engine break in - when to tune?
 

Hi folks.

I just cranked over my engine after my rebuild... fired right up. I just gave it a a quick test and shut it down. The carbs were popping like crazy but it ran relatively smoothly above idle.

So. I am adhering to the run it hard school of engine break in which leaves me with this question. When to tune the carbs? I am planning to warm the motor up and then do some break in runs. Should I tune prior to doing these runs or just go with the lousy carb set up? I am no maestro with carb tuning so that means if I tune after the warmup there is likely a half an hour or so of running while tuning the carbs. Bad idea?

Opinions?

I'd tune the carbs - the popping sounds like lean idle jets. You can always swap them later, but get the pop out.

What he said.SmileWavy

You should always start an engine break in with 20 minutes of 2000rpm idle to wear everything in. Failure to do this can ruin a new engine. After that, oil change then tune. THen do not run it very hard for at least 500 miles or so, let the internals get comfortable first and give it a few more oil changes. IF you really watch our gas mileage you will see when it finally breaks in fully.

What he said ... here's my favorite engine break in video...

YouTube - Engine2

The 20 minute break-in above 2000 RPM applies to new cams/rockers when they need to seat. The 2000 RPM ensures proper oiling to these surfaces. If you reused your cams and rockers in the same place and just did a refresh, this isn't entirely necessary.

Your idle jets are only for idle (Well up to about 2500 RPM or so). I recommend a "run it like a scalded cat" break-in period keeping a conservative approach to revs (I keep my 3.0L below 6000 RPM on break in). You'll need to run it hard early to ensure proper seating of the rings. Heavy use helps build gas pressure against the rings and helps them seat. The longer you idle it (say, for example, spending 30-60 minutes dinking with carbs) the better chance your cylinders will glaze and the rings will never seat.

If the idle is really bad, sure give the idle jets a tweak, but generally two turns out will get you by untill you have time to do it properly.

So what do I do? Fire it up. Make sure it basically runs. 3000+ RPM always runs the same with the Webers because the jetting is still the same. The I warm it up for 10 minutes, take it out on the track and beat it for 20 minutes. Done. Change the oil and call it a day. Never failed me yet.

I am now at 500 miles post build.
 

I have changed the oil twice (crappy 10/40) and am getting ready to do it again, this time with Amsoil.

I have tuned the carbs with a color-tune, which was time consuming but educational, using the color-tune helped me to understand the sounds, so now I can tune by ear. Its hard to explain.

Your plugs may foul quickly while tuning, so have a fresh set or a way to clean them.

Turn your sound down before viewing the video of my engine break in;

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+ 1

That's probably the best free advice you can get on this topic.

I'm undecided on this approach on boosted engines, as the positive pressure is working to drive the rings on the intake stroke as well. I'm not saying I have completely ruled this process out, rather that I envision a slightly higher likelyhood of over heating new rings. Would love to hear comments on this.

Part of the ring setting process involves deceleration to get the rings seating both ways. I never babied mine, but kept the R's in a reasonable range for a few hundred miles.