Best Way To Run In Overhauled Engine

[big wheeler]

Hi i will be getting my engine bits back next week new piston re nicosiled barrel etc what is the best way to run it in and what petrol to oil mix should i use.Can anyone also explain how to set up the mikuni carb fitted to my bike[tr34] as i suppose this is critical so i dont run it too lean but i dont know what all the screws are for yours mark

[charliechitlins]

Everybody's got their own ideas, but here's mine.

I would ride the bike easily until up to operating temperature, then shut it down and let it cool; being very aware of obvious differences, especially knocking and/or excessive heat.

Have a look at the sparkplugs and make sure they're a nice, toasty brown.

I would do this 3 times and re-torque everything.

Then I'd put another 3-5 hours on it before really thrashing it.

Generally for Mikunis, the big screw is for idle speed, and the little screw is for idle mixture.

Generally for all carbs: if the little screw is in front of the slide it's a fuel screw and opening it will add more fuel (richen) to the mixture, and if it's behind the slide, it's an air screw and opening it will add more air (lean) to the mixture.

[rob w]

Potentially a controversial topic as everyone I've ever discussed "running in" with has their own opinion. Also we don't know your engines history. Ie was it running fine before the rebuild, or have you sourced a different carb from somewhere??

In a nutshell - this works for me:

Use your usual oil and oil mix - maybe a bit more oil if you are one of these folks who run miniscule amounts (say about 70:1 for a trials motor ridden in a trials fashion. If you ride it like a motorcrosser then 35:1)

If the engine was running fine before, then leave the carb settings. You could consider going one step richer on both main and pilot jets in your carb, but this is not vital.

Start the bike, warm it up gently then ride it. DO use lots of different throttle positions and different gears. DONT hold it wide open or make it labour in to high a gear. LISTEN for any knocking noises, especially under acceleration or deceleration. These may indicate lean air/fuel mixtures which are potentially damaging. If you hear these stop and change carbie jets.

Keep riding until the engine is at running temperature and then ride for as long or short as you like. When you stop riding, let the engine cool to room/ambient temperature (ie. completely cold).

Do this four or five times and your engine should be fine for normal use.

Off course there are always exceptions and I have seen motors run in on the start line.

As for carburetor settings..... Probably just leave them as they were before your rebuild. But a good clean inside and out never hurts. Otherwise, it is a bit complicated to explain here. I suggest searching the web for a site that explains technical operation and reading it carefully. Then we can help you with the specifics like jetting and mixture screw settings.

Good luck

Rob W