I own a 1981 440 Yamaha. My problem is that it takes about 40 pulls to start the thing. It’s not flooding, there is no carbon on the plugs and it seems to have a fair amount of compression. It seems to start better when it is cold, but is a bugger when it is warm. What is wrong?
This is a difficult one to diagnose with such little to go on. Yet…
Remember the requirements to make a two stroke run. 1. Fuel 2. Primary compression 3. Secondary compression 4. Ignition at correct time
What you are telling me is that when the engine is warm it will not start, and that you are not getting too much fuel, correct?
Most basic is to verify the quality and freshness of the fuel. “Summer” gas will not start well in the winter, so make sure you have fresh gas.
How strong is your spark? Gap a plug at 0.125 for test purposes, ground against the head and pull the rope checking for spark. This wide gap will show if the ignition system is strong or weak.
If you have good spark, get the rear of the sled up on a stand and squirt two or three squirts of fuel into the carbs. If the engine starts but soon stops, check the fuel system (lines, filters, pump, impulse line, carbs).
If the engine does not start pull the plugs and check the plug tips for traces of fuel. If they are dry, the fuel is not being transferred from the crankcase to the combustion chamber. this means you have low primary compression- worn rings, leaking end seals.
To prove this, squirt some fuel into the plug hole and install plugs. if it starts then stops, time to overhaul the engine. If it doesn’t start, check secondary compression and confirm ignition again.
Hope this gives you something to work on.