1. Some members were not receiving emails sent from XJbikes.com. For example: "Forgot your password?" function to reset your password would not send email to some members. I believe this has been resolved now. Please use "Contact Us" form (see page footer link) if you still have email issues. SnoSheriff

    Hello Guest. You have limited privileges and you can't "SEARCH" the forums. Please "Log In" or "Sign Up" for additional functionality. Click HERE to proceed.

rough idle, slow shut off.

Discussion in 'XJ Technical Chat' started by hornet, Dec 4, 2006.

  1. hornet

    hornet New Member

    Messages:
    4
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Lincoln, England
    hi, guys, requiring assistance with possible carb problem, Recently aquired a 1982 xj750 seca ?, bike run like a pig when i first got it, replaced plugs, ht caps, trimmed leads, replaced fuse box, cleaned every connector on the bike, still no better, removed and cleaned carbs with cleaner and air line, no better. removed carbs again, on closer inspection, i noticed that the pilot jets were three different types, with only two being actual jets, the other two were just headless bolts with a hole drilled in them. replaced the pilot jets for the correct type as listed in the manual, bike started ok, but ran really rich. adjusted mixture screws down so as bike was at least rideable and had plenty of power and didnt black smoke, but i now have a problem were i have a very lumpy tickover, unless you hold the throttle at about 1500 rpm, and also the annoying fact that the throttle doesnt shut off fast enough, so when you change gear the revs shoot up to about 3500-4000 rpm, also the revs stay high when you are slowing for a junction etc, unless the hold the engine back with the clutch, and then eventually the revs die down.
    any ideas as to what the problem might be, as i getting fed up with taking it to pieces every other night.
    p.s sorry for waffling on my first post
    cheers, Hornet
     
  2. WeAreZilla

    WeAreZilla Member

    Messages:
    233
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Yellow Submarine
    Welcome to XJBikes hornet.

    I'm assuming you've had the carb rack off the bike, since you've replaced jets. And possibly dismantled and reassembled the carbs further. Our bikes tend to be a bit finicky concerning the carb adjustments, and is really best to properly adjust the mixture screws and synchronize the carbs.

    You can adjust the mixture screws well with a ColorTune plug. And synchronizing is best done with a four-gauge vacuum set - and with the YICS tool if your bike is so equipped.

    You will be surprised at the difference in performance with only minor adjustments in these settings. If you need more advise on these settings don't hesitate to ask.

    Z
     
  3. hornet

    hornet New Member

    Messages:
    4
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Lincoln, England
    hi, thanks for reply, engine is the yics type and i have had carbs off bike and cleaned on bench, currently running .40 on pilots and .120 on mains, but i didnt realise until reading a few more posts that the bike doesnt have a standard exhaust system, as its fitted with a motad 4-1 system, will this effect the running of the bike.
    cheers, Hornet
     
  4. OU812didntU

    OU812didntU Member

    Messages:
    157
    Likes Received:
    1
    Trophy Points:
    16
    i think so....i know theres a few post in here that deal with the adjustments to the carbs when you dont run a stock exhaust, do a seach and see what you can come up with.... i think you have to go up in size but dont quote me on that.

    you can buy a carbtune ll from morgan to sync your carbs and also you can pick up a colortune from them to set the mixture, like Z says you`ll notice a big diff.

    www.carbtune.com
     
  5. WeAreZilla

    WeAreZilla Member

    Messages:
    233
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Yellow Submarine
    Our bikes were so finely tuned/set-up from the factory that little changes in settings makes a big difference in performance. And big changes in gear, for example air filter pods or exhaust, can be disastrous. I have read very few success stories in changing this gear; indeed several have regretted the choice to make these changes and wish their old equipment was back on the bike.

    In your situation though, you have to work with what you have. There is a strong possibility that the tune up I suggested will get you right again. There may be someone close to you who has the tools noted. Or if you are so inclined, you may order the tools from the link in OU812's post. I believe it is the only place to buy the ColorTune plug and CarbTune vacuum gauges.

    Of course you could also pay a shop to do the work for you, but we encourage everyone to DIY whenever possible. You'll know the job is right, you won't be overcharged for the work, you'll have the tools again for future use (if you buy them), and you can take pride in the effort.

    If all else fails, and it comes down to changing the jet sizes, you will do best by getting with someone who's done this work before and has had experience and success with a similar situation. I believe it's a fair bit of guesswork to get the jet sizes right.

    Z
     
  6. Nick

    Nick Member

    Messages:
    969
    Likes Received:
    3
    Trophy Points:
    18
    Location:
    Vernon, BC Canada
    Welcome to the site hornet.

