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iTrader: (3)

Reserved for break in instructions etc. etc.

Posted 07/25/16



2) The infamous break in question lol! We're a racing company and make engines for racers, what I have found is that talk to 4 different racers and you will get 4 different opinions on how to do it lol! You wanted a detailed answer though so let the book writing begin lol!

The way that I normal do it is to set the HS needle to flush with the end of the housing and then with the air filter off, fire it up and leave it on the box. Blip the throttle a couple of times and then let it come back down to idle. Then I start to screw in the idle stop screw until I see around a 2-2.5mm air gap (opening on the slide)

******* Update 5/27/10 I'm changing this a little as we are now all using the 2010 aluminum carb. The easiest way that I have found to set the air gap mentioned above rather than try to measure 2-2.5mm etc. is just to turn the idle stop screw in 1 1/2 complete turns in from flush. This I have found is a little less than the maximum that the slide can be opened with this screw and not bind*******

When you are doing this your idle speed will start to increase so you are basically going to have to start richening your low speed needle a couple of hours (until you get a smooth, steady idle) then do a couple of hours on the idle stop screw and back and forth until you see the 2-2.5mm+ air gap (***update from above, keep screwing in the idle stop screw 1-2 hours at a time and then richening your ls a bit to bring the idle back down, repeating this until you hit the 1.5 turns in from flush on the idle stop screw as indicated above****) that I mentioned. As this is a two stroke engine, performance is always dictated by air/fuel ratio and as we are now talking about the low speed needle (remember we set the HS needle flush with the end of the housing and there is no need to touch this again for a while) if you have too much fuel (rich setting) you will have a low idle, if you have too little fuel (lean setting) you will have a high idle). It basically is a no brainer if you are too rich or lean because your engine will tell you!

Once you get a steady idle going with the large air gap that I mentioned (large air gap means a lot of air flow, to get a steady idle means that to compensate you will have to dump a lot of fuel through the engine= guaranteed rich condition and you can not damage your engine right off the bat by being too lean) I idle it through the first tank on the box. This is done basically to pump a lot of oil through the engine to flush out any metal particles in the engine and remove the minute bit of metal particles that are always released initially during break in.

Now with the radio gear on, engine off and the slide closed look down the throat of the carb and slowly start to pull the trigger. Take note of the how much throttle you are giving at the point that the low speed needle (which is connected to the slide) comes out of the spray bar (the hollow tube) on the opposite side of the carb. We will use this as a referance for tuning later on but basically what is happening is that during the range of throttle movement that the low speed needle is embedded in the spray bar, the low speed needle will affect fuel delivery (for the purist we both know that this is a simplified explanation as the fuel first travels through the HS needle circuit before going to the LS but since we already set the HS to a rich setting and will not be touching this for a while it's pretty much a mute point). At the point that it is out of the spray bar the fuel delivery (or tune) is affected solely by the high speed needle.

Then I re-install the air filter, fire up the engine and toss it on the ground. Start slowly doing figure eights at say 3 to 4 mph until you run through the tank. Then for the next tank i fire the engine up again and back the idle screw out a couple of hours. You will immediately hear the idle speed start to reduce, to compensate for this I then lean the low speed needle a couple of hours until I again hear a smooth steady idle. Once I have this I then start doing figure eights again but now a little bit fasted until the tank is empty. Next tank fire up the engine, back idle screw out a couple of hours, lean LS needle a couple of hours, do figure eights a couple of mph faster.

Basically what I'm doing with this system is slowly reducing the amount of lubricant being pumped through the engine while at the same time slowly increasing the amount of load that is being put on the engine. This I keep on repeating until I get to approximately the point that I'm pulling the trigger far enough that I know the low speed needle is being pulled out of the spray bar (remember we checked this initially while we had the air filter off) at which point your air gap (the amount the slide is help open by the idle stop screw) will have been reduced to aprox. 1-1.5mm.

****Edit 07/19/11. Once you have reached the point that you are going faster than roughly 1/2 throttle as mentioned above you are running on the HS needle which you will start tuning below. Before you do that make one final adjustment to you idle stop screw/LS needle by setting your air gap (amount that the slide is held open by the idle stop screw) to roughly 0.5mm with the reducer out. Once you have set the gap to 0.5mm, fire the engine up blipping the throttle on the box, your LS will now be rich which you will see by a low idle speed, lean the LS a few hours, blipp throttle and allow to come back to idle. Keep adjusting the LS (leaner (in) for a faster idle, richer (out) for a slower idle until you get a smooth, steady idle. By setting the air gap to 0.5mm reducer out you have now set this to the appropriate point for final tuning and you will not touch the idle gap anymore.*****

Once we get to this point we now need to be concerned about the HS needle. What I then do is re-fuel and fire the vehicle up, putt it around for a couple of minutes to heat saturate the case and the chassis and then do a quick high speed run around the track (do not hold it maxed out for a long time on the straight, this is bad). I pull it back in, temp the engine and adjust the HS needle so that I see right around 200 degrees. Then let the engine drop back down to idle and see how the idle performance looks. If the idle is now fast (it has now increased) this means that you need to richen your low speed needle (for the amount of air flowing into the engine, there is too little fuel flowing into it = lean condition) don't touch the idle screw just the LS needle. If the idle is low this means that you now need to lean your low speed needle (for the amount of air flowing into the engine there is too much fuel flowing into it = rich condition) again don't touch the idle screw.

Then I toss the car on the track for another 6-8 tanks with the engine running around 200 degrees as explained above running close to race speed but rolling off the throttle mid way down the straight. Once I'm done with the 6-8 tanks doing this we would have run around 12 to 15 tanks total through the engine in all of the steps above. I now consider the engine pretty much broken in and I'll get close to race tune on the HS setting the engine around 220 degrees. Again check to see what happens to the idle speed and adjust your low speed needle to compensate if it is high or low. Run a further 6 or so tanks through the engine driving it as you normally would and you are good to go to full race tune which will be in the 220 to say mid 240'ish range and I would consider the engine broken in and ready to be pounded on.

A long explanation but using this system helps avoid one of the most common mistakes faced by newer tuners which is setting their low speed needle too lean because they have too little air gap (the carb is hardly open help open by the idle stop screw so to compensate they set the LS needle super lean easily causing damage to the engine).

I also like to use this system because I often end up tuning and/or breaking in a lot of different types of engine with people. Using this system i never even worry about knowing what the factory needle settings are or anything along those lines. I just set the HS and LS flush with the end of the housing, set the air gap so that the slide is open 1-1.5mm (Please note as indicated above with ****Edit 07/19/11. in front, this measurement has been revised to +/- 0.5mm assuming a fully broken in engine) and fire the engine up. How it idles immediately tells me if the LS needle is too lean or rich so I set this, then check the temp after a high speed run, adjust the HS needle to be in the 220'ish range, check idle speed and set LS so that it is smooth and steady and the engine is ready to go. Takes about 4-5 minutes total on an engine that could be completely out of whack and I've never even seen or ran before lol!