Low Compression VS800 w/ 13K miles
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  1. #1
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    2005 Suzuki VS800 Boulevard S50
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    SLC, UT
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    Low Compression VS800 w/ 13K miles

    New to the forum here. Just bought a 2005 boulevard S50 VS800 with 13.3K miles for $800. It came with a box of carb parts and the promise that it just needed to be put back together to run fine. The bike had sat in his garage for 4 years...never ran in that time even once. I put it together and...

    -Bike makes no power over 1/3rd throttle and has pathetic throttle response. Has fuel, strong sparks and I cleaned the air filters. Bike will idle but not the greatest. Coolant is clean, oil looks like oil. synced the carbs and I quadruple checked the float heights. All carb settings are factory oem set. All valves were at .005" according to factory specs.

    -I ran a compression test and it has ~110psi both cylinders. I've used 2 compression testers with the same results. I added oil to each cylinder and they came up to about ~140psi, so we have largely a top end issue. Manual says it should be 188-232psi

    -I pulled and disassembled the motor and visually, I can't see any issues. Valves look good (but I have not removed them from the head), no obvious gasket issues, pistons, rings and piston walls look good. cylinder wall looks good, chain tensioners seam to function fine, ect... I obviously haven't been able to check the guides yet.

    -No indications that the motor has ever been pulled apart prior to me doing so.


    I think getting the head pressure tested is a good start at this point...

    Any other ideas? Thanks in advance!

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  3. #2
    M-J Lifetime Achievement Award
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    If it isn't sticking valve/s then bore and pistons need to be measured. They may look good but be worn. A rebore and new pistons shouldn't be too much and 800 for an 05 is fairly good IMO. If the rest of the bike is in good nick then you got a bargain....I would do the timing chain tensioner spring while its apart too.
    Smoke me a kipper I'll be home in time for breakfast

  4. #3
    Newbie
    My Bike(s)
    2005 Suzuki VS800 Boulevard S50
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    SLC, UT
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    It shines up nicely! I'm hoping it doesn't turn into a bad purchase haha. Its a comfortable bike for me as a beginner (with road bikes) so I'd love to get it reliable and put some real miles on her.

    Tomorrow I will look closer at the valves and seats. They all appear to be sitting where they should be but I will try compressing the springs and see how they pull back. I'll also clean the carbon out of the combustion chambers and look for cracks.

    I'll need to pick up a cylinder bore gauge to check that, but still most of the compression loss was above the piston so I'm not too worried about the bore/pistons.

    Tensioners seemed to be in excellent shape but i'll look at replacing them anyway if the price isn't ridiculous.

    -Any chance this could have been a cam timing issue? Upon disassembly I noticed that with the rear cylinder at tdc on compression stroke only one of the cam gears had the two notches actually parallel with the head. The other was a solid 40 degrees counter clock wise (retarded timing?) from parallel. But that wouldn't explain low compression on the other cylinder so maybe I'm mistaken. No damage to the gears either, they look great.

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  6. #4
    Super Moderator

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    My first guess would have been stuck rings.

    You should have done a "leak down" test before you took it all apart.

    If it WAS a sticky ring problem, it might magically run a lot better if you just put it back together.

    P.S. A buyer should NEVER accept "It only needs......." anything, more than putting gas into the tank or an oil change because......well you are finding out why.
    Some sellers honestly don't know but most know and just aren't telling.
    Don't believe everything that you think.

  7. #5
    Newbie
    My Bike(s)
    2005 Suzuki VS800 Boulevard S50
    Location
    SLC, UT
    Posts
    20
    Yeah, so far I'm still not finding any issues with it mechanically on inspection. I am waiting for a valve spring compressor tool still though. I'm hoping your right on the rings.
    I've never done a leak down test, but will not hesitate in the future seeing as I'm left pretty confused without it at this point...

    Thanks for the info. I'll take a closer look at the rings/bores.

