Re: Cylinder Compression Questions

Posted by Fish'n Jim On 2014/11/24 10:15:04

Assuming the fuel presence is from the pump overwhelming the float, just rebuilding won't necessarily solve the pressure issue. It may need to be regulated/return line. The float seat just may not have shut off due to dirt, residue, dry elastomer, etc.
Make sure the cylinders/manifolds are dry. No residual oil or gas in the combustion chamber.
If the carb is not filled, only need about 20cc, <2 tbsp of liquid gas, down the carb throat to start. Give it a half a minute to spread out and vaporize before you crank it. I use a 60cc syringe, and they usually fire on the first and start/run on the second or third dose if they're going to start. That's enough fuel to spin it up to get the fuel to the carb with a mechanical pump. If it tries to start, repeat once and if it's much more than that it won't run as is.
Gas like most hydrocarbons only burns in a narrow range in air. Once it's (super rich) over the UFL it won't ignite at all. You have to air it out at that point. You also have to limit the fuel so you don't ignite it too rich and carbon off the spark plugs. That's one reason they spark outside when clean and dry but don't after you put them in the cylinders. Light oil will also burn/soot.
Turn it by hand. It should not take alot of effort until you reach compression stroke. If not, somethings stuck.
Crank it with starter first for 30 seconds or so with no fuel and coil wire off to make sure it's turning fast enough and get the oil pressure up before introducing fuel. That will tell if you have battery / cable / starter / oil pressure or other binding issues. Once all the electrical signals are good, motor turns freely, it should fire easily. It may not run well but it should start even if it's got issues.