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I'll share some data, please share your thoughts.

Discussion in 'The Garage' started by Scottrt, Nov 3, 2019.

  1. Scottrt

    Scottrt XS650 Enthusiast

    1983 heritage special with 16600 original miles. Bike appears to have been well taken care of but I do not know how long it may have been sitting.. I did not buy it from the previous owner directly... I got it from a private dealer. It seems to run out of breath around 5000 RPM. It will pull to red line but not impressively, and not in 4th or 5th. top speed seems to be about 75 miles an hour and that takes nearly wide open throttle to maintain in fifth gear.TCI seems to work well, all the advance in by around 3,000 RPM. Warm compression 138 PSI dry, 155 PSI after four squirts of oil. Both cylinders exactly the same. Starts easily with enricher on, idles well after it's totally warmed up, but I have not cleaned the carbs or checked the valve clearances yet... They could be tight, I don't know, and it might be starving for fuel on the top-end, I don't know, but pulling some enricher on does not seem to help, it seems to hurt at high RPMs. Timing chain is quiet but I can't really assess its condition because the bike came with fresh oil and a clean strainer. I've only put two rides on it for a total of 50 miles since getting it a few days ago. It's only in the low forties temperature wise, tires and chain are properly aired and adjusted and the bike rolls easily, but I weigh 360 lbs , 6ft 4in, and cut a lot of wind resistance with those buckhorn bars especially. 41 years ago when I was in college I bought a brand new 78 400XS special. I weighed two hundred pounds less but that bike would do a hundred miles an hour reasonably easy, and my friends 650 would leave me behind. I'm a retired engineer that loves projects but I don't want to spend money just for money sake. I forgot to mention it's 17teeth upfront and only 32 in the back. do you think this bike would benefit from re-ringing if the bores measure okay? Are those compression figures good to very good? If a guy did Mike's 750 kit will the original air boxes, carbs and exhaust get along just fine with some simple rejetting or would they hold it back? I just want to be sure she runs as good as she looks but don't I know how much my size is hindering it's giddy up.
     
  2. 5twins

    5twins XS650 Guru Top Contributor

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    Struggling at higher speeds and RPMs is often related to the carb diaphragms, as in they may have some small holes in them. This will give only partial slide lift.
     
    gggGary likes this.
  3. Bushyeyed1

    Bushyeyed1 XS650 Addict XS650.com Supporter

    Just needs a little TLC! Start small and get it running before the big bore kit. Just my opinion of what I would do before I blew my load.
     
    lakeview and gggGary like this.
  4. Scottrt

    Scottrt XS650 Enthusiast

    LOL, I would be quite pleased with myself if I could put some significant time riding her before I blew my load.
     
    gggGary likes this.
  5. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Sounds like you know which end of a wrench to hold. Invest the time and do a proper wake up drill.
    Brutal perhaps, but flogging a sick horse seldom improves it's health. Any BS34 bike (yours) needs the carbs stripped and the screens above the float valves cleaned the o-rings replaced. Many many other things need doing. If you are diligent you might get a chance on a nice day to see if things are improving before winter REALLY shuts you down. http://www.xs650.com/threads/guide-...checklist-for-the-condition-of-your-find.367/
    Yes a 32 tooth is a bit tall for a guy your weight. But if it's healthy it should pull red line in 4th.
    At this age stock air filters usually have started shedding the "mouse hair" into the final screen before the carbs.

    this_thread_is_worthless_without_pi.gif :cool:
     
    Moabite and grizld1 like this.
  6. Scottrt

    Scottrt XS650 Enthusiast

    I will definitely check the valve clearances and go through the carbs in the next couple of days. What do you guys think about the compression figures?
     
  7. Scottrt

    Scottrt XS650 Enthusiast

    The first thing I did before I rode it was pull the left hand air filter... assuming it would be all crumbly foam if it was original and indeed it was and it was. I diligently removed the old foam and all the glue that secures it to the structure of the filter and planned on using new filter foam around the original air filter frame. I found all the material including neoprene for the new front seal on the filter. fortunately I pulled the right filter before pulling the trigger on the new foams only to find it bent and caved in and not suitable for rebuilding. Partzilla sells new ones for a really good price that are Yamaha brand but are they 35 years old? Or do you think they would be relatively new stock?
     
  8. Scottrt

    Scottrt XS650 Enthusiast

    So I just pulled the carburetors off my bike and was surprised how clean they are inside. The diaphragms look good but the float level on both bs34 s was exactly 20 mm and if I'm correct it should be 22 mm, so I guess that would make it run rich and perhaps bog it down a little...? the gaskets look new so somebody must have been in here very recently, but I will still pull the Jets and needle valve out and blow all the passages good. IMG_20191103_230208126.jpg IMG_20191103_230208126.jpg IMG_20191103_230310970.jpg
     
  9. Scottrt

    Scottrt XS650 Enthusiast

    also, is it just me or is it necessary to remove the intake manifolds to gain enough room to pull the carburetors out around that backbone tube that comes down?
     
