Lawn Mower

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  #1  
Old 11-17-03, 01:33 AM
gmcfan
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Hello All!

Recentely we moved into an old house, and while exploring the property, I found a Lawnmower sitting in a small creek. I pulled it out, because I am interested in old junk, and small engines, and dragged it back to the garage. I checked the engine number on the shroud, 1976 Briggs & Stratton 3.5 HP 9.02 Cubic Inch engine. I checked the oil in it...nothing. It was empty. I took out the drain plug, water came out. I cleaned off the crankshaft and pulled the crankcase apart, and cleaned it out, let it dry out, put it back together. Put oil in it. Put gas in it. Pulled the cord, and just as I expected, nothing. First thing I checked was spark. None, so I figured it was the points. To make things easier, I just borrowed the electronic magneto from a newer motor, pulled the cord, and it started up the first time! Runs smooth. Heres my question. Is there anything I can do to improve the performance. I am into taking engines and seeing how much power I can sqeeze out of them. I have heard of people putting turbos and blowers on these! How would I go about doing this? I also heard you can advance the valve timing, ignition timing, how would I go about doing this? thanks in advance.
 
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Old 11-17-03, 10:33 PM
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Hello gmcfan!

The engine you have is kind of limited to what can be done for performance. It is not one that people normally enhance. You can change timing by slotting the coil mounting holes or changing the flywheel timing. You can adjust the valves by grinding the stems, and you can shave the head for compression. I suppose the carb could be modified a bit, and other stuff... The biggest increase in power you can make is to open up the exhaust. Put a 6" straight pipe on it and wear ear protection. Mind if I ask why in the world you would want to soup up a 3 hp push mower? For way less than you'd pay for some kind of blower, you could buy a 7hp engine and bolt it on. I don't know of any blowers for engines like these.
 
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Old 11-18-03, 12:42 AM
gmcfan
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I want to see how long it takes me to blow myself up.

Just kidding. Since I was a kid, I have been a tinkerer, modifying things to make them better, or just taking my brother and sisters toys apart. I have played with simular engines, I have tried modifying a 1995 3.5 HP briggs & stratton easy spin by giving it full compression by grinding the exaust valve stem, definately made it harder to start! I also made an EGR for it.

I want to see how far I can take this engine and what I can do with it.
 
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Old 11-18-03, 06:41 PM
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How did you make an EGR for it? EGR systems actually reduce power.
 
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Old 11-18-03, 08:08 PM
gmcfan
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Drilled a hole in the back of the muffler and ran a steel tube that led into the carburator. It didn't seem to change performance much, and I don't know if that would be considered an EGR or not.
 
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Old 11-18-03, 09:59 PM
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I suppose that is EGR. You were re-circulating exhaust gasses, and that's what EGR does. Interesting....I never thought of that on a small engine. I wouldn't be surprised if we see that in the future of small engines. I think the exhaust gasses would need to be introduced behind the throttle plate...into the intake tube, to be effective at reducing emissions. Keep the ideas going! You never know what you might come up with!
 
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Old 11-19-03, 04:08 AM
Fisher
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Grinding the valve stem to get rid of the compression release
would hurt your overall performance, rather than increase it, as
the valve is not open as long.
Fish
A simple boost could be reducing the cumbustion chamber
volume and advancing the ignition timing a hair.
Remove the head and take off the head gasket and paint the
head with some gasket shellac and reinstall. Run a little and
listen for leaks, then retorque the head bolts. If you are lucky,
it won't leak and you will have a lot more power. Advance the timing by removing the flywheel key and placing the flywheel
where you want it to set. The key's function is to just hold the flywheel in place while you tighten the nut.
 
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