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'82 XJ750 Maxim revival

Discussion in 'XJ Technical Chat' started by Jeromey Green, Oct 23, 2019.

  1. Jeromey Green

    Jeromey Green New Member

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    Got my dad a 1982 XJ750 Maxim for free as a project for us. He wants a motorcycle but doesn't have the money for one and I had a friend with this just sitting and he wanted nothing for it. She's a tired old bike, that's for sure, according to the key chain it spent 15 years in the motorcycle training course. 43k on the odometer, leaking from basically every seal, and she's had some genius playing in the wiring in a couple of areas, but she was free. I've done the initial inspection, replaced the oils, oil filter, spark plugs, and air filter. She started and idled on starting fluid so it's time to start putting real effort and parts into her. I did a compression test and all cylinders have compression, it's a hair low but it was still in the acceptable range (from my general knowledge of motorcycles) the lowest one is 110 psi which while low could be due at least in part to the leaking upper head gasket/43000 miles worth of crap built up on the valves but we will see (that is the cylinder by the most visible leak in the upper head gasket). I replaced the fraying clutch cable and the cut off kickstand position sensor. I got a used one on eBay and tossed the tattered old boot, for now it has surgical tubing as a temporary boot to hold it together and keep it greased. I've pulled the carb rack and went to remove the hard and cracked boots from between the carbs and engine and sheared the first bolt head off, so I left them on for now, I'll remove them when I pull the engine for the upped end refresh. For the moment, the carbs are my issue and are what I'm going to do first because you know, one step at a time. Someone at some point broke one of the supports for the float in the middle right carb and tried to use a JB weld or epoxy to fix it. Came right off when I took the bowls off so I'm going to have a friend weld it together so that won't happen again, yippee. Does anyone know how well the cheap carb rebuild kits are, I'm going to buy a lot from XJ4ever but need to save money if possible. I'll need the throttle shaft seals, throttle blade bolts, and a metric ton of seals and hardware from them but if possible the kits that replace the needles, float valve, float valve seat, bowl gaskets, etc. seem like a good deal, if they work. (https://www.ebay.com/itm/Yamaha-XJ7...a=0&pg=2047675&_trksid=p2047675.c100005.m1851) anyone have experience with these?

    That's probably more than enough to post for now, I'll stop here.
     
  2. jayrodoh

    jayrodoh YimYam Premium Member

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    Welcome! Great story, once you and your dad are done with the bike you’ll have a good sorry and some bonding time. Most importantly, take your time and have fun.

    I’d steer clear of those eBay kits, the quality is usually crap and those include parts that you normally don’t need to replace like the jets and mixture screw. Chacal xj4ever has quality parts and you’ll never have to worry about fitment. That eBay set is per carb, once you buy four it adds up quickly.
     
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  3. Polock

    Polock Well-Known Member

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  4. Jeromey Green

    Jeromey Green New Member

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    I have taken them apart, I'm considering ordering the kits mostly for the gaskets, needles, and float valves? (don't know the proper name but they prevent the bowls from over filling). One of the needles won't come out for the venturi at all, I'm going to have to pull the venturi and put it in a vice (very carefully) and break the needle loose with lock jaws and penetrating fluid. Not sure how it got this impressively lodged. I had to pry all four of the slides out of the channels they sit in, not sure what happened to this poor bike, other than it sat. Are the diaphragms supposed to be smooth cones or do they come rippled from the factory? If they aren't supposed to be rippled does anyone know how well the JBM Industries diaphragms work (http://jbmindustries.com/HITACHI.html)?

    Sorry for incorrect terminology I'm self taught and have some names incorrect in my head.

    My ninja 250 is running great on one of those cheap kits I got on eBay though so they have that going for them.
     
