What is spark plug gap on 4 stroke 70cc engine?

.028"

0.024
http://www.globaldenso.com/cgi-bin/global/plug/usa/pw/pw-plug.cgi?filename=pw-14.txt

Check on any safety interlocks.
Is there oil in the engine? Some engines have low oil interlocks.
Are there any other safeties?
Is there a key or on/off button?
Stick a phillips screwdriver in the spark plug connector, hold the screwdriver close to the engine, spin the engine, is there spark at the gap?
If so, try a new plug.

It all depends on the model of engine. If it is a twin engine doesn't it have two magnetos.Very unusual for both to go bad It will depend on the type of ignition(points or solid state) The wire going to the magneto could be the kill switch (kills when grounded) Disconnect it and see if you get spark. IF so then it is in your safety/ignition circuit. If you replace magneto usually the gap is .008-.012

Before adjusting anything, check the condition of factors that pertain to the proper running as: fresh fuel mix, plugged fuel filter, air cleaner, and muffler. Poor fuel lines, and loose carburetor fasteners. Remove the spark plug, and place it on engine metal (wire attached). Pull the engine through smartly--the spark should be blue and snappy. Plug gap should be ~0.020" and the insulator should be light to medium tan in color. Try a new plug if in doubt. When these things appear to be correct, turn both jet screws CW to stops (lightly), and then CCW each back out 1-1/2 turns. It should start and run fairly well at this point. Allow the engine to warm up, pull the throttle full on. The engine should be 4-stroking--turn H needle CW until the engine starts to speed up, but still 4-strokes. Proper adjustment is when the engine 4-strokes, but immediately 2-strokes when cutting. Allow to idle and adjust L CW until the engine runs fairly smoothly, yet allows the engine to 'follow the throttle'. Set the idle speed screw so that the chain doesn't turn, but the engine doesn't stall out. If you can't get the above to work, you may need to clean and re-kit the carburetor first. Hope this helps!

For a 2001 Yamaha F115 4 stroke use NGK Plugs LFR6A-11 gapped between 0.039 and 0.043

it could be the spark plugs are to long and the piston is hitting the glug

Hi there, No problem.
Recommended fuel mix ration if using Husqvarna brand premium Two-Stroke Oil is 50:1. If using another two-stroke air cooled engine oil, you should use 25:1 fuel:oil ratio.

Regading the spark plug, the recommended plug is a Champion RCJ7Y with a plug gap of 0.5mm (or 0.020 inches).

What does the spark plug look like? Make sure you are getting spark.

Hi

I suppose is 4 stroke engine.Before adjusting the breaker points gap at .020 check if the breaker points are burned.Also check the condenser(change it).Change the spark plug with a new one with the same heat range.The plug gap is .030.

best regards savumihai71