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My 2 steps forward 1 step back bike build

Discussion in 'The Garage' started by short1, Jun 24, 2018.

  1. short1

    short1 XS400 Addict

    Where is your negative battery cable connected? I'm trying to diagnose a no start/weak spark issue. Wasn't sure where it went when putting it all back together and want to rule it out. Thanks! Build pics are on page 2..
    Last edited: Jul 26, 2018
  2. 1978 xs400
    mine runs from the battery pole via quite a heavy duty cable to a bolt on the crankcase on the rear of the engine - so it earths via the engine cases which themselves are earthed to the frame via the engine mounting bolts

    regards dave
  3. short1

    short1 XS400 Addict

    Thanks, that's pretty much where I have it. After some checking, the leads to the coils show 12v switch on but when cranking drops to 7v. Battery is 13v drops to 11.5v when cranking. Is all that normal? Orange spark from plug and cap when cranking so it's weak. Cleaned the contacts from the ignition box didn't make a difference.
  4. xschris

    xschris XS400 Guru Top Contributor

    Full size 12ah battery?
  5. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Do you have electronic ignition? Have you tested the coils? Did you trim the plug wires off a bit where they screw into the plug boot?

    It could be the plug wires are all chewed up at the ends.

    My battery seems to carry more juice since Ive gone back to points ignition....? Im not sure if its just because I bought a new battery or what..

    You could have bigger problems like your regulator going bad.
  6. short1

    short1 XS400 Addict

    Actually no, 8.6ah battery

    It's an 81 sohc, pretty sure it's electronic? Not sure how to test the coil... Plug wires and caps are new.
  7. spectra

    spectra XS400 Junkie Top Contributor

    Yes electronic and as for testing the coils its easy......have a meter ? if so there should be instructions in the destructions that came with it.

    If not there are a few threads on here I think just have to search.

    Try this to https://www.mikesxs.net/manuals/IgnitionCoilTesting.html
  8. short1

    short1 XS400 Addict

    I just checked the coils, they both tested 3.5 ohms and 14k ohms, so I guess those are good
  9. short1

    short1 XS400 Addict

    So I'm an idiot, when i put the wire loom back on the bike I put the coil leads on the wrong side. Switched the connectors and it fired right up. However it's snapping and popping every few seconds and doesn't want to stay running for long, I think it may be running too rich? I'm going to take a video and post a YouTube link shortly, maybe you can tell me what you guys think..
  10. spectra

    spectra XS400 Junkie Top Contributor

    I had the same issue on my latest build........wired it according to the book but when the coil wires were swapped it ran.......as for popping what did you set the carbs to ? Also any other adjustments made to them ? Factory exhaust ?
  11. short1

    short1 XS400 Addict

    It's been 2 years since the carbs were gone through, they've been sitting in a box on the shelf, unfortunately I don't recall what I set anything to. I recall i copied someone elses setup that had uni filters and emgos, gonna have to search for it.

    After another try tonight it stayed running and with barely any popping, HOwever when it started warming up the crankcase breather hole was puffing smoke pretty good, didn't really smell like anything but seemed a little excessive. Don't recall it doing that when it last ran 3 years ago..
  12. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    My bike will backfire a lot when the timing is way out of whack.
  13. xschris

    xschris XS400 Guru Top Contributor

    8.6 is a small battery for using a e-start. Kick only is ok.
  14. short1

    short1 XS400 Addict

    Today is a new day, couldnt get it to start again, checking the plugs they are ngk bpr5es so I swapped them out for some bp7es plugs and it fired right up. Looking at it today letting it warm up, the crankcase breather never started puffing like it did last night...It won't idle unless choke is all the way out and I noticed the right side carb boot is what was popping. I'm sure those are alot to do with my troubles! Has anyone tried repairing them before? I've got a can of clear flex seal laying around I thought about trying for the hell of it. I'll also pull the carbs apart and relearn what I've done haha. Is it ok if i change the thread title so I can keep all my progress and questions(many to come I'm sure) in one spot?
  15. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    If you have spark plug boots with resistors, then you use spark plugs without resistors. Same goes vice versa.

    You could have caused damage or premature failure of the coils if you have too much resistance.

    How is the carb boot popping? Is there a visible hole? If so then you really should replace it.

    You can find repro carb boots online.. make sure to get the vacuum caps for each one too. And a little tip about new carb boots, put some oil where they mate to the carbs. It will be a lot easier to fit the carbs on and youll minimize the risk of the boots tearing..

    sync your carbs and verify timing.
  16. short1

    short1 XS400 Addict

    Actually the inside of the boots look good, the outside is cracked pretty good. After pulling them off I noticed I hadn't cleaned off the old gasket material on the right one, might not have been sealing good. I'm gonna go ahead and order some but in the meantime I'll play with the flex seal. I've read a little about this resistor/nonresistor thing and I gotta be honest i don't get it. How do you know which has which? Is 3.5 at the cap too much?
  17. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Better off to replace the boots and gaskets. Im not sure if the flex seal is heat or fuel proof but I wouldn't take the chance, especially when you need to depend on the thing to get you home. At least try high temp RTV sealant.

    I have both resistor caps and non resistor caps. I switch them out depending on what type of plug I use. Right now that I have the stock points ignition, Im using a resistor cap with NGK BP7ES plugs. I have switched to BP6ES before because I have a long highway commute. Ive been sticking with the 7s lately though.

    You should be able to test the caps resistance with a volt meter. Im not sure if it would be a valid reading because the cap isnt at operating temps? There should be a marking on the cap that give its resistance, I know my newer caps do. Itll be a number followed by the omega symbol, which is the symbol for resistance.

    The whole resistance thing is sort of confusing for me as well. I think a lot of it has to do with antiquated technologies, but I haven't ever read up on it so that's why I don't know.. If you have a resistance cap and a resistance plug. You might have too much resistance. This will make it harder for the plugs to fire and put more load on the coils. And that's about all I got for you.

    It would explain your orange sparks.
  18. short1

    short1 XS400 Addict

    Pulled my carbs apart, I've got 145 mains and 45 pilots. Uni filters with emgo turn out mufflers and some no name head pipes. Mixture screws are 3 turns out. I've got the NGK BP7ES plugs with NGK LD05F caps, is that ok? Still not sure which, if either is resistor or nonresistor.

    After cleaning up the boots mating surfaces (don't know how I overlooked that) it fires up easy and no problem running off choke. I did coat the boots with ultra copper gasket maker but do plan on eventually replacing them. Still need to sync the carbs and make adjustments once I can get it on the road but I'm happy that it runs!

    I've been getting the electrical figured out and now have working running lights, brake light and blinkers. Using an eBay digital tach/speedo and I got rid of the ignition switch in place of a toggle switch and am going to put the headlight on a switch due to a bad relay and I'm a cheap ass haha
  19. short1

    short1 XS400 Addict

    Tonight I got my clutch cable linked up and finally have a front brake thanks to Petew.

    I've been torn about the front fender, I wasn't going to use it due to it being dented and twisted with pitted chrome but I know it helps the rigidity of the forks, so tonight after some massaging with a hammer, a little sandpaper and a scotch brite pad with some wd40 I ended with something I can live with. It's not the prettiest but it matches the theme lol

    Attached Files:

  20. spectra

    spectra XS400 Junkie Top Contributor

    Looks good and yes something needs to be there for rigidity purposes. You can always go with a fork brace.

    I have a fender on one but trimmed it down a brace on the other.

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