Rejetting

[LucasCustom]

I'm needing to rejet~I have an '81 engine & carbs on my chopper I just built over the past month~It runs great on full choke~Not so happy of half choke or off choke all together it pops and sputters~So I keep it there on full choke~However it fouls out my plugs w/black soot in no time~I took out the brass caps covering the primary screws and have them backed out way to far and it run to rich~I don't know the stock 81 jet size~I can remove them on the bike and check~But I'm the kind who likes parts in hand for it to go back together imidatly when I take somthing apart~I would like to try one size bigger~then adjust the primary screws back down so I don't keep fouling plugs and have to push it back home in this heat~I get alot of exersize that way~but I have much better ways of getting that~Not to mention how embarrising it is to have harleys drive by gawking~That I can live without~This is a biker magnet town~I switched it over to straight pipes and pod aircleaners~Thank you in advance for any info~Sincerely Rob lucas

 

[5twins]

Go to the top of the page and click on "Tech". Find and read the carb guide. That will tell you all you need to know. We wrote all this stuff down for a reason - namely so we wouldn't have to repeat it every 2 days, lol.

It's highly unlikely that changing one jet one time will tune your carbs. It's more involved than that. If you want the "parts in hand", I suggest you get the next 3 sizes larger on mains and one size larger for the pilots.

 

[LucasCustom]

Thank you 5twins~I knew there had to be something here someware that I could find~When I google XS650 rejetting it always comes back to this forum but always seamed like there was nothing that fit my chopper's problems~I will go check out what you have suggested~Thank you again

 

[grizld1]

WARNING: RANT AHEAD

5t, among the great mysteries of life are these two: Why don't these guys read BEFORE they start asking questions, and why don't they read and ask questions BEFORE they start tearing shit up for "the look" and "the sound"? What we hear from the Sawzall Set is a bunch of noise about independence and individuality and blah, blah, blah, but half of 'em expect to be coddled and spoon fed as soon as they figure out they're in over their heads. Hey cats, you wanta talk the talk, start walkin' the walk.

 

[LucasCustom]

Thats Funny!!! I did read it all already~before I asked~Did anyone ever get it right?? That would be my question?? I have 8 of these and the only one that I drive is a stock 77~Why was that one made so perfect and all my 3 81s and my 82 Heritage Specail don't run for more that half a second??

 

[LucasCustom]

I have spent a small fortune on my 82 testing everything and it starts then dies~I don't need spoon feeding~I would like to talk to somone that sayes ~I have done that been there and this jet works for pod filters w/straights~I have read everything I can google and my 2 shop tear down manuals~Most of what I have read here is on the '81 ~Did anyone get their 81 to run right??

 

[LucasCustom]

I have a 70 thats seized~That one should be the best running out of all of them~I have all the parts in stock to restore it~Next in my line up will be my 72 then 75~They will perfom better then my 77~Seams impossible??But the later year bikes have been a complete nightmare carbs and electrical~I'm a freindly guy and thought I would join a forum of like minded guys that love these bikes half as much as I do>>?? All it takes is one bad apple

 

[angus67]

what altitude you at? im at sea level, and have pods/straight pipes, and run 140mj's, 46pilots third notch on xsjohns needls. johns needls are no longer available, but you can convert your bs34's to canadians by switching to canadain needle jets with canadian needls.

 

[LucasCustom]

Hi Angus~Just checked~I'm at 700-to-1000 feet above sea level~Thank you so much~

Griz~I have bought all my XS650s from eBay in basket case form~so I have saved and put back on the road what most consider junk or just parts~Pushing my 81 home yesterday~I had a guy stop and tell me that he had saw my bike outside my house earler and took many pictures of it and that it is the best looking bike in the world~Thats a pretty tall order!! Even not running it sold it's self~He has a B.A. check on it's way from the Army~and he is going buy this '81~So I'm on to my next build~I hate to say it but it to is an '81~I have made my own wiring diagram using 3 differnt refrences~But I have tryed to carfuly remove the pilot jets and they are seized~I've had to deal alot with them in the past in this condition~I'm 42 and have been building go-karts & motorcycles out on the farm seince I was 11yrs old~Briggs and Stratton 3 horse was my first on my Corvette pace car go-Kart and I haven't stopped turning a wrench yet ~I hope you get feeling better~As I know no one can be that grumpy all the time~Sincerely Rob lucas

 

[5twins]

The problem with the 34s is they came set up very lean from the factory, too lean in my opinion for even the stock bike. You make any change at all to the intake or exhaust and you usually need to re-jet. You can sometimes get away with minor changes on the earlier BS38 equipped bikes without having to re-jet or re-jet much because they came set up richer from the factory.

