Best Performance Carbs?

[maxrageous]

later 1980 special carb issues

Hi guys. I'm impressed with how much you folks know about these bikes. I'm rather new at this and playing a frantic game of catch up. Here is my question. I also have a 1980 carb that has had one of it's float posts broken off. What is the best repair for this. The other three are just fine and it would be ashame not to keep the quads together as a "family".

Max

[SFerinTEXAS]

I'm impressed with how much you folks know about these bikes

Are you reading a different post than this? Or just easily impressed?

[SFerinTEXAS]

OK. I am a Texan. I think I have seen pretty much all Dan Hodges has posted on this subject. And with all due respect it appears he was always working with late model engines. If he did any detailed work with 78-79 s, I missed it.Any resources to the contrary will be appreciated

[natemoen]

Hi guys. I'm impressed with how much you folks know about these bikes. I'm rather new at this and playing a frantic game of catch up. Here is my question. I also have a 1980 carb that has had one of it's float posts broken off. What is the best repair for this. The other three are just fine and it would be ashame not to keep the quads together as a "family".

Max

Do a search for float post repair. I know there has been a few write ups for it just don't know where.

[XS1100 Newbie]

Keep an eye on fleabay for the carb body.

[crazy steve]

...Here is my question. I also have a 1980 carb that has had one of it's float posts broken off. What is the best repair for this. The other three are just fine and it would be ashame not to keep the quads together as a "family"...

Ok, here's a float post fix if it's not busted clean off...

http://www.xs11.com/forum/showthread...at+post+repair

If yours is broken below what's shown, there is an outfit that can reweld the piece back on if you have it. Not cheap; $60 and up plus shipping.

If you look for another carb body, remember that while all four carbs are based on the same body casting, each one is machined different from the others, so you need to find one that fits in the same place in the 'order'...

[nikole.957]

LOL..at least she seems a bit more harmless than the Rajneeshees in Antelope, Oregon were...

The other thing I've noticed is there hasn't seemed to have been much exploring of different needles in these. From playing with Keihins on other bikes, changing the needle taper can show pretty big improvements in the midrange without a jet change. This would appear to me to be the key to the Dynojet kit and whatever improvements it shows.

[natemoen]

If you look for another carb body, remember that while all four carbs are based on the same body casting, each one is machined different from the others, so you need to find one that fits in the same place in the 'order'...

You can switch 1 and 3 can't you? But not 2 and 4 cause of the back advance nipple.

[rpgoerlich]

#3 typically isn't tapped to secure the choke handle to it like #1 is. Nor does it have the hole for the detent spring and ball to hold the choke rod in position. You would have to swap the butterfly shafts also.

I have used #2 for #4, swapping the shafts also and just put a cap on the advance vac tube. You just lose the extra detent on the choke rod.

[natemoen]

#3 typically isn't tapped to secure the choke handle to it like #1 is. Nor does it have the hole for the detent spring and ball to hold the choke rod in position. You would have to swap the butterfly shafts also.

I have used #2 for #4, swapping the shafts also and just put a cap on the advance vac tube. You just lose the extra detent on the choke rod.

Ah yes I was not thinking about the choke screws. The ball and spring wouldn't be critical as long as the #4 still had the hole for them, that is though if you could tap holes for the choke lever as you pointed out. plenty of people run with just one of the ball and springs anyways cause they loose the other.

[Dan Hodges]

Parts vs Parts

OK. I am a Texan. I think I have seen pretty much all Dan Hodges has posted on this subject. And with all due respect it appears he was always working with late model engines. If he did any detailed work with 78-79 s, I missed it.Any resources to the contrary will be appreciated

Simply put, the 80-81 heads have larger valves and valve bowls than the 78-79 heads do and will flow about 10% more air however the combustion chambers in the 80-81 heads are larger and should not be used with the early pistons due to the 3 cc smaller domes on the early pistons. You can use the late pistons with the early head and pick up some compression which will result in more steam below 4000-5000 RPM however with the same cams and other factors equal the higher flowing head will make more power from 5000 rpm up.

