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Old 06-10-2012, 09:25 AM
WorkinOnIt WorkinOnIt is offline
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Briggs Micro .75HP Engine No-Start

Briggs Micro .75HP Engine
Briggs 021032-0112E1-0405182A 34cc 4-Stroke "L-Head" engine. Has new head gasket, new coil, new gasket and diaphragm kit in Walbro Rotary carb, valves ground and lapped to .007" and .010" stem to tappet clearance. Compression 60psi bone-dry. 90-100psi with few drops oil. Engine ran 1 week ago but would not idle. It died and wont start since. Fuel introduced into spark plug hole OR carb intake immediately gets blown out through the crankcase breather tube when pull-starting. The breather tube connects to the end of the camshaft (which is hollow and made of nylon). There appears to be no damage to nylon crank gear and nylon cam gear. This engine has an aluminum block. The air gap on the magneto is set at .010". Does anyone know why there is a no-start condition? The repair manual states the compression should be 50-60psi. I know Briggs doesn't normally list their compression ratings for their larger engines. Thanks for any help!
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Old 06-10-2012, 07:26 PM
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piston slapper piston slapper is offline
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The crankcase breather tube should be hooked to the barb on the carb..
It pulses the fuelpump in the carb....
If its not connected you will have a bad air leak....it won't run...
Just a guess....
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Old 06-10-2012, 07:48 PM
WorkinOnIt WorkinOnIt is offline
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Briggs Micro Carb

The carb is a typical 3 stroke diaphragm carb used on Echo trimmers and the like. It has the built in purge bulb. Both lines OUT of the carb go into the fuel tank. I checked compression earlier: 90psi. There is no vacuum created to activate the fuel pump in the carb when the starter is pulled. It does operate on the pulse from the crankcase breather ...but there is none. It ACTS like it wants to start with Carb clean...but does not. I always find a grey colored smut on the plug after it attempts to start. Could bad and worn compression rings cause the induction pulse through the intake manifold be real weak or non-existent? I checked the cam again and at TDC compression stroke the mark on the cam gear is at exactly 6 oclock. There are NO marks on the round worm gear on the crank that I could see.
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Old 06-10-2012, 08:10 PM
WorkinOnIt WorkinOnIt is offline
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Walbro Carb

I made a mistake I need to clarify. This rotary carb works on impulse directly through the intake manifold. There is an impulse channel on the end of the carburetor spacer. The Crankcase breather is connected to the hollow nylon camshaft itself and is mounted on the air filter plate ending with a duckbill valve. Sorry about any confusion.
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Old 06-10-2012, 08:33 PM
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piston slapper piston slapper is offline
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With the engine initially not wanting to idle down...
Its usually an air leak ....leaning out the fuel.....
This can make the rings stick or sieze..and cylinders scar..
Could be a crank seal...carb block crack or leaky gasket..
When you replaced the head gasket...did all the parts look ok...

Maybe somebdy with a little more experience will chime in...
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Old 06-10-2012, 08:43 PM
WorkinOnIt WorkinOnIt is offline
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It was running Hot....real hot...and lean too. I could smell it. It smelled metallic. Lean can cause it to heat up right? I ran it hard at WOT off and on for a few minutes before it died altogether. I restarted it a few times within those few minutes or so. When I replaced the head gasket, the cylinder had some very light scratches, that was all. Normal carbon buildup. No burned valves or valve seats. I concur with crank seal. In lieu of doing a leakdown test, I pumped air into the engine at TDC compression stroke. There was ONLY a pretty good little flow of air coming out of the crankcase breather.
Leaning out the fuel. Under C.A R.B. Tier 1 or 2 EPA regs, the carb is leaned out bigtime from the manufacturer. I went one size up on the main jet with a hand drill. Fuel inlet from the main to the throttle nozzle is unbelievably small. It definitely was running lean. These rotary carbs are FAMOUS for being set REAL lean. I checked the carb block for a crack today...a good call...didnt find any. I see VERY few threads on here about Briggs & Stratton; more commercial stuff than anything else. Thanks for replys!
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Old 06-11-2012, 06:59 PM
WorkinOnIt WorkinOnIt is offline
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Leaking Intake Valve

Further pressure testing on the head today has shown a small leak in the intake valve @ TDC compression stroke. The intake manifold is directly above and in close proximity to the crankcase breather...therefore the oversight. Back to the drawing board!
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Old 06-11-2012, 07:29 PM
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dutch1 dutch1 is online now
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Just out of curiosity, what is this little Briggs on. Looking at the breakdown of the engine, it appears to be made for a trimmer or hand held equipment of some kind but I've not seen anything of the sort.

I can't be of any help but would like to know what the application is.
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Old 06-11-2012, 08:31 PM
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piston slapper piston slapper is offline
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Dutch....its Briggs answer to the Ryobi 4 stroke..
I think Troybuilt used them....
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Old 06-11-2012, 09:09 PM
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dutch1 dutch1 is online now
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Slapper, I assumed that might be the case. Saw a couple of 4 stroke TB trimmers 3 or so years ago but they were Ryobis-- have yet to run across anything that is Briggs equipped. It must not be making much of an impact on the trimmer market as I do quite a bit of trimmer work but haven't seen one as yet..
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