1950-1966 [Subscribe to Daily Digest] |
>> Lastly, when I do get the beast running, how should the car be driven to avoid fouling plugs as I hear it's a commom problem. >>
I have owned and driven 3 two-strokes in my lifetime. Plugs in 2-strokes foul easily because of the oil/gas mixture - the oil forms a film on the spark plugs, which can cause fouling if not burned off. When SAAB sold "Hi-M" 2-stroke oil, it greatly reduced plug fouling, but "Hi-M" hasn't been available for probably 25 years, so we need to look at the principle reason for plug fouling in 2-strokes: because the plugs don't get hot enough during engine operation. This can happen for two reasons:
1. The plug is the wrong heat range, i.e., "cold" heat range plugs are meant primarily for high speed (aka high rpm) driving; "hot" heat range plugs are meant for low speed/rpm driving. A SAAB 2-stroke is one of the few cars where this heat range thing actually makes a difference, in that if you have "cold" plugs, and do mostly around town/low rpm driving, the oil in the gas/oil mixture will cause your plugs will foul quickly. Conversly, if you have "hot" plugs and use them on the highway (high rpm), you run the risk of burning a hole in the top of one or more of your pistons. I preferred the risk of fouled plugs (much less expensive to resolve), so I never drove my 2-strokes with "hot" plugs, even though 80% of my driving was under 50 mph. I knew other 2-stroke drivers that would actually keep two sets of plugs in their car, and change them when they went from low rpm to high rpm driving, and vice versa. Instead of changing plugs back and forth, whenever I lubed the car (every 1500 miles on pre-1965 SAABs), I would also remove the plugs, clean them up with a "wire brush" wheel, and regap them to the correct gap. As long as I did this, I never had any fouled plug problems.
2. Too much of your driving is at very low rpms. This reason is related to the first. If all of your driving is under 35 mph, even "hot" plugs will foul sometimes. They simply don't get hot enough to burn off the coating of oil they get from the gas/oil mix. The solution to this is simple - keep the rpms up! If you can't get the car on a highway periodically to drive at 55 - 60 mph, then shift later so that the rpms build up in each gear. The more frequent the spark, the hotter the plug gets, and the more it burns off the oil coating that can foul the plug.
This whole discussion reminds me of why I liked the 2-strokes so much - they were so simple. Understanding their operation and quirks was a matter of simple physics and mechanics - no computers, no complicated vacuum systems and lines, no emissions controls, no fuel injection, just simple mechanical devices. Ah, for the good old days!
Good luck, and enjoy your 2-stroke.
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