GPZ5500s Carbs

[Bruff]

Hi all,
I'm pretty new to this site,but it has helped me already and gave me some good ideas. If anyone is having carb trouble like i was,then get yourself a set of GPZ500 carbs. Mine being a '79 XS650SE,it had the BS38's on it,which gave me constant grief.. It was imported from America in 1995. Now i'm not sure if it's our lovely british weather that made it play up or not,but i've had it a year and i could not get it to run right. So i got myself a set of carbs of a 1996 GPZ carbs,no idea if they would fit or work. Firstly i had to get some new inlet manifolds for a 1980 onwards XS,(34mm inlet) then they went straight on. What a difference in weight too. I had a switchgear from a later XS lying around anyway,so rigging the choke up was easy. I used a 40mm cable adjuster for the throttle cable mounting on top of the carb,so throttle set up was really easy too. All in all it was a lot easier than i thought it would be. I changed the main jets in the GPZ carbs to 127.5,(originals are 130,but it ran a little rich.) I've got K&N filters on it and a free flowing exhaust on it now (Bloody loud!) Anyway,my bike runs sweet now,shame we haven't had the weather over here in the UK to use it. Hope this helps people who were pulling their hair out like i was.

 

[jd750ace]

I'm pretty sure that would be an EX500 over here. Thanks for the tip. There are lots of EX500 carbs floating around the states, since thousands were removed and flat slides installed for club racing.
Any chance to get some pictures of the installation?

 

[Bruff]

Hi bud,no probs. Yeah i think it may be the EX500 where you are,but we had both over in the UK,the EX being the earlier model. The carbs would be the same whichever model they come off i'm sure. I tried to upload photos i took when i was doing it,but they failed to load,don't know why. They work very well,being modern carbs they are more efficient,and they are flat slides too. I didn't know that until i got them. The instulation is straight foward enough though,like i said earlier i thought rigging the choke up and the throttle was going to be a headache,but it was easy. I'll have a go at loading the photos again later.

 

[jd750ace]

Thanks. As you may see from my signature, I have the same year bike, and I would like to see the setup, as my EX500 ran like a champ! Shaft seals don't go bad either. I believe they are Kehin 34 MM.

 

[Bruff]

hi again,yeah they are keihin 34mm. A couple of things i forgot to mention,because the throttle cable has to go through the cable adjuster i had to use solderless nipples,the brass type you screw onto the cable. I used one for the choke cable too. You could solder proper nipples on if you are that bothered but i used the solderless ones because it was a bit of trail and error at first to get the jets right,so it was easier for me to take apart. The other thing,the pilot air screws located by the bottom of the carb inlet,needs to be two and a half turns out otherwise you may have trouble with tick over. Other than that,as long as all the vacuum tubes are connected/blanked off,you're away. Oh yeah,make sure you connect the fuel pipes to the correct place. Not like i did at first,i turned on the fuel tape and my fuel ran all down my engine and onto the floor. Doh!

 

[weekendrider]

Bruff, does this carb have a pull only throttle cable(like the xs) or a two cable pull-pull set-up? If the two cable how did you adapt?
Thanks for the jetting and mix settings.

 

[XS1961]

I had an XS with ER500 carbs on a few years ago, it ran well ,I didnt fit them so Ive no idea what the jetting setup was ,from that experience I bought 3 good sets of GPZ/ER carbs a few years ago ,theyre sat on a shelf waiting for me to get my arse into gear & fit 'em.
I might have a bash this week

 

[XS1961]

Note;The later models had a fuel anti-icing setup that needs to be blanked off. ..
Heres mine,all different...

 

[Bruff]

Hi weekendrider,the carbs only needs a single throttle cable for operation,i just used my old one. As for the anti icing pies,they only run at the bottom of the carbs by the fuel bowls. I just took the pipes off and left it as is. Went out to Bob today,i haven't touched him for over a week,1st kick and Old Bob burst into life. I let it run ticking over sweet as a nut for about 10 minutes. Got a leaky fuel tap now,so a new repair kit is my next purchase. Not long now til the Rock and Blues bike festival,got to make sure Old Bob is up to the task. ;-)

 

[Bruff]

Oh yeah,as you can see by XS1961's pics,on the GPZ carbs they are a twin throttle set up,but the return spring is strong enough to be used with a single cable as long as there are no kinks in it and the cable is new or lubricated. The cable i used on mine is the one that came with my bike,i just tipped some oil down it and refit the inner cable. I hope this helps,it has helped me heaps. I've now got a bike i can go to at any time and start and ride (weather permitting!) without the spitting and farting it used to do. The jet settings are for our bloody damp country and work well. If you live in a warm part of the US,you may have to adjust accordingly. But it's a good place to start.

 

[XS1961]

Nice one Bruff. I'll pop a set in this week, my rebuilds just about ready, well at least I have a set of VM34's as a backup if theyre f****..
Yep, the R&B ,a bloody good show that, Ill be nipping up the M1 to that one..

 

[Bruff]

Mmmm,VM 34's..! I thought about going that route,but i couldn't find any without getting in the shit with the Mrs for spending our monthly budget on them! But the gpz carbs work well and i only paid £30 for them off good old ebay. I drained my tank this morning,the seal has gone on my fuel tap,it was pissing out. I must have lost nearly half a gallon of liquid gold this week. Still,i'll get it done this week now and hopefully i can go a blast the weekend. (If it's not pissing down again that is!)

 

[weekendrider]

I was discussing this exchange with a guy at the Kawi shop he wonders if the 650 will have enough vacuum to pull the slides all the way up. Citing the difference in rpm range.
Bruff--xs1961 what do you think?

 

[grizld1]

Vacuum shouldn't be a problem--bigger pump, lighter slides. I wouldn't be inclined to run that setup without a push-pull throttle, though.

 

[weekendrider]

Thanks grizld1
I did measure 102mm center to center so...they are wider.
Some fyi. Stock vs. Kiehins.
The center is matched on the right intake.
Ohhh not as deep. Maybe you can leave the cam chain adjuster cap on.
(Not pictured is the height. Overall from top to drain spigot tip the Kiehins are 2-3mm shorter. But from the center of the intake to the top is taller.)
The throttle plate seems 2mm deeper on the Kiehins.

 

[grizld1]

I think you transposed a number there; XS650 spigots are 120 mm. center-to-center, and the match to the Keihins looks really close; no difference there that flex in the boots won't accomodate.

My guess is that those Keihin flat slide vacuum carbs are capable of better street performance than the venerable VM's; the technology is a couple of decades newer.

 

[XS1961]

I just bolted a pair on this evening, exact fit to stock rubbers - no problems at all regarding size/shape/dimensions...
They ran great on the XS I had a few years ,really crisp, my concern was that as I hadnt personally installed them (the previous owner had ) I had no idea what changes were made internally ..I bought a few pairs but never got around to using them as I assumed Id need to mess around experimenting with settings,Im way too busy with work & family

 

[Bruff]

They work well on mine,i've had no probs up to yet and done over 100 miles now since fitting a couple of weeks ago.. I only run a single throttle cable on mine. Like i said before as long as the cable flows freely with no kinks there isn't a problem. I would have done more only our damn weather has been crap. I thought of trading my XS for a jet ski at one stage..!

 

[XS1961]

Yeah, mine was single cable too.
re. the weather,Im sick to death of this pissing rain, its been constant now for near on 3 months

 

[timbeck]

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