So far so good for the conversion. It's a Murray-Briggs and Straton 4.5hp(don't buy one of these, seriously) which has broken on me at least six times in the past year and I haven't even owned it a year yet. I bought it from Home Depot with a two-year warranty, after it broke I found out the warranty doesn't cover engines! First the gas tank was rusting out clogging up the fuel screen with rust particles, so I took it off and coated the inside of the tank with gas tank paint. Then the carb gasket wouldn't seal right so I replaced that, then the push button primer dry rotted and stopped working. Then the o-ring on the manifold wouldn't seal so the engine would surge and barely idle. Sigh. I bought this stupid thing because it was cheap and I had no intention of experimenting with alcohol-conversion on a $350 Honda mower. I was looking for a used mower originally but couldn't find one.
So after fixing all these things and having the carb apart the last time, I added a motorcycle fuel filter, cutting the pickup screen off the end of the pickup tube, replaced the Champion spark plug with an NGK v-groove one, and bored out the main jet on the carb. These are the two main things to converting a gasoline engine to alcohol, hotter spark and a slightly richer mixture. The smallest drill bit you can get at pretty much any hardware store is a 1/16"(I hate imperials, BTW). This is still way, way too big. I found a machinist supply shop here in Lafayette, LA and they had all kinds of tiny drill bits to choose from. I found one slightly bigger than the plastic main jet on the carb and hand twisted it in. The bit cost $1.30. Carb rebuild kit $6.60. The other thing I had to make sure I had access to was a local supply of ethanol(usually hot rod or speed shops). The price went up recently, I checked on it a while back and it was $3/gal, now it's $3.50(this has very little to do with dino crude prices). I do have a still to make my own ethanol and the price per gallon for me will drop to about $.50/gal.
Anyhoo, I fired it up with a 80/20 mixture of gas to ethanol. It ran way, way rich. So much that it fouled out the plug. It also used a lot more fuel to cut the yard than it did before, about a 1/3. I cleaned off the plug and added straight alcohol and it runs fine. I plan to run the opposite mixture now, 20/80. The only idle adjustment on the carb is bending a throttle spring which I want to reset one more time. I think I did overbore the main jet too much though. Make certain when you size up the drill bit that's only one or two sizes up from the actual size of the jet bore. I.e. find a bit that will just pass through the jet no problem, then go up from there. Since I will be making my own fuel the economy of the motor isn't so important.
So after fixing all these things and having the carb apart the last time, I added a motorcycle fuel filter, cutting the pickup screen off the end of the pickup tube, replaced the Champion spark plug with an NGK v-groove one, and bored out the main jet on the carb. These are the two main things to converting a gasoline engine to alcohol, hotter spark and a slightly richer mixture. The smallest drill bit you can get at pretty much any hardware store is a 1/16"(I hate imperials, BTW). This is still way, way too big. I found a machinist supply shop here in Lafayette, LA and they had all kinds of tiny drill bits to choose from. I found one slightly bigger than the plastic main jet on the carb and hand twisted it in. The bit cost $1.30. Carb rebuild kit $6.60. The other thing I had to make sure I had access to was a local supply of ethanol(usually hot rod or speed shops). The price went up recently, I checked on it a while back and it was $3/gal, now it's $3.50(this has very little to do with dino crude prices). I do have a still to make my own ethanol and the price per gallon for me will drop to about $.50/gal.
Anyhoo, I fired it up with a 80/20 mixture of gas to ethanol. It ran way, way rich. So much that it fouled out the plug. It also used a lot more fuel to cut the yard than it did before, about a 1/3. I cleaned off the plug and added straight alcohol and it runs fine. I plan to run the opposite mixture now, 20/80. The only idle adjustment on the carb is bending a throttle spring which I want to reset one more time. I think I did overbore the main jet too much though. Make certain when you size up the drill bit that's only one or two sizes up from the actual size of the jet bore. I.e. find a bit that will just pass through the jet no problem, then go up from there. Since I will be making my own fuel the economy of the motor isn't so important.
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Louisiana
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Re: Converted the lawnmower to alcohol
Fri, September 22, 2006 - 7:59 AMnice job! thanks for the writeup.
eventually i'm doing this to my BMW 2 liter. hopefully the fuel injection computer is flexible enough (i'm using Megasquirt) to allow me to modify mixture without changing injectors. -
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Re: Converted the lawnmower to alcohol
Sun, October 1, 2006 - 9:33 AMThat was the other reason I wanted to convert the mower, to cut my teeth on how ethanol effects mixture, hp, and idle before I turbo my '86 Golf. It runs on CIS injection now and I plan on keeping that(it's actually from a '77 so there is no computer in the system, all pressure based) and run a secondary set of injectors further up the manifold based on a tuneable computer to enrichen the turbo when the boost kicks in. This isn't a new idea of running secondaries, but ethanol will keep the detonation down as well.
I'm curious though, will you run a premix in your BMW or will the computer have maps built into it to keep the mixture at a set ratio like the newer cars? -
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Re: Converted the lawnmower to alcohol
Fri, October 13, 2006 - 1:05 PMi'm not really sure how i'm going to do it. the BMW project is behind a lot of other stuff in the pipeline and i have to re-learn all the Megasquirt stuff as I haven't touched it in going on three years now.
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