I'm finishing a top end rebuild (rebored cyl, new piston, rings, wrist pin, gaskets, etc.) on a Trail Blazer 250. What break-in procedures are recommended?

 

You want to take it easy for sure for a tank or two.If your oil injector is still hooked up,you will also want to run a premix ,basically doubleing the amount of oil.Vary the throttle position and be ready to foul a plug or two.Watch the engine temp to,since you willl be riding slower=less air over the cooling fins.

Mike or Bubba or Modquad? If these guys say different listen to them for sure PeterinAZ!

 

You can add a premix of 100:1 to the fuel but remember the oil displaces gas so it will run leaner than before, I would bump the main jet up one size and raise the needle one notch, turn the air screw in a half turn. This will richen it up, on initial start up I do a 60 second run then let it cool completely (use a fan to force air over the motor) 2- 2 minute runs letting it cool in between, then 2-5 minute runs at a fast idle and finally a 10 minute run all with cooling time in between. Now ride it varying your throttle with nothing over 1/2 throttle for 20 minutes. The remainder of this tank of fuel can be run out then with moderate short bursts of accelleration. The breakin should be complete, no need for any more premix. Check your jetting/carb settings, do some plug checks at various throttle positions . You want your plug to resemble a brown paper bag in color, not white or grey (which is lean)

 

Sounds like how we break in nitro motors on r/c trucks. Some good advice.....more than I do, but some really good advice. I just make sure to use good oil while assembling, then take it easy for a little while........hmmmm, little while normally means a few miles. Erroring on the side of caution is always a good thing though.


Ken