One each for the:
High speed/top end [normally sticks up some what vertical]
Idle/air speed [normally a much smaller screw entering the carb at an angle]
Low speed/minimum [located in the end of the slide OR on the opposite end of the carb body]
Midrange [also located in the end of the slide OR on the opposite end of the carb body]
Note: if there are adjustments on both the slide and the carb body one is an adjustable mid range and the other the low speed!!! Check with the engine manufacture before attempting to adjust these types of carbs!
It is very important not to use the mid screw to adjust the low end by mistake; it is very easy to get the carb way out of sync.
Normally I recommend not attempting to adjust the mid range even if your carb is so equipped, the gains are VERY small and mostly limited to minute midrange drivability/economy changes that only the most sophisticated driver will recognize!
The negative is a carb that is so screwed up only an expert can get it back in tune!
Please note the above descriptions will apply to 99% of the modern car carbs being manufactured as of this writing with the exception of the Picco TORQUE carb that use’s no mid range needle at all.
It utilizes a fuel management ramp built into the slide; the carb also has two completely independent fuel delivery spray bars/jets.
I wish I could tell every one exactly how to tune their engine but I cannot!
My hope with this article is if I can help racers to more understand How your carb works, all the other instructions and guides will make more sense!
Best Regards,
Ron
Paris Engine Tuning Tech Tips From Our Web Site:
Should I seal the carb with silicone?
Many racers find this a must! [Particularly in off road] Here are a few tips.
1} Be sure to use ONLY non-volatile silicone [it should say oxygen sensor safe on the tube!] you can find it at any auto parts store.
2} Use sparingly, apply a thin bead on the carb neck just below the main carb body [even if there is an o-ring present.
Do not put it in the engine case bore or all around the carb neck. [That would glue the carb into the engine for good!]
You just want a thin bead to squish out from between the engine case and carb body just as you fully insert the carb.
3} After positioning the carb were you want it tighten the pinch bolt assembly that holds the carb very snug!
Then add a dab of silicone to both ends of the pinch bolt assembly.
4} Let fully cure before staring engine.
Optimal carburetor settings:
There is no such thing with any size or brand engine that has a predetermined optimal carb. Setting! If there were, all engines would come without adjustments. There are many variables that must be taken into consideration. Glow plug, fuel type and nitro, manifold type and length, pipe type and were the pressure filing is, clutch adjustment, gear ratios, tire size, ambient humidity, temperature and altitude etc, etc, etc.
The point I'm trying to make is no one can tell you were to “set the Carb” only some one they’re with you can fine-tune it! BUT IT IS NOT THAT HARD IT ONLY SOUNDS COMPLICATED. 95% of all problems are that the directions were not followed correctly.
Ideal engine temperature:
First let me say that there is no IDEAL temperature for any engine.
There are many variables that affect it; Ambient temp, fuel type and nitro content, altitude & barometric pressure, Pipe/manifold type and setting, clutch setting, glow-plug, gear ratio, available traction, How hard your driving, on road or off road Etc. Etc.
All information is based on the Paris/Exergin probe; it is the only probe designed for model engines and has worldwide patented Emisivity compensation. We tested dozens of devices before we started working with Exergin and introduced infrared tuning to the model industry.
All of the following conditions MUST be met before any temperature can be considered correct, the engine is assumed to be in good shape.
1} There must be a visible trail of smoke when accelerating from EVERY corner.
2} The idle is stable.
3} The glow plug wire stays somewhat shiny and the coil stays round [UN-distorted]
4} The performance is good.
Picco on road average conditions 20 to 40% nitro 205 to 230 degrees f
Picco off road average conditions 20 to 30% nitro 215 to 250 degrees f
Nova on road average conditions 20 to 40% nitro 220 to 260 degrees f
Nova off road average conditions 20 to 30% nitro 230 to 270 degrees f
How to “READ” your glow plug:
OS and Turbo glow plugs go gray sooner [easier] than McCoy plugs; this is not necessarily bad. Actually when A new plug wire just goes slightly gray after a 5 or 10 minute hard run it means your very close to an optimal horsepower tune, but be careful the next step is TOO LEAN!
My rule of thumb.
1} Wire and surrounding bottom of plug wet, with like new shiny wire = rich side of optimum power 85%
2} Wire and surrounding bottom of plug starting to dry and wire starting to gray = Very close to optimum power 95%
3} Wire and surrounding bottom of plug dry, wire totally gray but not distorted optimum power 100%
4} Wire and surrounding bottom of plug dry, wire distorted = slightly lean DANGER!
5} Wire and surrounding bottom of plug dry, wire broken and distorted or burnt up = extremely lean possible engine damage!
Note: You can only “Read” your plug in a nearly new state [Wire like new and shiny] A gray plug can still operate well. After it has totally gone gray, performance can start to fall off. To test just put in a new plug and if there is no difference in performance save the gray one or put it back in. If your engine does not feel or run right tray a new plug before making major tune changes
Effects of changing manifold to pipe length:
Rule of thumb:
Longer manifold = more bottom end torque. [At the expense of some rpm]
Shorter manifold = more top end rpm [at the expense of some torque]
BUT you can go to far with either direction causing the engine to run erratic or HOT! You must keep it in the “sweet spot”
Bottom line: there is no set length for every engine or pipe, experiment with the length to suit your driving style or track needs.
Does it mater were you put the pressure fitting in your pipe:
If you’re talking about a single chamber pipe like the Associated or Paris AL12T no big deal.
But if you’re talking a two-chamber pipe, and you go from one chamber to the other you will have to re tune the engine.
Even then it is not a big deal once it is tuned for that location there is little if any performance difference. [It is all relative to available pressure Vs needle setting] I recommend tapping into the first chamber on two chamber pipes [the intake side] were the pipe is at its largest diameter. The second chamber has more constant pressure but can be more difficult to tune in high altitude or fast changing weather conditions {Countinued on page 3}
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