A Basic Tuning Guide By Dazzi
Tune in order, make sure the car is at its base settings - the setting you broke it in with. Its should very rich (boggy/lots of smoke/ possibly stalling) at these settings and the performance will be poor.
Note: Most engines are happy with changes to the needles in 1/8 increments however in my expericience I've found Traxxas engines to suit 1/16 and also Cen engines, tuning them using 1/8 increments will only have you pulling your hair out
1. High Speed Needle
Turn the HSN clockwise (to lean) in a 1/8 increment and drive down a straight, each time you do this you'll see a small increase in performance (and a good trail of smoke), keep doin it until:
A : there's little or no smoke from the exhaust
B : the car gets slower at full throttle (down a straight) or stalls at full throttle
at this point turn anti-clockwise (richen) 1/8, if it's still no good turn another 1/8, that will be enough.
Untuned HSN Symptoms:
Too Rich - Lots of smoke/slow-poor performance/stall/groggy sound to the engine - Turn clockwise
Too Lean - Little or no smoke/very fast/loss in performance at full throttle or stall - Turn anti-clockwise
2. Low Speed Needle
Tune the LSN in the same way, but only make adjustments in very small increments at a time. The LSN is very sensitive and you can potentially cook your engine if it's set too lean. You are looking for fast and smooth acceleration with some smoke, a steady idle with some smoke and a bit of unburnt fuel won't hurt
Note: it takes time for the LSN adjustments to be visable, it helps to accelerate at full throttle for 5 seconds then brake and idle for a few seconds then accelerate again, repeat until you see the improvement in acceleration then carry on making adjustments.
If it stalls, stutters with high revs / no smoke on acceleration then turn anti clockwise 1/8, if no good unscrew another 1/8 - this should be enough
Untuned LSN Symptoms:
Too Rich - Lots of smoke and unburnt fuel at idle/slow acceleration/stall
Too Lean - little or no smoke on acceleration/immediate stall on throttle or stutters / high engine revs
3. Idle Screw
Your idle may be affected after these changes, make adjustments in small increments at a time,
Turn anti clockwise if it runs too fast at idle - wheels spin with no throttle
Turn clockwise if its too slow/low - eg revs drop then stall, stalls on throttle or when starter is removed.
Once tuned your car should have a fast smooth acceleration, impressive top speed, steady idle and ALWAYS a good trail of smoke
One of the most common newbie tuning problems I've come across on here is instant stalls on throttle or when the starter is removed.
If you have this problem then its one or a combination of the following (check in order below):
1 - Glow Plug dead - replace if needs be
2 - Idle is too low - open the carb via the trim on the radio
3 - LSN too rich/lean
4 - HSN too rich/lean
5 - Engine too cold
- if the setting is too rich you'll hear the engine being groggy at idle and see plenty of smoke and unburnt fuel
- it the setting is too lean there will be no smoke at idle and the engine will scream/high revs
A more indepth tuning guide by Scorching Savage from Savage-Central.com
The question seems to keep popping up about Carb adjustments- what does it do, which do I adjust first, etc.. Here a basic guide explaining the internal carb components, what they're responsible for, and how to tune it properly.
Assuming you're at the manufacturers recommended starting point with the idle opening gap already set and the engine running- the first thing that must be set is the HSN. The HSN (main needle) controls the maximum amount of fuel flow through the fuel inlet/spray bar. Since it does control total fuel flow- the HSN setting WILL AFFECT the LSN setting. Therefore, you MUST adjust this setting 1st before finalizing your LSN adjustment. Setting your LSN 1st will only cause you to have to reset it again once you alter you HSN adjustments. You must typically match this maximum fuel flow through the carb with the maximum amount of air flow through the carb. Maximum airflow through the carb can only be achieved with the carb at WOT and the engine at max RPM. It doesn't matter how fast you accellerate at this point- just get the engine to maximum RPM's doing several high speed passes and make a judgement based on maximum speed and smoke trail. Adjustments should be made at hourly incriments. Once you get to a point where top speed is no longer improving, richen the HSN between 1/8-1/4 of a turn out just to ensure adequate lubrication at that maximum speed.
*If the engine suddenly cuts out at high RPM's - you too lean
*If the engine lacks high RPM response with excessive smoke- your too rich
See picture 1 of carb at WOT (please ignore misspelled word)
Picture 2 borrowed from RCCA website illustrating the HSN and how it affects fuel flow
If your engine's is starting to run excessively hot even while your fuel mixture is excessively rich...try switching to a cooler glow plug, one step cooler than the one your using. ( If your using Dynamite plugs like an MC-59, switch to an MC8, then to an MC9 if necc- if your using OS plugs and using an OS8, switch to an OSA5, and then to an OSR5 if neccesary. DO NOT JUMP FROM ONE MANUFACTURER TO ANOTHER WHEN EXPERIMENTING WITH GLOW PLUG HEAT RANGE. THERE IS NO INDUSTRY STANDARD FOR THEM TO COMPLY WITH SO KNOWING WHICH PLUG IS HOTTER THAN THE OTHER BASED ON IT'S GIVEN RATING IS NOT SOMETHING THAT CAN BE DONE BETWEEN 2 MANUFACTURERS)
When the throttle is anywhere between 1/2 open to fully closed, the LSN enters the fuel inlet/spray bar and restricts the amount of fuel that can flow through it. Less fuel is required at this point since the smaller carb opening is also restricting the amount of air that can flow through the carb. The deeper the LSN enters the fuel inlet, the more it restricts fuel flow- to match the restricted air flow.
