Backfire on startup

[presdough]

I have a 2001 GS500 that doesn't want to start cold.  It acts like the timing is way too far advanced and backfires so hard it will blow the carbs off.  Once it is started it will run fine.  Starting it warm it cranks slowly like it has too much timing but it will usually start once it gets past the compression stroke.  The bike only has 580 miles on it, I've checked the cam timing, been through the fuel system a number of times, new battery.  I'm thinking that the ignition timing has to advance as the RPM's increase and maybe it is stuck advanced.  Can anyone tell me how the ignition advances?  I can't find any info on it.  thanx, Tom.

[lucas]

The ignition advances with an electronic box that is located on the left side (the rider's left) of the battery box.

It receives signals from the signal generator located under the Suzuki logo on the right side of the engine.

[Big Rich]

That's awfully low miles for a 15 year old bike..... I think there's something else going on. 

The ignition advance isn't generally something you can change since the timing pickup is bolted in place. Maybe the plate is loose and that's throwing the timing off? Personally, I'd say somebody swapped the speedo for a newer one, and your valves need checked. Couldn't hurt anyway....

[presdough]

The bike was a demo at a motorcycle school.  I got it with 28 miles on it.  The ignition cover is missing so I can clearly see that the breaker plate is in and tight.  I checked the valve clearance and it is dead on.  The exhaust cam was off a tooth, it has been corrected.  I replaced the battery with one with more amperage because the engine had a hard time cranking past the compression stroke.  I smoke tested the intake system and there are no leaks and I've been through the carbs a number of times.  The only mods on the bike are a K&N lunchbox air cleaner and I raised the carb needles.  Does the ignition box advance the signal at high RPM or retard it at low RPM?  Thanx all.

[Watcher]

The only mods on the bike are a K&N lunchbox air cleaner and I raised the carb needles.

Did you rejet?

Stock jets are lean anyway, installing a K&N will only further lean it out.  Might not be the only source of issues and might not be enough by itself to totally prevent the bike from starting, but too much air and not enough fuel will definitely cause hard starts when cold.  The choke can only do so much...

You're really dead set on the ignition timing to be the issue, but I think if the timing was off enough to cause starting issues that it'd cause apparent idling issues as well.  I think it'd be more obvious.
I'd be more inclined to say it's in the fuelling.
Could be a combination of both...

[gsJack]

According to my old 97 GS owner's manual the ignition timing was 12* BTDC @ 1200 rpm and 40* BTDC @ 4000 rpm and the  California models were 5* BTDC @ 1000 rpm and the same 40* BTDC @ 4000 rpm.  I assume my 02 GS was the same as the 5-40 California models.  Unless this is a typo in my old OM the bikes are both the same 40* advance from 4000 rpm to redline.

[presdough]

I have been through the carbs a number of times and can't find anything of concern.  I have raised the needles and played with the pilot screws.  The other reasons I'm stuck on ignition  is that it does not idle nicely (Has a lot of what sounds like cam chain noise even though the chain and tensioner are new and tight) and even when warm the engine cranks like it has too much compression.  It will stop the starter and I'll have to hit the button three or four times to get it past tdc.

[Big Rich]

Have you actually tested the compression yet? You can get the gauge from Autozone / Advanced / etc as a rental. Just make sure the proper threaded adapter is included.