GZ 250 Forums - Wont start despite Fuel, Spark & Air.

Hey y'all, thanks for letting me join the forum.

Have a heck of a head-scratcher in getting this bike to fire.

Got a fairly clean '03 GZ250 for $250 from some feller. Bought a parts bike w/ a disassembled head for $75, which i promptly stripped down for parts.

'03 had a leaky generator cover gasket and a bad run switch, both of which i fixed.
Has a new battery, and freshly rebuilt carburetor (by me, w/ a rebuild kit).
A/F mix screw is 2.5 turns out.
Jet sizes unknown, exhaust baffles were drilled so possible that someone put some bigger jets in.

Has decent looking spark, spark plug is what came with the bike but i cleaned and gapped it (24-28 thou)
Verified that carb is getting fuel, and also tried using various amounts of starting spray with no luck.

Compression test shows about 140 cold. On the low end of the range, and I haven't done a wet test yet.

Intake valves had some crud & rust on top of the valve, in the intake. Cleaned as best i could w/o removing head.

Took off the igniter & R/R for diode testing. Got some very wonky results (compared to what service manual says you should have). Did the same for the igniter & R/R from my parts bike (which has unknown running condition), with the exact same results.

My symptoms seem to be the same as this post

(http://www.gz250bike.com/forum/showthread.php?t=2380)

Is anyone willing to test a known good igniter and R/R for me to compare to? Service manual doesn't make sense to me. Why would a diode test have similar results when polarity is switched? Much confused.

PO said he had a battery drain problem, which is why the bike sat. Sounded like a bad R/R to me, or a short somewhere. I measured 0 milliamp draw from the battery w/ ignition off.

Ignition coil resistance tested fine

I've only had 3-4 single instances of the motor firing (one fire each time), and all seemed to be backfires, with smoke in the air box. So, seems like timing may be bad, mechanically or electrically? No idea how mechanical timing could have jumped, but it's possible ignition timing is bad from the igniter.

To do:
Buy brand new spark plug
Inspect exhaust valves for sticking (intake valves are moving freely)
Check that timing is still good mechanically
Test voltages to igniter from pickup & test voltage to coil from igniter (gotta make a peak voltage adapter for my Multi-meter)
Order stock jet sizes and install to establish known baseline
Adjust valves to spec.

Anything else? It's been a frustrating experience. I'm fairly well experienced in motorcycle mechanics, I've had dozens of bikes and fixed countless electrical issues, although of course there's always more to learn.

I've attached my excel table of values from my igniter and R/R. Top tables are from '03 bike and bottom tables are from parts bike. "NC" means "No Change", as in the multimeter display did not change.