ORIGINAL: Hobby_Services
The initial settings for the carburetor of your DuraTrax .18 engine are easy to set.

First, close the high-speed needle valve and open it 2-1/4 turns out from closed. This is the initial setting, and is a rich setting. You will have to lean the engine from this point as you drive the car.

To set the idle mixture needle, which is the grey screw in the center of the throttle arm, inside the chrome barrel, you must be able to see into the carburetor. Remove the air cleaner from the carb so you can see what you are doing.

Open the throttle to the full-open position. Inside, you can see the idle needle and the fuel nozzle. Adjust the idle mixture screw until you have a gap of 2mm to 3mm between the needle and the nozzle when the carburetor is fully opened. You double-check this by looking at the head of the idle mixture screw. It should be sticking out of the chromed barrel by about 1/32". This is an initial setting, and is a bit rich.

When you start the car, you can leave the clip-on battery attached to the glow plug for some initial running. As you run the car, it will be a bit rough. Adjust the high-speed needle until it just stops running rough. You can then adjust the idle mixture needle and the carburetor throttle opening until you can have the car stopped, but with the engine running smoothly. If you release the brake or stop holding onto the car, it may tend to ease forwards, just like a full-size automobile with an automatic transmission. This tells you that you have the correct setting.

Now go out and enjoy running your R/C gas car with your DuraTrax engine!

ORIGINAL: Frost_

The issue of tuning comes up frequently, so I thought I'd modify a piece I did about big-block tuning that has been floating around the Savage forum. A variation of this was told to me a while back.

Guys, FORGET about asking what other's settings are, once you do this a few times you can take any old strange engine (meaning one that is working, but unfamiliar to you) and start from nothing, that is, knowing NO settings and get the most out of it.

For some reason even in the mags when they tell you "how to tune", they have you pinching the fuel line and timing the result in seconds to "set" your LSN. No doubt this is a good way to get in the ballpark, but it is FAR from precise.

The following will asume that you have your top-end tuned to a decent temp. range for your normal style of driving. If you AREN'T running lean (stuttering, you hear it, you know what it is) you can very safely tune the top-end to 250-260 with no reduced life (AGAIN this is if it isn't going LEAN). This temp. is a range for many, but not all smallblocks. Some like to be run even hotter (TRX 2.5 makes it's best power at 275F +) Once you get the top-end set here is how to really make it take off fast. If you are heavy-fingered this may be better for the pavement. Before you begin tuning the LSn, get the engine up to operating temperature first.



1. Since off the line "snap" can be given or taken away by being lean OR rich on the LSN the first move is a guess (well it won't be after you get a feel for it, but this will get you going quickly)...

2. Pull the truck up in front of you and let it idle for 8 seconds. Then pull the trigger to WOT... Did it scream and take off? If no:

3. You have to go one way or the other... choose richer or leaner (suprisingly to many beginners, off the line stutters can be caused by too lean conditions just as easily as too rich) and turn the LSN in that direction 1/16th of a turn. Make a short pass at medium to high throttle and return the truck to in front of you.

4. Let it idle 8 seconds and floor the throttle. Did it take off better or worse? If better, turn it a 1/16 in the same direction, if it got worse, turn it 1/8th the OPPOSITE way. Either direction you started in, now you will be going one way based on whether it got better or not... either richer or leaner.

5. Make another short pass at medium to full throttle (AFTER you made the change to the LSN) and return the truck to you. Let it idle 8 seconds and floor it. Is it still getting better? If so, continue to lean or richen using the pass/idle 8 seconds method until you lose preformance and back up a step...

If your temps are in range this is how to quickly get your truck to "explode" off of the line... Always make the pass to clear out the engine and then let it idle 8 seconds. The idling will allow it to either lean out or load up, depending on which way the current settings are off... Get the hang of this and your truck can really take off. If you end up leaning the LSN out excessively make sure to keep an eye on temps, your top end needle may need a bit of enrichment.


Copy this text and print it out if you need. Once you have done this you will realize how you are affecting positive change and it only gets easier.