    These bikes also have a problem with the seals on the butterfly shafts drying out/cracking and causing air leaks and runaway throttle symptoms.
     
  7. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

    Messages:
    9,170
    Likes Received:
    1,977
    Trophy Points:
    113
    Location:
    The room where it happened
    And the bike revving between gear changes and refusing to come back to idle quickly can be traced to slide pistons that are sticking. The often-imitated but never-equaled RickCoMatic has a fine write-up on this subject which you can review and revel in at:

    http://www.xjbikes.com/Forums/viewtopic ... ction.html

    My ugly first-time experience with these bikes has leaarned me a lesson: get your carbs clean, Really Clean, ZESTFULLY CLEAN, or you life will be miserable and you'll waste alot of time, effort, money, and alot of prime riding time if you don't get those carbs unbelievably, meticulously, next-to-Godliness clean.

    Good luck........

    P.S. Someone really needs to create an aftermarket bolt-on fuel-injection system for these bikes and get rid of these insane carbs...........
     
  8. hornet

    hornet New Member

    Messages:
    4
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Lincoln, England
    Thanks for info, guys, got myself a colortune £19 english, Bargain !!, guess its time to whip off the carbs and clean them out again, not forgetting the the slides, Thanks to chacal, " top link ". let you know how i get on later.
    Cheers, Hornet
     
  9. hornet

    hornet New Member

    Messages:
    4
    Likes Received:
    0
    Trophy Points:
    1
    Location:
    Lincoln, England
    Booo, Hisssss, having stripped carbs down to nothing, held slides up to the light, found two diaphragms with pinholes in, guess thats not going to help with it running smooth, can diaphragms be repaired or do you have to change the piston and diaphragm as an assembly ??
    cheers,
    Hornet.
     
  10. OU812didntU

    OU812didntU Member

    Messages:
    157
    Likes Received:
    1
    Trophy Points:
    16
    ive heard of people using some sort of rubber cement to fix the diaphrams, a bit on each side kinda thing but am not sure about that being a viable solution to the problem, allthough they said they didnt have any problems after doing that. I think the diaphram assembly to buy are a bit expensive if you can find them. And i seem to remember you being able to buy the diaphram seperate from the piston.
     
  11. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

    Messages:
    9,170
    Likes Received:
    1,977
    Trophy Points:
    113
    Location:
    The room where it happened
    Hey Hornet, I have some good used slides/diaphram units (yes, they have to be replaced as a unit, like Humpty Dumpty, IF you ever get them apart you'll never get them back together again........).

    I have some great used units off a XJ650 carb set, I believe they're the same as on the 750 carbs but maybe someone else will pitch in an verify for sure? Send me a PM if you're interested in them and we'll talk price......
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

    Messages:
    9,170
    Likes Received:
    1,977
    Trophy Points:
    113
    Location:
    The room where it happened
    Hey Hornet, I just checked the XJCD cross-ref and it shows that the XJ650 carb "diaphram assembly" interchanges with all XJ750's.....so they'll work!
     
  13. Nick

    Nick Member

    Messages:
    969
    Likes Received:
    3
    Trophy Points:
    18
    Location:
    Vernon, BC Canada
    You can check this company out.

    http://www.nrp-carbs.co.uk/yamaha_carbu ... hragms.htm

    This is a quote from their home page....

    We cover Mikuni, Keihin, Hitachi, Tokei and TK Kikaki carbs from 1970's to 00. Where as an original part the diaphragm is only available as a complete sealed unit, we offer a service where we refit a new diaphragm to your original slide. Where the original part can be improved to ensure long and trouble free service, this is incorporated into the design.
     
  14. shamus

    shamus Member

    Messages:
    131
    Likes Received:
    0
    Trophy Points:
    16
    has anyone tried using a MegaSquirt?
     
  15. WeAreZilla

    WeAreZilla Member

    Messages:
    233
    Likes Received:
    1
    Trophy Points:
    18
    Location:
    Yellow Submarine
    I'd be interested in a ready-made FI system too, but I'm not sure this one qualifies. From the MegaSquirt website:
    There's been lots of talk about modifying our bikes to FI, but I'm fairly certain it's never been done. My understanding is that FI is very complex, not only with all the additional hardware and sensors, but especially with the software mapping that makes it tick.

    And then I found this: Stan's XJ1100 Fuel Injection Project. It took an electrical engineer who works for NASA, seven months of evenings and weekends and almost $1000.00 to complete the conversion. But he says it works very well, and has improved his gas mileage. He provides excellent details on his site, linked above.

    I'd still be interested in a complete, purpose-made kit.
    Z
     

Share This Page