36mm Flats on an '80 1085 motor

[Guest]

Sent a set of 36mm rs flatslides off to Chef to rebuild and need help setting these up for my 1980 1085 motor in the Wes Cooley. Chef has informed me that the carbs have 130 mains and 17.5 pilots. These carbs were being run on an '83 1166 motor with mild porting and web cams (but not by me; by PO).

The 1085 motor has a stock head, and I am running pods and 4/1. Looking for advice on mains,pilots and needle setting. Or are these simply going to be too much? Thanks in advance for any help.

[trippivot]

your stock head flows under 65 C.F.M.

your 36mm carbs flow over 130 C.F.M. the math is simple.

over carburetion is common, no bottom end and lack luster top end. We hear all the stories . You'll never get the potential power at W.O.T. with those, you'll have to close the throttle to .75 to get the intake velocity up to speed.

the proper matching ratio is .85 of the intake valve diameter = the venturi diameter for smooth bell curve power and peak H.P.

so a 38mm intake valve head would perform BEST with a 32.3mm venturi. i.e. 33mm smothbores or 32mm CVs' optimal

it really is not the volume of air as much as it is the velocity of the intake charge. this is where the 300 ft/ sec value is what we are trying to achieve.

street engines need smaller carbs than the average tuner wants

[posplayr]

your stock head flows under 65 C.F.M.

your 36mm carbs flow over 130 C.F.M. the math is simple.

over carburetion is common, no bottom end and lack luster top end. We hear all the stories . You'll never get the potential power at W.O.T. with those, you'll have to close the throttle to .75 to get the intake velocity up to speed.

the proper matching ratio is .85 of the intake valve diameter = the venturi diameter for smooth bell curve power and peak H.P.

so a 38mm intake valve head would perform BEST with a 32.3mm venturi. i.e. 33mm smothbores or 32mm CVs' optimal

it really is not the volume of air as much as it is the velocity of the intake charge. this is where the 300 ft/ sec value is what we are trying to achieve.

street engines need smaller carbs than the average tuner wants

So if I read between the lines a little , and assume that the 85% rule is really a valve area rule I get the following

(16V) 27mm => 1145cm^2 (85%= 973cm^2)
(16V) 28mm => 1231cm^2 (85%= 1047(cm^2)
(16V) 28.5mm => 1276cm^2 (85%= 1084cm^2)

in comparision:

a 36mm carb throat is 1017
a 38mm carb throat is 1134

This seems to work well for GS's, but I know the Oiler GSXR 750 can go as high as 38mm carbs and the 1127's up to 40mm CV flatslide (factory). Off hand don't know what size valves the 750 GSXR had, but all of the 1100;'s were 28.5mm intake. My 1052 came stock with 34mm but works well with 36mm cv flatslide. It is the 2nd gen 750/1127's that got the monster bores.

[russr33]

your stock head flows under 65 C.F.M.

your 36mm carbs flow over 130 C.F.M. the math is simple.

over carburetion is common, no bottom end and lack luster top end. We hear all the stories . You'll never get the potential power at W.O.T. with those, you'll have to close the throttle to .75 to get the intake velocity up to speed.

the proper matching ratio is .85 of the intake valve diameter = the venturi diameter for smooth bell curve power and peak H.P.

so a 38mm intake valve head would perform BEST with a 32.3mm venturi. i.e. 33mm smothbores or 32mm CVs' optimal

it really is not the volume of air as much as it is the velocity of the intake charge. this is where the 300 ft/ sec value is what we are trying to achieve.

street engines need smaller carbs than the average tuner wants

That is what I needed to know. Thanks Tripp. If anyone else has anything to add please chime in.

I'm running the stock 34mm CV carbs now with DJ kit. Is it worth the cash to get a set of 33 smoothies? I know I've read they can be a pain to get dialed in.

[chef1366]

I paid Mr. Pivot to say that so I could purchase those 36s to put on my 1230 kit.

[gshub]

Carbs

So would stock Gs1000s 29mms be up for it as mine wouldnt have cams just a 1085cc
kit fitted with a pingel fuel tap.
sorry for invading your thread.

steve

[russr33]

So would stock Gs1000s 29mms be up for it as mine wouldnt have cams just a 1085cc
kit fitted with a pingel fuel tap.
sorry for invading your thread.

steve

I'm assuming you have a '79 Hub? Did the '79 S come with 29mm smothbores stock? If so I would think that would do it. An '80 can't run 29's.

[rudy]

I'm assuming you have a '79 Hub? Did the '79 S come with 29mm smothbores stock? If so I would think that would do it. An '80 can't run 29's.

As far as I know, Aussies and New Zillund folks got the 29's on the 1000S, whereas the Americas got the 27's, same as the stock E, C, and G 1000's and 750's. England could have been included in the 29's as well. Or maybe it's an import, or different than stock carbs.

[49er]

As far as I know, Aussies and New Zillund folks got the 29's on the 1000S, whereas the Americas got the 27's, same as the stock E, C, and G 1000's and 750's. England could have been included in the 29's as well. Or maybe it's an import, or different than stock carbs.

NZ and Aussie 1000S came with 28.5mm VM's, they are not 29 mm smoothbores.

Some folk call them 28's and some 29's for obvious reasons. They are basically the VM26's bored out.

[hampshirehog]

The non-US 1000SN bikes came with VM28 carbs (which confusingly measure 29mm diameter). In addition, all except the early 1000Es came with VM28s in the UK (of course post 80 they had CV carbs).

Most UK GS1000STs came with the CV carbs though a few came with the VM32s that the down under lads got.

VM29s will pop straight into a UK GS1000SN (and a lot of our Es as well). They will add a bit of pep (though they aren't cheap).

[chef1366]

So has anyone set these carbs up on a 1085 with a stock head with any success?

[Billy Ricks]

So has anyone set these carbs up on a 1085 with a stock head with any success?

I can give you the jetting specs Mikuni suggests using.

[posplayr]

I can give you the jetting specs Mikuni suggests using.

well please do

[Billy Ricks]

The main and pilots are exactly what is called for by Mikuni. Shouldn't need to be more than half a turn out on the pilot screws and 3rd notch down on the needles.

You just have to learn to roll the throttle a bit more and take advantage of the accelerator pumps rather than just whacking them open like you would with CV's. Once you hit redline in whatever gear you're in then you can just hammer the throttle on upshifts without bogging the engine.

[Mysuzyq]

Maybe Billy is referring to this set-up recommended by Mikuni for 1100/1150 applications. If the carbs are purchased new, they will come jetted as per these specs, and by most accounts are good to go, with a little fine tuning & sync. I have a set of RS36 carbs that I plan on trying this summer, using these settings to get in the ballpark.... always nice to have actual setup info from the manufacturer, for our specific application.