Best Stock Carb Combo?

mo650chopper · Posted: September 21, 2005, 5:55 pm Post subject: Best Stock Carb Combo?

From my understanding the 80's models of the XS had the best cam but were lacking on getting the needed air / fuel mixture through the engine. Would putting a set of 74-79 carbs be the best streetable mod to bring my 80's performance up a bit? And is $70 a reasonable cost for a pair of rebuildable carbs?

grizld1 · Posted: September 21, 2005, 10:57 pm Post subject: Re: Best Stock Carb Combo?

You know what I think--and you've seen how the '80's engine pulls with BS38's on. For my money, the '76 and '77 carbs are the pick of the litter; I like the single-cable system, but some guys prefer the older dual cable units. I'd avoid '78 and '79; the slides aren't easily available if a diaphragm goes bad or the slide comes loose from the diaphragm collar, and those problems are more common than you'd like to think. I'd pay $70 for good BS38 cores with sound slide/diaphragm assemblies. I love those late engines, except for the itty-bitty performance killing carbs --compression was raised back to 8.7:1, the cam was lively, and unlike the early engines, the '80's units had the stronger small-wristpin rods.

meangene · Posted: September 23, 2005, 11:36 am Post subject: Re: Best Stock Carb Combo?

.. big carbs will make you faster on the top end but will take away some bottom end pull .. it wont be as fast off the line,even worse with a fat woman on the back.. also your fuel milage will drop, more flow more fuel
.. unless you are racing the bike i would stay with the 34s
when i want to go faster i pull out the 1100 it has four 34s and it's a real pig [27 mpg] but it's fast!
..just my 2 cents..

mo650chopper · Posted: September 24, 2005, 7:48 pm Post subject: Re: Best Stock Carb Combo?

Is the 34MM, & 36MM the measurement of the inside diameter of the venturi / butterfly or outside diameter of the carb?

meangene · Posted: September 24, 2005, 10:25 pm Post subject: Re: Best Stock Carb Combo?

.. 34mm is the inside diameter of the venturi/butterfly
the cost of gas here today is $2.80 for the cheap stuff how is it where your at?

xs650mike · Posted: September 26, 2005, 9:08 am Post subject: Re: Best Stock Carb Combo?

Gas here in northern California runs from $3.059 to $3.359 for unbranded 87 octane regular. My XS1100 burns more gas (38 mpg average) but runs well on 87. My XS650s like 91 octane but get about 50 mpg. Gas price spiked really high after Katrina but after the state attorney general announced an investigation into price gouging the prices dropped a bunch within a couple of hours! It's illegal in California to raise prices more than 10% during a government declared emergency.

mo650chopper · Posted: September 26, 2005, 11:13 am Post subject: Re: Best Stock Carb Combo?

I paid $2.67 today here in Missouri.

xs650mike · Posted: September 26, 2005, 6:57 pm Post subject: Re: Best Stock Carb Combo?

Strangely enough I was just over a couple of counties away from where I live and unbranded 87 octane gas was only $2.899 and the major brands were at $2.999. This is considerably lower than my own county where it's been at least $3.00 a gallon since weeks before Katrina.

mo650chopper · Posted: April 11, 2006, 9:37 am Post subject: Re: Best Stock Carb Combo?

The bigger 78 carbs really woke up my 80 motor! And I'm still getting 50MPG!!! Wish I would have done this last year. Maybe another season or two then it will be time for a big bore kit, cam, port polish and some 36MM smooth bores.

RainLand · Posted: April 11, 2006, 10:58 am Post subject: Re: Best Stock Carb Combo?

I'm putting a set of 750 barrels on a '78 motor. I thought I'd get a set
of 36mm carbs, but maybe I'll stick with the 34mm and just jet it for a
pair of stack filters.
Anyone try this combination?

xs650mike · Posted: April 11, 2006, 11:33 am Post subject: Re: Best Stock Carb Combo?

You're gonna like that 750 kit, gives a real torque boost. Sweet.

4lungfreak · Full Member Joined: Apr 15, 2006 Posts: 10 Location: Texas

Sorry to resurrect this thread, but I have a few questions for mo650:

I also have a '80 XS that already came with the BS38's. But it's not running right, I think it may be too lean.

So, my questions are,

How can you tell which BS38's you have (I understand the 78-79 were different from earlier models)?

What jets are you running?

Where is your needle set at?

What air filters are you running?

What mufflers are you running?

On the stock 1980 tank were there 2 petcocks or one?

Thanks in advance to mo650chopper (or anyone else who can shed some light on the matter)...

4LF
Paul

mo650chopper · Posted: May 22, 2006, 8:36 am Post subject: Re: Best Stock Carb Combo?

This may help a little www.mikesxs.com/tech_tips.html

80 tanks had one petcock on left side.

I'm running the pod filters from Mikes XS, open 1 1/2" pipes / no mufflers, again from mike's XS

Needle in middle postion, This is from memory but it should be the stock setting.

#35 Pilot Jet , #147.5 Main Jet but will probably go up one more to a #150. I started with the recomendations on Mike's XS and tuned from there. All Carbs / Bikes are unique.

I don't have the info handy on how to tell the 78/79 from the 76/77. Maybe someone else can shed some light on the subject.

mo650chopper · Posted: May 22, 2006, 1:56 pm Post subject: Re: Best Stock Carb Combo?

If you look at the bottom of a float bowl you'll see a round boss with a letter stamped in it, This will tell you what carb you have. Now where a list is with this info is I don't know but I'm sure someone here can provide us with an online source.

xsjohn · Posted: August 10, 2006, 10:17 pm Post subject: Re: Best Stock Carb Combo?

I have carb kits now for the 80-84 CV 34MM Carbs.........Makes them kick ass and smooth.......I think these are the best carbs Yamaha made with these kits in them........
Old Yamaha Mechanic John Underwood

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