Question Hoss.

Discussion in 'Mechanic and Repair' started by metro-hp_48, Apr 18, 2004.

  1. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Man, this 17 hp is driving me crazy..... So wierd. Hate to bother you (anyone feel free to reply), but you've always been the resident expert machanic, so....I hope you don't mind.
    This question could pertain to any 4 stroke engine.

    What could make one cylinder (a twin in this case) run so lean, and the other is burning perfect. I could see if both plugs were lean, or if each had their own carb. Just started doing it (will drop about 600RPM.....or be fine) Takes along time to come up to 3200 RPM (high as it will go) under laod (3650 usually underload)

    Seems like with the compression the same on each, it would mean that the valves are seating right (but does "spit" alittle mist of gas out........and I was wondering if it was getting around the intake valve from the combustion chamber.....) normally I would say timing.

    Starts great, and runs great, just low rpms, and no power when deck engaged. (I know power = compression....
    Bottom line, I can put in a new plug, and with-in 3 mins. it's white.
    Don't want to run it with that cyln. that dry/hot. Anything you might could think of that would make a plug lean out so bad so quick? (need it running bad)
    Might get a 23hp Kaw just and worry about this 17 hp later.
    (Thanks Hoss)
    (all started after the carb./airbox got loose, and was sucking much air (15 mins. tops is all it ran)
  2. LynyrdSkynyrd

    LynyrdSkynyrd LawnSite Member
    Messages: 179

    Have you did or had a compression test done and compared the cylinders?

    Valves (burnt, bent, chipped, carbon build up, seals).
    Blown Head gasket. Loose Head bolts.
    Bad intake gasket.

    Can cause a lean condition.
  3. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Yeah did check the comp. on both today (and earlier in the week)
    Bad cylinder is about 5 pounds better than the good cylinder. Did take the intake off, incase it was leaking around there (had checked it running with Either for leaks yesterday. Wasn't any.

    Have to wonder what could go wrong with it (running real lean) in just 15 mins. One cylinder perfect, and one will lean-out very quick. Weird. Just hated to take the head off, and look at the valves, without another head gasket handy.
    The wierdest part (in a way) was it was bad (sick) (plug never felt right, as far as tightening it up) and just tightening the spark plug that extra little bit made it run perfect, but the next time I ran it, it went right back to sick.
    Did check the valve lash (to see if it was extreme, but didn't know the lash amount), and made sure they were working properly (looked at the stems, and appeared fine (most burnt valves I've seen, show the heat damage on the stem, too)

    The comp. gauge I have will hold the measurements until released, but I wish it would let me know if it was bleeding off.
    (seems if it was bleeding off too much, the comp. wouldn't be so high)
    So the FH500V has a decompression release on it, for easy starting? prob. not? (always wondered how those worked) Just curious, because the exhaust valves open the least bit, before it goes to TDC. (both cylinders do it)

    Well, as far as the comp. goes, it went right up to 90 psi. with one pull of the rope. (both plugs out, and full thottle) and every pull did increase the pressure up to about 160? (can't rember now)
    Did figure the cyl. was dry with running so lean, so I did add oil, and on the first pull it went to 120.
    The "spitting mist" of the gas makes me think intake valve. (seems the pressure is getting by the intake valve and blowing out the carb. but wanted diff. opinions before taking the head off)
    2 valve realted questions I have is; Are the head bolts made to be reused (have to ask now days....esp. an import motor)
    and what is the valve lash? (have the Kawasaki manual here, but not located it yet)
    Crazy. Starts great, and runs good.........just no power (and not up to speed) Seems it is going to die, before the blades start turning. (grass getting tall.........mower is weak)
  4. Mikes Machines

    Mikes Machines LawnSite Member
    Messages: 112

    Its kind of hard to tell from the picture in the link below but usually if there is a spring with the cam shaft the engine has a compression release.

    If your engine has a decompression feature you should not be getting more than about 80 or 90 psi. 120 is too high and 160 definitely shows that it is not working.

    Too check the valves you need to do a leak down test. This pressurizes the cylinder through the spark plug and measures how much air is leaking past the valves or rings. If it is leaking you can hear it coming out the exhaust or intake. If it is leaking past the rings you will hear air coming out of the oil filler. For one cylinder to be leaner than the other something has to be different on one. It cant be the carb so it has to be an air leak or maybe a weak ignition on the non lean side. There are two coils who knows. I hope this helps.
  5. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Thanks Mikes Machines. Have been trying to think of a way to check for bleed-down, and forgot about pressurizing the cyl.
    Will deff. do that tomm. Trying to think of anything I can before taking the head off. (the comp. would go up with each pull of the rope to about 160, but just on 1 pull it would go to 90. (pretty much have narrowed it down to the valves (figure the intake, since it does want to spit gas some....Enough to get your hand damp, if it's right in front of the carb.
  6. ducky1

    ducky1 LawnSite Senior Member
    Messages: 252

    May sound dumb but I would try another plug.
  7. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Wouldn't sound dumb at all, Ducky1. Have tried atleast 5 diff. plugs (although the same brand and type) Put the original plug back in, always the same thing. Woing with a NGK, or Nippon, but these Champions since new, have always worked good, and still good in this other cylinder. (amazing that a new plug(s) could turn so white, so quick)
  8. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Woing with a NGK....... oops. "Going" with a NGK....... (took me a min. to figure that out)
    Don't mind changing the valves if need be, but would not want to change the rings. (as far as what it takes to get to the rings) Makes more sense that the valves would be affected first..I hope.

    Thanks for the help, everyone.
  9. 65hoss

    65hoss LawnSite Fanatic
    Messages: 6,360

    How many hours are on this motor?
    I think I would check the spark also.

    Does the spark plug hole seem striped out to you??
  10. metro-hp_48

    metro-hp_48 LawnSite Senior Member
    from TN
    Messages: 874

    Thanks for replying Hoss. Tightening any plug in that hole, has not felt exactly right, for awhile. Seems I could always go alittle tighter, but afraid to since the head's aluminum. Did pick the RPMs up, after doing nothing but tightening the plug even tighter, but the next time I ran it it was back to 3250 (at best) under load. What was making me think maybe the intake valve was bad, is that if you hold your hand about 2" away from the carb, your had would be wet [damp] (really only does that at higher RPMs)
    Seemed like the only way to get pressure back into it (carb) would be leaking around the int. valve. (figured there wasn't much of a way to adjust any timing, which I figured could make it spit gas back out?)
    Starts real good, runs good, but real slow gaining RPMs (maybe 5 secs) and 500-600 RPM down.
    I wonder what would more likely get hurt by it sucking so much air. (head gasket less than 8.00, valves not much more, and the head is only 102.00 (not that I would want to buy one), but really don't want to take it down re-ring it.

    (this mower doesn't see much use, since it's the only one I ever bought new, and have others that I have alot less in) so it's only got 220 hours. (but, out of warranty .................for awhile now)
    Still looks new.
    Thanks again,Hoss. (just had a big Mustang show @ the Nashville Speedway...........didn't get to go, but saw many fine Mustangs going down the road)

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