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Just Bought My 1980 XJ650 Maxim and have questions

Discussion in 'XJ Technical Chat' started by DFinchy23, Apr 18, 2023.

  1. DFinchy23

    DFinchy23 New Member

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    I recently bought a 1980 Yamaha XJ650 Maxim. Seems to be in ok condition. Changing out the starter solenoid and battery. Was able to get it to start up with the help of a battery charger on jump start mode but the solenoid would click until I stopped and tried again until it would actually try and turn over. First question is about the battery. I currently have a conventional battery because that’s just what came with it. If I switch to an AGM battery will the rectifier ruin it unless I purchase a new one or will it work just fine?
    Second question is to do with the carburetor. The guy I bought it from messed with it a bit. Said #1 and #4 are getting too much fuel and #2 and #3 are not enough. I was planning on disassembling the carb and maybe rebuilding each one with new parts. Any good places to get parts for them? And is it tricky to get them all tuned back properly? I’m not too familiar with carburetors. Any help is appreciated
     
  2. jag3

    jag3 Member

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    A lot of people get their parts from Len at info@xj4ever.com. He carries everything for these bikes and I just got a new fusebox and rear brake switch. I've also purchased many other parts from him. There's a link at the top right to the catalog of parts, arranged very well. You can email him and he'll help out with the parts you need. He ships quick and is great to work with. As with the other questions, sorry I can't help there. For the carbs everyone says read in the church of clean before rebuilding them.
     
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  3. jayrodoh

    jayrodoh YimYam Premium Member

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    AGM battery will work fine with stock electronics.
     
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  4. Melnic

    Melnic Active Member

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    I would evaluate where you are before changing the carb jets.
    Will it idle? If you ride it for 30 minutes, what do the plugs look like?
    There is a LOT of reading you will want to do from various sources including what you read here.
    If you pull the carb apart a couple suggestions.
    Get a JIS *2 bit for your driver. they are NOT Phillips heads.

    For my first carb, someone changed the jets slightly and I changed them back.
    My bike was not running and I had to totally break mine down part by part, cleaning and replacing a few jets.
    Nearly everything in the carb is resuable (if jets are what you want) except for the following (IMO)
    Float needle
    float bowl gasket
    Butterfly valve seals (these are special and NOT o Rings)
    O rings for the fuel tubing between carbs (I used Viton o rings from Harbor freight)

    Read about syncing carbs both bench and using vacuum gauges

    Read about testing vacuum leaks on the intake boots (between head and carbs)

    Read about testing function of the petcock.

    Read about setting float levels and doing a wet level

    Read about measuring and swapping valve shims

    Read about "church of clean" and watch the Mezzmo engineering videos on carb on youtube.

    Good luck
     
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  5. DFinchy23

    DFinchy23 New Member

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    I haven’t rode it yet. Trying to get it to run consistently first. Will run for a few seconds then die which is why I was wondering about the carburetor.
     
  6. DFinchy23

    DFinchy23 New Member

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    Thank you. Much appreciated
     
  7. DFinchy23

    DFinchy23 New Member

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    UPDATE: Installed new battery and solenoid. Bike tries to start up no problem. But now it won’t start and every 5 seconds or so I’ll get a pop from the exhaust and it also smells like fuel. So now I’m assuming the engine is being flooded with too much fuel to start? What does this mean?
     
  8. Timbox

    Timbox Well-Known Member

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    You have to clean them carbs and the enrichment ckt in the float bowl. https://xjbikes.com/forums/threads/in-the-church-of-clean.14692/ Read through that and then take your timing doing a good job.

    Sometimes when you get a good used bike it wants to run the first time you put gas to it. Then later on the next day it just does not want to do anything or pops and really is frustrating. I have found that the old gas in the carbs the first time around lets the bike start or even run a little. But when that new gas sits over night it turns the old hard stuff in the carbs into gel and then all the jets and other passages get plugged.
     
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  9. Melnic

    Melnic Active Member

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    As an example, My bike would not idle but would run a few seconds with carb start sprayed into the carbs.
    My friend who sold me the bike pulled the carbs before giving it to me.
    Things that kept my bike from running were:
    Faulty Petcock, petcock filter stacks fell off allowing crud into the carbs.
    All 4 carb filters were clogged up pretty good (the ones on the inside of the float bowl needle that you can only see by pulling carbs apart, and removing the float needle valve/housing.
    All 4 fuel enrichment channels in the float bowl cover were clogged.
    Multiple internal passages in most of the carbs were clogged.
    Float needles were cracked/damaged.

    Bike would run after I rebuilt the carb and replaced ALL RUBBER/GASKET parts including fuel line and replaced the petcock.
    It ran better after I:
    Adjusted/replaced/shuffled around valve shims to being back to spec
    Synced the carbs
    Replaced plugs

    I did NOT have to replace my boots, neither the boots between carb and head, nor carb and airbox. I consider myself lucky.

