Best Performance Carbs?

[crazy steve]

After acquiring my various 'extra' XS11s, I've been seaching the forum for the best combination of OEM parts for performance. It appears that using the late head/pistons (with it's larger valves) along with the early cams/ignition advance offers the most power for the least bucks. Swapping between the early/late exhaust cam will move the power around on the curve a bit.

But I didn't see any info on the 'best' carbs, i.e. early (78-79) vs late (80-81). I know the later carbs do have considerable differences and were 'calibrated' more for emissions rather than performance. But will a careful rejetting of the later carbs eliminate these differences? Or is there some inherent difference that can't be changed?

[dbeardslee]

After acquiring my various 'extra' XS11s, I've been seaching the forum for the best combination of OEM parts for performance. It appears that using the late head/pistons (with it's larger valves) along with the early cams/ignition advance offers the most power for the least bucks. Swapping between the early/late exhaust cam will move the power around on the curve a bit.

But I didn't see any info on the 'best' carbs, i.e. early (78-79) vs late (80-81). I know the later carbs do have considerable differences and were 'calibrated' more for emissions rather than performance. But will a careful rejetting of the later carbs eliminate these differences? Or is there some inherent difference that can't be changed?

TRbig used to caution against that combination of heads/cams before he got banned. Can't remember why, but IIRC it had something to do with a very poor idle. As far as the carbs are concerned, the 78/79's draw all their gas through the main jet tunnel, while the 80/81's draw their gas for the pilots through the open pilot tunnel. It's kind of six of one, or a half dozen of the other. The main thing is to have your mixture (jetting, slide needles, and mixture screws) set properly for the amount of air that your drawing (stock, drilled airbox, or pods). Gas will only explode in a relatively narrow air/fuel mix ratio. Colortune helps a lot as far as getting them dialed in, but it's about as much art as science.

I just noticed that you're from Yelm (spent a couple years on FT. Lewis, back in the day, and I've been through Yelm many times - used to like to enter the post through the back door ). Prometheus578 is located in Olympia, and he's one of our most knowledgeable members. If I was in Yelm, I'd be developing a relationship with Prom. He can probably answer your questions on heads, too. JAT

[crazy steve]

TRbig used to caution against that combination of heads/cams....

I just noticed that you're from Yelm (spent a couple years on FT. Lewis, back in the day, and I've been through Yelm many times - used to like to enter the post through the back door

I spent several days researching any/all posts I could find on the various head/cam combos (paying particular attention to Dan Hodges posts), and that seemed to be the general consensus for the best 'cheap' power increase. 'Matching' the ignition to the cams was noted as being important, which was why Tod had issues. The discouraging part was how little additional power was to be gained (short of very expensive custom machine work). But there was nothing about the carbs. You're probably right, it's likely a wash as to which carbs you use as long as the jetting is right. But I figured it wouldn't hurt to ask...

I don't know how long it's been since you've been here (Yelm), but you would probably not recognise it now. It's gone from one three-way stop to go through town up to six traffic lights now since I've lived here, and it actually has a 'rush hour' in the late afternoon. Luckily, I don't live 'in' town, but 15 miles out (very near Dechutes Falls if you know where that is). Most of the rednecks left when the ramsters moved in, so it's 'flavor' has changed quite a bit.

[dbeardslee]

Yeah, it's been over 30 years since I was there, and it was a one horse town then. Dechutes Falls isn't ringing a bell, but I used to know where the Dechutes fire tower was. If it's still standing I'm guessing they're probably pretty close. Spent many a lazy hour drifting down the Nisqually River too . Had to be pretty careful close to the res, though - every now and then members of the tribe would take pot shots at patrols .

[TomRodgers]

Most of the rednecks left when the ramsters moved in,

Being from Chicago....living in NW indiana....... WTF is a 'ramster'????

[dbeardslee]

Cross between a Dodge and a child's pet?

[81xsproject]

Oh where to start. First Todd's obviously lacking some knowledge. He was probably using the colortune and doesn't have a clue otherwise. Don't listen to others opinions, try it for yourself and see. Personally, I didn't have any idle problems and the early cams with the late heads make a huge difference on both ends (running carbs). The earlier cams have more overlap, thus making more top end (4k up) power and less bottom end. As far as XS carbs, stick with the carbs that match the head. I don't know about early heads with late carbs, but late heads don't perform as well with early carbs. Just my personal experience from rebuilding and tuning XS carbs and testing on my late model.

