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]

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 tooLot 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 :crazy:

[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 :crazy:

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

[sammcj]

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

No I don't think it does...
Yep one is going in today!

[Max Preload]

My money is on insufficient ignition advance.

[CookMySock]

My money is on insufficient ignition advance.I think it will still run if its under-advanced. It will just have no performance.

Since the choke makes a big difference, I reckon its carb related. Maybe float level is way too low.

Steve

[sammcj]

Carb has been replaced today!

Popping and stopping went from dieing every 10secs / 1min to.... not dieing on idle, and stopping about every 5th set of lights! so I'm happy with that.

over 4,000rpm bike is fscking guttless as hell, so I'm going to finish the 1000km run in and then KG is going to reduce the jet a small amount.

[sammcj]

I just wanted to say a BIG thank you to everyone on the forum that has helped me out with this.!

[jonbuoy]

Good stuff mate - well I guess if its carb related its either too much or not enough juice - as DB mentioned if you can get to the choke safely whilst up at 4000+ you can crack the choke open a little - if you feel the bike pick up its too running too weak - if it bogs down more its too rich. Theres no splits or leaks in the carb to cylinder head boots??

[CookMySock]

Popping and stopping went from dieing every 10secs / 1min to.... not dieing on idle, and stopping about every 5th set of lights! so I'm happy with that.Good. Try the choke-partly-on trick again and see if that problem goes away. If it does, you are running way too lean - dont ride it! If you leave it idling for a while, does it get real hot? Does the engine revv freely when you squirt the throttle, or does it fart and miss like a cold engine, or does it sound flat and just not revv?

Do the exhaust pipes run real real hot - like nearly blueing themselves? Does someone have an infra-red temp meter you can check it with?


over 4,000rpm bike is fscking guttless as hell, so I'm going to finish the 1000km run in and then KG is going to reduce the jet a small amount.I'd strongly suggest you didn't do that run-in yet. If its running way too lean you will fuck it in less than half that distance, and then it will be a smoky rattly piece of shit.. Get someone to check that exhaust gas temperature or exhaust CO.

Be careful.
Steve

[sammcj]

tried it out on my way to work today,
turning the choke on while riding bogged it down

1/3 on - bogged it down a bit.
full on - bogged it down a lot.

i asked the mechanic at kg and he wasn't worried by it at all, he is doing to decrease the jet size to 150(?) in 500,
If i get any problems he will be the one responsable to fix it.

Oh and the engine / exhaust is running no hotter than it has done before!

[jonbuoy]

tried it out on my way to work today,
turning the choke on while riding bogged it down

1/3 on - bogged it down a bit.
full on - bogged it down a lot.

i asked the mechanic at kg and he wasn't worried by it at all, he is doing to decrease the jet size to 150(?) in 500,
If i get any problems he will be the one responsable to fix it.

Oh and the engine / exhaust is running no hotter than it has done before!

Keep us posted mate sound like he was on the right track!

[CookMySock]

Good, coz running real lean will eff it pronto. Keep us informed. Retarded timing is my guess, or blocked airfilter or something wtf stupid like that.

Sparkplug gap isn't closed up real real tight is it ?

Steve

[sammcj]

Gap is all g.
Timing is all automatic.
KG told me when he took the air filter side off it went a lot better, but yeah wait until after the 1000km is up to see!

[CookMySock]

KG told me when he took the air filter side off it went a lot better, but yeah wait until after the 1000km is up to see!Thats a big hint it's giving you there I think. I'd do a quick air-filter-off check, and if that solves the whole problem then its new air filter time (I'd put a new air filter on a new engine anyway) or at least get to the bottom of "why it do dat."

I post again just because I reckon its unwise to do 1000km on a brand new engine with such a serious fault that hasn't been diagnosed. If we KNEW it was retarded timing (for example) then do the 1000kms coz that PROBABLY won't hurt it. But we don't know.

Anyways, good luck!

Steve

[jonbuoy]

If it ran better without a filter could also be an indication of running rich. As long as its not chronically rich and getting petrol wash on the walls of the cylinders it probably won't do any harm in the short term. Being aircooled it might keep the temperatures down until its run in.

[Max Preload]

Timing is all automatic.

Not automatic. Fixed advance map based solely on rpm. Big difference. Huge.

[sammcj]

Not automatic. Fixed advance map based solely on rpm. Big difference. Huge.

Do go on... I'm quite n00b at this!




BTW - Re-jetting new carb on wednesday.

[Max Preload]

Well, it's not automatic in that it doesn't allow for any variation from factory specs. It's preset with the advance based solely on engine speed, not load (throttle position) and doesn't get feedback to retard timing like a closed loop engine management system with a knock sensor does. It's just engine speed = set degrees of timing advance.

That said, even closed loop factory engine management systems often won't allow sufficient deviation from design baselines as would be required for a modified engine.

[craisin]

so did the new carb do it

[craisin]

:doh:I missed a page

[sammcj]

so did the new carb do it

Sure did!

Doing the jet today!

[XRKID]

All ya fuses and connections, as these can become dirty or poorly connected, they can cause high resistance and cause the bike not to spark properly. I ran my xj for a week when it was cutting off under low revs to find out the fuse was bearly sitting in there, meaning it realy needed 13.4-14 volts to actually go fine instead of the standard 12.5-13 v when idling.

[sammcj]

Finally, The whole thing is just about over.

It still pops and stops on idle, we can't figure out whats doing it, replacing the carb definitly made a good difference but its still not right.

It was lacking some serious power, KG replaced almost every bloody thing on the bike until last night we found that at the upper end of the exhaust there was a very restrictive.

Just took it for a spin, and the damn thing felt like it wanted to rip me' nuts off! (in a good way).

Bad news: clutch is now slipping! - New Clutch Friday