Engine not starting, despite fuel and spark

Ollie White

New Member
Aug 17, 2017
My 80cc engine from China (eBay) has not started since it was assembled a week or two ago.

Fuel is getting to the engine, as the spark plug was wet when checked after cranking - for some reason it refuses to burst to life upon releasing the clutch. The engine will turn over after releasing the clutch level, and sounds somewhat promising, but will go silent as soon as I stop pedaling and pull in the clutch. The engine has never felt hot after trying to get it going.

I have replaced the spark plug with the NGK B7HS, and am quite sure that the ignition system is working (I pedaled with the plug earthed to the fuel cap, heard a fast clicking and electrocuted myself by accident - seems to me as if its sparking OK outside the engine, just not visibly due to sunshine).

I reassembled the carburetor, making sure to tighten everything well to avoid air leaks. The throttle mechanism is working.

I feel like there's not a lot more I can do to fix it without your help - could there be a lack of air getting to the fuel? Any reason for the engine components to be incredibly stiff?

Many thanks for any help that can be offered!

Ollie, UK

Steve Best

Well-Known Member
Sep 22, 2012
First off Ollie, ignore the Chinese instructions for 16:1 oil on break in. It is too much and fouls the plug.
Use 24:1 with a good quality oil. Here in Canada the low octane fuel is quite poor, so (while not strictly needed) using the better stuff does not hurt. The wet on your plug may be more accumulated oil than fuel, and the low octane fuel here is less volatile especially if stale.

Visually check that your throttle is opening, and that your choke really is closing. Make sure.
Check that your head nuts are properly torqued (use a torque wrench). Look for intake manifold leaks and torque nuts.
Getting a shock is not sufficient (that happens at 50v+), you need a bright yellow spark that makes an audible "click" (10,000v+)
Check that your exhaust pipe is not plugged (even from new) or try starting without it. I had one plugged with bits of red silicone sealer. The catalytic pipes are very prone to plugging, resulting in a no start or no power.

Pull the fuel line at the carb and see that you have a flow of fuel. Easy check, just do it.
Put the choke on, pedal up to speed, let the clutch go, slowly roll the throttle open, listen (and feel) for response. It may take 50 meters or more on a new engine, so keep rolling. Once it starts, keep it going for a while, then clutch and pull over to a stop to take the choke off. It should start great after that.

If this routine doesn't work, check that the rotor magnet is at about 1 o'clock at Top Dead Center. Occasionally these are installed backwards or not properly magnetized (timed wrong), in which case it will have to be replaced. This should get you started (pun intended!)