GPZ500s carbs...

[dextersaurus]

Well, with my new purchase not starting, i decided to strip the carbs, and clean them out. Found that the jets were blocked up, so cleared them and fitted it back on.
I then started it up on full choke, and it ran for about 3 mins, idling at about 3k rpm. It was smooth enough, no wierd noises coming from the engine, then it started to bog down and then it just died and refused to start again. There was plenty petrol in it, and the petrol tap is functioning properly...

I left it for 5 minutes, then turned it over, and it spluttered, then just kept turning over, not starting.

Is it a carb issue?

And would starting it without an airbox on it cause this problem? i'd have thought it would make it run crappy at the most...

Cheers

Dunc

[Paddy Blake]

It could have dirt in the tank. Fit a fuel filter.

Also open the fuel cap incase the tank breather is blocked.You know it is blocked if it runs longer and unblock breather.

[dextersaurus]

Next time i get the chance, i'll take the tap off, drain the tank and carbs, wash it with new petrol, then fill it up...

And i'll post results.

Already tried that, the breather seems fine since it wasn't starting regardless.

[Ingah]

[Kickstart]

Hi

Other thing to check is the plugs, after running it on the choke for 3 minutes it could have fouled them up a bit.

All the best

Keith
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[dextersaurus]

Checked the carbs and they were fine, just a bit dirty with this black gunk...

Cleaned it up and tried again, and it didn't change anything.

There was a weak spark from one plug, if cleaning out the tank doesn't work i'll get 2 new plugs.

Cheers

Dunca

[Paddy Blake]

[el_oso]

Replacing the coils on my friends gpz500 fixed the weak spark issue. It now seems to start almost on the button. Never really take
more than two or three cranks of the engine though
____________________
Duke 390
Previous: '05 XR125L | '96 XJ600S Diversion |'05 Suzuki GSXR1000 | '05 Honda CBR125-R | '97 YZF 600R Thundercat | '11 Honda CBR250
Car: Jeep Wrangler 4.0L

[dextersaurus]

So, if replacing the spark plugs doesn't work, i'll replace a coil.
flush tank with new petrol, clear jets on carbs again...

If it doesn't start after i've done that i'll shout on here

Cheers

Dunc

[c_dug]

With the GPZ the_godfather is on about cleaning up the terminals on the coil made a noticeable difference before you go replacing parts needlessly

c_dug
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I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Kickstart]

Hi

Also worth checking the condition of the HT leads (and see if you can replace them). Same for the plug caps. Think with the GPZ you can swap the coils over without any great problems (ie, the leads are the same length) and see if the weak spark moves to the other cylinder.

All the best

Keith
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[dextersaurus]

Well, since i've not had much time to actually work on the bike recently, i spoke to my old man (who is more familiar with old british bikes - he has a Royal enfield and an old Francis Barnett) who i let do the pilot screws on the carbs, and he told me that he had screwed them 2.5 turns from the end... so that'll be why it's not running

I'll post up when i sort that and see what happens.

Dunc

[dextersaurus]

Yo guys.

So today since it was nice and sunny, i took the carbs to bits.
Cleaned up everything, sprayed the jets through with carb cleaner and let them soak before fitting everything back together, then sorted the pilot screws.

It did take a VERY long time to start, backfired through the airbox

But then it fired into life, and sounded quite good.

Ticked over at 1.5k revs on choke so the idle screw needs sorted...

But me being me, i forgot to attach the petrol tank so it used the petrol in the carbs and then died.

So when i attached it again, all it was doing was turning over... then the battery died.

So i'm leaving it on the trickle charger overnight, and i'll get back to it in the morning - see what it's doing then.

I also checked the spark from both plugs - It was a strong spark from both, but they were kind of white which goes with the fact it's been running lean from when it had the pilot screws done wrong.

So it's definately getting a spark, and the carbs are definately getting petrol, so the problem is lying in the fuel getting from the carbs to the plugs.

To be honest, i have no idea how to properly strip and clean a set of carbs, so i only took the float chamber covers off, and the top covers (of the diaphragms) off and cleaned about inside there - never split everything. I think that may be a job for someone more technically minded or experienced than me.

On a side note, can someone direct me to a replacement set of screws for the carbs on the GPZ? the ones on it are.... old to say the least - need different screwdrivers for each screw.

They are keihin carbs, and the replacement screws i bought don't fit as they are all too small.

Cheers

Dunc

[Casper]

Duncan

Is that CV carbs on that thing? could be air not getting in the tank. Next time you get it running and it stops on its own open the tank and if you get a quick hiss then the lack of air will stop the fuel. Or run it on prime if your tap has it and try with petrol cap off or open. You could also have sticky choke, looks good when the cable goes back but the gubbins in the carbs might still be stuck on.

R

[dextersaurus]

Tried that and the tank seems fine, the breather isn't blocked.

Also, i cleaned the choke bits today, it's not that - They are definately moving freely.

The battery is charging now, so i'll go tomorrow to fill up the tank with fresh petrol, and see what happens then.

Also going to stick the new air filter in and change the oil, see how that affects things...



Cheers

Dunc

[el_oso]

go to a fasteners place and get some allen head screws. much easier to get out.
____________________
Duke 390
Previous: '05 XR125L | '96 XJ600S Diversion |'05 Suzuki GSXR1000 | '05 Honda CBR125-R | '97 YZF 600R Thundercat | '11 Honda CBR250
Car: Jeep Wrangler 4.0L

[dextersaurus]

[c_dug]

Either that or when I was doing my TDR a while back I used a carb specialist in manchester somewhere, im sure they will stock the original screws (or ones that fit) I found them online, I made a post on the TDR forums about them so i'm sure i can find the website again if you can wait a day or two?

They were really good and very helpfull with advice
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[c_dug]

[dextersaurus]

Got an update here.

Well, i emptied the contents of my fuel tank into a bottle, and attached the fuel line, so it was gravity fed.

I then started turning it over - after checking and cleaning the plugs.

All it did was backfire and huff.

Now i don't know but to me that sounds like the timing is off...

Would i be right in saying that if the timing is off, the bike won't start and it'll just backfire - maybe running for a few seconds etc.

If anyone can confirm this may be the problem, i'll get onto it tomorrow morning...

I'll clean the carbs again anyway, just to be sure.

Cheers

Dunc

[Kickstart]

Hi

Are the coils connected to the correct cylinders?

Could be the timing being way out, but not really any way of changing it.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[dextersaurus]

Since there is only two of them, the left is connected to the left and the right to the right.

There can't be a lot of things that's stopping the bike from running.

Cleaned the carbs, now it just backfires and coughs
Cleaned the Plugs - got a nice strong blue spark
Changed air filter/oil

Probably be checking the valve clearances tomorrow though...

Anything else?

Dunc

[Kickstart]

Hi

Double check the wires to the coils, and try a strobe light on it to check the timing is right, but I would suspect it will be fine (although on an older one with the self destructing flywheels you might have odd ignition problems if some bits of magnet go astray).

If you check the valve then the first thing to check is probably the cam timing. Also worth doing a compression check while you are at it.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[dextersaurus]

Cheers keith, i'll get on that and post up when i know more

[dextersaurus]

Gah, another update.

Went outside and thought i'd try to start it.

Turned it over and it started up off the button.

It hasn't got a fuel tank on it, so it'll just be the petrol i had in the bottle going through the line and into the carbs.

How confusing is this bloody bike.

So.

Why wouldn't it start when i had it with a fuel tank/bottle on it, but an hour later it starts off the button with no tank on?

Looks like it is the carbs afterall.

Cheers

Dunc