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*****Help with 82 xj750*****

Discussion in 'XJ Technical Chat' started by Codysc843, Mar 16, 2020.

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  1. Codysc843

    Codysc843 Member

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    So I got a 1982 xj750 basically out the scrap pile there's a few wires behind the headlight bucket that have broke ends mismatched colors etc but I put a new battery in it cleaned the 4carbs cut the airbox out with a sawzall etc the whole time after I wired the 4ignition wires (cause key was lost) the headlight always worked I got it running but when kicked in 1st gear itd automatically shut off I kept tinkering a couple hours here there and got it to ease out with the clutch handle while running went to test drive around neighborhood and it was sucking too much air so I shut it off tinkered the idle mixture screw went to drive off it fired up but is back to shutting off in gear also the headlight will not cut on now at all the bike will fire up but no headlight no drive this thing is really aggravating also temporarily until I can get to Walmart and get a couple inline fuse holders I took the glass style fuses out tied and taped each of the wires together at least to drive it around once and park it until I'm able to replace fuses my question is how the hell can I get the headlight working and this thing rolling in gear instead of shutting off I'm confused it worked I shut it off 5 min later it's all f***ed up any ideas? I've read something about a inline fuse near the airbox but I haven't seen one
     
  2. Codysc843

    Codysc843 Member

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    Also relay under left side cover is 4u800 omron and near 4carbs is 4h701 omron I think these might need replacing idk what exactly they control or how to bypass to see if it fixes it
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    your sidestand switch is dirty pull the 4u800 relay to test

    other is starter safety relay remove and jump red/white striped wires together

    is this a Maxim? if so the headlight will turn on with key the starter button is the headlight connection when not pushed.

    look on bottom of ignition switch you will find the key code and can have a key cut for 10$
     
  4. Codysc843

    Codysc843 Member

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  5. Codysc843

    Codysc843 Member

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    Headlight won't turn on at all now it used to as soon as I twisted 4ignition wires together how about when I put it in gear from running in neutral it shuts off
     
  6. jayrodoh

    jayrodoh YimYam Premium Member

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    If the headlight came on when you twisted the wires together then someone has modified the factory wiring. When new, the headlight would come on after starting the bike, this was designed by Yamaha to reserve battery power for starting. These bikes are are known to be a no start if you do not have full or near full voltage when cranking. If it used to work and does not now check the basics - Fuse, move switch back and forth from hi beam to low beam, bulb may have burnt out. Since it is modified the factory troubleshooting methods will not work and you'll have to do some digging.

    @XJ550H Hit on this too. These bikes have a safety system to prevent you from taking off with your sidestand down etc. Most commonly the switch on the stand gets dirty/gummed up and the bike "thinks" the stand is down and shuts down when you take it out of neutral. The service manual has a good section on troubleshooting this circuit as there are many components (side stand switch, neutral switch, clutch switch, diode pack). You can just pull the replay to defeat the safety but ride at your own risk if you do.
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    If he has a Maxim 750 the headlight comes on with key as the 750 maxims have no headlight relay. check your headlight fuse.
    starter switch runs headlight it may be dirty it is the wired in connection so that headlight goes off when starting


    if your wires are gone in headlight bucket check clutch lever for the switch and see if it is there and plugged in . if you are missing your clutch safety switch bike will not start except in neutral unless connector in bucket has been jumpered.

    pull the sidestand relay ID above to bypass sidestand switch

    your other relay is working if you can start the bike.

    the sidestand is a second way to shut bike down when in gear it is a safety feature.
     
  8. jayrodoh

    jayrodoh YimYam Premium Member

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    My mistake, thank you. Forgot some had the starter button interrupt for the headlight.
     
  9. Codysc843

    Codysc843 Member

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    So now there's the problem of not firing up plugs got fire but won't vroom even with starting fluid I had this bike firing every time headlight worked etc how this just blam don't work is weird as f*** so the other day start button wouldn't work I jumped 4h701 red/white stripe wires and unplugged 4u800 start button works got little fire to the plugs (I put screwdriver in plug wire and shocked me a little) any suggestions yall?? My next attempt will be charging the battery I'm thinking possibly it's not turning over fast enough to fire up?
     
  10. Codysc843

    Codysc843 Member

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    Anybody got suggestions?
     
  11. jayrodoh

    jayrodoh YimYam Premium Member

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    Yes. Even my painstakingly restored XJ won't start without a fully charged battery.

    I think your expectations for a bike that you got "basically out the scrap pile" and has some twisted wires etc. are pretty high. We've seen some pretty trashed bikes brought back to life, and there is a ton of knowledge on here but without some patience and a methodical approach you'll just end up frustrated with a bike that still doesn't work.

    On your bike I would:
    • Charge your battery
    • Go through all the electrical connections and make sure they are tight and clean
    • Clean/lube the sidestand swtich unless you plan to leave that relay out
    • Fix/replace the shoddy fusebox
    • Check/replace your plugs (might be fouled up now and that can prevent startup)
    • Find a new airbox, you'll be sorry you cut that out when you do get to ride this
     
  12. Timbox

    Timbox Well-Known Member

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    The carbs on these bikes are designed to work with that airbox. You can make it work without an airbox and pods but it will take more tuning then maybe you want to do. Without some pics to a link to some pics we can't really determine what you are working with. If it was in a junk pile do you even now if it has a title or you can even get one? Is the frame straight and the bike was never in an accident. Forks are not bent or for sure they are straight?