  10. 5twins

    5twins XS650 Guru Top Contributor

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    Well no, the intake manifolds don't need to come off, but it is sort of a "Rubik's Cube" affair getting the carbs in and out. Removing the acorn cover nut on the cam chain adjuster, the throttle cable bracket on the left carb, and the butterfly shaped plate between the carb tops will help.

    Yes, a 20mm float setting would have the fuel levels pretty high and could cause rich running. I don't see the rubber caps over the pilot jets in your pics. Did you just remove them or were they missing? The bike won't run right without those either.

    [​IMG]
     
    Last edited: Nov 4, 2019
    gggGary likes this.
  11. Scottrt

    Scottrt XS650 Enthusiast

    Yes, I remove the rubber caps over the pilot Jets just to take a peek inside. When reassembly time comes, I will go ahead and put my intake manifolds on first and then remove the acorn cam chain cover and leave off that upper butterfly that mounts to carbs together and solve the Rubik's cube. Thank you so much for those insights.
     
  12. xjwmx

    xjwmx XS650 Guru Top Contributor

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    tilt the front of the carbs down and hold the carbs solid against the backbone. then rotate the carbs to the left, still holding them solid against the backbone. acorn nut off helps, but not strictly necessary. probably worth the trouble to remove it though. no need at all to remove manifolds (a big effort with carbs in place)
     
  13. Scottrt

    Scottrt XS650 Enthusiast

    To do it your way, does the breather hose that runs along the backbone also have to be removed first?
     
  14. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    They do look good inside. But that's why you got a deal the PO couldn't figure out how to make it run right. With your organized attack you will get to the bottom of this! I and others have bare air filter frames suitable for new foam. NOS stock filters are prolly fine, in dry temp controlled environment they would last a long time. Hint tug a bit on the mouse hair on any suspect stock filter, if it's bad it'll fall apart.
    On carb removal; I always pull the manifolds, really it's the easiest way. Hint; a long arm ball end 5mm allen wrench.
    Yes on cleaning jets, specially pilot jets. check the orifice in the bottom front of the float bowls. Often forgotten is to tap out the needle jets (emulsion tubes) and check the cross holes. Also the air jets found in the intake bells. I highly recommend the washer mod for jet needles if the stock no clip adjustment needles are still in place. Check jets against the chart and that they are OEM Mikuni jets.
    650carbspecsreducedsizeey7.png
    Get a voltmeter on it check for proper charging the stock TCI is quite fussy about having a enough voltage. Check plug wires, plug caps for correct ohms, caps are occasionally weak points. Clip a 1/4" of insulation off the plug wires rebend the wire cores at the caps.Check, set your valves. set cam chain, use the while engine is idling method.
    Keep posting, you will get this! Make sure the cap is on the RH vacuum port on the manifold and it's not cracked. Check the vacuum line to petcock make sure the petcock is functioning properly. Cap the manifold vacuum port, use the prime position as a test. A leaky petcock diaphragm can flood the LH cylinder. Replace any original fuel lines with tygon or oregon brand 1/4-3/8 fuel line, from a small engine dealer. (translucent yellow).

    130 pounds compression is enough for it to run well, once running right, give it a couple hundred miles, recheck compression. A decently cared for XS650 motor is generally good for 30-40,000 miles if the front cam chain guide remains intact. :confused:
     
    Last edited: Nov 4, 2019
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  15. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Do the drop test on the diaphragms. Note that good choke plunger action, seal at bottom is needed for correct piston action. Throttle shaft seals..........
    It's kinda rare but collapsed inner exhaust pipes have happened! Mouse nest plugged muffler(s) can happen... Cracked or poor seals on intake manifolds.
     
    Moabite likes this.
  16. XSLeo

    XSLeo XS650 Guru Top Contributor

    If someone was in the carbs he may have gotten a kit with new needles and such. If so they may be the wrong parts. Most of the kits come with the wrong internals. Gaskets work but the rest don't.
    gggGary posted a chart. With your carbs off is a good time to check to see if the parts are right. Remove all your parts. They will have the numbers on them to compare to the chart. If stock they should also have the Mikuni square in a square symbol on them.
    Best to use genuine Mikuni jest. Several places online have them for about the same as some part sellers sell Chinese knock offs.
    Leo
     
    gggGary likes this.
  17. Scottrt

    Scottrt XS650 Enthusiast

    Thanks Leo, will definitely do that. The main jets are 132.5, I remember seeing that, but they also looked old. I have read that needle jet openings can wear... Does that occur on our Yamahas?
     
  18. 5twins

    5twins XS650 Guru Top Contributor

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    Not so much really. What can happen is the insides get eaten away by varnish if the carbs got all gummed up and were allowed to sit that way for a long time. Then the metering orifice is too big and they run rich. Do pull and clean them as Gary said. They can (and often do) get all gummed up down the sides. The little holes down the sides add air to the mix so if plugged, you'll run rich. Also as Gary mentioned, this jet is often overlooked.
     
    gggGary likes this.

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