The early cams have 12 degrees more duration and will make 2.5-3 hp more from 3,000 rpm up than the late ones as verified by myself and several others on the dyno. The early cams have the same intake lift as the late ones but have about .020 less lift on the exhaust. The early cams have 101 degree event angles while the late ones have 105 degree angles. The late cams generate fewer emissions, get slightly better gas mileage, make a little more grunt from off idle up to about 4500 rpm after which the party is over.

All XS carburetors have 34 mm throttle bores and 30 mm venturis however the air bells differ slightly and the slides in the 78-79 carbs are completely different from those in the 80-81 carbs. Either will work if you get the AF ratio set properly. The early carbs have adjustable needles and the late ones don't but you can adjust the height of the needles in the late ones by using shims/washers however none of the stock needles have the proper taper hence the reason I use the needles from the Dyno Jet kit.

The ignition timing curve on all of these things varied from model to model and the 78-79-80 used mechanical advancers and the 81 was all electronic but the curve on all can be changed/modified including the 81.

The proper ignition curve will depend more than anything else on what your pumping compression is and that is determined by cubic inches, static compression ratio and the intake timing closing event. Of course your pumping compression will also dictate the octane rating of the gas you use.
The stock pumping compression on these things was 142 psi to 146 psi and with those numbers you can burn practicullay anything short of oil soaked shop towels but once you start making over 150 psi you need preimum gas,90-91 octane or you will need to retard the ignition timing. An air cooled engine will not tolerate the same levels of compression that a liquid cooled motor does because of heat issues.

The bottom line is this, if you have a loaded down XS with a big windshield/fairing you want to build a torquer motor and if you have a glitzed out XS with the 750-850 FD you will want all the torque you can get and hope you got enough.
The parts you use will depend on the application you intend to use them on and at the end of the day, that's the beauty of the XS because it can be built to fit many applications.

Good luck and happy New Year.

Dan

[crazy steve]

....however none of the stock needles have the proper taper hence the reason I use the needles from the Dyno Jet kit.

I'm curious, is there another source for 'better' needles other than the DynoJet kit? I would be surprised if Mikuni didn't have other needles for other applications that could offer the same or similar taper as the DJ ones. I know that's the case for Kehin carbs, don't see why this couldn't be true here also. And do the DJ needles have to be used with the DJ jets?

And Dan, thanks for confirming my part choices...

[SFerinTEXAS]

WoW. Good to hear from Dan. An honor. But I'm still perplexed.

In regards to the original post here are my thoughts. Mostly all depends on which model is the prime subject, early or late.

I have 2 completely different animals for sure, A screaming stock SF and a nicely tuned yet anemic ( in comparison ) stock XJ. Both get high 30's mpg but that SF is a demon I should would like to have a little of in the XJ.

Have not had the pleasure of comparing to a late XS.But I firmly believe the oft mentioned fact that out of the box an early model has significant advantages over later ones.

[crazy steve]

...I have 2 completely different animals for sure, A screaming stock SF and a nicely tuned yet anemic ( in comparison ) stock XJ. Both get high 30's mpg but that SF is a demon I should would like to have a little of in the XJ...

The big difference is in the cams, with ignition curves being an important secondary factor. Longer duration = bigger charge on the top end (all else being equal) with a corrosponding loss in the low end. More aggressive ignition curves can make up that low-end loss to an extent. But the later bikes were tuned for emissions (in order to meet federal standards) over power as long-duration cams are inherently 'dirty', so the later bikes don't have that big 'top end' (and is the reason the later bikes are noticably slower). That was the reason for the wholesale switch to roller cams on factory hi-po cars when they reappeared in the late 80s. You can have a faster valve 'opening rate' with a roller cam compared to a flat-tappet cam, so have the same 'effective' valve opening in a shorter event and reduce overlap. You could have custom cams ground for the XS with faster opening/closing ramps to have the best of both worlds, but the tradeoff is much increased wear/stress on the valvetrain.

Want to 'convert' that XJ to the early XS power curve? Install early cams, block off the YICS, and recurve the ignition to the early specs...

[SFerinTEXAS]

.

Want to 'convert' that XJ to the early XS power curve? Install early cams, block off the YICS, and recurve the ignition to the early specs...

Happen to have everything on hand to do that.

How about you Dan, would you agree with that combination? Just asking.