[dbeardslee]

I don't know about early heads with late carbs

I put a set of 80/81 carbs on a 79SF this past summer, and they worked great. It will change the mixture a bit though - at least it did on these. The carbs came off DGXSER's totalled Thunderstruck (81 SH) where they were right on the money. They're running slightly lean on the '79. If that holds true going the other way, you'd probably be bit rich with the 78/79's on an 80/81 head. Again I go back to jetting and mixture. The head has no idea what kind of carbs are attached - it only knows if the air/fuel mix is correct. If you get that dialed in, it shouldn't matter which carbs you use. As the jetting does seem to be affected by the different heads, it might be easier to stick with the carbs that came with the heads though. My $.02

[DGXSER]

Those carbs have the 110 main jets in them. They ran great on THunderstruck and always gave me plenty of power when and where I needed it. But I did not ever put the colortune on them that I felt I had things right. I always went by plug color. So they may be slightly lean as that was ho the 81 was setup to run for emisions purposes. I am sure you could throuw some 120 jets in those carbs and cure any lean issues.

I'm in a similar process to 81XSprojects myself. I bought a couple sets of rebuildable carbs and doing just that. Sold the late model set to another member who put them on his bike an dsaid they ran great, just need some fine tuning like any carbs thrown on a different engine.

I have the early set rebuilt, but getting gas flowing down the carb bowl on #4, so I am guessing the fuel T is leaking. Need to hook fuel up off the bike and check. Then I can see how they run. The bike is stock air box and kerker 4-2 exhaust, no crossover. I'll let you know when I get that corrected and see what they do.

I agree with Doug though, if the carb will bolt to the manifold and is capable of producing the flow rate the engine needs, then it can be jetted to get the mixtures right. Hving been through both styles fairly thoroughly. I see no reason tey ar ento interchangable and still get the same level of performance wiht the correct jetting. My belief is that if stock jetting for the late style works well then stock for the early style should also work nicely. Again, that is a theory I will test when I get this fuel leak issue resolved.

[crazy steve]

A Ramster is...

Being from Chicago....living in NW indiana....... WTF is a 'ramster'????

Our local 'celebrity' is J.Z. Knight, who 'channels' a 30,000 year-old warrior from Atlantis named Ramtha (I swear, I'm telling this straight). She runs a 'School of Enlightenment' for her followers here. She used to tour for this, but after receiving numerous death threats on the road, now does this here. Well, when she quit touring, many of her followers moved to Yelm, and they're from all over (there's quite a number from Australia/NZ for some reason). Strange group to say the least; pretty good collection of long-haired men/short-haired women (heavy on the latter), if you know what I mean...

J.Z. was a news item for a while; it seems Ramtha recommended buying some thoroughbred horses that J.Z. just coincidently had for sale (that croaked shortly after purchase), and there was a messy divorce from her AIDS-infected husband. Add in some weirdness like her chrystal-chandelier-equipped horse barn and airial photos of her followers all standing nude in a field, well, you get the idea...

Anyway, after several culture clashes and a couple of injunctions, they learned to keep their heads down; a local wit nicknamed them 'ramsters' and it stuck.

[Guy_b_g]

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

[crazy steve]

...As far as XS carbs, stick with the carbs that match the head. I don't know about early heads with late carbs, but late heads don't perform as well with early carbs. Just my personal experience from rebuilding and tuning XS carbs and testing on my late model.

Ok, now that I've cleared up the 'ramster' thing, lets get back to carbs...

What specific issues did you have with the early carb/late head combo? These carbs are circuited differently internally, and the late units seem to be more for emissions/mileage, which is not a concern here.

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.

One of the reasons I ask all this is in my recents acquisitions, I've gotten three, maybe four sets of late carbs (all disassembled to some degree and no doubt all need rebuilding; I have 3-4 bodies with broken float posts) and before sinking $$ into them I'm trying to get a feel for what bits I should get. I'm no fan of Dynojet kits (they seem to be a waste of money on Keihins), but that may be the choice here...

[crazy steve]

...This would appear to me to be the key to the Dynojet kit and whatever improvements it shows...

Interestingly enough, a search of Dynojet kits reveals that they don't offer a kit for the early (78-79) carbs, so does that mean only the late carbs are compromised in terms of performance? Hmmm....

[bikerphil]

Steve, they just don't make the Dynojet kit for the early carbs anymore, but they used to. I've tuned many of both types of carbs, and I will say that the late type are easier to tune, but the early ones produce more HP when correctly dialed in, JMHO.

[crazy steve]

Steve, they just don't make the Dynojet kit for the early carbs anymore, but they used to. I've tuned many of both types of carbs, and I will say that the late type are easier to tune, but the early ones produce more HP when correctly dialed in, JMHO.

Thanks, that's the feedback I'm looking for. As to the Dynojet kits, I wonder if the disappearence of the early kits had to do with the fact that the early carbs already had many of the 'benefits' that the DJ kit offers?

The setup I'm looking to do will be late head/pistons, early cams/ignition, OEM 'standard' exhaust, K&N filter, and maybe alter the airbox (I just don't like the look of pods, plus the 'sleeper' effect). I realise that a 4-1 exhaust may offer more top end power, but like pods, I just don't like the look of them.

Some food for thought anyway...