    Last edited: Oct 26, 2019
  5. Jetfixer

    Jetfixer Well-Known Member

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    The diaphragms can dry out from sitting , you can try spraying them down with silicone spray lube , see my post on why you should replace butterfly seals, xj4ever has the correct seals , and replace the fuel rail O rings ...please note these are not a common O ring again xj4ever ...you DO NOT want these to leak after going through carbs , the ONLY WAY to clean carbs is to break the rack full tear down and soak I have a one gallon of Berrymans carb dip , put one body at a time for about half an hour each, then wash in hot soapy water and dry , reassemble with new seals, this is ONLY way to do carbs . Spray carb cleaner will not get into the small passages . One other thing the float bowl has the fuel enrichment jet ,soak the bowl , rod it out with .20 safety wire , try to use a can of spray cleaner with a nozzle point away from you spray both directions if it is clear you should get a spray pattern out of it. I rebuilt several sets of motorcycle carbs ,just take your time .
     
  6. Jeromey Green

    Jeromey Green New Member

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    The fuel rail o-rings is good to know, I forgot all about them. I definitely have to do the shaft seals and I'm upgrading the butterfly valve screws to Allen style bolts. The rack already has to come apart so I'll definitely soak everything I can. The diaphragms I'm looking to replace while I'm in there. So I wondered if any of you had experience with these aftermarket ones, they seem like they should work
     
  7. kerriskandiesinc

    kerriskandiesinc Active Member

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    I have a set of Chacals....XJ4Ever stainless allen head bolts, they are the proverbial dogs wotsits (they're good!)

    I must confess though, in the past I have used NRP-carbs.co.uk. and their excellent (proprietary) diaphragms....mainly because

    The owner Andy was my ex courier mate
    They are based in the UK....where I was, at the time

    I'm sure you'd be better trying XJ4ever first, certainly before possible 'Chinese' made Ebay ones.....
     
  8. Polock

    Polock Well-Known Member

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    i think they were smooth back in the day but i've never seen a set that were still smooth. they still seem to work fine with the "ripples" in them.
    there have been people on here that reported back that new ones from that place work fine too. if the ripples were a problem, i don't know what the symptoms would be?
    it might be a case of fixing something that's not broke
     
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  9. Jetfixer

    Jetfixer Well-Known Member

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    The rubber bits of the carbs are the butterfly seals 2 per carbs inboard and outboard and each fuel mixture screw is a small O ring you may to fish it out (ie back screw out may come out with screw but will probably be at bottom of bore) and the diaphragms of course . You mentioned the post of one carb was broke this is common , I had a carb body that was repaired the PO had drilled a pilot hole with music wire in both ends and JB weld on outside . This repair was solid and appeared to been done for awhile ago .
     
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  10. Jeromey Green

    Jeromey Green New Member

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    I wanted to replace them because my experiences with motorcycle carburators has been get rid of as many potential sources of error as you can before you start because trouble shooting is easier with less options for issues and they looked wrong. I had never seen the rippled diaphragms before but this is the oldest bike I've worked on with easily the oldest rubber components so it's no surprise that there were a couple of surprises. I definitely don't have the most experience so I'll look around and see what, if any, issues the ripples cause. If they don't cause any I'll leave the diaphragms alone because there are no other issues with them. The broken part of the carb had been epoxied/jb welded into place but came right off during disassembly so I'm going to have one of my friends who can weld aluminum weld it together for me for longevity, it seems like the most reliable fix.
     
  11. Ryengoth

    Ryengoth Active Member

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    Don't go cheap on any of the carb parts. K&L makes a quality kit for Mikuni gaskets, seat/needle, idle jet caps and o-rings for around $20 on eBay. You will not likely be able to weld that float post back on without it being off-plumb. It's brittle cast that's been soaked in oil. Be prepared to pick up a used carb body and make sure you get that specific carb body if you do. I picked up a use body for my #4 (someone broke the idle jet tube off trying to remove a seized jet) and somehow got a #3 so the outside fuel path is open, not plugged. I had to fab up a plug for it. The shaft seals need to be replaced, they will cause all kinds of tuning headaches if you don't. The toughest part is getting the butterfly screws out without the heads stripping.
     

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