    In addition to the carb rebuild as already mentioned by several, I totally believe any garage/bar find should have tank drained and petcock inspected
     
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  10. DFinchy23

    DFinchy23 New Member

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    So basically I need to pull the carbs off and disassemble them and then give them a good cleaning? Also noted yesterday when I pulled the spark plugs, they all had black residue on them meaning a heavy fuel mixture correct? I plan on replacing them and cleaning the carbs. Little nervous just due to no experience with carbs and all. Just want to make sure it all goes back correct. Any info or videos on how to tune them up and how many turns you need on the needles or jets? Sounds pretty stupid but just want to make sure I get it right the first time
     
  11. Fuller56

    Fuller56 Well-Known Member

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    @DFinchy23 , as was stated above, check out this thread https://xjbikes.com/forums/threads/in-the-church-of-clean.14692/
    These are pretty basic carburetors and a great introduction to cleaning, rebuilding, rehabilitating carbs. They do demand you pay attention to detail and do it well but are not difficult if you do. A couple of good tips to make it easier, get a JIS screwdriver, Vessel sells them on line, Chacal has them also. JIS screw drivers fit the Japanese screws so much better where as phillips screw drivers do not and will ruin your carb screws, especially the little ones that hold the throttle plates in. Also hit a dollar store and get some sort of trays or bins to separate all your bits and pieces of the individual carbs so you can keep track of them and back in their original homes. If you still think you are over your head start a conversation with @hogfiddles about sending him your carb rack. He does an EXCELLENT job, you can put them back on and be 99% of the way done. Whatever other issues your bike has you can be confident the issue is not the carburetors.
    Good luck, and mostly....HAVE FUN!

    John
     
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  12. Melnic

    Melnic Active Member

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    Spark plugs, Keep in mind that you don't know how the bike was run to get them black. When I got the bike, before I ran it, I thought plugs did not look too bad. When I was doing the work on the carbs, I was doing a LOT of idling. My plugs turned pretty black showing it was rich. I purposefully kept my idle on the rich side. I changed the plugs and they stayed black as I continued to work on it and idle a lot. But now that I ride the bike, I have pulled my plugs once a week as the weather has been changing and they are just fine. Now that its warmer, I have thought about re adjusting my idle mixture screws and maybe doing a synchro, but you know what, bike is running fine so I'm just leaving it alone for now cause I have other bike projects.

    BTW, don't get resistive plugs if you can help it unless you are going to change out the plug caps to non resistive.
     
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  13. DFinchy23

    DFinchy23 New Member

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    What does resistive plugs and non resistive mean? And what does running a hotter or colder spark plug mean? Is it a big enough deal to know the difference and pick one or the other or will any work?
     
  14. Melnic

    Melnic Active Member

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    My bike had NGK BP7ES (non resistive). I had tried BPR7ES (resistive) and they ran for a while then one plug failed on me. Its resistance climbed 1K and that cylinder stopped firing.

    I found some new ones on ebay. I ordered twice on Amazon and they shipped resistive plugs.
    the coil,wire,cap plug has a resistance spec and if you exceed the total, it can cause problems I understand. I am not fully versed on all of that but can just relay my experience. I know others will suggest changing the resistive caps to non resistive as a better solution then buying the more available resistive plugs.
    For you, you might think about just brushing the plugs clean for now until you get it running before spending more $.
     
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  15. DFinchy23

    DFinchy23 New Member

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    Where are the coil, wire, and cap located at exactly? And I have BP7es on all 4
     

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  16. DFinchy23

    DFinchy23 New Member

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    Any good people or places to get a full carb rebuild kit from? I’m going to change all 4 out. I found a jet or something under the seat in the little storage area from previous owner so I’m just going to change them all. No idea what was done.
     
  17. Franz

    Franz Well-Known Member

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  18. Fuller56

    Fuller56 Well-Known Member

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    as above, start a conversation with Dave Fox, aka, Hogfiddles. He does an awesome job with carburetors. "Conversations" here are the private message areas of this forum. Or as @Franz says Len Chacal at XJ4EVER has the parts you need to make your XJ as new and is the best guy to do business with you will ever run across.
     
  19. Melnic

    Melnic Active Member

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    Just keep in mind that Jets can get expensive if you are doing all of them, we are talking 2 fuel jets and 2 air jets per carb. That's 16 total.
    I would suggest you not buy anything till you pull the carbs apart and look at what you have.
    Nearly everything brass can be cleaned and re used.
    You may run into a part that is really hard to remove (like a jet) and you will be deciding to remove it or break it (and not the aluminum casting) to remove it then replace it.

    I would caution the notion that one can just "buy all that is needed" and then do the work in one weekend.
    I have only rebuilt 2 XJ650 carbs so my experience is limited but reading so much before I did it told me that you never know what your going to see when you open those up.
    first carb, the diaphragms were fine, 2nd one I needed to replace 2 so I replaced all 4.
    First carb I replaced 4 jets cause what was there was not stock for my bike. 2nd carb everything was perfect.
     
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  20. DFinchy23

    DFinchy23 New Member

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    UPDATE: Removed the carburetors and cleaned each of them. Found out the floats were all off and the first float would sink and completely flood the carb. Cleaned em all up and synced them all up. Replaced the petcock, fuel lines and fuel filter. Got it up and running fairly smooth. Took it for a test ride and did pretty good. Going to change the oil and oil filter next. What type of oil is best for these older bikes? And how about brake fluid? I’m planning on replacing the brake lines and fluid. I’ve been hearing something about the rear brake seats or something locking up from age?
     

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