Posted: 09/13/2005 12:03:31 AM
Can I change a 1984 Honda XR350 from two carburetors to one and if so where can I find parts to make the change?
Reply by shannon on 09/13/2005 09:06:53 AM
Why do you want to switch to single carb??! Yes you can switch to a single carb but, it is a lot of work and i dont think there will be much benefit. Keep the old XR's alive!! Shannon
Reply by Boydnar on 10/10/2005 12:56:17 AM
Shannon, I have an '83 XR350 and I too would like to change to one carb. You ask why Because two carbs are a total PAIN IN THE POSTERIOR. I have to yank the head anyway to replace a burned exhaust valve, so I might as well change to one carb while I'm at it. Please, PLEASE tell us how it's done. What combination of parts will adapt a single carb to the head. -Boydnar
P.S. Are you aware of what happened to the head engineer who made the executive decision to use TWO CARBS on the XR350 First he was run down with a truck, then he was stabbed, then shot, then burned at the stake, then he was FIRED. (They also took his retirement away.)
P.P.S. First time I've ever used smilies. I'll get better at it.
Reply by shannon on 10/10/2005 11:30:47 AM
i guess ill be the first to thank him for making this design. i really like the design myself, to each his own though. if you really want one carb go to a newer bike. sell the bike with dual carbs. ill take it off your hands if you think its such a pain. one thing you might try doing is doin away with the primary/secondary type deal. and goin with 2 regular carburetors instead of having them linked together. just an idea. Shannon
Reply by hn7609 on 10/10/2005 6:40:06 PM
I've got the 84 xr500r with the twin carbs and it's a pretty good set up. I did have trouble with a big bog off idle when i would open it up. Cured the problem by bending the fork that opens up the second carb all the way over so it doesn't hit at all. Now the second carb only comes on at about 90% throttle. It runs better thru the entire rpm range with this set up. Give it a shot....it doesn't cost anything & can be reversed by bending the fork back. Bill
Reply by Boydnar on 10/13/2005 01:39:56 AM
Shannon, dude, you've gotta be kiddin' me. The proper question here isn't "Why do you want to change to one carb?" The proper question is "In light of the fact that 99.99999999999% of the worlds single-cylinder bikes do extremely well with one carb, why would anyone want the added complexity and headaches of TWO carbs on a single-cylinder bike?" Have you ever tried to take those carbs off when you're out in the middle of the desert? It's a freakin' nightmare. Only Honda in the 80's would think.
"Let's add some completely needless complexity to this bike -- and that'll make it better! Hey, more part numbers! More servicing difficulty! Twice as many things to go wrong! Our actuarials have calculated that if we add all the complexities and hassles and implications of a SECOND CARBURATOR TO A SINGLE-CYLINDER BIKE, somewhere in the powerband we'll reap a 0.000000000001% increase in power. We don't know exactly WHERE in the powerband this will happen, but we can say with 100% ontological certitude that it WILL happen SOMEHWERE. Wow! That sounds like a good engineering compromise and a good cost/benefit trade-off. Hey, we're all over that! Yeah!"
Ever wonder why, after two years of two carbs, even Honda itself abandoned the two-carb nonsense and went back to ONE CARB on their XRs -- and have stayed with it? For the past twenty years? And, at last check, one carb seems to be working just fine on every racebike/dirtbike/playbike from ALL of the manufacturers.
And yet you ask, "Why do you want to switch to single carb??!"
So. We're back to the original question: Does anyone know exactly which parts will adapt a single carb to an '83 or '84 XR350 head? Does anyone have experience doing it? -Boydnar
Reply by b_king on 10/13/2005 03:43:59 AM
If I am correct, no one part will allow the adaptation of a single carb to a dual carb setup cylinder head. Simply because the dual intake ports are separated on the outside of the head, no joined and then separate such as the newer single carb models have. Thus, you would have either home make a unique intake manifold which will have a large enough mounting to reach to either intake port..OR.. Replace the cylinder head with one that is designed for a single carb setup, replace the intake boot, carb (why not while your at it, a pumper would be nice), air boot, air box...unless you can modify the existing to allow the amount of airflow you are looking for to that now sinlge carb from the 2 boot airbox. Adjust valves, check all sorts of things before buying...such as fit, and what not....
