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XJ750 Running fine but general issues.

Discussion in 'XJ Technical Chat' started by Maxwell Partridge, Jun 24, 2019.

  1. Maxwell Partridge

    Maxwell Partridge New Member

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    Hello, first off I just purchased a 1982 Yamaha Maxim 750, I've just did alot of general maintenance on it such as: Fresh oil and filter, brand new air filter, brand new spark plugs, tore apart the carbs and cleaned them best I could with carb cleaner and compressed air, fresh gear oil in the final drive (don't know how to access the front side of the drive-shaft to change the gear oil if there is any there), and washed the bike.

    My general issues I've been having and hoping to seek assistance on are as following: Bike MPG is 27 and when at idle I can faintly smell gasoline while sitting on the bike which makes me think it it overly rich, when starting from a dead stop the bike bogs immensely and acts like it's having serious fuel issues and loses nearly all power unless the bike has been properly warmed up and ridden for Abit already. If not you need to hold the bike at 3k rpm while starting to be able to go without issues, the bike doesn't want to start when cold unless you use starter fluid to get it warmed up first, and finally the starter grinds really loudly and doesn't turn the bike over when attempting to start it but I think the starter just needs to be replaced.
     
  2. Timbox

    Timbox Well-Known Member

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    Welcome to the site! I think you need to take a look at those carbs...If the bike has been sitting for a long time not being run, the carbs are need need of some TLC.
    https://www.xjbikes.com/forums/threads/in-the-church-of-clean.14692/
    That is the link of how to do the carbs the correct way. There are no short cuts go getting these carbs to work okay and think that will work. They need proper care and respect when you have them off the bike.

    As for the starer, I hope you are right. I think some of the 750's has started issues but I have been lucky so far. I would guess another informed member will be along in a bit to help you with that.

    Congrads on the bike, looking forward to more of you posts on getting her running the way you want her.
     
  3. Maxwell Partridge

    Maxwell Partridge New Member

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    Well the thing is too @Timbox , The person I bought it from gave me an extra set of carbs with it, but they look different. So I don't know if their the carbs that were supposed to originally come with the bike or if the ones on it now are the originals. Even if they are different shouldn't adjusting the duel-air mixture allow me to run them anyways if their not the original carbs?
     
  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    1. I agree that the carbs need to be pulled and properly cleaned.

    2. The starter motor should be rebuilt, not replaced. Parts (for darned-near everything) are available from @chacal
    Replacing your starter motor brushes w/ pics
    The battery must be in top-shape, and the switches and relays in the starter system must also be in good condition so the starter can spin as fast as intended, or the starter clutch will slip.
    The charging system should be checked as well, just to make sure the battery stays charged properly.

    3. Having said that, the most common cause for the starter clutch to slip is having the wrong oil in the bike. Choosing Oil for a Wet Clutch Motorcycle
    What oil did you use?

    4. The engine is of unit construction, so the transmission and engine share oil. There is no seperate gear oil, aside from the final drive.

    5. Read This First
     
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  5. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    You need the correct carbs for the engine. There are ways around that, but simply adjusting the idle mixture will not make the bike run correctly unless the carbs have the correct airflow rate (which is a function of the size of the inlet) and jetting.

    Carb identification can be a bit tricky because Hitachi didn't mark them very well, and some of the parts used to identify them can be swapped.
    The best way is to look for the Hitachi logo on the carb bodies, and note which main, and pilot jets are installed.
    Hitachi logo:
    [​IMG]

    You might also look on the bottoms of the float bowls. They were ink-stamped at the factory, and sometimes the ink is still legible.

    At your 6th post you can link pics. Post a few more times and then put up pics of both carb racks so we can help you identify them.
     
  6. Maxwell Partridge

    Maxwell Partridge New Member

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    Alright I'm at work right now, I work night shift 13 hour shifts, I'll post pics and such tomorrow. Thanks for the information so far everyone!
     
  7. tradmedic

    tradmedic New Member

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    I don't have a 750, I'm sure someone will come along with more machine specific knowledge, this is a great place for that.

    I'll second the church of clean write up. I've not suffered the worst of it, but there are all kinds of posts here of mystery issues that resolved when somebody finally gave in and took their carbs to church, properly. If you haven't come across it yet, the Information Overload post is a fantastic bit of reading. It'll help get you up to speed on just how to care for your new, vintage bike.

    Also someone will mention, at some point, don't forget to check your shims, as well as your brake line and tire date codes.
     
  8. Maxwell Partridge

    Maxwell Partridge New Member

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    Okay, now that I'm on a computer instead of my phone I can reply to afew things. I already cleaned the carbs best I could with carb cleaner and compressed air, I've worked on carbs before in the sense of cleaning and adjusting them but I have never actually known when I needed to change jet sizes and such, I just took the starter off and am planning on either just taking it apart and trying to clean it up best I can and lubricate it, or buying the rebuild kit to do it properly with. The battery I know is good because it's the same battery that came off my sports bike, he didn't sell it to me with a battery. Also something else I guess I should just throw in here till I hit the "6 posts to be able to post images" is that the dash has all the warning lights on, like every single one. It's warning me about anything from the headlight all the way to the oil pressure which cannot possible be correct so I think the master warning fuse or something in the dash is blown, the gas indicator works though, that's a plus. One of my neighbors who is an elderly mechanic says he can hear it not firing properly on one of the cylinders, and I should take a laser thermometer and see which piston is running cold by checking the exhaust. The bike sounds like it is running fine to me, if not it does have a small short hiccup every now and again where it feels like a single cylinder isn't outputting the right power so I believe him. Once I get to 6 posts I'll send pics of both carbs onto this thread.
     
