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trouble with cold starts.

Discussion in 'XJ Technical Chat' started by Marc browning, Feb 6, 2019.

  1. Marc browning

    Marc browning Member

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    I have rebuilt my carbs, synced and color tuned them. If I let the bike sit for a few days it will give me a pop as the starter is hit, but then nothing, will not start at all. I have checked that there is fuel in the tank, yes it is fresh fuel. Fuel is in the bowls. Choke is on. When I pull a plug it is dry, telling me there isn't any fuel in the cylinders. My question is, does the idle mixture have anything to do with the fuel enrichment circuit ? SO if my carbs are a bit lean at idle will that effect fuel flow with the enrichment on?
    I do have another set of carbs and they never do this at all, they will start within 5 seconds all the way down to 20 degrees. So I know it isn't plugs, or the ignition system causing the problem.
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    Do you have the stock vacuum petcock ? If so set it to PRI and see what happens when you try to start. ( make sure you set it back to ON after start or letting it sit) .
     
  3. Marc browning

    Marc browning Member

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    I do have the stock Petcock. I normally put it on prime to start it also, not change. Odd is I waited an hour after trying to start it and it started fine. Like the fuel isn’t getting in the enrichment circuit. I have all new seals in the carb.
     
  4. Tim O

    Tim O Active Member

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    Sounds like what mine does.... I have a manual petcock and I've found if I don't ride for a week I need to turn it on for 5 min. then start. It's like the carb bowls evaporate over time and need to refill.
    If I just turn on fuel and start I get nothing...
    If I just turn on fuel and start and have ridden her in the last two days it starts right up...
     
  5. Marc browning

    Marc browning Member

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    I’ll try that this weekend. Mine have no leaks.
     
  6. Timbox

    Timbox Active Member

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    Do both sets of carbs have the same jetting? You said the other rack you have starts down to 20 degrees, so if the troubled rack does not, then I would guess it is in the carbs. If the carbs went to "church" and the jets all the same, have they been synchronized? I hate to say it but it sounds like the troubled carbs are not as clean as they should be.
     
  7. XJ550H

    XJ550H Well-Known Member Premium Member

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    so the bike will not start at all or just after sitting a few days?
    under what conditions does it start to be left un started for a few days?

    the enrichment circuit is separate from pilot jets. it consists of the well in the bowl body, pick up tube and plunger. check to make sure they are all clean. shoot spray down the well in the bowl wall where the enrichment tube goes and see if it comes out the tiny hole at the bottom of the bowl. wear safety glasses
    next would be to spray up into the tube with the enrichment plungers lifted and see if the spray comes out in the hole in the carb throat

    I would start with this because it does not require removal of carbs to try.
    if lean at idle open the mixture screws a little more about the width of a dime, the pilots do work with the enrichment circuit to start the bike.

    when you spray cleaner into the pilot jet does fluid come out all the little holes in the top of the carb throat?
    are the jet washers flat?

    this sounds like it is in the carbs. do you have the internal filters in the carbs still?.

    check the carb clamps make sure they are tight

    are the air jets in the correct locations ?
     
    Last edited: Feb 9, 2019
  8. Marc browning

    Marc browning Member

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    The bike will start if I start it everyday. If I let it sit for about 3-4 days, I have troubles starting it. I do believe it is the idle mixtures being to lean. I used a color tune, and most likely have the carbs set to lean, they sure did sound great, but after riding it for 30 minutes, it would have a stumble right after idle. So i have richened up the idles with a color tune again, but this time much closer to the beginning of an orange flame. It does seem to start easier, but I've only tried after a day. Will let it set for 3 days and see how it goes.
    both sets of carbs have the same stock jets in them. As xj550H has said the the idle mixture does evict starts and the enrichment circuit. I do have the filters in the carbs if you mean the screens at the fuel inlet. The enrichment is working as I can change rpm and richness with the choke lever, I do notice that it doesn't like full choke, I only use about half for the bike to start. While it is running for 30-45 seconds and I add full choke it will die and go very rich.