I have several sets of BS38s I run on my bike and over the last few years, I've amassed quite a collection of jets and carb parts to tune them .....

I have every size main from 125 to 155 and every size VM22/210 pilot from 25 to 35. I have needle shim washers, several different needles and needle jets. Now, I'm not saying you need to go this far but you will need to get several different jet sizes and try them if you want to do the job right. One of the 1st rules of jetting is when you think you're right, try the size above and below to confirm that.

 

[LucasCustom]

Thank you so much 5Twins for all your help today~I will go out and remove my mains and see what # is on them~Best place to start this ball rolling in the right direction~Thanks again~Sincerely Rob lucas

 

[kopcicle]

...All it takes is one bad apple

Here you have at least two . I'll only speak for myself . Reading doesn't fix all your problems neither does understanding what you read . You have to put it into action over and over again . The mind remembers what the hands do . Not meant as an apology of any sort , 5t , griz and I answer the same questions about gummed up carbs , dwell and timing , electrical and charging every spring . It gets old . I realize even I had to start somewhere and must have been a royal pain at times . That is why and the only real reason why I still answer the same questions withe the same answers year in and year out . I reserve the right to bitch , abuse , denigrate , demean and otherwise flail the unwary as I see fit as long as in the end I provide some constructive input .

Now go out and completely go through a pilot circuit or three as many times as it takes to get it right .

http://kopcicle.multiply.com/journal/item/18/More_BS
http://www.dotheton.com/forum/index.php?topic=22587.msg246112#msg246112
http://www.dotheton.com/forum/index.php?topic=22587.msg246115#msg246115
http://www.dotheton.com/forum/index.php?topic=23084.msg247272#msg247272

More BS and the timing rant were written for 4 cylinder bikes but you can read between the lines .
Preliminary diag is that you have a plugged or partially plugged pilot jet and or carbs well out of sync

Valve adjust
Dwell (gap)
Timing
(repeat as necessary)
Sync
Idle Mixture
(repeat as necessary)
You would be surprised how many other symptoms can and will crop up while performing just these steps in order .
Battery voltage , Charging system , Float height and needle valve seat issues , Air leaks around the manifolds , rodent deposited crap in the pipes , tears in diaphragms ,
Just a few of the things that crop up in a tune up .
Start basic and work your way deeper .
Just beware of treating a symptom rather than curing a cause .

~kop

 

[LucasCustom]

Thanks Kop~I don't mind ranting and raving when kept in porspective~There are some words I shouldn't say as I'm working on somthing that Just wont work over and over again no matter how many differnt angels I run at it lol~There is no other kind of bike for me~I've either owned or driven them all~All others have somthing I hate and cannot live with~XS650s are perfect handeling sound vibration(Girls love)Now that I have been divorced 3 months after 14yr marrage~ dating several chicks~They love my bike rides~So This is the only bike for me~Now and in the future~I want to thank you so much Kopcicle for your time and effort~It has not been waisted I assure you~I will put everything I hear(Within reason hehehe) into action to get these newer bikes to perform as good as the old ones~Sincerely Rob lucas

 

[grizld1]

Right, kop, it's necessary to develop experience; but it's also necessary to know the principles. Rob, glad you have a sense of humor, and here's my point minus the rant. When you're tuning a carburetor you have to work from engine function (which is why, as kop stresses, you make damn sure everything else is right first); the response of the motor is what tells you what to do, and since every change alters the mixture both upstream and downstream of the component you've changed, you have to proceed in cycles of change and compensation. In a sense there are no special situations, and in another, every situation is special.

 

[LucasCustom]

Thank you Griz have a great Sunday ) I will keep working on it to get her perfected~Sincerely Rob lucas

 

[6772man]

I would just like to chime in and say thanks. This weekend i printed off the carb rebuild pdf, and flew back home to Arkansas from Orlando with two layovers and read that file over and over.Great info! I greatly appreciate the time involved it takes to put that together.

 

[Classic]

It bothers me that you ask if anyone has gotten their 81 to run right... There are thousands of '81s on the road today that run perfectly. The xs is a bulletproof bike and all you have to do is spec out the engine and learn how to jet and you can have a bike that starts on one kick and runs like a top. The first thing that you should know about jetting is that you cant take someone elses tune and expect it to work. There are differences in wear, compression, ignition timing, valve timing, intake air temperature, and altitude just to name a few.

