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Manual petcock issues

Discussion in 'The Garage' started by Mjk, Jul 26, 2017.

  1. Mjk

    Mjk XS400 Member

    Hello again all, and I apologize for the wall of text,

    For reference, I'm working on a 1978 xs400E.

    After changing the exhaust to a more free flowing pair of slip ons from stock and to K&N pods on the stock H pipe, I rejetted +2 both pilots and mains to 47.5 and 147.5 on each, and also got new carb boots and gaskets. At no point before or after any of the switches did the bike appear to skip a beat, running a touch rich but I would take the richness over possible damage from being too lean. However, the original vacuum petcock recently went bad, and taking advantage of the down time for a new MANUAL petcock from mikesxs to arrive, I cleaned the interior of the fuel tank with vinegar and nuts. The interior of the tank is now spotless and couldn't have turned out better in my mind (I avoided flash rust by rinsing with baking soda water then marvels mystery oil). The bike unfortunately doesn't agree with something now that everything is back together.

    Long story short, the left cylinder is now running very rich, while the right appears very lean by reading the plugs. I followed setting guides for the pilot mixture screws, but the right cylinder cannot seem to have it unscrewed enough while the left screw appears happy at 2 turns out. The carbs were bench synched and I'm working on a manometer currently. The floats are both set to 27mm from the gasket surface. Timing as been checked and checked again, and the barb on the right carb boot has been sealed when I switched to the new petcock.

    Issues right now include: inconsistent but generally high idle(2000-3500 ish, but jumps around and dies; idle screw that is at an angle between the carbs is all the way out to the point that releasing the throttle all the way doesn't cause the spring loaded linkage and cable holder to hit it) wanting to die and then dying when sitting in traffic unless I blip the throttle, particularly when braking. Also of note is that pushing down on the left carb fuel inlet or body even slightly causes the idle to decrese quickly and will shut off the bike in a second or two.

    My initial and continued thoughts are A) vacuum leak and b) the manual petcock doesn't draw fuel across to the right carb like the vacuum one did.

    Any help is greatly appreciated. I just feel a little exhausted after having run through everything a few times and would appreciate a fresh perspective.
  2. BBS360

    BBS360 XS400 Guru

    Did you plug the vacuum port that's now unused?

    Check for vacuum leaks at the boots by spraying WD40 around the boots when running. There are better writeups on this elsewhere on the forum.
  3. NewHavenMike

    NewHavenMike 1976 XS360C

    Ive noticed with my manual petcock, the dial indicator isnt as accurate as it should be. When you switch it to "open", make sure that youre getting the best flow at that spot. do the same for when its in a closed position too because i know mine isnt exactly perfect and you can still get flow when you think its closed.

    Also verify flow to both carbs by opening the screw in the 2nd bowl
  4. arfstrom

    arfstrom XS400 Guru

    Like BBS360 said, Once you removed the old vacumm petcock, the that part that created the vacuum, needs to be plugged. doesnt take much, if you have that rescue tape, that handles 500 degrees, just (worse case/ easy) wrap the entireity of the intake boot, or just put a bolt into the small opening of of that hose, and just cut it short, and plug it up...(truthfully there are many ways to plug it.) I would forget to plug that tube in, when I was working on the petcock, easy fix.
  5. Mjk

    Mjk XS400 Member

    That boot vacuum port is plugged with a bolt in the hose, and maybe there's just something I'm missing. I'm going to get after it today and see if I can find out what exactly is the issue, probably run through the carbs and just make sure it's all clear.

    I think the issue might actually be a vacuum leak from the choke port, as the right cylinder backfires like hell on any choke setting but completely closed but simultaneously appears to be running lean as previously mentioned.

    Thanks for the help everyone, I'll let you all know what happens if I can get it today.
  6. Mjk

    Mjk XS400 Member

    After running through everything, It's not perfect, but definitely better.

    There were no vacuum leaks around the boots or choke after testing with carb cleaner, and the internals in the carbs were all clean and in order. There was a bit of incredibly fine rust dust in the bowls of the carbs (would be <30 microns as that is what size my fuel filters are) which is concerning but it didn't clog anything and I don't think there's much more I can do.

    The key appeared to be syncing the carbs with a manometer, so that they both pull the same now throughout the rev range instead of one dying earlier and bringing the other cylinder down with it. Another issue I need to address and which I think is the main source of the issue is that the springs linking the carbs and throttle appear a bit tired and don't close all the way. Replacing these will probably even things out completely.
  7. arfstrom

    arfstrom XS400 Guru

    I had similiar type of rust in my carbs, I had been using a paper filter between the petcock/carb, Like you said it was not affecting the system. (I discovered this during my winter, late spring a couple years ago. so the fuel had long evaporated, leaving a ton of rust powder. I have also Koted the inside of the fuel tank with something like POR 15. amazon has a few other examples
    Then with the paper filter, you can track how dirty its getting.
  8. Mjk

    Mjk XS400 Member

    I too use a paper filter (just a simple one from the lawnmower section of Menard's) that says it's rated for 30 microns. I have no idea how accurate that is or not in terms of sizing, but I can definitely see it picking up tons of red coloration while the bowls still get that super fine powder. I am considering going with a one of those coatings, but I see it as a possible complication given their tendency to break down over the course of a few years being exposed to ethanol in the fuel, or so I have been told as I have no real experience with it. That being said, nothing is off of the table, and I appreciate your input.
  9. arfstrom

    arfstrom XS400 Guru

    I know I get under my colleagues skin, when I say this. Ethanol is corn syrup. 10 percent or what ever. carbureted vehicles as old as ours bikes, don't do well with the corn syrup. my experience is that I can use it, but if I don't drive the bike with in 3 days, the corn syrup sets up, and makes hard to start after two days. So if you need the $$ savings, great, drive it daily, using ethanol gas, if you drive it on weekends you want to find gas stations that have 100% fuel. (no ethanol) Ask Google for the closest non-ethanol gas station near you. and this site has some, but not all, as the one or two near me, did not show up on this web site. https://www.pure-gas.org/
    My fear on that resource is that it doesn't denote if that pump shares ethanol gas with non-ethanol fill valve (nozzle). I suspect you will get about pint to quart of ethanol gas before the pure gas comes out. I can do the math, I am just lazy, 10 feet of hose, plus/minus 6 more feet to the valve section. at 5/8 inside diameter hose.I would have to look up a co-efficient, since I am a part time fire fighter, I should be able to find that to get the total amount of fuel in the line.

    The problems I have had with the sealants were my own in origin. I had sealed up the gas cap vent hole, and strangely enough with out that vent,you can only drive about 3 to 5 miles, before you get some thing like a out of gas syndrome. So I did it twice. I think I tried Pur 15 first, (got it for free) it was marked for motorcycle. I have to believe the brain-y-acs, know what will be fine with the fuel coat/liner. as long as you have a kit for the motorcycle, it should be fine. check out that amazon, go though the reviews. I am sure the negatives reviews could mitigated down to forgetting something, or something. so check out the other bike forums. one of them going to sell you a good idea, and it wasn't that hard.

    hope that helps.
    spectra likes this.
  10. xschris

    xschris miles of smiles =)

    The non-ethanol gas I get come from a pump/hose specific to the gas. No other stuff goes in it. I used ethanol (10%) for many years with no issues. I also put the yamaha ethanol fix additive with it so that may have something to do with it. My bikes sat for weeks with no issues. I did have a dirt bike that I forgot to mix the additive with it and that had gel form in the petcock. So I know it can happen. I would also give the tanks a shake with the bikes on their center stands before I would prime the carbs. That will mix the ethanol with the gas making it easy to start.

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