Now, for Shannon's defense, the XR lineup was originally designed as a offroad performance lineup of motorcycles, not motocross, offroad performance. When racing/riding offroad, more torque and low to mid range power is preferred over motocross mid to top. Honda cleverly designed a number of their small and big bore thumpers with two carbs because it aided in not only throttle response, but in torque development throughout the rpm range buy mainly focusing on the low to mid range; perfect for offroad racing.
Now, when you said even Honda finally switched over to single carbs on all models, it was basically for cost production purposes, and I guess someone may have figured it was slightly more difficult to tune the jetting perfectly. All things come with experience though, I'm sure someone has perfected dual carb to sinlge cylinder jetting issues.
Hope this helps the "discussion," as I am an outside party, with both a dual carb bike, and a single carb bike, non biast opinion.
Reply by shannon on 10/13/2005 09:34:15 AM
If i had the time, which i dont at the moment, i would defend myself. But, i have mid-terms at college at the moment and dont have time to reply in depth. so in the words of Arnold. I'LL BE BACK!! Shannon
Reply by NordieBoy on 10/14/2005 01:40:59 AM
My understanding of the twin carb issue is that with a main and choke carb setup it aids smoothness through the rev range. A big single carb will always be a compromise either down low or up top - very difficult to tune for both. The twin carb setup is still a bugger to tune but the results are worth it.
Reply by Boydnar on 10/15/2005 12:00:54 AM
Wrote a long response the other day to b_king’s post of 10/13 and while I was "previewing" it, the website lost my GD post. ALL MY FRICKING WORK. I'm so fricking mad I could chew nails. That's what I get for not being smart enough to write it in Word and then copy it to the posting page.
Briefly, I readily recognize and admit that having both a low-speed and a high-speed carb setup is, in SOME measure, better, but it is no revelation to say that that advantage is largely theoretical. I bet if any one of you were placed alternately on two different versions of the same model of bike – one version with one carb and the other version with two carbs -- not ONE of you could ride the bikes for 30 minutes each and then tell which was which without looking. Yes, the advantage is there, but it AIN’T WORTH THE DISADVANTAGES: more maintenance labor and headaches, increased initial cost, more weight – and did I mention more HEADACHES?
NordieBoy said, “My understanding of the twin carb issue is that with a main and choke carb setup it aids smoothness through the rev range. A big single carb will always be a compromise either down low or up top - very difficult to tune for both.”
OK. That is so much theoretical bluster. By saying “very difficult to tune for both,” you make it sound like single-carb bikes run like crap. Think about it. That’s the clear implication. But nothing could be further from the truth. Difficult to tune??? How difficult? So difficult that millions of people enjoy single-carb bikes and ride the piss out of ‘em and NEVER say to themselves, “I wish this thing had TWO CARBS.” Single carb bikes run VERY well with just one carb and the number of people who would, given the REAL choice, trade their single-carb bike for one that has two carbs can be counted on the fingers of one foot.
My XR650 starts on the first or second kick, idles well, has outfrickingrageous low-end grunt, terrific midrange, and pulls your arms out of their sockets all the way to redline. And did I mention that it has only one carb?
Again, for those who have already forgotten what I said four paragraphs ago, I gladly and openly admit that, given proper execution and sufficient refinement, two carbs would be “better” than one, but IN THE REAL WORLD, two carbs represent a compromise that exceedingly few people would be willing to make if they were fully informed about the downsides: needless complexity creating more risk of problems and failures, far more difficult maintenance, greater initial cost and greater weight.
