The XR400 Thread

Discussion in 'Thumpers' started by Hayduke, Jan 16, 2008.

  1. HopheadRed

    HopheadRed Adventurer

    Joined:
    Mar 16, 2011
    Oddometer:
    15
    yeaaaahhhh...:huh What would cause a sheared flywheel key? I just don't understand the fact that it was running previously with the DS kit - kinda makes me lean towards wiring?

    Yes, the valve was not bent - He initially thought it was, but that was prior to removing the head to find the screw. He said the valve was surprisingly not damaged and seals fine.

    Choke assembly and carb are in good order and clean. Spring is tight, etc.

    This def crossed my mind - after what I've read between here and TT, I was thinking along the lines of this knowing you have to kick this machine like you mean it. But I would think between the drill and the car-powered roller to try and bump start it it would fire.
  2. HopheadRed

    HopheadRed Adventurer

    Joined:
    Mar 16, 2011
    Oddometer:
    15
    +1 on the custom adapter btw! Sweet!
  3. IronSpadeCycles

    IronSpadeCycles Button Pusher

    Joined:
    Aug 8, 2009
    Oddometer:
    242
    Location:
    Houston TX
    David, I did a big ride in CO last year down near Durango after driving up from the TX gulf coast. My Mikuni/Sudco catalog suggests a reduction of one jet size per 1750 vertical feet of altitude change. Are you running a Trail Tech computer? I'd use it as a tell tale to help you with final jetting. If your riding around at 70-80F degrees air temp and getting CHT (cylinder head temp) in the 190-230F range your about right jetting wise. I was getting in the 295+ range with several situations of it going over 300F when it got hot riding down around 6000 ft. I ended up going back to what I thought was stock jetting.

    Although I had a suggestion for jetting from the local area Honda shop in Durango, my bike ran very hot the whole weekend at altitudes in the 9-11K ft range near Telluride. Turned out the shop was basing the jetting figures on stock jetting for a 2001 XR4 (which is lean to begin with) but my bike was equipped with a high comp piston I was unaware of, (I bought the bike used and it had changed hands 3 times in 10 years). The jetting I had in the bike at sea level was running lean at best and probably restricting it so when I blindly changed over to what the shop suggested I really leaned her out, well beyond what I needed for 9000ft+ altitude.

    Jetting is a very touchy subject, we can all make suggestions and when you blow up your bike taking our advice, who's really to blame? The trick is to have some kind of data collection device like the Trailtech computer, it will give you all the needed info as well as help you keep from running out of gas while on your ride. One suggestion is because the spark plug is such a bitch to get to in an XR4 the heat sensor should be attached to the top valve cover bolt between the upper engine mounts instead of the spark plug. While doing this figure the actual CHT at the combustion chamber is probably another 30-50 degrees hotter than what will read at the outer most extreme of the valve cover. Take this in consideration. So with the sensor placed there on the top of the head your ideal CHT read out on the TrailTech should be between 150-200 depending on outside air temp (obviously it will read hotter if ambient air temp is hotter then 80 degrees)

    I hope this helps. I've purposely not just given you an ideal jet size cause every bike is a little different and your idea of "uncorked" may be very different than my interpretation. So if you know your bike is spot on at sea level and your intended riding area is on average 7000 feet, you would reduce the jet size by 4 sizes (7000ft/1750= 4) (Mikuni jets are in steps of 10 equals 1 full step and 05 is a half step) So if 162 was stock dialed in sea level jetting a reduction to 122 main is what they suggest, but again this is only a suggestion.

    I found another link that explains it a little better and I hope this helps you out. Best thing you can do is get several main jets and a couple pilot jets. If your having trouble starting the bike change the pilot jet, if your running hot overall change the main jet. Always error to the fat (rich) side, worst thing is you'll run cool and foul a plug, error to the lean side and well grenades make noise. The two circuits will work together but just changing the main for areas in the 3000-5000 ft range won't really be a big deal, anything higher you will need to change both. Leaving in your stock pilot at 3-5K ft and you won't need your choke to start the bike, anything over 5K ft and the bike might not start at all and just flood out the plug.

