How To 'Break In' a Two Stroke


New Member
Apr 1, 2007
Two Stroke Engine Break In

After engine has been installed and all fluids replenished (coolant/water, gear oil etc) you must then break the engine in properly. Improper break in results in lower reliability and possible engine seizures. Use the gas and oil mixture ratio that you intend to run after the break in. Check all fluid levels periodically during the break in. Check the carb jetting periodically during the break in.

Part 1 - Idle:

Start engine and let idle with a fan blowing on the radiator to help it cool properly. Let idle for 15 minutes.

Cool Down: Shut engine off and let engine cool for a minimum of 30 minutes.

Idle: Repeat first step.

Cool Down: Repeat second step.

Part 2 - Note:

Be careful not to put unnecessary strain on the motor during the break in. Do not climb large hills or go through deep mud. If possible use a mild treaded tire. If you are on the sand do not use sand paddles.

Ride: Ride for 15 minutes varying your RPM not to exceed 50% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

Ride: Ride for 15 minutes varying your RPM not to exceed 60% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

Ride: Ride for 15 minutes varying your RPM not to exceed 70% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

Ride: Ride for 15 minutes varying your RPM not to exceed 80% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

Ride: Ride for 15 minutes varying your RPM not to exceed 90% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

Ride: Ride for 15 minutes varying your RPM not to exceed 100% of normal riding pace.

Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
I got 2 things to say. 1: this sounds boring as hell. 2: I thought you werent supposed to let 2-strokes idle without holding the clutch.
Not everything is fun. Wake up.

You have to break-in a brand new ATV.
If you don do it properly, you've basically flipped it up.
These are instructions for those who need them.
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hey thats a great how to.....the break-in takes a decent amount of time just for the simple fact that if u do it wrong ur basically screwing urself....and its by far the hardest part for the reason u just want to get on it and let it lbwd gets rep points from me
great How to.

Dont forget to change your spark plug and check the jetting after your finished with the break in. Also wouldnt hurt to do the whole break in process a couple of times.
2 stroke break in

I've only ever gone through 3, 4 at the most heat cycles to break in 2 strokes. The most important points to breaking in a 2 stroke is to let it warm up fully each heat cycle before riding it (should take about 10 seconds with choke on but no throttle, followed by choke off and 50 seconds fast idle on a 70 deg F day), varying the rpm while keeping the rpms in the range for the step you are on AND putting a lot of load on the engine. This helps the parts work against one another and makes everything seat in really good. If you dont get enough load on the engine during break in, you might not fully break it in. Which is the only reason I can guess someone would suggest to run the process again, but it should not be necessary.

I dont think I'd let the engine idle in the first step. The first step breaks two (of my) rules of thumb, one is it doesnt put any load on the engine and two it doesnt vary the rpms.

Some tips I use, slight grades (in dirt, not sand... dont think i'd break one in on the sand) are great for putting a load on the engine. Always vary the rpms though within the range for the step you are on. I usually do one 0-50% throttle, then the 2nd up to 75% then the last at practice pace with a couple smooth straightaways to W.O.T., but backing right down once reached. If you do a 4th, you can ge to W.O.T. and hold it there for 1-2 seconds or so. Try to break it in on a 70 deg + day. If you must do it on a cold day, you can use a heat gun/hair dryer to warm the cylinder. This will help prevent cold - seizing the engine. (this happens when the piston expands faster than the cylinder and gets stuck, it usually damages the cylinder wall) Also be very sure to warm it up fully before riding on cold days. You usually know when an engine is warm if the cylinder is warm to the touch through your glove.

The heat cycles are just that. The engine should reach operating temp and then fully cool down. If its hot out or cold out, if you have an air cooled or a liquid cooled engine all will determine how long to let it sit between steps. So the 30 minutes is a guideline, but make sure the cylinder is totally cool to the touch with your bare hand. You usually will need to change the plug after break in because you havent really been keeping it cleaned out the whole time and they also tend to come rich from the factory.

The first break in is the most important because it is fairly easy to cold seize the engines if it is your first time. Also, the crank and big end bearings will be very tight. The spec on most crankshafts is +/- 0.0001 too. So its a pretty precise part. Always run the recommended mixture. I usually break in with non-synthetic too. I've heard from some that some synthetics are too slick and can cause your engine to not break in fully. Also, if you are supposed to run 32:1, but you plan to buy a synthetic then run 40 or 50:1, you are now running RICHER. (you now have more fuel to air because you have less oil) Which will make the break in process harder since you are most likely jetted rich from the factory in the first place. Not to mention you are taking precious oil away from your very tight spec'd engine parts. Run what the manual says for mixture. Its cheap insurance!
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Directly off of CT racing web site

Break In Procedures

1) Start your engine and let idle occasionally blipping the throttle for four to five minutes. Allow the engine to cool completely. Repeat this "heat cycle" process four more times.

2) Warm up the engine again and ride the bike for five to seven minutes at a very easy pace, vary the rpm, don’t ride at one speed. Don’t ride at more than 1/3 throttle or more than 1/3 rpm. Let the engine cool down completely and repeat the initial break in ride. Let the engine cool down.

