Posted by Bruce (VA) on September 29, 2010 at 12:59:50 from (71.62.51.74):
In Reply to: 8n wont start posted by Chuck H on September 29, 2010 at 12:48:35:
The compression results are borderline, but w/ good spark & fuel, it will start & run. So, you need to narrow the problem down to one or the other (or possibly both)
There are ways to check for spark & fuel that work & ways that don't. For example, having gas to the carb is nice, but having it past the float is what counts! That’s why removing the bolt in the bottom of the carb is the way to do it. And, same thing w/ spark at the plugs. Some folks think that checking for spark means pulling a plug wire off & looking for one. Well, it's the distance the spark jumps at the plug that gives you the info you want. It takes about 17kv to jump a 3/16" gap & 22kv to jump ¼” in the open air, so that's why you need to use a spark plug. Or, a store bought plug checker. Remember, it’s 14psi outside of the engine & about 90psi at a 6:1 compression ratio in the cylinders & compressed air creates electrical resistance, so you really need the 17-22kv to fire the plugs when the engine is running.
So, how did you check for spark & fuel?
First, replace the plugs. If you flooded it, they're fouled & it will be it next to impossible to start. You don't need to toss them; heat the tips for a few seconds w/ a propane torch to burn off the invisible spark-robbing deposits from today's additive filled gasoline........or wash them in lacquer thinner.
Next, do you have battery voltage across the points when they are open? Verify the gap on the points at .025. Then, dress the points by running a piece of card stock or brown paper bag through them. New points sometimes have an anti-corrosive dielectric coating on them & old points can corrode or pick up grease from a dirty feeler gauge or excessive cam lubricant. (I always spray my feeler guage blade off w/ contact cleaner.) Make sure you have voltage across the points, as in past the insulator on the side of the distributor. That is a very common failure point on sidemounts, along w/ the attached copper strip. It's hard to find a short there because it is usually an intermittent . So 'wiggle' the insulator & the copper strip a bit when you are doing your checking.
Next, make sure the battery is fully charged; you need a strong battery to turn the starter & get you a good spark.
Next, get a can of starting fluid or a hand held propane torch. Remove the breather hose to the carb. Crank the engine for 2 -3 seconds, then spray the starting fluid or propane in the carb throat.
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