    Later Travis

    http://www.4strokes.com/tech/howtojet.asp
  4. IronSpadeCycles

    IronSpadeCycles Button Pusher

    Joined:
    Aug 8, 2009
    Oddometer:
    242
    Location:
    Houston TX
    I almost forgot, keep a 6mm 1/4" drive socket with a short extension and ratchet in your tool bag with a 17mm wrench and a short Phillips and straight blade screw drivers. If you need to change just the main jet on the trail it can be done in about 10 minutes, if you need to pull the bowl to change the pilot it will take about another 5 minutes. Trust me I know I did this several times over a few weeks and 5200 miles logged from Durango CO to Portland OR and back to my home town of Port Lavaca TX. You don't need to remove the carb or even turn it, just drop the lower bowl drain screw with the 17mm wrench. When you get the main out take care not to loose the small white plastic skirt that shrouds the jet. I often used a dab of grease to hold it in place each time I changed a jet.

    Hope this helps.

    Later Travis
  5. Davidjohnson

    Davidjohnson Been here awhile

    Joined:
    Jul 15, 2010
    Oddometer:
    181
    Location:
    South Texas
    Travis, thanks for posting this. I will need time to digest all of it but it is very helpful. I do not have any kind of monitor that reads temp but will look in to that.

    David
  6. IronSpadeCycles

    IronSpadeCycles Button Pusher

    Joined:
    Aug 8, 2009
    Oddometer:
    242
    Location:
    Houston TX
    David, the TrailTech runs about $120 and honestly it was an eye opener to be able to see exactly how fast I was going and mileage I was getting with different gas from different areas of the country. In CO and UT I made better than 60 miles per gallon but in Nevada and AZ it dropped to just above 45mpg. I'd call that a significant difference based on how much ethanol was blended into the fuel. You might just be trail riding in the CO mountains but if you've only got a stock 2.5Gal tank, if set up properly, at best you'll get 120 miles before you go on reserve. At worse you'll run out of gas before getting back to the station and pushing a 240lbs bike up any hill in CO just plain sucks ass.

    Just my .10 cents. Later Travis
  7. Luke

    Luke GPoET&P

    Joined:
    Aug 25, 2004
    Oddometer:
    4,260
    Location:
    Beaverton, OR

    No wonder you were having trouble with jetting. Mikuni and Keihin jets sizes have nothing to do with each other. According to the manual, if your correct main jet at sea level was 162, you should run a 152 at 7000 feet. Not 122.

    Here's the chart:
    http://john.rushworth.com/Pics/XR400/XR4FAQ/main_cor.htm
  8. Luke

    Luke GPoET&P

    Joined:
    Aug 25, 2004
    Oddometer:
    4,260
    Location:
    Beaverton, OR
    ...
  9. Luke

    Luke GPoET&P

    Joined:
    Aug 25, 2004
    Oddometer:
    4,260
    Location:
    Beaverton, OR
    Thanks guys! Licking a finger and grabbing a wire is another way to check for 100v, but I was never brave enough for that. I've done it enough times by accident. :D
  10. Brewster

    Brewster Adventurer

    Joined:
    Apr 16, 2011
    Oddometer:
    43
    Location:
    Arizona
    +1


    Cheers
  11. HopheadRed

    HopheadRed Adventurer

    Joined:
    Mar 16, 2011
    Oddometer:
    15
    So, I just hung up with John and mentioned what you said regarding the drill. He clarified a few things for me -- The spark is strong, when it sparks. He said using the drill with the plug grounded out on the head it will spark 4-5x and than not spark again at all. Consistently inconsistent? Lol.

    He said while using a car powered roller on the back wheel it will fire and run for a few seconds and die. Won't fire again for seconds and than same thing.

    I'm all :ear .....If he can't get this thing to run before I get back to town, how the hell do I go about squaring up with this guy since he's put quite a few hours into this thing but no results?!? I won't be happy paying out a bunch of cash for a bike in pretty much the same shape I dropped it off in...

