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Engine/carb issue with xj650 maxim '82, please help

Discussion in 'XJ Technical Chat' started by Nick S, Mar 25, 2020.

  1. Nick S

    Nick S New Member

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    Hello, I got this bike about a year ago (summer of 2019) and have been working on and off (since I have to be at school during the spring and fall terms) whenever I get the chance. Since getting it there have been an array of issues, some of which have been dealt with, but the bike has never run properly. I've browsed these forums but have not been able to find a solution, so I'll describe the current issues I'm experiencing and what I've already done to diagnose so far, and hopefully there are some new ideas on how to fix. To start off, the bike itself: Yamaha xj650 Maxim 1982 with aftermarket pod filters and aftermarket 4-to-1 exhaust (before I'm berated about having aftermarket exhaust/pod filters, the previous owner did it). I have bought an airbox but am hesitant to install after realizing that the full process requires taking off carbs, intake boots, starter motor, battery, cylinder head, and moving the engine forward an inch, all the while I'm not sure if this will even solve the problem(s).

    SYMPTOMS:
    The problems are as follows: bike has difficulty starting and only starts on mid-choke, and when it does start (usually after a quick squirt of starter fluid) it will do one of two things: If the engine is warm OR if I used too much starter fluid, the engine will jump to 5-6k rpm at idle (very loud and very scary) and stay there. When I throttle it in this state the engine rpms increase as expected. When I take off the choke in this stage the rpms also increase. every once in a while I'll ignore my natural instinct to kill the engine and watch it for a minute, and sometimes the engine seems to calm down a bit and go to maybe 3k rpm, but I have never observed it settle back down to a normal idle (1-1.5k rpm) after jumping up to 5-6k. In the second scenario, which is usually what happens the first time I try to turn the bike on from a cold start (and a bit of starter fluid, maybe a second-long squirt onto 2 of the 4 pods) it will struggle to run but will idle at 1.5k rpm. It usually dies after 5-15 seconds in this case, and if I take off the choke it immediately dies. Also, if I pull the throttle in this scenario the engine immediately dies (I assume it gets too lean). What I don't entirely understand is why in scenario #2 the throttle causes it to die whereas scenario #1 throttle increases rpm from 5-6k idle to 8k rpm as a throttle should. Maybe because when it idles at 1.5k it's already lean and opening the throttle immediately kills it with too much air, but in the first scenario the airflow into the engine is already so strong that it can more quickly atomize the fuel and suck it into the engine. I also noted that after pulling on the throttle at the 5-6k idle, it will hang a bit at ~8k rpm and slowly return to 5-6k rpm, which I believe is also a symptom of lean mixture. As for other symptoms I have little actual experience (this is my first bike), so my hearing isn't acute enough to try to "hear" whether the engine is lean or rich. If I had to say, the exhaust smells like gas (a fuel-rich symptom) but I could be wrong about how it smells, as I've never been shown what fuel-rich and fuel-lean exhaust smells like. Lastly, at the 5-6k idle the exhaust AND one or two of the exhaust headers is smoking. I'm not sure if this is normal at such a high rpm, but could be indicative of a vacuum leak at the header (I took off the exhaust manifold once to do an oil change, but when I put it back on I also replaced the old exhaust gaskets). I know there are some weird things that can happen with back-pressure of air into the engine if exhaust headers aren't on properly and this may be partly responsible.

    WHAT I'VE TRIED
    I did a carb overhaul with a kit I bought online, which included rejetting to the stock fuel jets, ie a #40 on the pilot fuel jet and a #110 on the main fuel jet, as well as gasket replacement, new needle jet, etc. I am considering purchasing a new set of main/pilot jets to account for aftermarket exhaust/pod filters, but I'm not sure that such a small difference (I believe the calculator I used said ideally I'd have a #42 pilot and #116 main) in jet size would change much/be able to cause the problem I'm experiencing. I have also tested for vacuum leaks after replacing the original crusty intake boots and their gaskets (between the carb and engine) and have not found any. I tested throttle valve seals, intake boots, and petcock-to-carb vacuum hose for any vacuum leaks by spraying starter fluid at each location and trying to start the motorcycle without result, meaning I shouldn't have any vacuum leaks. I have also done a compression test (good on all cylinders, between 93-100 psi for all four) and replaced spark plugs which I am certain are all firing. When I removed the original spark plugs I examined them and they all looked fairly normal, no obvious signs of overly rich or lean, but again I'm no expert. I haven't yet tried checking out the intake valves. I've seen a couple people say to check the clearances and do some other things but I have not done that. I have extensively looked at the carbs and boots. The only thing I haven't done with the carbs is adjust float bowl heights, but all are relatively close to each other in height (within 1-2 mm).

