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85 maxim 750 stalling problem

Discussion in 'XJ Technical Chat' started by Jaded Marxist, Jul 20, 2019.

  1. Jaded Marxist

    Jaded Marxist New Member

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    Hi everyone
    I just brought home an 85 maxim 750. The bike fires up no problem, but stalls as soon as I'm off the throttle. So when I start it and keep the rpms up around 1500, it runs good and smooth but as I let off the throttle it revs down to a stall. Happens warm or cold choke on or off? Now my bike experience is very limited, and I've been told carbs need resyncd.
    I am experienced wrenching on cars but I may as well be looking at a space ship from another planet when it comes to this bike.
    I was hoping someone may be able to tell me where to start. I know so little about bikes I'm not sure how to take the seat off (sic).
    My first thought from car exp is throttle adjustment screw? Is there 4 adjustment screws on the bike? Sorry I'm sure I'll get some "you shouldn't ride a bike" posts but really I just need someone to get me started and point me in the right direction. Id appreciate any advise at all. What should I check now the bike is finally home? This will be my first bike and using it to learn to ride.

    Regards Jaded Marxist
     
  2. Toomanybikes

    Toomanybikes Well-Known Member

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    There is a main idle stop screw between Center 2 carbs. The screws between each carb are sync and 4 mixture screws front and centre on each carb. Failing that maybe they need the full Monty.

    Red arrow mixture screws
    Green “. Sync screws

    Second pic. Idle stop screw
     

    Attached Files:

    Last edited: Jul 20, 2019
  3. Timbox

    Timbox Well-Known Member

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    Jaded,
    Now you are getting into it! Keep all the questions about your bike on this thread and that way we will have a history of what you have done as far as trouble shooting.
    How long has the bike been sitting? For most of out older XJ's have to check the gas tank for bad gas, see if the tank is rusted. The carbs if the bike has been sitting will need to come off and you will have to clean them very well. Not just hitting them with carb cleaner, you will not get them as clean as they need to be. I can only guess that your carb bowls have gum in them and the enrichment ckt is all plugged.
    [​IMG]carbs_floatbowl_choke by Tim Brown, on Flickr
    If you take a bread tie and strip off the insulation on the wire, it works really well for poking the hole open.
    Using a lot of carb cleaner can dry out can crack some of the rubber inside the carb. The Throttle seals don't like carb cleaner. Once they get dried out and crack, they will need to be replaced or the bike will not idle well.
     
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  4. Jaded Marxist

    Jaded Marxist New Member

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    Awesome thanks for the info. I have started to tear down the bike this afternoon, but a storm moved in and since I have no garage had to qui kly tidy up and get the bike covered up. I was told by the previous owner it was on the road and driven daily up until 2 weeks ago. (in reality who knows).

    No rust in tank. That's the first thing I checked and it is fresh gas.

    I pulled the tank off and the air filter out and the filter was coated in a thick layer of oil restricting air flow. Tomorrow I'm gonna pull out the plugs to see what they look like but they look new as the previous owner told me, has new oil also.

    It's got a real strong gas smell when running not leaking gas but like running real rich. I'm gonna try the idle screw first when it does stay running its idle is at about 400rpm. I've been told it should be 1100 rpm.

    Is the blow by caused by possibably over filling the oil? I'm hoping the air filter being so plugged up by oil might be a cause or partly the cause for the stalling and low idle.

    Thanks again for the reply's

    Regards Jaded Marxist

    Hope I don't have to clean the carbs as I have such terrible luck with that.
     
  5. k-moe

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

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    Put the bike on the center stand and check the sight glass. Remove the oil oil cap and sniff.
    You very, very likely have leaking float needles, causing the oil to now be a mix of gas and oil. I marked the clues in red.
    If that is the case DO NOT run the engine again until after the carbs have been off and the problem solved. Do it once, do it right, IN THE CHURCH OF CLEAN
     
  6. Timbox

    Timbox Well-Known Member

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    If there is gas in the oil, you run a higher risk of hurting the engine. Bearings do not like gas oil mix when they are working. The carbs are normally messed up on these bikes just from sitting. Nothing against the PO, but normally unless you know them, nothing they say is true. Running just 2 weeks ago...hmmm.
     
