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1981 Yamaha XJ650 Maxim Valve clearance/ carb issues

Discussion in 'XJ Technical Chat' started by kcleft, Feb 11, 2014.

  1. kcleft

    kcleft Member

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    Alright guys, so I know there's a lot of stuff up already about valves and such, but I am wondering about my bike personally and what the XJ gurus on this forum think. So when I first go my bike it ran... decent, it had to be started with starting fluid and it took me a while to get it started (it didn't like it when I gave it throttle when it first started, also note that this is all happening in freezing weather, between 25-35 degrees) but eventually it would start and after it warmed up it would driving ok. when I gave it gas to ride it sometimes it would rev and other times it would bog down and I'd have to play with the throttle a little before it would rev at all. it did have problems with backfiring a little, but it wasn't terrible and it would idle at about 1.2-3k so it was high, but not ridiculous.

    I figured the bogging down was just a carb issue so I took them off and cleaned them, put them back on, and started it (it still didn't start under it's own power), and I started having problems with it idling (it didn't want to at all) and when I did rev it to about 4k it would stay there even after I left off the throttle, eventually it would drop and then sputter to a stop. I tried messing with the choke to drop it back down, but even with the choke all the way off it still would rev high and stay there. When it did idle however it would at about 2k and I would get quite a lot of backfire... So I took the carbs off again and I figured, while I've got the carbs off I could run a compression test (the engine was cold when I did this) and I was getting about.. 30psi across all of the cylinders dry, and about 45-50psi with a wet test. So I figure the rings are still pretty good, not great, but still useable. but those compression readings are probably most of the reason it wont start with the choke on. I was hoping that the camshafts were just a tooth off and all it would take is adjusting them, but when I put the engine at TDC the camshafts are almost perfect, one is just a little bit off, but it's not a whole tooth (still though it has me wondering if I went past the point on one cam then move it one tooth over on the other cam it might actually be a little closer). So I measured the valve clearances. and the results were all pretty close to each other, on the exhaust side they were all about .18mm and all the intake valves were close to .06mm I know they are probably out of specs (not entirely sure where they should be) but they were all really close to each other. maybe +-.01mm. I'm wondering if these readings would cause low compression, and be part of the reason it wont start without starter fluid.

    I'm aware that there is a good possibility in order for this bike to run great I'll have to get different shims, but I didn't spend a whole lot on this bike, and I don't want to have to throw lots of money at it. honestly all I really want it to do is run decently. so if you guys think that keeping the valves where they are is possible, and that I might be able to tinker with the carbs to get that idle down and for it to run ok, then that's what I plan on doing, I did mess with the mixture screws so I do need to get a colortune and adjust the mixture. and I did a bench synch so messing with the idle screw might help bring that idle down. I know I also have intake leaks, I believe the rubber boots that connect the air box to the carbs shrunk so they no longer go all the way into the air box (they will go in part way, but there's gaps) and the boots between the engine and carbs are also cracked a lot on the outside, I did inspect the inside of the boots and I didn't notice any cracks, so I think it's just superficial.

    I'm sorry this is so long guys! and I really appreciate the time you take to read this and I'd appreciate your input even more. I am a complete novice when it comes to motorcycles. this is my fist bike I've ever really even touched let alone try to diagnose, most of what I do know comes from working on cars haha.
    So thanks in advance!!
     
  2. ecologito

    ecologito Well-Known Member

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    Welcome to the site.

    The first thing you need is to get your valves in spec to run a compression test, otherwise you are getting inaccurate readings. Here are the specs:

    Exhaust: 0.16~0.20mm
    Intake: 0.11~0.15mm

    If all your intakes are at .06 that is way tight so replace the shims to get them in spec.

    The second thing you will need is to get an accurate reading on your compression test. 30 PSI is way low, even 50psi is really low. I believe this engine should be at least 120 to call it strong.


    That is just not going to happen, you will have to spend some money to get your bike running decently otherwise it will be one problem after another. Is like having diabetes and try to fix it by cutting your carb intake in half, it's just not gonna work.

    hogfiddles runs a shim pool so all you need is your old ones and a deposit and he will hook you up.