    Please, please, please if you have any ideas help me out. Apologies for the long post; I've spent a lot of time fixing up this bike and I refuse to take it to a mechanic! I've learned a ton about motorcycle maintenance and repair through this process but I think there are a few small things that I've overlooked, and I'm sure a couple of you with extensive experience could help a newbie out.
    Thanks in advance, Nick.
     
  2. Simmy

    Simmy Well-Known Member

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    this procedure needs the motor running, you're listening for an increase in RPM's. What you've done does not prove or disprove anything.

    a wet set is the only way to determine what the actual fuel level is. Have you done a wet set?

    You're making some serious RPM's there. Are you certain the throttle cable is not holding your butterflies open?
    Did you do a bench sync when they were off the bike?

    Did you read the church of clean information in Chacal's pages.
    I think ultimately you need to remove the carbs and dismantle them for a proper cleaning as per the church of clean.
    As an immediate measure have a look at the linkage and determine they are not being held open anywhere, disconnect the throttle cable and rule out it is not holding them open.
     
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  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    The first thing to do is confirm that you have the throttle cable up to the throttle and choke cable hook to the choke. Second thing to do it's the check your idle knob between card 2 and 3 at the rear and possibly back it out some see if it is making contact with the throttle plate.
    Allure pods on the bike the bike should run at normal RPMs etc on startup.

    Make sure your mixture screws I said between 2 1/2 and 2 and 3/4 from a soft bottom.

    replacing the air box does not involve everything you have written above. You do not have to remove the cylinder head you do have to remove the starter in the carbs. It is also not also necessary to remove the manifold boots. You will have to remove the motor mounts on the front of the motor and take the front long motor mount bolt out.
    This should allow the motor to tilt forward. You want to warm up the airbox with a hair dryer and then try to slide it in you may have to heat the edges of the box to get it past the frame.
     
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  4. XJ550H

    XJ550H Well-Known Member Premium Member

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    When you speak a float bowl heights is that the actual height of the float or are you talking about the fuel levels in the bowls?
    Starter fluid will make the motor rev high and will also follow your plugs if you use it too often, check your spark plugs.

    If you bought those cheap eBay kits to rebuild your carbs we're all four cops are done for around $40. I would suggest putting the needle Jets which I assume you mean the slide needles back on from the original parts. A needle jet set, those kits don't match any numbers but I seen the specs for the bikes I believe they are for newer bikes.
    On the main Jets and the pilot Jets are they flat what do they have a countersunk face to them with a whole score for the Jets? Again some of the Jets that come with these kits a flat and some have the proper
     
  5. XJ550H

    XJ550H Well-Known Member Premium Member

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    On the bike is cold you'll need half choke to full choke to start it. the choke will make the bike go up to 3 to 4000 RPMs as it warms up.
     
  6. Nick S

    Nick S New Member

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    Ok, after reading this today I took off the carbs, put the original needle jets back in and bench synced the carbs. I have read the church of clean and have cleaned my carbs thoroughly. I also confirmed that the fuel mixture screws had been at 2.5 revolutions from soft bottom and still are. I also ran the bike (after doing all this) with the throttle cable disconnected. It had difficulty starting so I sprayed a bit of starter fluid on the pods and it shot up to 5k again.

    Could you elaborate on what a wet set is?
    Next I'm going to try the vacuum leak test with the motor running and I'll also try messing with the idle knob to see if that does anything.

    The jets have a countersunk face. I have not measured the float bowl heights, I was merely saying they all seem to hang at about the same level so I would assume they're all okay since no single one of them is severely deviated from the average height.

    One other thing I thought about was the cylinder head. Based on evidence of a poor sealant job it's clear that the previous owner opened up the cylinder heads and must've done something with the engine or valves. As mentioned I have not checked the valve clearances or opened the cylinder head, is that something I should check out, and if so what would I look for?
     
  7. Nick S

    Nick S New Member

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    ...

    correction. I put the original jet needle back in. The needle jet (which to clarify is the cylindrical piece with holes in it that sits in the base of the venturi of the carburettor) is the new one I used to replace. Next time I get the chance I'm also going to lower the jet needle (which "plugs" the needle jet) one setting to see if that reduces fuel flow during the super high idle. Will update this thread once I've done those things
     
  8. Nick S

    Nick S New Member

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    Notes for a ~68 degree day:

    tried lowering the jet needles to see if too much fuel entering the carbs was the issue, but it made no difference.

    There is a hissing sound when the the engine is killed

    Lots of smoke, unsure where its coming from (definitely the exhaust pipe, likely elsewhere too)

    Noticed some popping sounds (lean?)

