix without adding nitro means you are reducing the nitro content. Less nitro means the engine settings are more difficult to get correct. Next you could be introducing something with the oils, too much oil can be as frustrating as not enough.

I would say in your case richen the regulator. This means turn it CCW a little. Since you say its dripping fuel out the carb it might not be too lean on the reg screw it could be that it has an air leak somewhere and this is making it lean.

Another option is could be trash in the regulator. This would block fuel from getting to the carb, yet keep the regulator from closing properly and hence the dripping.

Cool Power makes a " Pro Pattern" blend of fuel and this is good stuff to put in a YS engine as well. You don't need to add anything to it, just tap the bottle and run it.

Oil content is very different with different oils that could be used. YS puts a recommendation of minimum 20% oil. This is good and will not get you in trouble. Also since they can't know all the fuels around the world and all the guys that are mixing their own. So 20% is a number that is used as the standard. Most companies make a YS 20-20 blend. Depending on the oil that is used the volume needed could be different. Prime example is the CP 30% heli fuel has 23% oil because the oil is a low viscosity oil and is very thin. So you have to use more of it. If you used 23-24% of the regular oil the motor would not run well as it would have too much oil.


I would bet your problem is debris in the regulator or an air leak somewhere.


Troy Newman

Hi Troy!Thanks for the hints will get at it and see what can find.Have to get the parts list out to figure out what some of those things are.Thanks!!

I agree with Troy. Check the regulator but also this may be a sign of a backplate failure depending on old this engine is.

Hi;Still fighting with this engine.TRhink I said earlier it was a 120,my mistake is didn't look at side of engine when ai put it in is a 91AC.Tried it again today still no luck!.Fuel leaking out around the regulator,had a new diaphram int it afraid to tighten to it and strip threads .Also has fuel gushing off the airbox on back of engine.This is first attempt to run engine since returned from the YS shop where they replaced all gaskets etc for this problem.Ican't see any damamge to the regulator housing that should cause a leak?Checked all bolts on the airbox in back etc seemed tight.Engine is inverted which I hate but how the Harrier is set up.Fuel seems to be coming off the top?of the airbox and running down can't seem to see where it is coming from as is all covered with fuel running off it.Will carefully look for cracks was tired of looking at it yesterday.Maybe have to send it back again but this is the reason was sent in!Also had sent my 120 at same time same problem but haven't had anything to mount it in to try it!Thanks for your hints!!!

I would look for something wrong with the mate surface on either the regulator or the case. Also the air box parts. These pieces can be tightened up wrong and warp the part this can cause leaking. You don't want to even come close to torque enough strip threads. My guess is you may have tightened too much or maybe something else has happened. You can lap the mate surfaces if you are careful. I have done this many times and it will solve the leaking problem. If you don't have luck I would contact Service and they can help you out.

Fuel leaking anywhere there is a gasket will not allow the engine to run properly. This should not be hard to solve.

Inverted mounting is not an issue with the YS engines. They are actually designed around this with their pressurized system.

Troy Newman
Team YS Performance