Fuel Mixture is Critical
Achieving optimal performance in your 1/5 scale 2-cycle engine requires careful attention to your fuel mixture and tuning. Small changes in the oil-to-fuel ratio can significantly impact how your engine runs, and proper tuning ensures longevity, power, and reliability.
Lean Oil Mix (Too little Oil)
- Effects: Reduced lubrication increases wear, the risk of overheating, increased spooge, less compression, more engine wear, and less horsepower.
- Tuning: You will have to maintain a richer engine tune (higher fuel-to-air ratio) to prevent engine overheating and avoid engine damage.
Correct Oil Mix (Less Oil)
- Effects: Increased lubrication, reduced engine wear, engine runs cooler, increased compression, more horsepower, reduced spooge.
- Tuning: Consistent mixing reduces the need for re-tuning, easier fine-tuning keeps the engine running cooler and avoids damage.
Rich Oil Mix (Too Much Oil)
- Effects: Increased lubrication, improved protection, higher compression, increased carbon buildup, excessive smoke, increased spooge, plug fouling, reduced combustibility and horsepower.
- Tuning: You will have to maintain a leaner engine tune (lower fuel-to-air ratio) to ensure proper combustion and avoid fouling.
Spooge: A Common Symptom
"Spooge" refers to unburnt oil accumulating in or on the exhaust. It is typically caused by incomplete combustion due to overly rich oil mixtures or improper tuning.
- Key Tip: If spooge occurs with the correct oil mixture, it indicates your high-speed jet needs to be leaned out.
- To lean out, turn the high-speed jet IN (clockwise) carefully by 1/16 of a turn at a time.
- After each adjustment, run the engine for a while to evaluate the results before making further changes.
- A well-tuned engine will have very little smoke and spooge.
Lubrication Summary:
Running your engine with the correct lubricant can lead to:
- Improved compression due to a better seal between piston rings and the cylinder wall, reducing blow-by.
- Increased power by reducing friction.
However, excessive oil without proper tuning adjustments can result in spooge buildup, fouling, and poor performance.
Fuel Consistency is the Key to Great Running Long-Lasting Engines
Many hobbyists face performance issues and even engine damage due to inconsistent oil-to-fuel ratios. Even minor changes in the mix can alter combustion dynamics, necessitating frequent retuning.
- Stick to a consistent oil mix ratio (25:1 or the ratio recommended by your engine manufacturer).
- Use high-quality, non-synthetic 2-cycle oil designed for high-performance engines.
- Monitor your engine's performance and exhaust residue regularly.
You Cannot Keep Your Car in Tune Without a Consistent Fuel Mixture
Maintaining a correct and consistent fuel mixture is critical for keeping your car in tune. Below is a guide for mixing a 25:1 fuel ratio:
25:1 Fuel Mixture Chart
| Amount | Fuel (Gasoline) | Oil |
|---|---|---|
| 1 Gallon | 128 oz | 5.12 oz = 151.4 ml |
| 1/2 Gallon | 64 oz | 2.56 oz = 75.7 ml |
| 1 Quart | 32 oz | 1.28 oz = 37.9 ml |
| 1 Pint | 16 oz | 0.64 oz = 18.9 ml |
Quick Calculation Tip
To calculate the oil required for any amount of gasoline, divide the gasoline ounces by 25.
Example: For a 25:1 fuel ratio, divide 128 oz (1 gallon) by 25:
128 ÷ 25 = 5.12 oz of oil. Multiply by 29.5735 = 151.4ml
We suggest purchasing a 100 to 200ml syringe usually around $10 for precise, consistent oil measurements.
Engine Smoke:
Excessive smoke from a 2-cycle engine can indicate several potential issues, often related to the fuel mixture or engine performance. Here's a breakdown of what excessive smoke might mean:
- Too Much Oil in the Fuel Mixture: Can lead to incomplete combustion of the oil. Adjust the fuel mix ratio.
- Improper Tuning: Rich tune leads to incomplete combustion. Lean out the high-speed jet.
- Worn Piston Rings or Cylinder: Inspect and replace if necessary.
- Clogged Air Filter: Clean or replace the air filter.
- Excessive Carbon Build-Up: Clean engine components to remove carbon deposits.
Pro Tip:
Choose a reliable oil mix ratio, tune your engine for it, and ALWAYS mix your fuel the SAME way. This practice ensures consistent performance, minimizes maintenance, and allows you to enjoy your 1/5 scale RC car without constant adjustments.
When tuning, you will notice a pitch change in engine revving. A richer tune will be a deeper pitch and a leaner tune will be a higher pitch. When proper tuning is achieved (little smoke and spooge), you will come to identify the correct sound. Pay attention to the sound of your engine for indications of how it is performing.
Carburetor Tuning:
First of all, to the newbies out there. DO NOT adjust carburetor settings during break-in. Doing so will most likely result in engine damage.
Carb base settings:
- Close the (Left) high-speed needle turning it clockwise until it stops. Then turn it counterclockwise 1 1/2 turns out.
- Close the (Right) low-speed turning it clockwise until it stops. Then turn it counterclockwise 1 1/4 turns out.
Adjusting the needles even 1/16 of a turn can cause a significant change. Only adjust 1 needle at a time when fine-tuning. Do not over-tighten needles down, it will damage them.
Low-Speed Adjustment:
To set the (Right) low-speed needle, first adjust the idle screw to the desired idle. Turn the low-speed screw in or out up to 1/16 either way finding the highest rpm smoothest run at that idle setting.
Adjusting the high-speed screw is not something that you should do if you are inexperienced because leaning your engine out too much can lead to catastrophic failure.