See picture 3 showing LSN entering or leaving the Fuel Inlet/spray bar at 1/2 throttle
Picture 4 borrowed from RCCA website illustrating LSN and fuel inlet interaction
There are many methods people use to set their LSN. For me- I typically clear out the engine by doing a high speed run, bring the truck in and allow it to idle, then watch and see how it responds at idle speeds. If the idle speed drops right away or slowly drops within a few seconds ( or if temperatures start to drop too fast) = the LSN is too rich allowing too much fuel through which is loading up the engine lowering it's RPM. If it starts to climb in RPM ( or if temperatures also start to climb) then it's set too lean. Adjustments should be made at hourly incriments with a high speed run in between each adjustment to clear out the engine. Once I get the engine to idle for at least 20 seconds or so without excessive load up, once again, I'll clear out the engine, bring it in and idle the engine for 5-10 seconds- then hit the throttle to watch how it accellerates. It should accellerate smoothly and powerfully from idle all the way to max RPM's with a nice healthy smoke trail leaving the exhaust. Even finer LSN adjustments can made in even smaller incriments to fine tune this setting. Once your satisfied with your overall performance- you can adjust the idle speed ( if neccesary) by using the Idle stop screw. This basically adjusts how far the carb's slide barrel will close. The LSN will affect the idle speed/quality if it's not set correctly- so it is important you're able to achieve and hold a steady idle at the manufactures suggested setting (usually at around 2mm) before making it's final adjustment. Remember- you're not entering a contest which engine can hold the lowest idle speed so just set it to where it's comfortably below clutch engagement to prevent premature clutch wear.
Note: the ability to hold a prolonged and reliable idle is greatly affected by the heat range of the glow plug.. the hotter the better as far as idle quality. As far as high speed/max RPM running- the heat range of the glow plug will affect overall timing advance in which a hot plug might overadvance the timing causing detonation and/or reduced power output- the key is to experiment with something that will give you the perfect balance for overall bashing- cold plugs for tracks with long straightaways and extended high RPM use, and med/hot plugs in tight tracks where lots of decelerating at closed throttle followed by WOT acceleration is performed.
Picture 5 showing Carb in idle position- you can see how deep into the inlet the LSN is at this point
The Midrange adjustment does NOT control an actual needle- nor can it be set rich or lean (LSN shape and design has more of an impact as to how much more gradual fuel flow is allowed through the fuel inlet at mid throttle). It actually controls at what point of the carb opening, the LSN fully leaves the fuel inlet. Since the HSN should typically be set slightly on the rich side- the point at which the LSN leaves the fuel inlet will create a sudden small rush of fuel. This sudden richness can be beneficial to expert tuners by manipulating at what point it occurs in the throttle opening. To adjust the Midrange point, both the Mid and the LSN need to be rotated TOGETHER in opposite directions. In the picture below, this transition point takes place at 1/2 carb opening. If you want the transition point to happen at a later throttle opening- you'll need to adjust the mid range clockwise (deeper) into the carb body while adjusting the LSN counterclockwise in the same amount of turns. If you fail to adjust the LSN at the same time- you will affect your Low speed setting. The opposite holds true if you want the transition to occur at an earlier throttle opening. The affect of the Midrange adjustment is very minimal and is better off being left at the manufacturers base settings.
Picture 6 borrowed from RCCA website illustrating the fuel's path through a typical 3 needle carb- "Fuel enters the carburetor through the banjo fitting (1); it then travels into and through the main needle assembly (2) and eventually exits into the venturi via the fuel inlet (3). The low-speed needle as shown here isnâ€™t a factor at full throttle."
Remember- there are other factors involved in maintaining and regulating operating temperatures of your engine- while a excessively lean or rich mixtures will affect your overall operating temps- it is NOT the only factor involved. If your engine is approaching excessively hot temperatures while still spewing out lots of raw fuel/oil out of the exhaust due to an excessively rich fuel mixture, there is likely to be another problem with your engine (air leak, too high or too low compression ratio, wrong glow plug heat range, etc). Engines are set up and shimmed at the factory to work in most/average operating enviroments. If you live in an area that is always excessively hot (95F +), it may be neccesary to ADD an addition shim to reduce the compression of the engine to keep everything in safe operating range. If you live in area that are excessively cold year around...you might even want to consider removing the thinnest shim (.1mm) to INCREASE compression or even consider using higher nitromethane content to keep temperatures up where they need to be.
Tuning videos from HPI:
Tuning videos from Traxxas:
Traxxas setup 1 of 21 - Getting Started
Traxxas setup 2 of 21 - Fuel
Traxxas setup 3 of 21 - Gluing the tires
Traxxas setup 4 of 21 - setting up the antenna
Traxxas setup 5 of 21 - Installing Radio batteries
Traxxas setup 6 of 21 - Using your radio system
Traxxass setup 7 of 21 - Optidrive
traxxas setup 8 of 21 - Trx 2.5 engine
Traxxas setup 9 of 21 - Using the optidrive
Traxxas setup 10 of 21 - Setting up the carburettor
Traxxas setup 11 of 21 - Breaking in your engine
Traxxas setup 12 of 21 - Starting your engine
Traxxas setup 13 of 21 - Tank 1
Traxxas setup 14 of 21 - Tank 2
Traxxas setup 15 of 21 - Tank 3
Traxxas setup 16 of 21 - Tank 4
Traxxas setup 17 of 21 - Tank 5
Traxxas setup 18 of 21 - Tuning your engine
Traxxas setup 19 of 21 - Drive!
Traxxas setup 20 of 21 - Clearing a flooded engine
Traxxas setup 21 of 21 - Storage and Maintenance