    If you have carb intake leaks the bike will not run properly, I have not seen your bike but to me it sounds like you need to take your time and address all the issues that you have mentioned, you can't do something and skip others.

    Keep asking questions about how to do things but cutting corners is just not going to get your xj running "ok".

    Best wishes.
     
  3. MiCarl

    MiCarl Active Member

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    So long as there is some valve clearance they are not the cause of low compression on a (cold) engine. It is possible they've been damaged from being too tight on a hot engine.

    While you probably have carb issues, you'll never get a 30-50 PSI engine to idle properly or cold start.

    You need to confirm your compression results with a fully charged battery or a boost. Try a different gauge.

    If you still have low results you need a leak down test to see where the compression is escaping.
     
  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    +1.

    If it ran at all, the compression test was faulty. Re-do as above. If you want good numbers, get the valves in spec first.

    If your valves are out of spec, it's not a "possibility" that you'll need to replace some shims, it's a certainty. Job one. And every 5K miles, learn it.

    You DO have carb issues; and once properly serviced, the valves will need to be in spec to set the carbs up properly.

    If you want to properly recommission and ride this bike, you're looking at around $600 ~ $800 if you do the work. You'll need a service manual and be prepared to sink some man-hours into it. If you truly do know anything about working on cars, then you CAN do it; but you'll have to get a service manual and get serious or you'll just fail repeatedly.

    It CAN be done; personally I've done two XJs so far. I love 'em. But a lot of work was involved; and the above budget is inescapable.
     
  5. rocs82650

    rocs82650 Well-Known Member

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    kc,

    Welcome to the club. Bad news...I'm not one of the gurus. Good news...Fitz is. More good news...the advice and information given by Eco is as sound as any of the gurus. More bad news, sorry...Everything you've described is not the makings of a "decent" running 650. 28* here in Nashville. Rolled her out the garage, half choke, hit the starter...Varoom! Great news...you've come to the right place. Providing you have a good plant (engine) and you do the necessary work to bring your bike back I can assure you will not be disappointed. XJ series bikes are very strong, durable and well built bikes. Keep this thread going. As you dive deeper into the re-commissioning process use this thread as your Q & A thread. At the time you will have learned and done many of the things many of us have you can read your first post and tell for yourself how far "out" and "off" your bike truly is (was). Good Luck.

    Roc
     
  6. FtUp

    FtUp Well-Known Member

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    what fitz said...

    CN
     
  7. RickCoMatic

    RickCoMatic Well-Known Member

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    The soundest advice you'll get from anyone is this:

    Buy a Genuine Yamaha Factory Service Manual specific to your Bike.

    Having a "Factory Book" gives you the ability to illicit help from any Small Engine Tech, Automotive Expert Tech, and anyone else with Mechanical Skills.

    Having "The Book" takes all the mystery out of how to do anything from changing a light-bulb to rebuilding the Plant from scratch.

    You can place an ad on a Technical / Vocational School's bulletin board and get someone to help you.

    Having the Factory Book answers all the questions.
     
  8. kcleft

    kcleft Member

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    Wow, Thanks for all the replies guys!! I wasn't expecting so may people to read this haha. So after posting this I did realized that it would be pretty stupid to try to keep the valves the same and not mess with the shims.. so I am already planning to replace the intake shims, but it seems like the exhaust valves are within spec. I do have a Haynes manual for the bike, it was one of the first things I did after purchasing it. it is the electronic version however, so it takes a little bit of navigating. I plan on getting a hard copy soon though :D . BigFitz, thanks for the comment, I can tell you just by looking at this bike that there is A LOT of work. I plan on doing most (if not all) the work myself, but I'm not really in a position to spend hundreds of dollars on it to get it running perfect. I know it seems like I'm trying to find short cuts, and to be completely honest I am hahaha, that's why I'm trying to do everything that cost's as little money as possible first before I start throwing money at it (even if it does improve overall performance). I do understand that things like replacing the shims which will cost some money is a necessity and can be damaging to the engine if not addressed. Sorry if I'm sounding like a cheapo, but my situation wont allow me to be so giving with my money haha I hope you understand...