Theoretically, it’s better. But where “the rubber meets the road,” it’s just not worth it. Seriously not worth it. -Boydnar
Reply by b_king on 10/15/2005 12:19:12 PM
Well, we are all of our own opinions, and we are most definitely entitled to that. Like Shannon, I would sit here and argue away, but I realize their is no way to convince you to stick with the dualies, so best of luck to you on your project...just remember, all us dualies won't be here to help you when things go wrong! lol, jk, dont worry we'll be here.
Reply by shannon on 10/15/2005 1:21:50 PM
well, mid-terms are over, my bike still has dual carbs. and i still wouldn't trade it for an 85 single. its been said a 83-85 250 will beat a single carb 250(this is what i heard). does anybody know if it is the same for the dual carb and single carb 600's. who ever said the dual carbs were only put on bikes for 2 years doesn't know much about the history of dual carbs.
85-86 xr600r??(i think but not 100% sure?)
Reply by Boydnar on 10/19/2005 02:01:58 AM
Hey Shannon, you listed the years of bikes that were dual-carb, but I'm pretty sure you phase-shifted the 350 by one year. You listed the years as
85-86 xr600r??(i think but not 100% sure?)
but I'm fairly certain that the XR350 was dual-carb for '83 and '84. In fact you implied as much when you said that, ". . . i still wouldn’t trade it for an 85 single [carb]." Obviously this is a typo error due to brain-burn from your mid-term tests. Hope they went well. What's your major?
And basically, fellas, what I'm sensing here is that you are eager to proclaim the theoretical power advantages of dual-carb setups, but are reluctant to acknowledge my point about the real-world complexities and difficulties of servicing and maintaining two carbs that are shoe-horned into the small space on a dirtbike that is cramped enough when it has just ONE carb in it.
Let's say that the power increase afforded by two carbs is 7%. That's a significant power increase for a design "gimmick" (don't mean that pejoratively) such as dual-carbs. But think about it for a moment. On a 350cc bike, you could achieve that same power increase by increasing the displacement by .07 x 350 = 24.5cc. So what you’re saying is that you’re willing to put up with all of the drawbacks and hassles and headaches of a dual-carb system . . . just to have a 350cc bike that puts out the power of a 375cc bike. Is that really a good trade off? Is that really worth it?
Looking at it another way, assuming that an engine’s torque curve is relatively flat, you’re saying that it’s worth putting up with all of the drawbacks and hassles and headaches of a dual-carb system, just to have a bike that puts out as much power at 3000 RPM as a single-carb bike would put out at 3210 RPM (3000 x 0.07 = 210). Now, once again, is that really worth it? Will you still be saying, “Yes, it’s worth it,” when you’re out in the middle of nowhere and something’s wrong with your carb(s) and you need to remove them from your bike and doing so costs you an hour and your religion? Virtually NOTHING – and I mean N-O-T-H-I-N-G – is worth trading away easy serviceability. Certainly not the meager power advantage afforded by two carbs – however much it is.
To drive home the point, I submit this short text on the quick way to remove the carb from an XR650R . . . although the gist is in the TITLE.
5-Minute XR650R Carb Removal. Here's the trick, it takes only 5 minutes to pull the carb and about the same to hook it back up.
- Remove seat. May have to remove tank depending on which one you have (stock, IMS, etc... ). 4 bolts, 1 fuel hose into carb, one rubber tension strap to frame.
- Remove muffler. 3 bolts.
- Unplug wiring harness from ignition module.
- Remove double-pull throttle cables from carb.
- Pull up all rubber hoses (vent, overflow etc)
- Loosen the rubber boot going into carb and the clamp on the other side.
- Loosen the two rear subframe bolts.
- Remove top rear subframe bolt.
- Pivot the subframe back about two inches or so. This will pull the airboot from the intake side of the carb. Watch your wiring and your rear brake reservoir hose. I hate that stupid little pinch bracket securing the brake line to the subframe.
