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I have various F series powered mowers. Other then possibly different carburetors, how does one determine which one has 3 1/2hp or 4hp or 5hp? Are all the blocks and pistons the same? Can I take the Walbro carb off my 5hp 680553, install that carb on my 3 1/2hp 6280 and have a 5hp 6280? Thx.
 

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Deceased, April 2015
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This has always been a mystery to me. As far as I know, bore and stroke stayed the same throughout the F's production. Pistons, rods, and crankshafts will interchange throughout, keeping in mind that capstan and BBC cranks are different. I've done that. Carbs are swappable as well although mounting a metal Walbro to an engine that didn't originally have one requires drilling a small hole into the reed plate. Done that too.

The only thing I can figure is that transfer ports were changed some throughout the production run. Any F in my opinion has plenty of power when running right. My 8155 Schoolbus has a blade clutch and SP and plenty of weight but just zooms right along with the F.

If someone knows any more, I'd be glad to learn as well.

Charlie
 

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The Sea of Green Machines
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Im sure HP rating standards changed somewhat (advertising hype) in the industry so they had to "adjust" thier numbers to remain competitive. That is one reason there was a class action suit settled recently amoung the manufacturers.

Remember when you could buy auto speakers that were 20 watt speakers (rms), and later down the road the same speaker had 200 watts music power? Hype, pure hype.
 

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I was looking at specs for the 10515 it shows 4.5, 5.0, and 5.5HP across three consecutive years. No idea either on why they changed. I do know the manual calls for a different plug to be used in the 5.5HP engine.
 

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The Sea of Green Machines
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Never saw a 5.5 HP F. 5HP was the highest Ive seen on a label and that was a 10518. The carburetors were different on the various HP models but I dont know if the intake system was different or not.
 

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Never saw a 5.5 HP F. 5HP was the highest Ive seen on a label and that was a 10518. The carburetors were different on the various HP models but I dont know if the intake system was different or not.
Always possible it was 4.0, 4.5, and 5.0?? Not sure, just remember it was different in .5 HP increments each year.
 

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I have 3 different iterations of the "F" engine: 4.0, 4.5, and 5.0. Plus a 7268 that is not marked on the machine. The one marked 4.0 is the strongest by seat of the pants feel. Of course, that might be because that's the one I rebuilt, too!
 

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The Sea of Green Machines
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Always possible it was 4.0, 4.5, and 5.0?? Not sure, just remember it was different in .5 HP increments each year.
Yes, that would be how I recall them
 

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The Sea of Green Machines
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I have 3 different iterations of the "F" engine: 4.0, 4.5, and 5.0. Plus a 7268 that is not marked on the machine. The one marked 4.0 is the strongest by seat of the pants feel. Of course, that might be because that's the one I rebuilt, too!
Souping them up and super chargers added dont count dang it!
 
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