  9. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    The warning lights won't come on at all if the fuse for them is blown.

    More likely the systems monitor isn't hooked up properly, or the things that the system monitor looks at aren't hooked up. The oil level float (there is no check for oil pressure) can be sitcky from sludge and cause a low oil fault to be shown. the remedy for that is to run a dose of Seafoam in the sump until the next oil change.

    It does a self-check when you start the bike, and the only thing that should remain on is the LCD for the sidestand being down and the fuel gauge.
    SInce you're not using the orignal-type battery the systems monitor will throw a battery fault (because the battery acid level sensor is not hooked up). There is a simple workaround for that which will let you use a SLA battery and still be able to monitor the battery health.
    Pay attention toe Rooster's first post in the thread, as the resistor value is what allows the systems monitor to throw a warning if the battery voltage gets low.
    http://xjbikes.com/forums/threads/battery-sensor-we-dont-need-no-stinkin-battery-sensor.820/


    If you press the warning control button the big flashing red light will shut off for around 15 minutes.
     
    Last edited: Jun 25, 2019
  10. Maxwell Partridge

    Maxwell Partridge New Member

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    Well about the gauge assembly, it dosn't blink it's just a solid red and light, and the two buttons on it don't do anything. I have another gauge assembly for it but it's in like 80 bajillion pieces because the guy before me was trying to put brighter lights in it, but ruined it in the process. Does anyone have a wiring diagram for the Yamaha Maxim 750? I figured I was just gonna buy another universal head unit for it (one compatible with analogue Tachometer) and wire it in if I could find a diagram.
     
  11. Maxwell Partridge

    Maxwell Partridge New Member

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    [​IMG]

    This is her by the way, really clean looking for a 30+ year old bike.
     
  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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  13. raskal

    raskal Member

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    I'm curious about this bike and am hoping K-Moe can shed some light

    I have an '82 Maxim 750 same as Maxwell's but our gauges are very different.
    Was this a Canadian vs American thing?

    here is my cluster

    maxim.PNG
     
  14. XJ550H

    XJ550H Well-Known Member Premium Member

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    Raskel My XJ750j Maxim has the same cluster as yours. lights on the bottom.
    I suspect that Maxwell may have a seca set up for a cluster
     
  15. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Maxwell has Seca gauges on his bike in the picure from his last post.

    Which I didn't even think about, or notice before.

    @Maxwell Partridge
    The Seca gauges are not wired the same as the maxim gauges, and that's why yours don't work.

    This thread will be of more use than the one I provided earlier, unless you go ahead with fiting non-OEM gauges.
    Maxim gauges instead of Seca's? I have the answer for you!
    The swap is the reverse of what you need, but you should be able to work that out unless you have a set of Maxim gauges to install.
     
  16. raskal

    raskal Member

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    Is his bike actually a Seca and not a Maxim? I don't know what the defining characteristics are

    looking at other pics, the tank on the Seca has indents whereas the Maxim is smooth
     
  17. XJ550H

    XJ550H Well-Known Member Premium Member

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    this is photo from owners manual upload_2019-6-26_17-54-39.png light, s on the bottom and my service manual shows the same thing. the 82 and 83 maxims are a very unique bike as it does not share a few parts with the seca 750. no headlight relay, controls are just for the maxim 750 but are the same as the xj1100
     
  18. XJ550H

    XJ550H Well-Known Member Premium Member

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    his is a maxim just wrong cluster.
    maxim has a fat style tank and sidecovers are a triangle style made from aluminium and plastic trim
     
  19. Rooster53

    Rooster53 Well-Known Member Premium Member

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    That indicates that the CMS (Computer Monitoring System) is stuck in the standby state. The CMS does not become active until the bike is started and one leg of the AC generator supplies power to the CMS to enable the system. Odds are either the charging system is not working or the white wire from the AC Generator to the CMS is open. The check and warning reset switches will do nothing until the CMS becomes active.

    This is a good indication that the CMS is properly powered and should function.

    I believe you should be able to install the Seca gauges on the Maxim and have full function. Conversely, the Maxim gauges on the Seca will not work unless a ground is added to the 9 pin connector as the Maxim uses a separate ground connection for the CMS at the 9 pin connector.
     
  20. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    One easy telltale: The Maxim has the alimunim 'square' handlebars. The Seca has plastic covered round bars, and the brake master cylinder is not located on the bars.

    Another is the shape of the gas tank, and the lack of a rear cowling behind the seat on the Maxim. The Maxim also has chromed fenders, where the Seca has a body-paint colored front and a semi-hidden plastic rear.

    There's at least a dozen other small differences that are easy to spot once you know what they are.
     
    Last edited: Jun 27, 2019
    raskal likes this.

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