Steve Campbell
Elite Veteran
Location: Baton Rouge, LA
| 11x6 is a bit on the small side (that's standard size for .46 engines); 12x6 is standard for .60 class engines, but 12x5 is about ideal for bench break-in.
You can certainly use an 11x6, but be careful not to overspeed the engine.
As to rpm, I have broken in many engines on the bench, and have never put a tach on any of them. The exception will be a Saito 150; the book warns not to exceed 4000 rpm for the first few tanks, so now I have to procure a plank tach.
What I normally do is pay close attention to the sound, and to the exhaust. What I'm looking for depends upon what kind of engine (ringed or non-ringed) it is. The 61 SX-WC is a ringed engine, so you want the first few tanks blubbering rich (three or four turns open on the main needle); IOW, the engine is barely running, with plenty of raw fuel being spit out the exhaust.
Subsequent tanks can be leaned in a little bit at a time, until the engine is running strong with a good transition. Every 61 SX I have dealt with had an optimum main needle setting of between one and one and a half turns out. But to be on the safe side, use at least a gallon of fuel getting there.
I'm not minimizing the importance of knowing the rpm. But during break-in procedures, I think it far more important to ensure that the engine doesn't overheat or get run harder than it is ready for. A tach won't tell you that.
Steve |