  8. #6
    M-J Lifetime Achievement Award
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    I woudnt think a leaking boot would affect the compression test as it would need the inlet valve/s to be leaking too. You may get a slightly higher reading due to more air entering but even that would seem unlikely.
    Smoke me a kipper I'll be home in time for breakfast

  9. #7
    M-J Lifetime Achievement Award
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    (Quote removed.)

    How old are you?

    Moderators note: He's gone.
    Don't need stuff like that.
    Last edited by Easy Rider; 01-08-2018 at 07:58 AM.
    Smoke me a kipper I'll be home in time for breakfast

  10. #8
    Newbie
    My Bike(s)
    2005 Suzuki VS800 Boulevard S50
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    SLC, UT
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    Finally got the valves out. The intake valve seats all look shiny, clean and uniform.

    There is a small amount of pitting on the exhaust valve seats. I cant get a fingernail or even the point of a plastic gun cleaning pick to grab the pits so I don't know if that constitutes an issue or not. What do yall think? The pictured valve seats have been cleaned as best as I can. They did have carbon build-up on them (exhaust seats)...

    All valves appear free of any damage. Valve guide clearance hasn't been measured but they have next to zero wiggle. Dammit I should have done a leakdown test lol



  11. #9
    M-J Lifetime Achievement Award
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    They look good...if possible a valve grind/lap would probably not go amiss. The low compression would, IMO, not be caused by any valve/seat in the condition shown. You can do a basic leak down test with the head off. As long as the rest of the motor is left in-situ you can fill each bore with a set depth of oil and leave it overnight. Any major drop indicates a worn bore/piston/rings.

    Good luck
    Last edited by Aussie Steve; 01-14-2018 at 02:17 AM.
    Smoke me a kipper I'll be home in time for breakfast

  12. #10
    Super Moderator

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    Quote Originally Posted by Aussie Steve View Post
    You can do a basic leak down test with the head off.
    That's an interesting approach that I've never heard before.
    Alas, it only covers about 1/3 of a real leakdown test as it tells you nothing about the valves or heads (gasket).
    Don't believe everything that you think.

  13. #11
    Where Am I ?
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    Main jet maybe?

  14. #12
    M-J Lifetime Achievement Award
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    Yeah Ken saw a guy do a straight eight that way...admittedly it doesn't allow for any kind of compression but as a basic test for extreme wear then it is an indication.
    Smoke me a kipper I'll be home in time for breakfast

  15. #13
    Newbie
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    2005 Suzuki VS800 Boulevard S50
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    SLC, UT
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    Quick update. Came across a great deal on a sub 4,000 mile motor out of a 2008. I decided to hell with a rebuild as it would have cost more. Installing the motor hopefully by this weekend. Now I've got a spare bottom end/transmission etc... I can also sell a few components off of the old top end to take some of the financial hurt off. Overall I'm still into the bike about $1,900 and I'm good with that.

    Thanks for everyone's input and ideas, I appreciate it.

    In the future, a leak down test will always follow a bad compression test.

  16. #14
    M-J Lifetime Achievement Award
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    Good luck hope it works out...thats is still a pretty cheap bike in the end...esp with 4k miles on it.
    Smoke me a kipper I'll be home in time for breakfast

  17. #15
    Newbie
    My Bike(s)
    2005 Suzuki VS800 Boulevard S50
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    SLC, UT
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    Got it in. Cynced the carbs and replaced the fuel filter. It runs better but poor throttle response and no top end Now I'm second guessing my carb float heights lol.

    I'll take it out and run it for a minute at the point of falling on its face, then cut power and pull the plugs to "read" them for whats up with the AFR's.

    I've never been a fan but should I run some seafoam in case I missed a carb clog somewhere?

    I'll also start testing electrical components. Plugs are new but I'll look at wires, coils and the signal generator deal on the rear fender for starters.

    I'm going to be pro at assembling/disassembling this bike...


 
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