I have a new YS 63 and I started test running it today. It is doing the same thing my last YS 63 (the older design) did, it is surging wildly. I hold the throttle steady but the engine revs up and down erratically. I have tried richening/leaning slightly but to no avail. Then the engine just died even though there was fuel in the tank. I hear YSs have problems with surging, what can I do to fix it? Could this be just a normal break-in? Thanks

Not normal. Does it surge at full throttle?

Indeed it does. Brand new engine - but the same problem as my old YS 63 - this is the new model though.

If this is your second one that surges, I'd look somewhere other than the engine. It has to be fuel, fuel tank, plumbing, glow plug or adjustment. Are you running fueling valves? If so, get rid of them as they will not work with the high pressure a YS can generate.

No, I don't have any such fueling valves. The last YS had to be serviced and it was confirmed to be a problem with the engine. I have had many, many engines, and the two YS engines I have owned both have had this surging problem. To me this means that since YS is for high-performance, their engines are probably more finicky - kind of like owning a Ferrari - you get lots of power but you must baby it. I decided to go directly to YS for support. I am fairly certain my tubing or tank setup is not causing the problem.

Thanks for your advice.

Dave- I should add that after YS fixed my first engine it ran fine. I am guessing they can do the same for this one since it is under warranty. Currently it is on a Super Sportster ARF running 20/20 fuel. I taped up the fuel tank to make it more pressure resistant.


Anyway, thanks.

Guess you better send it. Can't believe you were unlucky with 2 in a row.

SORRY to bother you all again about this engine but --- I still cannot get it to stop surging. I am considering taking it apart and searching for internal problems. I ran a Saito 82 successfully on the same test stand so I know the tank/lines are OK. I have adjusted the regulator extensively 1/4 turn at a time but it still surges. I have examined the fuel line and fuel filter as well. I am wondering if maybe something is trapped somewhere that is causing the surging. Right now I have the needle valve at 2 turns out, and the regulator at 1.5 turns out. I have a new OS 4-stroke glow plug and I am running YS 20/20.

I also noticed that the carburetor will fill up with fuel and overflow slightly after the engine stops. So I will see if taking it apart reveals any blockages.

I've already advised that you send it in. The regulator is sticking.

Actually when I called you, you said to check the regulator setting and make sure I broke it in according to the instructions. You probably don't remember me calling; I guess you probably have to field tons of calls.

I will send it out asap.

Sorry I don't remember your call. Sometimes we are so busy I forget to put my pants on in the morning.