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  #11  
Old 03-24-2012, 08:57 AM
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piston slapper piston slapper is offline
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Sounds like incomplete combustion....poor compression....spark....or weak fuel.
With your background on turbines.....this will be childs play.......
If for some odd reason you don't get it right.....at least you won't startle 400 passengers, and a few pilots...........
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  #12  
Old 03-24-2012, 04:03 PM
Techno Techno is offline
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Things iv found on 6.5 quantum engines. The carburetors are junk first off. They have a rubber seat and solid float valve, which is a big problem with ethanol gas. As soon as the ethanol hit the seat it swells and makes the float 10 degrees lower than it should be. Best solution tho is not to replace the carb. Get an aftermarket seat from rotory and replace the original seat. When these are installed they actually make the float 10 degrees higher than needed. When they swell from the ethanol they will make the float near level then.

Another thing is the flywheels. Iv had many come in that were leaking. Take a screw driver and put it next to the magnet on the flywheel and see how much it pulls. If it pulls too hard its throwing the timing off from the magnet leaking over onto the flywheel itself.

Had many come in with leaking valves, either from loose valve seats, valve itself damaged or carbon buildup from the bad seat in the carburetor. Also make sure the valve lash is set properly. A little off on this engine and it wont start right.

I also take the compression releases out of these engines when rebuilding. They start better. Its not needed anyway.
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  #13  
Old 03-24-2012, 05:58 PM
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dutch1 dutch1 is online now
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Techno, your experience is entirely different than mine regarding 120000 series carburetors. The only carburetors that were junk were one that came in with water in the carb bowl--badly eroded barrels. By the way, the OEM seats are viton, not rubber and I haven't found their capacity to swell any worse than any other seat. I've tried several aftermarket replacements, from a variety of sources, for the Briggs 498260 kit and have found a 60-70 percent failure rate when pressure testing the needle/seat prior to reassembly. The orfice in most of the aftermarket seats are much larger than the OEM, which is why the float doesn't set level when installed and most likely the reason they do not consistently hold pressure.

Never experienced a leaky flywheel. The ignition current is created IN the CDI pack(coil) by the magnet in the flywheel passing the posts of the CDI. The air gap(distance between the flywheel magnet and CDI) is the only thing, external to the engine, that will change timing.

Maybe I haven't seen all versions of the 120000 series engine, and I've replaced numerous cranks, but can't recall seeing one with a compression release. On the other hand, maybe it's because I'm an old fart with a short memory.
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  #14  
Old 03-24-2012, 07:21 PM
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piston slapper piston slapper is offline
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Dutch.......Teckno's experience is ...........well .....you know....
Who knows????......he is not an authority on anything other than his own opinion.
We all know (those of us that have been inside thousands of briggs carbs ) that his findings are pure bunk.

Was waiting for you to check in on the school me and Rob held this morning. ..
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  #15  
Old 03-24-2012, 08:07 PM
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dutch1 dutch1 is online now
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I didn't get an invite, Slapper. If it had involved a plate of biscuits and gravy I'da shown up. But it appears, as I just read, that school is out, according to the Robster.

Matter of fact, I was busy making a little quick "walking around" money on what else, a Quantam--carb rebuild and a PM service. Need to go back out and check for the leaky flywheel though.
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  #16  
Old 03-24-2012, 08:19 PM
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piston slapper piston slapper is offline
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Those leaky flywheels can be elusive.....been hanging around with hundreds of those engines for years.....and ain't heard a peep from one yet.....

Nothin wrong with a little spendin cabbage....comes in handy round here.
I may have to reopen the school....those guys sure make me feel smart.....
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