Educate me

[mack]

I've been thinking about what Scott said in my "needle" thread and I'm stuck. I was under the impression that the carbs changed in 1980 to what I'd call "mickey mouse". I thought that the motors for specials and standards were pretty much the same. After reading Scotts reply it seems as though my assumptions are wrong. The special 80/81 carbs I have are all 110 mains with 300 x2 emultion tubes and 5GL-16 needles. Why would the standards have 115/120 mains with 300 x2 tubes with 51Z7 needles.
And as an after thought, if you guys with the 80 &81 standards had a choice, would you/could you run the old 78/79 carbs on your machines and get the same or better performance?

[GLoweVA]

What a coincidence,today I was looking at the difference in the carbs between my 80G &SG and noted that they are different.
Why?
Can I just swap the whole bank from bike to bike and plug and play?
Maybe the jetting is a little different because of the slight difference in stock exhausts.
Any ideas from all you gurus out there?

[3Phase]

Short answer

Specials have the 16" rear tire and less weight so they need less fuel.
Standards have a 17" tire and more weight so they need more fuel.

Specials are a little leaner and quicker; more of a peak and slow down stoplight hopper.
Standards are a little richer for sustained speeds with the center cylinders getting a richer mix to, theoretically, reduce overheating.

Long answer: how much beer do you have?

[XS1100_OEM4ME]

Confused?

OK, now I am confused, I thought the Qtr mile0 was about the same for the 78 Standard and the 79 Special, and MY 79 Special had richer carbs on 2 and 3 for cooling

Specials have the 16" rear tire and less weight so they need less fuel.
Standards have a 17" tire and more weight so they need more fuel.

Specials are a little leaner and quicker; more of a peak and slow down stoplight hopper.
Standards are a little richer for sustained speeds with the center cylinders getting a richer mix to, theoretically, reduce overheating.

Long answer: how much beer do you have?

[3Phase]

OK, now I am confused, I thought the Qtr mile0 was about the same for the 78 Standard and the 79 Special, and MY 79 Special had richer carbs on 2 and 3 for cooling

Mack asked about the different main jet and needle sizes on the '80 and '81 Specials and Standards, not the '78s or '79s.

Got another beer?

[XS1100_OEM4ME]

Cool

That is cool, I am still learning the diff. between the years / models. So the 80's Specials didn't have the richer mix center carbs, a were much faster then the 80's standards, Thanks

Mack asked about the different main jet and needle sizes on the '80 and '81 Specials and Standards, not the '78s or '79s.

Got another beer?

[XS1100_OEM4ME]

0 to 60

Compaire preformance spec's from year to year on these is hard to find. The fastest 0 to 60 I could find was 4.7 sec. I had a stock 6 cyl BMW roadster that was faster then that, but it sure seams faster while trying to hold on to the handlebars then when siting in car

[crazy steve]

OK, now I am confused, I thought the Qtr mile0 was about the same for the 78 Standard and the 79 Special, and MY 79 Special had richer carbs on 2 and 3 for cooling

The '78 was the quickest of all models, the '79 Special was about .2-3 of a second slower, and the '79 standard was another .1 slower than the Special. The big reason for the drop between '78 and '79 was Yamaha 'softened' the ignition advance (less initial advance, and a 'slower' mechanical advance); the motors were otherwise all the same (including carb jetting). The reason for the performance advantage of the '79 Special vs '79 standard was the smaller rear tire and 5 lbs less weight. The smaller rear tire effectively reduced the axle ratio from 3.3:1 down to 3.46:1, so that was most of the gain.

The only models with the 'rich' 2 & 3 carbs (according to the FSM) was the '80-81 standards... Lon, on your bike I suspect either somebody decided to mimic the later tune for some reason, or a later set of standard carbs have been fitted; that's not OEM

[mack]

From what i understand

the 78 E was quickest and fastest off all the XS's. Due in part the the mecanical advance being all in at 4K or so where the specials didn't get full advance till 5K.
Scott back to the 80's, the upping of the main jets was to conpensate for the loss of the 266 & 301 tubes as well as the pilot tunnel?
What about the aspect of the 78/79 carb swap for the 80's. They are pre emmision control are they not? Performance wise they should be better right?

[XS1100_OEM4ME]

Oem

No, their the OEM carbs, it was just that Phil told me the reason my center plugs looked rich, was because the 79SF had richer center carbs from the factory for cooling them

[crazy steve]

...What about the aspect of the 78/79 carb swap for the 80's. They are pre emmision control are they not? Performance wise they should be better right?

Mack, as far as which style carb is 'better' is open to debate. There are a bunch of differences, some related to 'emissions', but I think that due diligence with tuning would probably eliminate most of those in terms of performance. The early carbs are a bit easier to work on (adjustable jet needles vs the later 'fixed' units). Dan Hodges (who did more exploring of power-producing combos than anybody else on this forum did) preferred the early carbs and felt they were worth just a bit more in power, but not enough for the average rider to worry about.

[3Phase]

The '80s Specials aren't that much much quicker than the '80s Standards. Yamaha changed the pistons, top end, and ignition timing after the '78/'79 engines. They set up the carburetors for smog and what customers were likely to do with the bike after it rolled out the door.

A set of '80s Special carburetors on my '80 Standard worked okay. The bike was fine around town and got a little better gas mileage but top end power and speed wasn't there on the highway. A set of stock XJ1100 carburetors with the 47.5 pilot jets and 112.5 mains was better but still not quite right. I haven't tried a set of '80s Standard carburetors on a '80s Special because I don't have one.

[3Phase]

Yes, they staggered the main jets instead of the needles and tubes. I'm not sure what you mean by the pilot tunnel. The pilot jets are 42.5 from '78 to '81.

The '80s carburetor vacuum slide diameter is larger than the '70s and the vacuum slide return springs in the two middle slides can be a few hairs longer than the springs in the outer slides but I haven't been able to pin that down to:

'80s Standards only

'80s Specials only

'80s Standards and Specials

The slight difference in measured spring lengths really isn't all that critical and someone with a twisted sense of humor stuck them in the middle carburetors to mess with the next guy that opened them up

[DGXSER]

As to running different carbs on different engines, I know a fellow XSive that now has 81 Special carbs on their 79 Special and it runs great and has plenty power. And since they are the ones off my old SH I wrecked, I know they have 110 mains across the board, which is how I jet all my SH carbs.

I have put several sets of carbs on my 81 SH, some form 78-79 model, some from an 80 and the stock 81 model carbs. Honestly, all but the stock carbs were never final synched or tuned as they are/were all sets I was rebuilding to sell. They all let the bike pull good, and run up to red line.

So, while there are differences, unless your a real "power rider" and performance is real important (like you dyno the thing), I doubt you would notice any difference in your bikes performance with the carbs from one year or another after you tune them to your engine.

[jetmechmarty]

I have an XS1100SG. It's jetted 110 115 115 110. That's what I remember. I might be off slightly, but the #2 and #3 carburetors have larger jets.