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How to change oil and why am I idling at 3000 when fully warm

Discussion in 'The Garage' started by Floatxs, Apr 16, 2011.

  1. Floatxs

    Floatxs XS400 New Member

    I'm a new owner of an 81 xs400 special II and quite happy about it myself. It runs great but I have a few questions and concerns I've been reading the forums and I'd like to thank all those who respond to people I've learned quite a bit already but it's time for me to ask some questions.

    First I'd like to know how to properly execute an oil change and where everything is on the bike to do it and wether or not anyone recommends synthetic. Second after my bike is warm and I've been riding for a little bit 20 or 30 mins it idles at 3000 I feel as though this is a bit higher than it should be but I have no clue as to why it is doing it. I put some sea foam in as a preventative measure just to clean stuff out. Other than that it runs good and the bike was a steal. Also I've read things about a dip stick and I'm failing to find one anywhere I have an eye and a cap on the lower end but I can't find I dipstick and I'm hesitant to just start pulling on things.

    If anyone can help it'd be greatly appeciated

    Thank you
  2. filter is on the front of the motor between the header pipes...sometimes the bolt is a pain to get of...but you can buy replacements easy enough...I got one off ebay.
    oil drain plug is on the very bottom of the motor....likely a 15mm(?).
    It should say on the side cover near the oil filler cap( right side) what the capacity is...and the sight glass on the lower side cover should be about 1/2- 2/3 full (IIRC?)while the bike is on the center stand...not leaning over.
    As far as type...make sure it is motorcycle specific oil,as it bathes the clutch plates as well...and certain automotive motor oil types dont work well with clutches
  3. bcware

    bcware Well-read Top Contributor

    Idle should be about 1200 rpms. Does it idle around 1200 when cold?

    As a general rule if performance degrades as the bike gets hot you are usually running too rich. If performance improves as the bike warms up you are usually running too lean. Hotter air is less dense and therefore as the engine gets hotter proportionally less air is combining with more fuel.

    That being said, does the bike have any modifications to the exhaust or intake? If the bike is stock there are other possibilities that exist to explain your rise in rpms. As parts get hot they expand and potentially exacerbate leaks.

    Troubleshooting can be tricky because sometimes all of these conditions create ambiguous symptoms. Do you get any backfiring or popping when the bike is hot? Is there any stumbling? If you blip the throttle can you get the idle to fall? Have you pulled out the spark plugs to look at them?

    My dipstick is attached to a screw-on cap on the right (braking) side of the bike. It's obvious and just screws off. In general not many important parts will screw off the bike by hand very easily.
  4. bikerbob

    bikerbob XS400 Enthusiast

    The dip stick is connected to the cap on my 78. I read that you set in the hole rather than screw it in to check the level. I saw some folks on here recommend diesel oil so I went with Castrol GTX 10w40 Diesel oil, less than 5 bucks a quart. Jeep 4.0L engines are known to carry low oil pressure and this oil was supposed to be the cure, and it was (somehow). There are some real pros (I"m not one of them) on here, do what they say and you won't go wrong.
  5. Expensive synthetic is not necessary for our older design engines. Best oil: any name brand diesel 15W40 oil!! Why? It is formulated for hard working GAS and diesel engines and has more anti-wear additive than found in most any other oil. Unless you live in an exceptionally cold climate, use this viscosity oil. The diesel oil is ok for wet clutches found in bikes. Don't use diesel oil formulated for the new advanced diesel engines. I believe oil refill is 2.3 L with new filter or 2 L w/o filter change. I use Valvoline Blue 15W40 diesel oil because it has almost as much anti-wear additive as racing oil. I use the same oil in both of my older generation Mercedes gas engines and my scooter.

    As for your high warm idle problem, my bet is bad or missing very small "O" rings at the bottom of the air mix screw located on the top of each carburetor. Do a search here and you should find info about the problems caused by bad or missing o-rings at the bottoms of these screws. The screws may have a factory cap over them to prevent changing the setting. The caps can be carefully drilled out so you can get to the screws. Factory setting for the screws was 1.5 turns up (counter-clockwise) from seat. The bike runs better when the screws are adjusted to 3-3.5 turns up. When seating (clockwise) the screws, turn down gently so as not to damage needle or seat.
  6. Floatxs

    Floatxs XS400 New Member

    Yes when first started it runs about dead on 1200 once it starts to get hot the rpms slowly work up until resting at 3000. Performance wise there is relatively little change. No backfiring or popping has occured to date and the bike is totally stock. The rpms fall when I pull in the front brake. Whoever installed the plugs before me screw them in there unbelievably tight so its going to take some effort to get them out but I'll get them out today.
  7. My '80 behaved the same way until I replaced the o-rings. Never could get a proper low idle after the engine warmed up. If the factory plugs on top of the idle mix screws are still in place, most likely those o-rings have never been replaced and the mix screws have not been backed out to a richer mix. Backfiring may or may not occur if the o-rings are leaking air into the carb - just depends on how much air is leaking by the screws. I replaced the o-rings and the choke rod seals on each carb at the same time. No more problems and it will idle down to a nice beat. Just saying this is a known problem with these carbs and the age of the seals.

    If you have tried to remove the spark plugs and they won't budge, have you tried when the engine is warmed up? The head is aluminum so be careful how much you tighten the plugs when re-installing. I recommend anti-seize on the threads of the plugs. Check your plug type. They should not have an "R" in the plug number. This engine uses non-resistor type plugs because the plug caps are already 5-10K ohm resistance. A great plug brand for this engine is NGK. I use NGK BP7ES, that's a "7" heat range. Some folks like a "6" (hotter tip) or an "8" (cooler tip) heat range.
    Last edited: Apr 16, 2011
  8. lhaolpa

    lhaolpa XS400 Junkie

    Just to reinforce what previous poster said about stripping the spark plug threads,very important.Always use anti-seize on plug threads on aluminum heads.The packaging for new plugs has the torque value for the plugs:follow their recommendation.You might try to spray some penetrating oil on the plugs a few times,warm it up,try,then repeat until it loosens up.Good luck. lha:confused:

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