    With petcock at prime and choke fully on, the bike immediately jumped to 7-8k rpm. With petcock at ON and choke off, idled at ~2.5k until throttled, then jumped to ~4.5k

    On warmer days the bike immediately turns on without starter fluid (runs better on warmer days -> air thinner -> bike is running lean)

    Began to spray (small amount) WD-40 into pods to test for a drop in rpms (for the vacuum leak test, wd-40 (I think) is supposed to lower the idle rpms) but nothing happened

    Now the bike wont start, makes weird clicking sounds

    Also, bike wont shift past 4th gear while off. Not sure if this is part of the design or an issue with this bike specifically.

    This bike has always done weird things. The main issue now is that it won't start, and instead makes a weird clicking/rattling sound when I hit the starter. Again if anyone has ideas or advice it would be greatly appreciated
     
  9. Nick S

    Nick S New Member

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    Anyone have suggestions for a good place to get '82 xj650 maxim compatible shim kits? Also if I plan on only doing this once or twice since I'll probably sell the bike eventually does it make more sense to buy individual shims? Gonna do a valve clearance test/shim replacement next week
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    www.xj4ever.com. Sells individual shims. And there is a shim pool here
     
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  11. k-moe

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

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  12. Timbox

    Timbox Well-Known Member

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    I see you are starting to jump around a bit to find answers on the forum. There is nothing new posted here to tell us what progress you have made with the advice given? If you follow, read and then do the work the "k-moe" above suggested you will get the bike running.

    When I first started rebuilding these bikes, I pulled the carbs off six times to get them the way they should have been the first time. So what I am trying to say is take the time to do the carbs right. The carbs being right will really make getting the bike running easy. The valve shims can be done after you get the bike running as that is just part of normal scheduled maintenance.

    I recommend doing a bench scynch and to do a fuel level test with the carbs out of the bike supported in a vice or common setup. If you have fuel leaks from the fuel tubes it is so much eiser to see what ones are leaking from a bench then when the carbs are installed on the bike.

    The hardest part for me to remember when I get a new bike project is to take the time to do the things right. You get so excited to get it to run and or ride that you might not take the time needed to so some of the things correctly compared to half A**ing it.
     
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  13. Nick S

    Nick S New Member

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    Ok, thanks. I'll do it again. I already did a bench sync but I'm definitely going to replace throttle shaft seals and set the fuel levels. Thanks "k-moe" for the pdfs, I'm going to follow those closely. It's true about getting overexcited, and I'll remember your advice to do it thoroughly the first time around. About changing the shims, I was hoping for advice on whether that could be a critical issue causing my rpm problem or just something for maintenance later. I will update soon. Thanks all
     
  14. k-moe

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

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    Valves being out of adjustment will not cause a high idle. But you do need to check the clearances. Lots of owners neglect that bit of maintenance.
     
  15. Nick S

    Nick S New Member

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    So I took a look at the spark plugs to inspect them and they’re super dark, like theyve been carbon fouled. How can that happen with a lean mixture? These plugs were new when the high idle problem first arose so the coloration is related to the issue. Ill attach a photo below
     

    Attached Files:

  16. SQLGuy

    SQLGuy Well-Known Member

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    Clearly not lean. A vacuum leak through the throttle shaft seals, or elsewhere, will cause high idle. In addition, your mixture (probably) needs to be adjusted, but you need to solve the vacuum leak first.
     
  17. Nick S

    Nick S New Member

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    Going to do a throttle valve seal replacement, bench sync, wet set/check bowl heights, and then see what that does. Anyone know what the proper stock height for the jet needle is? I was messing with mine to try to fix my rpm issue but it might've made it worse. I changed from (of 6 height settings) the third lowest (fourth highest) up 2 to the second highest (ie letting more fuel through the main jet and emulsion tube I believe) and that made it worse. Will change back to the original height but previous owner might have also messed with those, wondering what the stock setting is.
     
  18. SQLGuy

    SQLGuy Well-Known Member

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    Pretty sure the stock needles aren't adjustable. The multi groove ones usually come with aftermarket jetting kits.
     
  19. Nick S

    Nick S New Member

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    Ok im in the process of taking apart my carbs and replacing throttle shaft seals and fuel rail o-rings. The butterfly valve screws (holding the plate to the throttle shaft) are pretty tricky, any thoughts on how to get them out?
     
  20. Nick S

    Nick S New Member

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    The pdf writeup said to get loctite and anti-sieze fluid for this job. I know the loctite is for the self locking screws, is the anti-seize fluid (I have molybite) for any other non self locking screw?
     

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