small engine help

Propane, Butane, LPG, GPL, C3H8, C4H10
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Joined: Sun May 14, 2006 12:47 pm
Location: Burlington, WI!!!

small engine help

Post by schwoch1 »

I know that this forum is more geared towards automotive conversions, but coming across any reliable information when it comes to propane conversions on small engines is quite difficult, hopefully someone here can give me some insight/help in my situation here!!!
What I am trying to accomplish is converting my Honda HT3813 riding mower (13HP liquid cooled 358cc inline twin) to propane, correctly....... not the "use a gas grill regulator with a ball valve and a copper pipe jammed into the air cleaner" method of conversion! I plan on using a Beam T60 regulator and a forklift tank for a fuel supply. Where I am running into issues is whether I should use a venturi or spud in method of conversion. I have no intentions of switching back to gasoline, so making permanent modifications on the carburetor is not a concern. I have found some info of the pro's and con's of both methods of conversion and I am totally confused on which method is better for what I intend to do. I also cannot find a reliable source for venturi's for in front of the carburetor, are these all custom made??????
Again, I apologize for the small engine conversion question on a forum geared towards automotive conversions, but I felt the most comfortable asking the question here. I am getting tired of getting bashed for my ideas, and everyone here seems to be open minded!!!

THanks in advance!
1967 GMC 2500, 351 V6, soon to have 430 Buick with propane

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Re: small engine help

Post by storm »

I'm really interested in the replies you get for this. I have a 4 wheel bike plus a ride on lawnmower I'd like to do a similar thing to.
Every job is a self-portrait of the person who did it. Autograph your work with excellence.

Fuel flow requirements calculations viewtopic.php?f=5&t=1638

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Re: small engine help

Post by C3H8 »

I don't see any reason the forum should be restricted to vehicles only any more then it would be restricted to licensed vehicles. We address modified engines, forklifts, off road vehicles, TC engines, etc. So unless our moderator (Frank) has a problem with it I don't think any apology is necessary. Small engines are known to be the biggest polluters out there so why not encourage their conversion.

The use of a venturii vs a spud in is strictly based on the owners desire to run gasoline or maintain the gasoline carb in its factory condition. A spud in makes a cosmetically neater installation however it requires permanently changing the existing carburetor to insert the spud in. The use of the T60 is an excellent choice as it can be used on liquid LPG withdrawal or vapour withdrawal. Since you have a liquid cooled engine I would definitely suggest liquid withdrawal. There are several companies that specialize in venturri for smaller engines close to you. One of the most knowledgeable is Carb & Turbo in Shakopee, Minnesota just outside of Minneapolis.

Carb & Turbo have decades of experience on small engines. They likely have both spud in and venturii systems for your model of engine as long as it is not a 2014 model engine. They also normally provide the kit as a T60 or Garretson option. Personally I prefer the T60 since it can handle liquid and full tank pressure. I have found the Garretson products very stubborn to set up and changed many Garretson to the T60 with great success. The kits normally include a lock off, reg, venturri, inline power valve and associated hardware.

Initial set up is a little fussy with the T60 to get the power and idle mixtures correct. Idle mixtures are controlled by a small whisker that pushes the secondary open to provide fuel. This is necessary as both spud in and venturri vacuum generated are too weak to pull the secondary valve open during cranking. The whisker as it is called is a small wire attached to an idle adjustment screw that applies opposing spring pressure to secondary forcing it open slightly to provide priming fuel as soon as the engine is cranked and to hold the secondary open during idling. Once converted these engines run great on LPG. The kit should be installed with a vacuum switch to shut off the electric lock off when the engine is off even if the key is on. This is because the regulator secondary is held slightly open and since the venturri or spud in cannot stop the flow of fuel it will begin flowing as soon as the key is turned on. An alternative would be the IMPCO VFF30 instead of an electric lock off. Whichever method you choose you will likely have to drill the intake for a vacuum source.

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Re: small engine help

Post by billg »

I used a spud and and a small vaporizer and it works great on my 12 hp snowblower, but I would probably use a dedicated carb on your rider. Propane and a snowblower are a match made in heaven because you never know when you are going to use it.

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