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Choke issues suspected help please

Discussion in 'The Garage' started by Yellow0206, Mar 6, 2020.

  1. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Now that I have a better idea of your situation, how did you set the timing? Did you remove and clean the ATU? Everything in that pocket is more important than the type of fuel youre using. Setting the timing by static method can only get you so far. You need a timing light to verify both idle and full advance on both cylinders.

    The ATU needs to be removed cleaned and lubed, I do it once a season. I check the points gap and timing with every oil change or when the bike tells me it needs attention, occasionally its good enough to skip. OK enough about timing for now. Then it goes down to valve clearance, its all connected...

    If you are using aftermarket jets, you will have more problems tuning. Aftermarket jets are a lot different from genuine jets. The sizing and orifice is just wrong on aftermarkets.

    I run my bike from 40 to 100+ degrees F and I dont feel the need to re-jet for temps. I may have slight issues at both extremes but its manageable. I should also mention that I use the factory air filters and H-pipe and have Emgo tapered mufflers. Therye the best option IMO if youre on a budget. They have a good baffle with a deflector inside. Theyre good for me when I start it up at 5am, and they are loud when you get on it going up the on-ramp.

    If the bike runs good initially and worse as it warms up, youre probably too rich. If you can start the bike cold with no choke, then youre probably too rich. If the plugs are sooty at all, I think youre still too rich. The plugs should be dry and black/grey/ashy color, any specks on the porcelain and youre too lean. The color should take a while to build up, like maybe 200 miles. If youre pulling out black or wet and sooty plugs before then, youre too rich.

    When you choose your main jet, the tuning has only just begun lol. I use 130 or 132.5 mains and I had to drop the needle jet one notch to lean it out a little. You should be able to narrow it down to two sizes for your main jet that will be acceptable. Above 6k rpm is where the main jet starts to come into use. You need to decide on the main size before you move on to the rest.

    CV carbs take time to react to your input, adapt the roll-on approach.
     
  2. Yellow0206

    Yellow0206 XS400 Enthusiast

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    Thks NewHavenMike- I have yet to set the timing with a light i just checked the points gap. I will remove and lube the unit and i do have a timing light and will check it/set it. I did go from 150 mains to 145 and they were OE or at least I bought them from a dealer - I do believe I am rich and they are larger than yours but you do have a 360, so maybe after timing if I still have issue I will try 142.5 or 140 if I can find them...thks. PS here is the bike 5C6E95F0-A42C-4B24-AAB8-21957DD59B7D.jpeg
     
  3. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    I did have a 360, transmission bearing went on it and had to replace with a 400cc block. XS360 carbs run richer from the factory as they are pre-EPA. 360 carbs are actually an upgrade for 400s

    timing with a light on both cylinders is critical. Set the left side first and then tighten the timing plate so it doesnt move. Then you can move the right side point independently from the left.

    The left side is the “master” and is directly connected to the baseplate. Right side would be the slave.

    bike looks great!

    I would go down to 135 jets and see what happens.

    Also, when I installed the 360 carbs on the 400; I made no jetting changes at all. The factory main jet on the 360 was 135.

    Modding a bike doesnt always mean you need to upjet. Every bike is different.

    Ive used exhausts similar to what you have, gave me a lot of trouble with overall smoothness. They work in a pinch but should be replaced down the road. Also they were just too loud, and this is coming from someone with an old Harley that has drag pipes.
     
  4. Yellow0206

    Yellow0206 XS400 Enthusiast

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    Thks Mike - I really do love the little bike and put a lot of time into the cosmetics/mods as mechanically its quite good as it had only 7k miles - did need the carb rebuild and changed plugs oil and filter of course - and not sure why it had 150s in it i think stock was 145 which does seem big too. I do need to do the timing. Yeah i did the pipes for looks I am planning to run it some times with the pipes that came on it which I think are off a 360 and with the chrome fenders i came up with (a 10/2 Kaw front and a cut down SR400 as a rear hugger with custom brackets I made. Heres a pic with that look. Ill post after I do timing and it warms up again mid week and I test ride it. 7443FD57-EEA8-42C3-AD83-B1CF3EE35382.jpeg
     
  5. xschris

    xschris a lifestyle not a trend Top Contributor

    Too bad the rear muffler stay brackets are cut off the frame. It makes it hard to have good support for the exhaust system. Stock 77 xs400 used 142.5 mains. Make sure all your jets are real mikuni jets all others are no good.
     
  6. Yellow0206

    Yellow0206 XS400 Enthusiast

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    Chris i cut those off on purpose - was going for a cleaner overall look — in my build and that was a necessary detail in what I wanted to achieve overall.... with the longer mufflers that may prove to be more of an issue than when I run the shorter mufflers....I did add a bracket/support at the front of the mufflers that cant be seen in photos.

    Mike/Chris (and anyone else feel free to chime in) latest is that I did check and set the points and timing. Bike still breaks up a bit at 7-8k, runs great at idle and midrange and upper end til there. Seems to run a little better under load and will break up more with harder quicker application of throttle, will clean up a bit by backing off throttle. Plugs look real good and I just bought another set of NGK BP7ES too and that did not change things. Its been around 45-55 out when im riding. From other things I am reading im now thinking it could be a little lean....Im pretty sure there are 145s in there, there were 150s in there when i got the bike...
     
  7. Yellow0206

    Yellow0206 XS400 Enthusiast

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    Update I had 145s in there I put in 150s and does not seem to have made a difference still getting the missing, unsmooth, not good power at 6 or 6,500 up - plugs look real good....I have only set timing statically so far and re-read Chris’ post and just realized the advance mechanism is behind the points so I will both clean and lube that mechanism and dynamically time it as well....
     
    Last edited: Mar 27, 2020 at 8:20 AM
  8. Yellow0206

    Yellow0206 XS400 Enthusiast

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    Update i got out my timing light (i used it last about 25 yrs ago as i have been more of a car guy til recently and my oldest was an 88) and timed up the bike - its timed correctly and the advance is working properly. My problem with high rpm 6500-up lack of good smooth power/ missing is still happening. I am thinking weak spark at high rpm? Can old points cause this (mine look good) or really only bad coil or coils. Mikes XS has points cheap but no one has OE coils or direct replacement coils cost effectively and I hate to throw parts at it if I dont know for sure its the problem....
     
  9. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    You can test coils to make sure theyre within spec. Aftermarket points are good but if you can find OEM Yamaha that would be better. Quick check of the coils, you can see if the plugs are getting a blue spark.

    When points need adjustment, you will get random popping and backfiring, uneven idle, misfiring. Similar issues pop up when the valves need adjustment.

    Are you using the highest grade gas you can get? I run 93 in all my bikes and try to stick to Shell, Sunoco, Mobil, Phillips.

    When my bike was stumbling and breaking up, the main jet was too big. When it backfired out of the carb and "ran out of steam" it was too lean.
     

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