Spark Plug Guide for the 1976-1977 Yamaha GS340 Snowmobile
Keep your vintage Yamaha GS340's two-stroke engine running strong with the right set of new spark plugs.
- The recommended standard spark plug for the GS340 is an NGK B9ES or an equivalent from Champion (N2C) or Denso (W27ES-U).
- Always carry a spare set of plugs and the tools to change them when riding.
- Avoid long periods of idling to prevent spark plug fouling, a common issue with two-stroke engines.
- Replacing spark plugs is a very easy and inexpensive maintenance task you can do yourself in minutes.
Signs of a Failing Spark Plug
On a vintage two-stroke engine like the one in your GS340, spark plugs can tell you a lot about how the engine is running. They are often the first part to show symptoms of a problem. It's a good habit to always carry a spare set of plugs and a plug wrench with you when you ride.
Common Symptoms of Bad Plugs:
- Hard Starting: The engine turns over but won't fire up, or takes many pulls to start.
- Engine Misfires or Backfires: You might hear popping or sputtering sounds from the exhaust, especially when accelerating. 🎬 Watch how new spark plugs can fix engine backfiring issues.
- Rough Idle: The engine runs unevenly or stalls when not moving.
- Loss of Power: The snowmobile feels sluggish and doesn't accelerate as it should.
- Increased Fuel Consumption: Bad plugs lead to inefficient fuel burning, meaning you'll use more gas.
Choosing the Right Aftermarket Spark Plug
For a 1976-1977 Yamaha GS340, you don't need expensive, fancy spark plugs. The original ignition system was designed for standard nickel alloy plugs, and they work great. The most important factor is getting the correct plug with the right "heat range." A plug that is too "hot" can damage the engine, while a plug that is too "cold" will foul easily. Fouling happens when oil and carbon build up on the plug, preventing it from sparking.
| Brand Tier | Recommended Brands & Models | Typical Price (Each) | Our Assessment |
|---|---|---|---|
| Standard Replacement | NGK B9ES, NGK BR9ES, Champion N2C, Denso W27ES-U | $3.48 - $7.00 | These are the workhorses and the most recommended plugs for your sled. NGK is often considered the original equipment equivalent and is a top choice for vintage Japanese engines. Champion and Denso are also excellent, reliable alternatives that meet OEM specifications. The 'R' in BR9ES stands for a resistor plug, which can help reduce ignition noise. |
| Premium (Iridium) | NGK BR9EIX, Denso IW27 | $11.00 - $17.05 | Iridium plugs offer a longer lifespan and a more consistent spark. While they can be an upgrade, they are not essential for the performance of a stock GS340 engine. They may provide slightly easier starting, but the benefits might not be worth the extra cost for many riders. |
Pro Tip: Two-stroke snowmobile engines are known for fouling plugs, especially if they idle for too long or if the carburetor mixture is too rich. Letting the engine warm up for a minute or two before riding, rather than extended idling, can help keep your plugs clean.
🎬 Learn why your sled might keep fouling spark plugs.Frequently Asked Questions
How often should I change the spark plugs on my GS340?
For a vintage sled, it's best to inspect your plugs every few rides and replace them at the start of each season or every 1,000 miles, whichever comes first. Since they are inexpensive, changing them regularly is cheap insurance against being stranded.
What does a fouled spark plug look like?
A fouled plug will be black, sooty, and may feel oily or wet. This is caused by unburned fuel and oil. 🎬 See this guide for troubleshooting and identifying fouled spark plugs. This can happen from too much idling, an incorrect fuel/air mixture from the carburetor, or a weak spark.
What is a spark plug's "heat range"?
The heat range refers to how quickly the spark plug transfers heat away from its tip. A "hotter" plug stays hotter to burn off carbon deposits, while a "colder" plug runs cooler to prevent overheating in high-performance engines. For a stock GS340, a standard heat range plug like an NGK B9ES is correct.
Is there a recall on the spark plugs for my Yamaha GS340?
No, there are no specific recalls or Technical Service Bulletins (TSBs) related to spark plugs for the 1976-1977 Yamaha GS340 snowmobile. Searches of NHTSA and CPSC databases found no relevant actions for this model and part.
Helpful Videos
Technical Specifications
OEM Part Numbers: 94701-00046 94702-00046 94703-00046
Thread Size: 14mm, Hex Size: 13/16" (21mm), Reach: 19mm (3/4"), Standard Heat Range (e.g., NGK '9', Denso '27').
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.