3) Check the base nuts and head nuts for proper torque, check the coolant level and add coolant as necessary.

4) Ride the bike for five to ten minutes at a moderate pace, vary the rpm, don’t ride at more than 3/4 throttle or more than 3/4 rpm. Let the engine cool completely and repeat this secondary break in twice more.

5) Replace the spark plug with a new one. Ride the bike for five to eight minutes at a moderate pace, vary the rpm and shift up and down the gears. Once the engine is up to operating temperature you can make a jetting pass. Start in second gear and ride at full throttle through fourth gear, fully revving out fourth gear. With the throttle wide open in fourth hold the kill button down, pull in the clutch and stop. This is called a "plug chop"

6) Read the spark plug. With a pocket flashlight and a magnifying glass look at the porcelain part of the plug only, as you view the plug from the center electrode look down the length of the porcelain to its base, at this point there should be a dark chocolate colored smoke ring. There was not sufficient time to thoroughly color the whole plug, so the nose of the insulator may still be white, as long as there is a visible dark ring at the base everything is OK. Remember we want break in jetting so the plug should read rich/dark. Richen the jetting as necessary. If your having a hard time reading the spark plug, after the jet pass put the plug in a vice and hacksaw around the plug at the washer. Break the threads off with vise-grips, and the porcelain will be easy to read.

7) Complete the break in by riding at an aggressive pace for fifteen minutes, vary the rpm and don’t cruise at part throttle, ride hard without revving the engine too high. At the end of this final break in session do another jetting pass/plug chop as described above. Check the spark plug for the correct dark/rich condition. Wiseco Piston equipped engines will require another one or two break in cycles, ride at a recreational pace not revving the engine hard, full throttle should only be used for very short periods, fifth and sixth gear should only be used to cruise, ride one tank of gas through the engine in this manner to complete the break in. We feel it take about two gallons of gas to break in a motor equipped with a cast piston and five gallons for a motor equipped with a Wiseco.

8) Replace the spark plug with a new one, ride the bike aggressively for eight minutes and do a jetting pass/ plug chop in fifth gear. If the porcelain color is still dark/rich, lean the main jet size one at a time until the smoke ring at the base of the porcelain is a light brown. If the porcelain base is white, don’t run the engine and contact CT. If the plug color looks good, continue riding at a race pace for ten minutes. Stop and let the engine cool. Check the torque on the cylinder base and head nuts.

9) More on jetting. If you generally run your engine flat out in sixth gear then make your jet pass/ plug shop in sixth. Motocross jetting is checked in fifth gear, therefore it is not safe to run MX jetting in the desert or down a road wide open in top gear. Desert jetting is richer than MX jetting. When running an engine at full throttle for extended periods be sure to chop the throttle decisively to slow down, just rolling out a little can seize a well jetted engine.
Man there's so many break in precedures. People do it there own way basically.

yes but do you see that there are common denomenators? Also, Id always suggest doing any procedure the way that the engine builder suggests. Since its their product and they have been testing with it year after year. Hence, why I followed CT's guide lines.

Also, Id always suggest doing any procedure the way that the engine builder suggests.

I totally agree with ya here. I know a lot of us here already know info in this how-to, and each of us may have our own preferred way of doing things based on our own experiences, opinions and advice we've recieved. I just wanted to share my experience for people doing the process for the first time so they can read all the posts and take with them what they will.

Though I would be curious as to why an mfg or builder would suggest to run the first step of the procedure in neutral. (I've never heard of that before) With no load on it, the engine has nothing to work against. I've always believed that a load is what makes the parts work against an opposing force causing them to 'seat-in'. So I dunno how much breaking-in a heat cycle in neutral would actually do. Also, with no load to work against, I've always been told, that the moving parts want to literally come apart. Of course this wouldnt happen blipping it a few times off idle. But I've always been told one of the worst things to do to any engine is hold it for long periods of time at WOT. The absolute wosrt thing is to hold it at WOT in neutral cause things can come apart.

I mean, I doubt a builder would be able to tell two rides engines (torn down) apart that both followed the break-in procedure you listed, but with one omiting the first step. So basically I'm just trying to find out the why if anyone knows. This usually helps me remember the what.

Its kinda funny they mention 5 gallons of gas through an engine to complete a break-in. Heck, I would re-ring my piston (i'd do the piston/wrist pin and bearing every other ring) once a month with about 4-5 hours on it. I'm guessing probably not much more than 8-10 gallons through it at that point. So my top-ends were always pretty fresh. After years of this maint schedule and getting a new ride (or two) each year, I got more lax with 'the' break-in procedure according to hoyle to the point that I adopted what I previously posted.


Im not sure why CT sugests warming the motor in neutral by just blipping the throttle. But Allen Knowles (owner of CT) knows his stuff, so I did not question him on it. Might be for just warming it up. But your comment about warming under load is interesting.

Axo959 - whats your back ground you seem like you know a little somthing about motors?

P.S. Auburn Wa. Hu. I grew up there.
Do you need to break an engine in after getting the top end bored out and putting a new piston in?
the clymer manual on the blaster says to leave it idle on the first step hit the throttle a couple of times then let it cool for 15 minns actual break in process is 20 hours