 

[blue900]

What they said: Read-mess with it and read it all again. If you are persistent you will eventually Get it right. Beware Its not easy and takes time, lots of it.
Also as they said the other systems if not correct will foil your efforts to get the jetting correct.
Even a worn out chain can make it seem wrong.

My advise along with the rest: be sure you have 12+ volts at the coil with the key on.
My 81 is getting close to correct its running better than ever. I will be a happy man when its over.

 

[Renegade600]

Your '81 is similar to my '82 in carbs and electrics....I have mine running pretty close to spot on right now. I have Uni pods, and open Gordon Scott drag pipes....

Initally I went up (2) sizes on the main (heard how lean these carbs were), added the canadian needles (2nd notch from top)and needle jets, stock pilots....way too rich on top and a so-so bottom end.

Dialed back the mains first and went one stage, then the other back to stock mains......mid range suffered....one step up on the pilots, and the mid range got better, but rich on the low end...tighten air screws and at one turn out it ran better...pulled out the pilot and put the stock back in....now it was cleaned up with exception of some mid range bog, so at this point I lifted the needle to the mid position, and cleaned up the rest with the air screws (about 3-1/4 turns out)....

So essentially I'm running stock 34's with the stock jetting with the exception of the canadien needles at mid position and the matching needle jet.....
Tom

 

[LucasCustom]

Good morning Classic~My '81 runs great~ till it don't~Then I have to push it home~First time 2 miles ~next time 1 mile~The third time 1/2 a mile~3 times in as many days~in 100 degree heat~I'm very muscular athletic 42 & feel 18 still~But pushing it back dosn't create the image I desighned into this bike~I completly cleaned another set of 81 carbs yesterday 132.5 main jets 42.5 pilot jets and 135 jets in the rear of the carbs~Pop the other carbs out and install these today~Classic my '82 runs worse than my 81s it starts for 1/2 a second and dies~I bought a new wiring harness w/automotive fuse holders(Very important)and then replaced every component~from a TCI to a new battery~It ran great untill it didn't~And wouldn't you know it ~It did it when a guy test drove it to buy it~Nice and slow went a block away ~I could see him turning around it was giving him troubles~The 82 will not sell unless it is running~My 81 chopper is selling regardless~The new owner dosn't even care if it don't run right~He's crazy about this bike~My daily driver trouble free rins like a swiss watch haven't had a problem with it in over a year~My first street bike I ever perchaseed was in summer of '86 it was a '78~Never had to do anything to that bike either just gas and go~My buddy Dave Roth is an all japaneese bike guru~When I started collecting these bikes~He said they were the Triumph's with all the bugs worked out~He said the 70 XS is AWESOME!!! and the '
71-73 were still strong runners~Then the less desiarable detuned bikes were the 74-78 and he kept going down hill as what he has worked on and seen all sorts of troubles with and hates to work on~I did not belive him~These engines are bullet proof works of art~I love dealy~I'm not insalting you~But my 81 I cannot depend on it to drive accross town of 1000 people~And the beautiful stock 82 heratage Specail~I have so much time and money wrapped up into that bike I can't aford to sell it~I don't have to worry bout that anyway as it runs for 1/2 a second at a time~The new ones run GREAT untill they don't~No warning either~With more electronics then the space shuttel on em they should have a flashing big red dash light~"T minus 5 seconds till melt down" Sorry bad humor~But it's hard to keep a smile when (I've spent full time I get up working at 3am till 10pm I never stop)~These when I should be working on somthing else~I work out of my home and all my time is taken up on these 2 bikes that should have been done weeks(If not months) ago~I have no paicence left for these 2 I wish I had a better story for you~Been beating my head against the wall~I will be taking my 77 to go get more parts for the 81 this morning~I've modifyed the 77 from the pipes to the seats just about everything has been tamperd with~It ignores everything done~Rus the exact same~Every day~I ride though the winter when the snow is not to deep to dump the bike~Not a lick of trouble ever~No fuse going out~I change the oil and fill it with gas~Thats all I'm not even close to kidding~Sorry to say my Pro builder buddy Dave Roth was right on the money~I have a 70 a 72 and a 75~I can't wait to play with those they should be more rewarding than my 77 and 78~Which at this piont I think would be impossible~I'll see~I love these bikes