Leak down help


7 replies to this topic
  • dweaver76

Posted January 12, 2015 - 04:56 PM

#1

Still no luck starting this bike.
I've searched and not found a good "how to" on doing a leak down test to include PSI ranges for my 03 WR450 from the grave project.

Help...

  • Krannie McKranface

Posted January 12, 2015 - 06:30 PM

#2

You can make your own, using expanding rubber plugs for the intake and exhaust, and a sparg plug air chuck adaptor.

 

You can also pull the head off, and turn the head upside down and pour gas in it.

If any escapes, you have bad valves and seats



  • dweaver76

Posted January 13, 2015 - 11:29 AM

#3

OK so. Leak down test was at 13% ish. Not amazing but dam it should start right?
I'm lost....don't know what to try next to get this thing to start.

  • dweaver76

Posted January 13, 2015 - 11:36 AM

#4

FYI that 13% wxas going past the rings on a cold (obviously) motor so probably a lot less if warmed up.

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  • grayracer513

Posted January 13, 2015 - 11:47 AM

#5

No plugs are required for either the intake or exhaust, and in fact, if used, they would defeat the ability of the test to locate leaks at the valves.  

 

Yes, it should run with 13% leak down.  Briefly, leak down testers are not made to a single standard.  The size of the orifice between the two gauges and the air pressure used for the test both influence the outcome.  The only really accurate thing that can be done with one is to compare the engine's current condition with an earlier baseline test.

 

Nevertheless, in order to run, you need compression, spark at the right time, and fuel.  Check your cam timing, check that TDC as marked on the flywheel actually is TDC at the piston, check for spark.  If that checks out, check to be sure fuel is being delivered to the carb.  Most starting problems traceable to the carb, and most of those are the result of an incorrectly set up or faulty pilot circuit.  Pilot jet orifices in Keihin carbs are very small, and can be functionally blocked by nothing more than a dried film of gas. 

 

Read: http://www.thumperta...o/#entry6879695



  • dweaver76

Posted January 13, 2015 - 12:00 PM

#6

Yeah I just used a standard leak down  tester, and a breaker bar on the flywheel to keep the piston from pushing back down.

 

My carb has been apart more than a few times and just in case I even replaced all the jets with brand new ones to eliminate chances of it being a carb problem.

The timing was off when I got it but have since corrected that so that the marks are lined up with the top of the head at TDC now.

 

That's where I am now....lost as to what to try next.



  • Krannie McKranface

Posted January 13, 2015 - 01:41 PM

#7

No plugs are required for either the intake or exhaust, and in fact, if used, they would defeat the ability of the test to locate leaks at the valves.  

 

Yes, it should run with 13% leak down.  Briefly, leak down testers are not made to a single standard.  The size of the orifice between the two gauges and the air pressure used for the test both influence the outcome.  The only really accurate thing that can be done with one is to compare the engine's current condition with an earlier baseline test.

 

Nevertheless, in order to run, you need compression, spark at the right time, and fuel.  Check your cam timing, check that TDC as marked on the flywheel actually is TDC at the piston, check for spark.  If that checks out, check to be sure fuel is being delivered to the carb.  Most starting problems traceable to the carb, and most of those are the result of an incorrectly set up or faulty pilot circuit.  Pilot jet orifices in Keihin carbs are very small, and can be functionally blocked by nothing more than a dried film of gas. 

 

Read: http://www.thumperta...o/#entry6879695

 

You use them one at a time to isolate the leak, if it's really bad



  • grayracer513

Posted January 13, 2015 - 02:13 PM

#8

If it's bad enough to worry about, you can hear where it's coming from through the pipe or the air filter (throttle open).






 
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