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Tool Talk Discussion Forum

Briggs 8 horse L head

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Eric Rylander

02-26-2006 19:00:57




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I'm messing with this freebee John Deere riding mower- it has an 8 horse vertical crank Briggs. The manual does not give compression specs, they say to use leakdown. I don't have such a gauge handy.

It has 70lbs compression wet or dry. I know these are low compression ratio engines. I have the carb off to clean it, the thing has a decent blue spark, but it won't fire while cranking when I spray gas mist thru a spray bottle in the intake port. Is the problem that it's too weak compression wise to fire?

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JT

02-28-2006 12:22:30




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:00:57  
have you got the fuel system spotless? You said carb was full of crud, if you have any water in the fuel system at all, even a drop, the engine will not fire, no matter what you do to it.



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Eric Rylander

02-28-2006 16:41:22




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 Re: Briggs 8 horse L head in reply to JT, 02-28-2006 12:22:30  
The carb was removed, disasemebled and the body soaked in carb cleaner. Then rinsed, blown out, reasembled- however, put back on without the bowl on it as I had to JB weld a pinhole in it and the JB had not cured yet. The fuel in question was me with a spray bottle in the intake while cranking it with the electric starter.

It did backfire mightily through the carb twice- which does point to timing being off.

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treeboy

02-27-2006 16:33:19




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:00:57  
flywheel key, you really have to tighten th e recoil spinner hub down, i use a large pipe wrench with a large screwdriver lodged in the fins of the flywheel, be careful.. lots of times the key will be partially sheared, throws off the timing to the point that it will not run, but will show spark when checking for spark..



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Bob

02-26-2006 19:32:00




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:00:57  
This may be a "shot in the dark", but remove the flywheel nut, and check to be sure the keyways in the crankshaft and flywheel are exactly aligned, meaning the flywheel key is not sheared, or partially sheared.



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Gene Davis (Ga.)

02-26-2006 19:18:20




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:00:57  
The 70# compression you have is plenty of compression. B/S usually does not give out a compression figure because of the compression releases they use on most of their engines. If you have the compression spark and gas and the correct timing inside the cylinder bore chances are you should be getting some action unless you have a bad spark plug, closed up plug gap,flywheel key partially sheared or bad gas in the spray bottle.

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Eric Rylander

02-26-2006 19:31:51




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 Re: Briggs 8 horse L head in reply to Gene Davis (Ga.), 02-26-2006 19:18:20  
Well then I'll go through the tuneup specs on armature gap etc and check the flywheel key. I'll put a new plug in it. The gas in the spray bottle worked in my chainsaw yesterday so it should fire on it.

The thing sat outside for a couple years and I intercepted it before it went to the dump. The carb was full of goo, and I cleaned it but the float bowl had a tiny rust hole through it and I am waiting for the JB weld to dry. I bought the carb kit and manual from Brigss and Stratton dot com, I must say VERY easy to deal with and had a great exploded view of the carb just by the engine number. The right parts shipped to my door without trying to find a small engine shop open on a weekend and driving all over to get them.

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buickanddeere

02-26-2006 19:13:21




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:00:57  
Are both valves opening and closing?



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Eric Rylander

02-26-2006 19:19:36




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 Re: Briggs 8 horse L head in reply to buickanddeere, 02-26-2006 19:13:21  
They seem to be, I took the cover off the side and watched them go up and down, did not check clearance though- I do have a factory service manual (VERY well written I will add) and I did not know to adjust the clearance you have to grind down the valve stems!



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Gene Davis (Ga.)

02-27-2006 20:25:55




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 Re: Briggs 8 horse L head in reply to Eric Rylander, 02-26-2006 19:19:36  
Grinding down the valve stewms is pretty universal for small air cooled flat headed engines of most every brand.If you have 70# compression I would say that probably the valves are sealing.



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buickanddeere

02-28-2006 07:01:50




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 Re: Briggs 8 horse L head in reply to Gene Davis (Ga.), 02-27-2006 20:25:55  
I was wondering if one valve wasn't opening. I've seen plugs and ignition wires fire decent spark through the air but won't fire under compression. Try a non resistor plug like a Autolite 216 and replace the plug wire. Some use a 1000 or 5000 ohm terminal. Go for a just a chunk of that spiral wound race engine radio supression wire.



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