2M pre-ignition problems

[crown69]

after at long last, after a spate of hiccups, I started crownie's 2M. It runs like a clock-except when switching off, though not EVERY time, it suffers from pre-ignition.
Anyone familiar with these motors can identify a probable cause? and how to go about it?
thanks and regards

[crownv8]

The basic things to start with are idle speed, float level and ignition timing.

I found with one of mine that had a similar problem was to idle it for 1/2 minute before turning it off. Seemed to help.

The problem is that the early carby didn't have the fuel cut solenoid built into the carb. Fitting a later model carb with the fuel cut solenoid should fix it forever.

Shane.

[crown69]

The basic things to start with are idle speed, float level and ignition timing.

I found with one of mine that had a similar problem was to idle it for 1/2 minute before turning it off. Seemed to help.

The problem is that the early carby didn't have the fuel cut solenoid built into the carb. Fitting a later model carb with the fuel cut solenoid should fix it forever.

Shane.

idle speed-running a little fast; though that can be attributed to auto choke since seldom start it.
float level-is that the glass 'cup' beneath the carby?if so what level should it be?
ignition timing-no idea what that is; excuse me for sounding stupid!

will try that trick to see if it does the same thing

re carby; those motors are as rare as white flies in this country!!!

[crownv8]

There is a glass circle on the front of the carby. In that circle is a small dot or a line. When the car is running the fuel level should be exactly on that dot/line.

Just check that the choke is not sticking on. Too fast a rev can cause it to run on. This is the issue I would be more concerned about at the moment. Run it until it is good and warm and lift the top off the air cleaner and make sure that the choke butterfly is straight up and down.

Ignition timing is the time that the spark fires. There is a line on the crank pulley and marks from "0" to "15" on the front timing cover. Using a timing light you set the ignition timing while the engine is running. You may need to get your mechanic to check it.

[madmont]

If the carby has idle fuel cut solenoid and the idle is too fast it will suck fuel from the main jet and cause running on

[Joshstix]

Mine does this a bit, things that contribute in my situation are:

Octane, rarely happens with 95RON, never happens with 98RON
Temp, the higher the engine temp the more likely it is to run on
Running speed, the faster it is revving when it's turned off the more likely it will run on.