1950-1966 [Subscribe to Daily Digest] |
Okay, so I can get a little stinky on the subject of two-stroke longevity, but I do get tired of hearing them bad mouthed by folk with little actual experience with them.
Herewith a true story from personal experience (with no name dropping) to prove beyond a shadow of a doubt that...
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"You Couldn't Kill It"
As I've previously mentioned, I owned and drove two-stroke SAABs for over twenty years, performed most of the required maintenance myself and once completely restored a '63 'snub nose' wagon... using GT mechanicals borrowed from here and there.
But even with the GT engine, the 95 was awfully slow off the line and I had always wanted to make a Beetle baiter, so I took it upon myself to hot up the carburetion a bit. Starting with the standard triple carb unit, I broke it down to the individual carbs, the common throttle body, and the manifold. I removed the throttle shaft and plates, and going by the recipe found in the Chilton's SAAB manual, I decided to open out the holes in the throttle body and substitute larger plates.
But I was either too cheap or too stupid - or both - to have the throttle body properly bored to size at a machine shop. Instead, I bought myself a brake cylinder hone and went to work. I forget exactly how much material had to be removed, but I think it was a full two to four millimeters off the inside diameter. Needless to say, it took quite a lot of 'honing' to cut that much away. The front bearing in the power drill I used was a little wobbly, and - not immediately apparent to me - the hone was chattering at the throttle shaft holes. As I got close to the diameter of the oversize throttle plates, I repeatedly tried to fit them so as not to go beyond spec.
When I was done, I had three of the finest oval throttle bores money could buy. I shrugged and said to myself "So maybe the idle will be a little high." I installed the shaft and the new throttle plates, reassembled the carbs, mounted them and fired up the beast. Indeed, the idle was more than a little high... it was barely controllable. I mucked with the mixture and speed screws and tried some smaller idle jets, but had little success bringing the 'idle' down from about 3K. I shrugged again, and decided to take it for a test drive.
I was living on a dead end road with about a quarter mile driveway for a test ground... but I never made it to the finish line. The engine was fully warm by the time I rolled out of my shop, and when I stepped on the clutch to shift to second, the engine started racing... and revved to blue zillion RPM (as a friend used to say)... even with my foot off the accelerator. Immediately - in the interests of preserving the engine - I shut off the ignition. The engine continued to race full tilt, ignition off. I said to myself "Huh?", unlatched the hood, jumped out of the car, raised and propped the hood, and in a thoroughly redundant effort, grabbed the ignition primary and yanked. Still the engine roared. I was not about to grab the secondary with bare hands (even with the coil disconnected), but it took me a few seconds to formulate another plan.
I literally ripped the air cleaner assembly off the carbs, tossed it aside and put two hands over two (of the three) carb throats. Even then, the damn thing wouldn't die. Finally (the anti-climax), I found that my upper forearm was just meaty enough that if I covered the front carb with my right hand, I could just manage to cover the rear carb with my forearm... my left hand cupping the middle carb. The engine obligingly settled down and quit.
Chastened, adrenaline flowing, I asked a friend to tow me the short distance back to the shop. I removed the carbs, re-installed a stock set and never looked back. I got quite a few more miles out of that engine, so I guess it didn't suffer too much, but the experience probably cut ten thousand miles off my own lifetime.
I can only conclude that pre-ignition was the cause... but it strikes me one could duplicate the conditions by shutting off a warmed engine, while holding the throttle partly open (with a standard carb set-up). In twenty years of driving those cars, I must have inadvertently done such a thing, but I never encountered anything like the same result.
Someone have a better explanation?
Baffled In Barneveld
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posted by 216.180.198...
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