- Pull the carb straight out of the intake manifold. Comes out hard. Tilt carb to the right side ( kick starter side ) and pull it up and out. Watch gas dribble out of carb onto your new sneakers.
Ever tried a 5-minute carb removal on a dual-carb bike? You'll need a chainsaw.
Now. Is anyone willing to agree that the REAL WORLD power gains of dual-carbs are probably not worth the REAL WORLD drawbacks? -Boydnar
Reply by AndyR on 10/20/2005 1:37:39 PM
I got an 84 XL600 with dual carbs. I think the benefit is extra grunt way way down low. I have never had to remove a carb on the trail...maybe I am lucky. I can't think of a reason I would want to though.I think you would need a custom intake manifold machined to do what you want. Probably easier to swap the motor out.
Reply by doughboy on 10/20/2005 9:54:38 PM
Well the next time I'm in a carb removal race I'll use a 2x4.... on the other guy. I have a 84 xl350 I just removed the carbs on and it wasn't that big a deal. The chainsaw only made it through the seat padding before I dulled it on the frame. Then I had to use a 8" grinder and a wonderbar.
Pertinent to thomas: If I really had to have a single carb bike I would buy a single carb bike. Anytime you try to change the original design it seems to get expensive for no good reason. But hey, if your'e going for it, good luck.
Reply by Boydnar on 10/21/2005 12:29:28 AM
Believe me, Andy, it has NOTHING to do with "want," and everything to do with "necessity." Stuff like a clogged main jet, or a stuck float bowl or float needle. Or maybe just fine-tuning the jetting in a new environment. -BoydnarOriginally posted by AndyR
"I have never had to remove a carb on the trail...maybe I am lucky. I can't think of a reason I would want to though."
Reply by AndyR on 10/21/2005 07:31:33 AM
I've been lucky. I can get to the main jets and floats, swap main jets, and tweak the idle screw without pulling the carbs. But a stuck needle would suck no doubt. If it was on the secondary carb, I think I could limp home. I often wish the bike just had one carb, but I deal with it. My XL is completely stock. I would like to see a single carb conversion done. Would be very interesting. Cheers
Reply by Momobadilak on 10/23/2005 12:42:41 PM
I do like the simplicity of design and implementation of a single carb, but I pulled the dual-carb unit off my '86 XL600 in about 15 minutes.
Here's the catch, included in that 15 minutes, I also had to pull off my seat and 4.1gal tank (sheesh).
The reality of it, though, was that everything was easy except for one small bolt that sits in the low-middle of the connection between the carbs and intake ports.
So, my 0.02 for this thread is that once you get some practice taking the dual carbs off, they don't seem to be that difficult - certainly more involved that a single though.
Reply by hilift on 10/25/2005 11:40:06 AM
Boydnar, can you please explain why the dual carbed 350's (339cc's) of '83-'84 make more power than the much newer, larger displacement single carbed 400's (397cc"s)?
Reply by Boydnar on 10/25/2005 11:09:09 PM
Dude, you gotta be kidding me. You want to draw me into a long discussion based on a completely unsubstantiated assertion? Show me the dyno graphs of the power output of those two bikes when they were new, along with the name(s) of the shop(s) that ran the tests, the dates they ran them, and the brand name(s) of the dyno(s) -- all of which is standard documentation -- and then we might have cause for discussion. Until then, I'll be out doing wheelies on my XR650R, which, by the way, has a re-geared top speed of 113 mph despite being crippled with just one carb. Ciao -Boydnar
Reply by doughboy on 10/26/2005 06:49:57 AM
Hey hilift, I would be very interested in where that info came from, too. Is there posted specs of the relative HP somewhere?
Reply by hilift on 10/26/2005 11:57:49 AM
Info is on this website! Honda must've really missed the boat on my streetbike, it's got SIX carbs. I guess one Holley double-pumper four barrel would have been better. Just pullin' your chain Boydnar!!