    "when you spray cleaner into the pilot jet does fluid come out all the little holes in the top of the carb throat?
    are the jet washers flat?"
    I did check this with air during the rebuild, all seems good between the 4 carbs. I did not check the jet washers, but did replace them on the rebuild. I would say the air jets are in the right place, this is my second set of these carbs being rebuilt, so I do believe they are right, all carb clamps checked a second time.

    Thanks again for all the help, I'll give it a few days and see what it does. I'll report back them, Thanks again for all your time.
    Marc
     
  9. Timbox

    Timbox Active Member

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    From the last post, if you are sure you are not getting too much fuel in the carbs from sitting. Turning the petcock off after each use to make sure no extra fuel is running into the carbs. I would guess you have a small battery drain some place. You would have to either go by sound of the starer or take the Volt meter and see if you have a good battery after it is sitting for a few days.

    The simple way would be to park it at the end of the day, then remove the ground wire from the battery. A few days later go try to start the bike by putting the ground wire back on and see if it fires right up? If so, you might have to look for an electrical gremlin.
     
  10. XJ550H

    XJ550H Well-Known Member Premium Member

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    what do you do to get it started after it sits for a few days?
     
  11. Polock

    Polock Well-Known Member

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    my 750 does the same thing, let it set a week and the carbs are empty or at least low. so i put it on prime and watch the CLEAR FUEL FILTER,
    when the bubbles stop it's ready to go.
    i don't know where the gas goes, i don't care
     
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  12. k-moe

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

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    Carbs are an open system. The fuel is evaporating as the bike sits. Totally normal.
    Set the petcck to PRI (prime) and wait a few seconds before starting.
     
  13. Tim O

    Tim O Active Member

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    exactly the same on mine
     
  14. Marc browning

    Marc browning Member

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    Timbox, there isn’t an off on the Petcock only on, prime, and res. As for the battery, it is new and always on a tender. Thanks.
    Like Polock has said, I use prime to get it to start. It just has to set for a few minutes.
    Thanks again for all the help.
     
  15. Marc browning

    Marc browning Member

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    So far setting the idle mixture richer has fixed the problem. She sat for 4 days and started right up with fuel turned to on. I’ll see as time goes on how it works.
     
  16. Marc browning

    Marc browning Member

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    And I was wrong. Temps are 27 degrees and it wouldn’t start again. Guess it is only a warm weather bike. Took 20 minutes to start. Only thing that seemed to help was to rock the bike from side to side.
    So I went out to the bike,turned on choke, turned it to prime ,hit the starter it fired and died. Hit starter again fired and died. Then Tried many times to start and nothing. Rocking the bike and waiting, then it started and stayed running. I have cold weather, before freezing for the next 6 days. I’ll ride it home and put it up till it warms up a bit. Wish the other set of carbs looked better, they run great.
     
  17. Timbox

    Timbox Active Member

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    Clean that second set up in the down time with the cold weather and then swap them out. For me, the confidence of the bike running to its best potential is better than the way it looks.

    Bottom line, a good known working part wins over looks to me any day. Make those other carbs look nice and then put them back on your bike.
     
  18. Marc browning

    Marc browning Member

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    I agree, but I like to figure out the problem too. Just takes time and effort.
     
  19. XJ550H

    XJ550H Well-Known Member Premium Member

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    you know it is the carbs.
    have you checked the wet set fuel level of the carbs?

    I would rather depend on ugly and functional than pretty and problematic during the cold weather. swap them out and ride.
     
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  20. Tim O

    Tim O Active Member

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    still sounds like starving for fuel to me...
    I chased a similar problem on mine for a while until I figured out it was the screens at the float valve inlets. Although mine would start and then randomly die 20 min. later when the bowls ran low. Just thinking of those since you said your other carbs don't do the same thing.

    If your bowls were low when trying to start they might not fill up fast enough, but will later after rocking the bike around for a while. When mine were clogged, I could tap on the bowls to get those cylinders to fire again briefly. Made me think the needles were getting stuck closed until I opened the carbs and saw the clogged screens.

    I echo just putting on the ones that work if you want to ride now. Just a few suggestions of what bit me.
     

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