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  7. Jaded Marxist

    Jaded Marxist New Member

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    Kmoe your right there was gas mixed in the oil. I also noticed the fuel petcock was in prime not on aand that's my fault as I thought it was primary before I joined the forum. The level of the oil is about where it should be but has the smell of gas. So I'm going to do an oil change. As it easy enough to take the carbs off. So gonna do that also.
    A question do I need to break the carb rack apart to clean them up? And after will I need to sync them up? As I don't have the parts to make the manifold needed nor can I get them today as it's Sunday!
     
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  8. k-moe

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

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    1. The petcock being in prime wasn't the cause of the problem, but it did contribute. Remove the fuel line and check that it does not leak when set to ON or Reserve, and only flows fuel in those positions when you apply vacuum (suck) on the smaller vacuum line.
    If it does leak they can be rebuilt Rebuilding the Yamaha Vacuum Fuel Valve w/pics

    2. The carbs should be broken, cleaned, and all rubber parts (aside from the diaphrams) replaced as a matter of course, simply because you have no idea when it was last done, and already know that at least one float needle is not sealing.

    IN THE CHURCH OF CLEAN
    Clean Your Own Carb's - The Whole 9 Yards - by: Rick Massey

    Why you should replace butterfly (throttle shaft) seals.
    Replacing your Hitachi throttle shaft seals

    Setting the fuel levels


    3. While many parts can be bought from any source that you like, going that route with carb internals is tricky. There are at least two kits being sold (I forget which ones) that do not actually fit correctly. Start a conversation with @chacal if you'd like to avoid that trouble.
     
  9. Jaded Marxist

    Jaded Marxist New Member

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    Thanks well I changed the oil and filter as that's what I can do for today and started the bike for fun. And it runs perfectly, for 5 min. Then I get a popping in the exhaust. Touch the headers with a. Damp rag and cylinder 4 is cold. Turns out there is no spark. If I was thinking about this in regards to a car, fuel in oil makes sense. Iam gonna order the parts for a full carb rebuild, like you said who knows when it was done.

    Do you know a good vender in Canada as to import anything from the USA takes so much time and is costly I've bought car parts that the import fees were twice as much as the item I was after.

    Could the coils stop working on just one side or would it just be that one side of the coil can fail?

    Thanks for all the advice. I'm not counting out the carbs but if there's any chance of me riding this bike this season I'd like to ride it. I hate waiting on parts and the season is almost half over for me already.

    I might just go buy a turn key bike for the rest of the season and then I'll have time to fully rebuild this bike. My wife is gonna leave me for all the garbage I keep collecting, this is now my 7th viechle. I'm running out of room fast lol
     
  10. lostboy

    lostboy Well-Known Member

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    Unscrew the spark plug cap and lop off about 1/4 inch of wire and reinstall the cap. Welcome to the forum. Is it as hot there as it is here. It's 25 feels like 31.
     
    Last edited: Jul 21, 2019
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  11. XJ550H

    XJ550H Well-Known Member Premium Member

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    ohm out the spark plug cap. also move the plug to another cylinder see if it is the plug
     
  12. Jaded Marxist

    Jaded Marxist New Member

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    I'm a dummy it has spark I just could not see it for the sun. I've actually got the bike putting like kitten now just ran it around the block wow what a difference to my buell blast. This bike is much faster. Also I thought a lighter bike would be better but riding the yamaha I like the feel of the weight.
     
  13. Jaded Marxist

    Jaded Marxist New Member

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    27 C here now 33C with humidity. Yesterday it was 45C for my us friends that's 113F the air was so thick you could chew on it. Where abouts ya from lost boy? I'm in southern Ontario an hour south of Toronto. I'm in need of a riding partner as I don't have any rider friends at all.
     
  14. Jaded Marxist

    Jaded Marxist New Member

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    Ah I see your not far from me at all.
     
  15. lostboy

    lostboy Well-Known Member

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    There few other members in this area.
     
  16. k-moe

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

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    Last night at Midnight (here, not there) it was 32C with 94% humidity.
     
  17. Jaded Marxist

    Jaded Marxist New Member

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    Oh man the humidity is what is killing me I bet I've been thru a dozen shirts this weekend it's still so humid here but they say it's supposed to be low humidity and low to mid 20s the rest of the month. Thank God for A/C in my work van cause I work outside. Although you can lay back and close your eyes and easily imagine that you on vacation in the Amazon rainforest lmao. A fast moving storm rolled in here last night and dumped 3inches of rain In about 10 min and it really cooled off nice
     
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  18. lostboy

    lostboy Well-Known Member

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    The worst thing I saw during this heat wave was a guy driving a diaper truck.
     

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