How to Convert a Honda GX50 to Run On E85 85% Ethanol

Discussion in '4-Stroke Engines' started by Fatbike, Aug 14, 2013.

  1. Fatbike

    Fatbike New Member

    I want to covert a Honda GX50 to run on E85. I do not want to debate the politics or negative reasons to not use this fuel. Brazil runs on E85 (and higher) ethanol engines for decades now. E85 works excellent IF done properly. My personal reason to run E85 is that I can get it 1/4 mile away, and I want the clean smell it leaves behind vs gasoline. I have an aversion for gasoline fumes, or having that smell cling to my clothes and skin.

    I've read there are two ways to do this. 1) Mod the carb jets to intake more air. There is a basic formula for this somewhere. 2) Lengthen the intake manifold? <-I could be mistaken. I thought I read something about this.

    Also, the motor may need some seals/gaskets replaced, though I've read modern gaskets should work.

    Amazingly, I find little information on the net how to do this on this popular motor. I have found info about buying carb-kits for Go Kart racing to mod those larger motors to run on methanol-nitro or e85.

    Unfortunately, I'm not a motor expert or have the personal knowledge/ability to understand how to do this. I would prefer to just buy a kit that would work, but it looks like I'm going to need some expertise & help to guide me to where I can get that help and information.

    Can anyone help out?


  2. darwin

    darwin Well-Known Member

    Thers a huge debate between industry/oil cos and the enviro Nazis going on about this right now. Industry says its not good for small engines/older autos and the Nazis say we don't care. Choose a side. Alcohol is corrosive on metals too not just gaskets and plastic/rubber parts.
  3. Fatbike

    Fatbike New Member

    This thread is strictly supposed to be about a "how to" guide with ideas how to do a Honda GX50 e85 conversion. See again OP. I hope we don't get sidetracked. Again, Brazil does it on a national scale with car engines and Go Kart engines too. E85 is used in race car engines in the USA too. I'm certain it is done in Brazil with these small Honda engines too. It can be done successfully with the correct mods.

    I'm willing to buy an engine to convert, but I'll need some advice about doing the conversion. See OP 'why' I'm not going to use gasoline except the small amount that is in E85.

    Please, let's just focus on the conversion. Politics, Pros/Cons... I'm waayyy past reading about it. No need to clog this thread "off-topic" about such issues. Thanks! Sincerely.
  4. darwin

    darwin Well-Known Member

    When addressing OP your addressing yourself, sort of redundant......If I were you I'd bing corrosive resistant rubbers, metals and plastics for use in small engines. Then you'll have a knowledge base to start from to make your own parts and be ahead of the curve that a billion $ industry says is detrimental to their products. Good luck in your endeavor.
  5. Purple Haze

    Purple Haze Active Member

    The Honda GX50 is a quality engine sold around the world. I don't see any problem using E85 with it. The carb jetting may pose tuning issues, though. E85 has less energy (btu) than straight gas, which could cause a lean condition. If you can find larger jets for the carb, it would be an easy fix. One other thing to consider; ethanol has higher octane than normal pump gas, therefore you could run higher compression to get more power without knocking, up to about 13:1. Don't worry about any plastics, most everyone uses plastic gas tanks, and they hold up much better than the old metal ones ever did. Good luck with your project.
    Fatbike likes this.
  6. Fatbike

    Fatbike New Member

    I went over to the Go Kart forum at and I found this about modding a Briggs & Stratton 4cyl Engine for racing on methanol, which is more "corrosive" than E85. I think these are excellent ideas to prevent residue varnish/water damage if the motor is not used at least weekly with fuel being used-up per tank at least monthly & preferably asap... as can be seen below carb-kits are available to do this too.

  7. darwin

    darwin Well-Known Member

    This article is from Consumer Reports which is a neutral party to the issue. Notice towards the end of the article the mention of E85 dissolving fiberglass gas tanks. ...................OP my point is not to criticize your attempt at improvements to your small engines, rather I wish you success. My point is E85 is so corrosive the materials to deal with it aren't on the market yet. New car warranties , Extended warranties , small engine warranties are all voided by use of E85. You can bet the best scientists on the planet are working on the problem but the answers havn't been found yet.
    Last edited: Aug 14, 2013
  8. Fatbike

    Fatbike New Member

    I found this on the Go Kart site (link in my post above) about converting the Honda GX50. Though this person did not actually do a conversion.

    Converting the honda to alky is a much better idea, 4 strokes are simpler, measure the carb's main jet orifice size, then find it's area, ( pi x (radius x radius)), multiply this by two to double the area, convert the new area back to diameter ( square root of the area divided by pi ) and drill it up the jet to this size, you need to double the AREA of the jet not the diameter, raise the compression ratio to take advantage of the alky's 120 or so octane and advance the ignition using an offset key in the flywheel, that's all, a tuned exhaust would help also but the noise might be objectionable, use a good non restrictive air filter, I would not recommend installing a bigger carb since you may loose the little low end torque this toy motors have.
  9. Fatbike

    Fatbike New Member

    What you suggest above is not accurate. Research Brazil and E85. A whole nation with a land mass larger than the USA runs on it. Back in 2009 a Honda E85 150cc bike was already being sold in Brazil much more so than the gasoline version.

    John Deere is now making E85 mowers for the USA:

    John Deere has introduced a brand new riding mower that can run on up to 85% percent ethanol blended fuel.

    Flex Fuels are American as Apple Pie: "The first commercial flexible fuel vehicle was the Ford Model T, produced from 1908 through 1927. It was fitted with a carburetor with adjustable jetting, allowing use of gasoline or ethanol, or a combination of both."

    Yep, Henry Ford, well known for his advocacy for ethanol, not gasoline, knew a lot about engine wear/tear 100 years ago!!! He knew a lot about engines, so let's drop the BS. It has been done, it is being done now, and it will be done too. This is NOT rocket science! Let's stay focused on HOW TO MOD A GX50 for E85.

    What actually works?
    Last edited: Aug 15, 2013
  10. professor

    professor Active Member

    Well, just open up a spare jet and go for it. Cars run on it and they don't change compression ratios.
  11. HeadSmess

    HeadSmess Well-Known Member

    im with this one.

    i run my moto on the stuff, run my old carby car, no probs. i tend to steer clear with EFI that does get better mileage with straight gas. something, in my opinion, of the alcohol screwing with the O2 sensor, perhaps. the higher octane rating should allow for leaner mixes and less fuel but then for calorific value,or max power, you need substantially more...

    maybe some slight rejetting or tweaking of needles, which is irrelevant because you have to do it regardless of fuel used.

    it is an abrasive fuel, like kerosene is. methanol and petrol are lubricative.

    if i had a few spare beer kegs, id try fermenting my own methanol. be just like the days of horses. everything runs on hay! :jester:
  12. Purple Haze

    Purple Haze Active Member

    Like I said before, It's all in the A/F ratio. Any engine is a time bomb running too lean. This engine (and many other similar ones) has high quality parts throughout and a good oiling system, which negates any corrosive qualities in the fuel, as long as regular oil changes are done. (some of these posts are misleading, they make it sound like ethanol is made outta hydrocloric acid!?) P.S. Thanks for the Henry Ford ditty, Fatbike. Sometimes the best way to go forward is to look back.