Z24 engine start immediately like theirs fuel in the cylinders

[NicktheMillwright]

Afternoon gentlemen

 

Ihave done alot of work to my engine, I have resolved my previous run on issue and have the engine running WAY smoother. Learning the ins and outs of the carburetor has been extremely entertaining to say the least.

 

Maybe this is my lack of experience with carbureted engines showing, but even after all that work, the motor is starting up like their is already something combustible within the cylinder that just needs a bit of a spark. This truck starts up better than my Mini Cooper does with ECI, like, the first crank better. It's making me a bit suspicious.

 

What I'm getting at is, are my suspicious correct in assuming there may still be unburnt fuel in the engine, and would there be a way to test/prevent this? 

 

A thinking thats contradictory, the fact that if there was something combustible, it would have gone off and kept the motor running until there isn't anything left, like what happened with the run on.

 

Input is welcome, regardless if I'm an idiot or not.

 

Nick

[datzenmike]

When you turn the ignition off the spark stops but the engine doesn't immediately. It spins a few times and of course there is unburnt gas in the engine. If the engine is warm it restarts instantly just needing ignition spark and the starter to get it turning. This is normal and how all carburetor engines behave.

 

With fuel injection, (I don't know for sure but...) beside the ignition shutting off with the key the injectors probably stops spraying fuel also. The engine slows and stops after several turns but the cylinders are mostly empty of fuel. Fuel injection engines always take a few turns to get started even when warmed up.

 

 

Run on or 'dieseling' is the ignition of the idle mixture without the spark plugs firing. All it takes is an added heat source in the combustion chamber that sets off the fuel. 'Run on' is caused by heat. This can be from too low an octane fuel (octane makes gasoline harder to self ignite) or too high a compression ratio. The engine may be running way to hot, engine is running too rich and builds up carbon that retains heat in a 'hot spot', there could be a sharp corner or edge in the combustion chamber or piston top that can't properly cool itself, a too tight exhaust valve that doesn't spend enough time on it's seat and over heats. Seat contact is how exhaust plugs cool themselves, or the spark plug is the wrong heat range and too hot, basically turning it into a glow plug like those used in a diesel engine.