    I was a little uneasy about the compression test as well when I was getting those results.. I was honestly surprised that an engine could run on such low compression like that, so I'll try to get another tester and see if the results change. As far as the power goes (I have ridden it) when the carbs would work with me it accelerated quite nicely! it didn't feel down on power at all!!

    MiCarl, thanks for taking the time to read all of this! I think Fitz is right, those readings were probably off, but when I bought it, it would actually idle. granted it was about 1-200 rpm higher than it should have been and it was rough, but it still idled. At least it would before I cleaned the carbs the second time and messed with the mixture screws, that's why I think I might be able to get it to idle if I tinker with the carbs :). and I am aware of the possibility that the valves were damaged, I'm crossing my fingers that they aren't though!!

    Also quick question about how my engine would rev high even though I was off the throttle, could my float levels be causing too much gas to be entering the engine by any chance? and if they do do you guys have any way of removing seized float bowl drain plugs? two of them are stuck in there really good haha.

    Thanks for all the support everyone, I really do appreciate it!! and I apologize if I sound like I'm one of those people who wants their transportation to get from point A to point B and doesn't care about taking care of their motorcycle at all. I promise I'm not, but there's only so much I can do... Thanks again! :)
     
    XJRider82 likes this.
  9. adrian1

    adrian1 Active Member

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    Courtesy of Chacal

    - A lean air-fuel mixture condition, which can be caused by a variety of problems......vacuum leaks, plugged or too-small fuel jets, etc. Old or "stale" gas may also cause a lean fuel-air mixture to occur temporarily (until the fuel is used up!).

    - A vacuum leak somewhere in the intake system.....intake boots, internal o-ring seals, etc.

    - Mixture screws not properly set or adjusted.

    - Vacuum piston sticking or stuck in a partially raised position.

    - Idle speed screw set too high, or set to create a "proper" idle speed when the engine was cold (and thus results in a "high idle" once the engine reaches operating temps). The idle speed when the engine is cold should be modulated via the use of the choke (enrichment) control system.

    - Butterfly valves opened too far; synch screws out of adjustment.

    - Throttle cable wear, adjustment, or throttle lever brackets installed incorrectly or interfering with other nearby objects (cylinder head fins, etc.).

    - Choke (enrichment) circuit is stuck "open"....this can occur even if the choke lever is rotated to the fully closed position, if for some reasons the choke plungers are not fully closing (cable wear, cable adjustment, bent finger brackets, or installation problems). In addition, even if the choke plungers are "closing" fully, if the choke plunger valve face or its seat are worn or scarred, this will allow fuel to leak part the plunger and richen the mixture even if the plungers are closed.



    Why your engine seems to be schizoid:

    A hanging idle---one that stays high and slowly comes down when decelerating---is a sign of lean mixture. The opposite case, where the idle drops dangerously low then rises, is a sign of rich mixture.

    A bike that runs better when hot is probably lean, and a bike that runs better when cold is probably rich.

    But sometimes a bike that can be adjusted "just right" when cool, but actually starts exhibiting signs of running lean (hanging idle) as it warms up. And if the idle speed is then re-adjusted while the engine is warm, but eventually falls and the bike dies (especially when sitting at a stop light). Or if the pilot screws are adjusted, then it's too rich when cold---all in direct contradiction of the above observations.

    Experience shows that this is a sign of worn throttle shaft seals.....the aluminum carb bodies expand with the heat, but the steel throttle shafts---resting comfortably in a nice cool airflow---don't heat up and therefore don't expand. Once the shaft seals get old and hard, they no longer are able to flex and fill the gap.....so the carb starts drawing air around the shafts, leaning it out.

    Drain screws:

    http://www.xjbikes.com/Forums/viewtopic/t=4281.html
     
  10. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    -Shortcuts don't work.

    -"Tinkering" doesn't work.

    Break the carbs down and properly service them. In the Haynes, this section begins on page 119. Float levels are covered on page 126 and 127; plus there's good advice here: http://www.xj4ever.com/setting%20fuel%20levels.pdf

    -Then once the carbs have been properly cleaned, serviced and adjusted, and your valve clearances are in spec, then you can synchronize them and get rid of the "hanging idle."

