Hello,
I have a 2003 Sunl 150cc. Gy6 engine. When I bought it, it was well-used with a no-start, no spark condition. I installed a new CDI (it had none) New Champion spark plug, fixed a shorted kill switch. I now have spark when the plug is grounded to the block. Had a leaking carb, so I got a brand new replacement and put it on. Still no start. Not so much as a pop. Set the valves to .004. Still nothing. Seems to have good compression. Shot some starting fluid in the carb. Still not a pop. I even removed the plug and shot a little in there. Still nothing. The gas line is clear and the carb seems to be filling. The only thing I can think of is maybe the rubber carb boot to head is leaky. I'm doubting that this will do it and I hate to just throw more parts at it. I'm stumped. Any ideas would be appreciated.
Thanks, Tom

 

still sounds like you dont have no spark put in a dark place and try starting to see if you can see any spark coming out of plug wire

 

personally, i've had problems with champion on quads. i use NGK. the champions tended to crack the ceramic for some reason giving me a shorted plug.

 

I've tried three different new plugs. The Champion, an NGK and a Chinese plug. Same results on all.
Thanks, Tom

 

have you put a compression gauge on the cylinder and see what the psi actually is?

 

Also, I checked the carb boot and it looks o.k. The spark is blue, but I've seen a fatter spark. Maybe it's weak and won't fire under compression???
Thanks, Tom

 

No, I don't have a gauge, but it pretty much blows my thumb off when I turn it over. That's usually plenty good enough.
Thanks, Tom

 

sounds like you got about 100-120 psig. that's good. well, i don't know what the fix is for a spark plug that doesn't fire under compression. . unsure, maybe a real expert will jump on it rather than me, a shadetree mech....

what gap are you using anyways? have you tried pinching it down a little?

 

Well I am stumped too. Spark, Fuel, Compression. With all of those it should start.

I would revisit all the things you've done again with a fresh outlook just in case you missed something. Check the spark again, valve adjustment, etc.

Check the ignition timing with a timing light. There is a rubber access plug on the flywheel cover to allow the timing light to shine through to the marks on the flywheel, though I've found it easier to remove the flywheel cover to get a better view. Although rare, I've seen people report sheared keyways which allow the flywheel to rotate on the crankshaft and fire the plug at drastically the wrong time. I've also seen reports where the CDI self triggers and fires erratically (and at the wrong time).

Else I'm out of ideas at the moment...

 

after cranking the engine, pull the spark plug immediately to see if it is indeed wet with gasoline. i gotta think some more on this one.