    Okay now that reality was talked about lets talk about the dream. If you want to cut this bike up and make it look cool that is fine, it is your bike and you should be able to do with it what you want. There are plenty of project bikes that have been turned into bobbers and cafe style bikes in this forum. You will have to do a little searching to find them but they are there.

    The above advice is just the basics to make sure this bike is able to run. Please take the time to do those things to give you a head start on a positive project. If you don't do those things you will be chasing gremlins for a long time.

    What does the inside of the gas tank look like. I hope yo are using an alternate gas tank to run gas to the bike. Even if you cleaned the carbs a little and then ran nasty tank gas back into them the work you did on the carbs is likely ruined. Take your time and do it right the first time, enjoy the process and enjoy your accomplishments in doing the work. Lots of people here will help you, just give us good details on what you are trying to fix.
     
  13. Codysc843

    Codysc843 Member

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    I'm giving all the details bud. Yes it came out the junk pile but I had it running and driving then encountered all these issues don't think it's been wrecked don't look bent I plan on riding to the dmv when I get it going enough that I don't think it'll break down, I am most likely going to get it going and sold for something better I've got $200 and a battery invested this far all that being said I've been told if battery drops below a certain voltage it won't crank so I'm going to charge it and tinker later tomorrow but as for air box I tried unbolting it got pissed off cut it out with a sawzall I've read online airpods require taping almost all the way through I'm thinking a DIY airbox 1/3 the side of the stock one so that I can pull it off without tearing the bike apart other than that anybody got suggestions to drive this thing around the block without it sucking too much air and shutting off
     
  14. XJ550H

    XJ550H Well-Known Member Premium Member

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    it will run with pods ok for running around the block as it is but you will have trouble at higher speeds with it stumbling and bogging . rejetting will likely give you a top end of 80mph with little performance in the power band. taping the pods no, a better idea would be a beercan sleave inside the pods to make the air come down the tube it creates. it would be like a velocity stack.

    the real concern about pods is running so lean you hole a piston, a stiff side wind will suck the air away from pods and of course the rain issue
     
  15. Codysc843

    Codysc843 Member

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    Well I taped the intake boots themselves off completely on one end of each then cut a hole in each about the size of a dime that's when the bike worked and I was gonna test drive it I kicked it in gear eased the clutch out and it sounded like it was sucking too much air about to shut off that's when I shut it off adjusted the mixture screw and tried to crank it again then all the issues occured it did fire back up but would shut off on gear I've jumped two red white wires in 4h701 relay and disconnected 4u800 relay shot starting fluid in all 4carbs nothing covered 2 carbs tried it nothing covered all 4carbs with rags and shot starting fluid nothing I'm guessing the battery needs charge and it's got 6v on it now I'll try again in the a.m my guess was it ain't turning over fast enough idk it was running what exactly caused all these errors with the bike I've got no idea. But if it does fire up tomorrow I've gotta figure out the air intake issue I'm thinking tape the ends of the boots poke one small pinhole in each and see what happens just to spin around the block then eventually a DIY airbox about 2.5 inch wide and long enough to connect all 4carb boots with a hose off the bottom to draw air
     
  16. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    How many sentences are in that??? I see one really long run-on sentence, and one not-quite-as-long incomplete one. I’m not gonna try and punctuate it myself. Re-do it, then we’ll read it.
     
    kosel and Timbox like this.
  17. Codysc843

    Codysc843 Member

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    I ain't into internet arguments so I'm just gonna ignore that slick comment.. anyways

    Update on the bike its firing up when I spray starting fluid in the carbs and have a couple covered with a rag but wouldn't stay running just fire up while holding the button I'll be finishing my diy airbox today and see if that fixes the issue considering it is most likely air intake that's the problem.
     
  18. Huntchuks

    Huntchuks Member

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    Your battery was on charge and had only 6V at the time? A battery should never have that kind of low voltage, usually means it is toast and won't hold a charge and will drop too much voltage when a load is put on it (starter).
     
  19. kosel

    kosel Active Member Premium Member

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    "So the bike ran at the push of the button then after it messed up etc I bypassed 4h701 4u800 relays bike sprayed carb cleaner in the jets (without unscrewing them) charged the battery replaced the bolts in the terminals now it will turn over great but not fire up it sounds like it almost wants to catch then nothing then backfires any ideas on how to fix? I even pieced together the airbox and put it back on sprayed starting fluid nothing but backfire y'all help me out"

    I copied the above from your other thread to keep everything in one place. Keep posting here, so people can follow the work you've done.

    These bikes have some finicky parts and you'll need to be patient and methodical in your approach. There is a wealth of information here and more helpful people than any other forum I belong to. But,everyone here volunteers their time and knowledge and may already have answered your question in another thread. Doing some reading and research shows how much you appreciate and respect their contributions. With the sermon over...

    Search this site for minimum wiring diagram and make sure you have everything wired up that you need.

    Then, search for 'church of clean' so you can do your carbs the right way. You can't go wrong starting with taking your carbs to church with an XJ.
     

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