    Once the motor's running, we need to talk about those 30+ year old brakes.
     
  11. MiCarl

    MiCarl Active Member

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    A hanging idle can be caused by a number of things. Most of them carb related.

    Low compression can also cause it. You need about 60PSI to make the engine run. But, it takes some time for the gas (not gasoline) to leak out so when the engine is running you have more compression than that. The more RPMs the less the leak affects the combustion.

    Now imagine you've got the thing running at about 2,500 rpm and trying to adjust the idle down. As you get to about 2,000 one of the cylinders leaks badly enough it doesn't keep firing and the RPM suddenly drops. Now the other 3 are in trouble too and it quits. This is why you can never get a leaky engine to idle properly.

    Get your compression sorted out. If you have some valve clearance and it's that leaky you're probably looking at a major expenditure. As long as you have ANY valve clearance the valves are closing and I wouldn't spend a penny on shims yet.
     
  12. TIMEtoRIDE

    TIMEtoRIDE Active Member

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    Compression test 101 (if you didn't know)
    - All 4 plugs out
    - Fully charged battery, on a booster, or jumped to a non-running car
    - Throttles jacked open
    - unplug ignition black box, or cross the solenoid, key "off"
    . . . (never fire the coils without the plugs)
    - crank for around 8 "hits", or until the needle stops moving.

    +1 on brakes & tires, and all the other great advise.
     
  13. RickCoMatic

    RickCoMatic Well-Known Member

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    With the Bike being three decades old, ... servicing the Carbs to bring them back to a "Like-new" condition is a MUST.

    Fortunately, the Carbs being Aluminum, Brass and Bronze allows for the rack to be rehabilitated to such conditions.

    Carb "Kits" are available to make the Float Valves, Gaskets and Mixture Screw Micro-Orings NEW.

    After 30 years, ... the Bores for the Diaphragm Pistons should be Scrubbed and Polished to allow for absolutely un-impeded movement of the Diaphragm Piston.

    Scrubbing with ScotchBrite Medium (Gray) and dressing with ScotchBrite Fine (White) will restore the Bore and rid the Cylinder of an oxide coating which develops after many years.
     
  14. kcleft

    kcleft Member

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    Ok, so do you guys think I should address the shims first? or try to get accurate compression results? I haven't tested it when it was hot, so it's very possible that could yield different results. And ya big fitz, I can tell just by looking at the front brakes I'll have to rebuild the caliper.. one pad is worn almost down to the metal and the other still has quite a bit left. haven't gotten to the rear brakes yet, but from what I've read there's a pretty good chance I'll have to replace those too haha. Thanks for the posts guys!!
     
  15. MiCarl

    MiCarl Active Member

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    Your front brake pads are wedge shaped. One is narrow at front, the other narrow at back. They're like that because the caliper pivots rather than sliding.

    They're not worn out until the wedge shape is gone.
     
  16. kcleft

    kcleft Member

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    ok, I'll take a look at the bakes again to see if I can understand them a little better. Also quick question, do you guys think if I replace all four rubber joints from the airbox to the carb, I'll get rid of that intake leak? I think the old ones just shrunk a little, just enough to make it too short to reach the airbox. Is there anyway to reuse the old ones and stretch them out a little without them trying to shrink back to a smaller size?
     
  17. Polock

    Polock Well-Known Member

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    can you put up a picture of the carb/airbox boots on the bike?
    i can't imagine them shrinking that much in length without shrinking in diameter. then they wouldn't even fit on the carbs and they'd be loose in the airbox. maybe their the wrong ones
     
  18. ecologito

    ecologito Well-Known Member

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    Yes, you should get the valves in spec and then run a compression test, otherwise you will just be chasing your tail.
     
  19. kcleft

    kcleft Member

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    Ok, so I just ordered the valve shim removal tool, so hopefully I'll be able to pull them out and get new ones soon. I've got the engine mounts out in order to remove the valve cover, so as soon as I get it all put back together, I'll take some pics of the intake boots. Thanks for the comments guys!!
     
  20. ecologito

    ecologito Well-Known Member

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