Reply by Boydnar on 10/27/2005 12:22:26 AM
Went to the post that has all the HP ratings and I STILL want to see the DYNO GRAPHS and the names of the shops and the names of the dynos. As you can clearly see on the post, all those figures came from a variety of people and, undoubtedly, a variety of dynos and shops. It even says right there in the post, “These are not official ratings and as we all know, HP ratings can be a little different with each dyno.” Also, some of the figures in that post could be “shaft” horsepower and some could be “corrected rear-wheel” horsepower. Apples and freakin’ oranges.
Nope. Not havin' it. Show me figures from a freshened-up old 350 and a new 400 taken, let's say, during the same week on the same dyno. Then we'll talk.
What's more is the fact that any HP lack on the part of the 400 could EASILY be explained by VALVE TIMING, which most likely would be more mild nowadays 'cause of the greenieweenie emission requirements. Was there such a thing as a "green sticker" in 1983? Were the 49-state federal emission requirements as strict 22 years ago as they are now? Remember, the cam has historically been considered the “brain” of the engine, telling it how much and what kind of power it will make. In order for the single-carb vs. two-carb power shootout to be valid, everything else must be equal – especially the valve lift and duration.
And if you’re saying that your bike is a Honda CBX, that’s one of my mostest favoritest bikes of all time. (But if you’re saying that your bike is a Bennelli, you can have that Italian piece of excrement.) But don’t MISapply my “one-carb for a single-cylinder dirtbike” rule to streetbikes. I didn’t say that the fewer carbs a bike has the better, I said a SINGLE-CYLINDER dirtbike should have just one carb. The CBX frickin’ ROCKS, man. All six carbs of it. Never had a CBX myself, but I did have a KZ1300 for some years and I did a nice transcontinental trip on it. What a monster. What a smooth, smoooooooth monster. I’d like to see a new six-cylinder bike done in the shrink-wrapped execution of the new generation of four-stroke dirtbikes. Imagine a liquid-cooled inline Six that weighs 485 lbs. rather than the CBX’s 600 lbs.
Doooood, I’m all over THAT! -Boydnar
Reply by hilift on 10/27/2005 04:59:21 AM
My "X" weighs 582 wet. Used to run a KZ13 for a while myself. Much more bottom end than the CBX due to the different characteristics of the engine. You can't wheelie them due to the shaft drive tho I too would like to see a modern equivalent of the 1047cc six banger done in the Hayabusa style. My X makes nice music now, could't image how she'd sound with that really short stroke.
Reply by Boydnar on 10/28/2005 03:19:20 AM
hilift said: "Much more bottom end than the CBX due to the different characteristics of the engine. You can't wheelie them due to the shaft drive tho . I too would like to see a modern equivalent of the 1047cc six banger done in the Hayabusa style."
The two major characteristics are 239 more cc and a very UNDERsquare cylinder in the KZ13.
Why do you say that the shaft drive keeps the KZ13 from wheelieing? A shaft drive bike still has all the forces that a chain drive bike has trying to make it wheelie. The problem with the KZ13 is the weight. The engine alone weighs about 232 lbs. My dresser version clocked out at well over 700 lbs. Simply too much weight for the engine and available traction to lift. I'm curious about what it is you believe the shaft has to do with it.
What I fantasize about is six CRF250/450 type cylinders all in a row. Maybe make the cylinders a little less oversquare to keep the width down. (I don't mean six free-standing jugs, I just mean CRF technology and lightness.) About 1200 to 1400 cc, light as hell, fuel injected, powerful, SCUH-REAMIN' and as smyoooth as a turbine. The smoothness of an inline Six is astounding. A totally different experience from them reg'lar motorcycles that mortals ride. I really regret getting rid of my KZ13 even though it was a love/hate relationship: the weight was freakin' ridiculous and it had been neglected before I bought it. But the six cylinders are like cocaine, man. Hypnotic and addicting. I just can't get the thought of that silky-smooth freight train motor outa my head. The propulsive force was deceptively strong.
