Gs odd ball carb question

[Guest]

just joined but have got an education off this site with this gs cheers for that ,

the help i need is a question of carbs I've gone though as much as i can looking for info on a unbiased option on carb choice,

I've got a 1982 gs 850g shaftie with 997cc top end fitted 1050cc pistons it got upgraded cams and I'm running bs34ss mikunis which I've ditched the air box (I know shoot me now:disillusionment but its what i want for the look of the build i cut my teeth on tuning them to put the "compromise" in ride around spot of the power curve , i grew up tuning dirt bikes so I'm no expert but i build my own motors because i wanted to learn plus its cheaper. so the question is I've sourced a donor gsx750 1985 "slabby" i pinched the front end for better braking- handling and a little lower look but mainly got it for the VM29SS FLAT SLIDES ( not smooth bore and not 28mm) they got acc pumps . i know i can just get a set of 36--38 rs mikunis new from tom at mikuni oz. but i want to do things my way theres a story to how i got the 85 gsx and the rest of the bike went to bloke with my same way of thinking.
I've heard of blokes machining them out to 33mm not gonna do that.
so to the question--- if 28mm smooth bores were the ducks nuts in the day on the gs1000 79 will i be able to get the VM29 flat slides to out perform the vm28ss smooth bores???? I know they are gonna be better than the bs34ss cv's (don't shoot me for that i love the cvs but doesn't suit where I'm trying to get) i guess i need a unbiased opinion on if spend the time on the vm29ss 'Slabie" flat slides or just get the 38mm RS Rack,
I've got the 29s cleaned up and i wanted to put them on as i wanted to stay time specific, but if I'm just putting a bandaid on a broken leg??? if so ill just go to the surgeon aka Tom at Mikuni oz and get the 38 rs . cheers lads

 

[sharpy]

no such thing as 28mm smoothbores, there are 29mm ones with a 17mm drain plug on the bowl. 38mm RS flt slide be a huge over kill. try looking for some mikuni 33mm smoothbore carbs. thats about as big you want to go on a 1075cc engine. CV carbs are always larger sizes compared to slide carbs

 

[GregT]

The gsxr carbs you've got weren't seen in the US - they were rest of the world model carbs on the H and I models of 750.
Yes, they're tunable. Common Mikuni jets but only two needles ever available for them. a lean one for everywhere except Japan - and a rich one for the home market cos the pilots are achingly lean on those for emissions reasons....I can hunt in my records for the numbers if you need them, the home market ones we saw here were gray imports.
Another level of tunability is that you can run both, one or no accelerator pumps, simply by pulling the operating rods.
Worth a crack on the engine you're running, I'd have thought. Probably a better street carb than the 29 smoothbores.

 

[Guest]

like i said sharpie I'm no expert but after an expert opinion .......i can't spell but i can arm wrestle right.... same diff lol.
greg the ones i got are Australian version as I'm in queensland cheers the numbers i got in these carbs are
Piolet-20 mikuni
main 57.5 with a r stamp think they been drilled no stress got a bunch from the bs34 tuning
needle -6dp3 was on clip 4
piolet screw was at 2 3/4 turns out


thought 120- 130 on the mains would be a good starting point as got pods and a 4 into 2 cut down that flows like a 4into 1 built by me
not sure which needle it is at moment
but would i be better with the lean needle and inrichin the pilot jet (don't need to pass emissions here in sunny qld cops love the look lol)
and the other question is will the acc pumps cause havoc on the side draught motor ????
much appreciated for your wisdom in this adventure....:stung:

 

[chuck hahn]

Original poster..go to THREAD tools or ADMINISDTRATIVE at the tool bar and move this to the PROJECTS section of the tech forums. This spot is exclusively for our website founders build bike.

Or maybe the carb / exhaust section.

 

[steve murdoch]

We will need some pics of your hot rod G.
Welcome to the site.

 

[GregT]

Without going to my records I think that's the lean needle. Doesn't matter as most of the response comes from the pilots in these. 20 is pretty standard. Given your biggish motor, I'd stick with the 20's as a start and run the pumps. Mains usually finish up in the 125 area.
Everything is sized for a 4V head which gives a very strong vacuum signal as soon as the valves open. You're going to get some compensation for the loss of signal with a bigger engine - so don't go too far away from where they are jetted now.
And yeah, move the thread....

 

[Art H]

No Replies? I have a set of smooth bores on my 79 GS1000, they do not have the vacuum port for the petcock so I know they are custom. Anyway the motor is stock except for a 4 to one exhaust and all I can say is that it rips! I picked up the bike for $400 w/ 22k miles, painted it, new continental radial tires and for under $1500 I have a great bike.

 

[Guest]

Heres a pic of my gs I've been building

 

[Guest]

another pic

 

[Guest]

the front end

 

[Grimly]

I just want to clear something up.
Is this engine originally an 850, or did a PO or you replace it with a 1000G engine?

 

[Guest]

i bought it off a bloke who's brother had built the motor he had sadly passed away he was a bike mechanic .
the story i got from the bloke he had a 850g with a bad top end and a 1000g with gear problems so he machined the 850 cases to accept the 997 crank and over sized the cylinders as well as added a cam package. its stamped 850 on the bottom cases and 997cc on the cylinder. i did all the fab work on the cafe style

 

[Guest]

 

[Guest]

so got the gsx750 29mm flat slides working thing goes heaps better .
next problem the final drive is the gold one and has started to fall apart picking up another final drive tomorrow see how it goes .
question though the secondary gear drive has the way to much backlash so ill pop it out and have a look . it hasn't got the Zook problem nuts still on there but what would cause the secondary drive to develop so much back lash ? the bearing at the back maybe??? I've looked at a previous forum were u guys helped a bloke to to the drill tap technic after he broke the thread on the end of the shaft off and he had posted a video of how much back clash he had mines the same but still not sure if i have to shim the drive back to spec?????? cheers lads

 

[Guest]

figured out the secondary drive is fine . searched though foums for an answer...
so the final drive i got is much better than the one i had i post a few pics of the old one then the new one cheers

 

[Steve]

It's not the final drive the fails, it's the driven spline in the rear wheel. Much easier to check and change than the final drive.

.

 

[Guest]

cheers steve i started a new thread on the rear end matter i posted pics

 

[Guest]

final drive mix and match this is the new thread as i got the carbs running cheers for all the help love this site .

 

[Grimly]

i bought it off a bloke who's brother had built the motor he had sadly passed away he was a bike mechanic .
the story i got from the bloke he had a 850g with a bad top end and a 1000g with gear problems so he machined the 850 cases to accept the 997 crank and over sized the cylinders as well as added a cam package. its stamped 850 on the bottom cases and 997cc on the cylinder. i did all the fab work on the cafe style

Goddamn, so it IS possible. I'd always made the assumption there simply wasn't the case room to accomodate the 1000 crank. IE, that it wouldn't be thick enough to allow machining without break-through or weakening it too much.
If the 1000G crank were known to drop straight in, then many folks would have done it by now. Obviously, it's not a straightforward mix'nmatch, like some other conversions, but it's not impossible. I think yours is the first I've heard of.
Over recent years, those who wanted bigger power and more grunt in an 850 bike would have easy access to the 1000G and 1100G engines, which just fit straight in, more or less.