    He insists its electrical still - what are the chances the "working" CDI from and my existing CDI have the same issue? Would an issue with the wiring harness cause these type of symptoms? I think that's the only part of the ignition system yet to be replaced. baaaahhhhhhh!!!!!
  12. IronSpadeCycles

    IronSpadeCycles Button Pusher

    Joined:
    Aug 8, 2009
    Oddometer:
    242
    Location:
    Houston TX
    No Luke I wasn't running a 122, I was just making a point based on Mikuni as I have a MIkuni 34mm on my XR600. And I realize that I made a mistake in my advice just today. Another reason not to take everyone's advice blindly without doing your own homework.

    I have the stock Keihin in my XR4 and I think I had a 168 at sea level but I still wasn't sure it was right. I didn't have the Trailtech hooked up till I got to CO so I really didn't have a baseline to go off of. When I got to CO the shop in Durango suggested a 142 and I even thought that was wrong but I went ahead and got it with a 148, 152, 158, 162 and a 166 cause they had them. I was wrong all the way around. I ended up putting in the 166 in Moab for the whole rest of the trip till Reno and it ran better but not perfect. I also pulled the top end in Reno and discovered the 10:1 piston and about 1.5mm of carbon build up on top of the piston. Those two factors raised the compression to around 11.5:1 and once I got it cleaned off the temps came way down and I jetted back to I think 152 above 4000 and 162 at sea level to 4K. The only damage I noticed from the high heat problems was a noisy cam bearing that cost me $12 at the Reno Honda dealer.

    Owell she held up and my compression is still very good. I'll probably put a 440cc kit in it when it needs freshening and rejet all over again.

    Thanks for the link about the Kehin. Later Travis
  13. booger1

    booger1 Been here awhile

    Joined:
    Mar 10, 2010
    Oddometer:
    972
    Location:
    Arizona

    Just had this problem, weak to almost no spark witht the e-botton. I had also done mine with a kick starter and it would start with that very well. however when the motor got hot it was very hard to start. I tested the excitor coil leads and was only getting max of 30v, your suppose to get 100v min. I installed a 200 watt stator and it works great now. I had also replaced the cdi before the stator with no results. Try there next.

    Sorry, I jsut went back and read the post, you already changed the stator, but the wires may be reversed in the plug and you'll have to sort that out. But get a voltage reading from the excitor coil.
  14. huckleberry

    huckleberry BACK ROAD BOMBER

    Joined:
    Sep 19, 2008
    Oddometer:
    1,106
    Location:
    N.E. Pa.
    ok so now i belong ---- new owner of a 97 xr4! where's the best place for stock parts?:lol3
  15. Brewster

    Brewster Adventurer

    Joined:
    Apr 16, 2011
    Oddometer:
    43
    Location:
    Arizona
    I use Bike Bandit for all my OEM needs.

    Cheers,
  16. Ace100

    Ace100 Monkeywrencher

    Joined:
    Jun 17, 2008
    Oddometer:
    447
    Location:
    Landers, baby, Landers!
    +1 on BB. Not as consistant on aftermarket goodies but really good on stock.
  17. Whistling Weasel

    Whistling Weasel Adventurer

    Joined:
    Dec 11, 2007
    Oddometer:
    14
    Location:
    Brisbane QLD
    I'm trying to find some info on using the mikuni TM 34mm carb on my 2004 xr400. I know some people have used it but can't find any info on their experience and or problems. Any help would be greatly appreciated. Thanks
  18. Tspoon

    Tspoon CRANKIT

    Joined:
    Feb 14, 2006
    Oddometer:
    30
    Location:
    Penticton, B.C.,Canada


    Lots of carb info here

    http://www.thumpertalk.com/forum/showthread.php?t=822033
  19. Whistling Weasel

    Whistling Weasel Adventurer

    Joined:
    Dec 11, 2007
    Oddometer:
    14
    Location:
    Brisbane QLD
  20. booger1

    booger1 Been here awhile

    Joined:
    Mar 10, 2010
    Oddometer:
    972
    Location:
    Arizona
    I think your thinking about a TM36. that's is what I have and can't believe the differance it made in starting and power delevery.
    Well worth the money.