Got a cigarette?
Hey, 'lift, what year is your X? I've seen a few of them in "Cycle Trader" lately and have secretly harbored dark thoughts of buying one. It really is more of a museum piece than a daily driver, though. I mean, you can obviously use an X as a daily driver, but their value really is as a collector's item. I'd probably actually buy one only if I could park it inside the house and display it as a piece of art. -Boydnar
Reply by hilift on 10/28/2005 08:00:23 AM
My X is a '79 with 62K km - 36k miles. She's Candy Glory Red, has the sports bars and rearsets, stage 3 Dyno kits and a six-into-one Wolf pipe. Never down, always garaged, she looks showroom and IS my main ride. Of course, she's for sale at the $5K range (everything has it's price!) As a collectible bike it gets a lot of notice from fellow riders who know what it is. My only concern riding her is the racking of mileage. That is my only reason for letting 'er go. It's too nice to not ride and it's too nice to ride - it truly is a dilemma. Im leaning towards a VFR800 as it's replacement. I understand your inline six addiction. The music out of the pipe is blood-boiling. Mine sounds like half a Ferrari V12 wailing at redline. I'd like to see a another six done but with a couple of changes as you've pointed out. Injected, 1400-1500cc's, flat crank, six speed gearbox, liquid cooled, a much higher compression ratio. I'd like the engine dropped lower in the frame as well. (Just HAD my cigarette after typing that!) As for shafties not wheelieing, everybody knows shaft drives can't! LOL!!
Reply by Boydnar on 11/15/2005 01:41:56 AM
Hey, hilift, have you seen in one of the new bike mags that SUZUKI has a 6-CYLINDER concept bike out??? They call it the "Stratosphere," and say that it's a vehicle for "showcasing next-generation technology." They say it's barely wider than a GSX-R1000, which means that the cylinders aren't radically over-square like most of today's screamers. I'd love to see it make it into production. -Boydnar
Reply by hilift on 11/15/2005 07:34:53 AM
1100cc's, 180hp, radially mounted front calipers, Katana silhouette. What's there not to like!!? Hopefully we get a better engine reliability package than the TL/TR's and a perimeter frame. Sign me up for one, I'm ready!
Reply by Boydnar on 11/15/2005 11:49:14 PM
Speaking of mega-bikes, have you seen that next year Kawasaki is going to offer a 1400cc (1352cc actually) version of its ZX1200? It's less of a hard-edged sportbike and more of a ZZR/'Busa/Gran Touring model. Just my style. Ya gotta love a motor that could pull stumps. And my vote on the Stratosphere is that the displacement be bumped up to 1400cc. Hey, it's not 1979 -- or even 1999 for that matter -- and displacements are ramping up to Super Sizes. Ya wouldn't want your SuperHyperSix to be blown out by a 1400cc Four. What a come-down that would be. -Boydnar
Reply by hilift on 11/16/2005 06:31:44 AM
In my estimation it's FUGLY! I like the concept mind you. Big bore, pulls like a freight train, handles decently. Just what the 'Busa did when it was introduced in '99. I like the new Beemer more than the Kwacker. Everthing is there, including the outrageous price tag! Gotta agree with you on the 1400cc six-potter - at 1100cc's the bike'll end up like the '81-'82 CBX's with saddle bags and the tag of Grand Tourer instead of it's birthrite moniker of Super Sport.
Reply by Boydnar on 11/17/2005 01:24:01 AM
Yeah, it's pretty ugly and um ungainly. But I could get used to it. Kaw's makin' a mistake by settling on 1352cc's. They should utilize every available cc that the name of the bike allows. It should be 1399cc's. Thanks.
Reply by jerry m on 11/18/2005 3:31:03 PM
Search the flat track sites for (DAVE BYRD). he makes single carb intakes for the daul carb heads. jerry
Original URL: 4strokes.com/forums/topic.asp?TOPIC_ID=19785 © 2016 4Strokes.com