GB500 Won't always idle / 'pops and stops'

[sammcj]

Just had my GB500 made into a 600 and it keeps stalling

Before this was done (by KG motorcycles in CHCH) it would ocasionaly either stall or make a 'popping' noise (like air out the valves or something?) and stop.

Now that it is a 600 its really bad, every set of lights once the bike is warm it stops. I've had the guy from KG looking it over head from toe and he can't figure out what it is.

The poor guy has spent WAY too much time on this and its really giving us both a headache.

He is 99% sure it is electrical and it sounds like the timing randomly gets advanced.

You can by now probably tell I'm not very skilled up on such things.

He has amongst other things:

-Replaced CDI
-Replaced Regulator
-Checked valve clearances
-Disconnected battery and checked charging rate
-Replaced coil under clutch cover (can't remember the name of it)
-No air leaks coming into carb
-Carb has been fully disassembled twice and checked over.
-Spark plug and gap is fine
-Carb re-jetted

The bike idles nicely until it stops.


Any help / ideas would be greatly appreciated!

[Bonez]

Who said jappers don't have character?

[FROSTY:Me]

dude the GB400 used to have EXACTLY this issue when they first came out. Sorry I don't remember what the solution was.
Do give spang a yeodle though---his GB500/600 took a bit of fettling too

[Ixion]

I take it all back. They do.

Obvious answer is do what all old skool tuned big banger riders did, and just keep blipping the throttle. Which also adds +6 street cred.

Was the carb rejtted after the big bore. And it would not be at all surprising if the timing needed changing. After all the motor has gone up 20% in capacity. And I presume on the bore, which means a significantly longer flame path.

[sammcj]

Hey, yeah carb was rejetted, timing is all automatic.

problem is, as you come up to the lights, hoping they'll turn green or whatever, the bike will just die as it enters the 2000rpm range.

Thanks for the reply

[Ixion]

yes, but the automatic timing may need to be different automatic.

That's the problem with automatic timing! Give me a good old fashioned manual advance and retard any day. Good as an extra gearbox.

[sammcj]

yes, but the automatic timing may need to be different automatic.

That's the problem with automatic timing! Give me a good old fashioned manual advance and retard any day. Good as an extra gearbox.

Hmm....
I don't quite know where to go with this then...

[sammcj]

yes, but the automatic timing may need to be different automatic.

That's the problem with automatic timing! Give me a good old fashioned manual advance and retard any day. Good as an extra gearbox.

Hang on, but it idles fine then just suddenly stops, mostly when its warmed up.
Some times it can idle for a min, some times 10 seconds....
So it seems like something is actually faulty and advancing the timing every so often...

We've tried 91 and 98 fuel in it.

[Bonez]

dude the GB400 used to have EXACTLY this issue when they first came out. Sorry I don't remember what the solution was.
Do give spang a yeodle though---his GB500/600 took a bit of fettling too

Lot of things were tried. Valve clearance made greater, valve/seats reground seated properly, auto decompression disconnected etc etc.

Mine quits somethimes at near idle coming to a standstill. A chap at last years coldkiwi mentioned there was a fuel cap breathing issue.

I've tried setting idle a bit higher but still occurs occasionally.

[sammcj]

KG thinks it is the carb, it looks clean but hes pretty sure theres something he can't spot somewhere, going in tomorrow and he's going to install a replacement carb.

[jonbuoy]

Is it when coming to a rolling stop or when the bike doesn't move at all just sitting still? Carb float level correct? Carb idle path as clean as a whistle? If its got worse since the big bore you would think it would be more carb/fueling related than ignition? Like its starving out. Ramblings of a backyard mechanic so feel free to ignore

[CookMySock]

Does it make any difference with the choke partly on ?

Steve

[sammcj]

Is it when coming to a rolling stop or when the bike doesn't move at all just sitting still? Carb float level correct? Carb idle path as clean as a whistle? If its got worse since the big bore you would think it would be more carb/fueling related than ignition? Like its starving out. Ramblings of a backyard mechanic so feel free to ignore

Hi there,
It does it on both, it'll jerk around coming to a stop if it feels it wants to stall and it will do it on idle!
KG has disassembled the carb twice, Float is correct and idle looks good.
New carb today so we'll see how that goes!

Thanks for your suggestions.

[sammcj]

Does it make any difference with the choke partly on ?

Steve

Yes but it revs the hell out of the bugger! Idle should be 1300~ and goes up to between 2300-3200~ on 1/3 / 1/2 choke.

[CookMySock]

Yes but it revs the hell out of the bugger! Idle should be 1300~ and goes up to between 2300-3200~ on 1/3 / 1/2 choke.

Good. Does the bike still cut out when you ride it with the choke partly on?

You can see where I am going with this.. Can you get your hands on another identical carby to try?

Steve