Motor keeps bogging and dying.

Discussion in 'Engine' started by Boostwhipped, Sep 16, 2018.

  1. Boostwhipped

    Boostwhipped Member

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    So I'm helping my buddy with his blaster and it's been a nightmare. Rebuilt the motor put new crank bearing weisco crank seals and honed topend with weisco piston. Started great and ran great took it out 3 times has probably 10 hours on it then went to take it out yesterday and it was a biotch to start. Probably 10 kicks finally got it started went to ride sounds like crap and kept bogging down no power. Changed the spark plug checked compression it's at about 110psi and getting spark and fuel. I'm running 40:1 gas mix any suggestions what could be the problem?
     
  2. Larry's Shee

    Larry's Shee Active Member Technician

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    110 psi is way low. What was it when first rebuilt, after heat cycles?
    What was your break in procedure?
    Did you retorque the head and cylinder after the heat cycles?
    Have you done a leak down test?

    IMHO, putting a new piston in an old hole is a waste.
     
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  3. Boostwhipped

    Boostwhipped Member

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    I didnt check the compression after I did rebuild, what do you mean by heat cycles? And the break in I first started let it idle for about 6-7 min turned it off and cool completely down and repeated that 2 or 3 times and changed oil before riding. Like I said this has been a night mare after I did the rebuild It was leaking oil from the drain plug so I bought one online and it was just a hair to long and broke off on the shifter drum inside the motor so I had to take the whole motor apart AGAIN get that chunk out and put the motor back together and it lasted about 10 hours of riding great. I will admit the last time we rode it we were doing trail riding through some rough terrain creeks and really steep hills through the woods
     
  4. jbuckster07

    jbuckster07 Active Member

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    Leak down test, heat cycles, re-torquing, the break in are some of the most important things you can do with a fresh rebuild... Looks like you only did 1/4 of the items...

    Leak down test...HAS to be done. You HAVE to know if you have an air leak, air leaks cause lean conditions which can and will blow a motor. it is imperative that this is performed right away

    After heat cycles, you have to re-torque the head and cylinder. Its possible they have wiggled loose. If this doesn't happen, this can cause a airleak and ultimately a lean condition which has the possibility of blowing up the fresh engine.

    Breaking the motor in involves running 1-2 tanks of fuel through it without riding it hard, putting around the yard, not going past 3/4 throttle. You need to seat the rings to the cylinder walls and hopefully find any problems that may have occured during rebuild without going WOT through the forest..
     
  5. Boostwhipped

    Boostwhipped Member

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    Well sh*t so I probably ruined the new topend is what your saying. With 110psi of compression it should still start right run right? Would low compression cause bogging?
     
  6. Larry's Shee

    Larry's Shee Active Member Technician

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    Maybe yes, maybe no. Full testing is only way to determine problem.
    What brand compression tester did you use? Schrader valve must be at end closest to spark plug hole. A Craftsman should be cheapest you should use.
    Retorqueing is important, especially for the head.
     
  7. Boostwhipped

    Boostwhipped Member

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    It's just a cheap tester off of Amazon. I'll try retorquing all the bolts and do a leak down test and see what happens
     
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  8. Larry's Shee

    Larry's Shee Active Member Technician

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  9. Boostwhipped

    Boostwhipped Member

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    So I did a leak down test today and it was perfect. I pumped it up to 6psi and it held as long as I left it on there without dropping a single psi. So I'm assuming that means my topend is messed up
     
  10. Larry's Shee

    Larry's Shee Active Member Technician

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    Time for physical inspection. Pull exhaust and look in port at piston, does it still look new? No scratches or scars, odd wear pattern?
     
  11. Boostwhipped

    Boostwhipped Member

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    Looked in there and had my finger in there I didnt feel or see anything wrong
     
  12. Larry's Shee

    Larry's Shee Active Member Technician

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    Time to start checking all electrical. Ohm spark plug cap separate. Trim 1/4" from wire before installing cap, if coil ohms good. Remove/disable TORS. CHECK continuity of switches. Ground should be clean metal. Pull flywheel and check magnets for rattle and clean of rust. Ohm stator and pick up coil.
     
  13. jbuckster07

    jbuckster07 Active Member

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    Question....did you buy a new piston and have the cylinder honed to the piston, or did you buy the same same piston and have it honed without the piston....
     
  14. blastorious

    blastorious New Member

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    it sounds stupid but it could be your air filter, I had the same problem with mine, I took it off and it started first kick. if you cant see day light through it its junk or you could try and clean it.
     

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