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Propane carb vs hose barb

Greg M

Registered
I've not messed with propane but would like to have a 9crack at converting an engine.
What are the advantages/considerations when choosing between a propane carb and throttle body (ie CA100) and a simple spacer with a nipple downstream of an existing gas carb (used strickly as an air door)? I'm not interested in dual/tri fuel, just propane. I'm thinking an engine between 3 and 10 hp to start.
Thanks,
 

Tracy T

Subscriber
Last Subscription Date
07/16/2019
from my limited experience you will need some type of demand regulator, it uses engine vacuum to determine how much fuel to give the engine.
 

Tracy T

Subscriber
Last Subscription Date
07/16/2019
i think the mixer is for liquid, and i know the demand regulator is for vapor. not very much to a vapor system. check out the onan section of the stak. a lot of imformation there! my generator is 4 cylinder set up on vapor.
 

DKamp

Registered
One NEVER brings liquid fuel to a mixer... propane is always 'converted' to gaseous prior to getting to the mixer.

A carbeurator regulates and meters a controlled volume of liquid fuel (gasoline or kerosene), while at the same time MIXING it with air, to provide a combustable mixture.

A gaseous fuel system regulates and meters fuel to a mixing point, where it's mixed with air, to provide a combustible mixture.

The 'add on' to which you refer, is actually an engineered and calculated 'venturi'... a narrow spot that creates a pressure differential suitable for 'drawing' fuel from a demand regulator... aka... zero governor... aka negative pressure regulator.

in a liquid fuel carbeurator, there's a supply of liquid fuel a known distance below a metering orfice within the carb venturi. As air flows through the venturi, pressure drop in the venturi 'sucks' fuel up the tube, through a metering orfice (that limits max flow, nothing more). Once drawn into the airstream, the fuel 'tries' to evaporate, then flows into cylinders where that which is evaporated, has mixed with oxygen and burns. That which did not evaporate, doesn't burn... so it washes cylinder walls and gets sent out the exhaust pipe unburned.

In the gaseous fuel system, the 'spud' in the venturi 'sucks' fuel from a regulator that's designed to flow fuel only when there's a certain amount of NEGATIVE pressure (very slight suction). gaseous fuel (metered by the demand regulator) gets drawn into the venturi airstream, where it's mixed with oxygen, and goes to burn.


Hence, the device at the engine intake is called a 'mixer'.

To convert your engine, you need to either install a secondary venturi in the intake, or at the front end of the carbeurator, or install a 'spud' in your existing carbeurator, into the venturi... and in all cases, plumb it to a demand regulator, that's fed from an appropriate fuel source and dual-stage regulation.

Demand regulators typically require fuel to appear at 11" of water column... some however, include first and second stage regulation. Depends on what model and brand of demand reg you buy.

For your engine, I'd recommend a vapor-withdrawal system with 10psi regulator (suitable for at least 50,000btu) at the tank, and a second-stage regulator at the engine end that'll drop your gas pressure from 10psi max down to 11" W.C., then connect that to a demand reg like a Garretson KN, then connect that to your venturi or carbeurator.
 

Greg M

Registered
Great information there but I'm still wondering what if any advantage something like a CA100 would have over a nipple threaded into a gasoline carb or block between said carb and intake manifold. Perhaps it's an OEM thing where there is no gasoline carb in the system to start with? But then why a carb if a throttle body and nipple would do? Still confused.
 

FWurth

One Millionth Post
Last Subscription Date
07/29/2019
Converting to LP is not too complicated, there's proper equipment out there. It's always best to do it right or not at all, a cobbled up home made attempt will make a simple reliable system into a nightmare and cause more trouble than it's worth. There's reasons why successful LP set ups work, correct components are on there for good reason. LP was real popular back when it was sold for pocket change, but when the price came close to the gasoline pump price, it lost it's major advantage. It does burn cleaner and the engines are cleaner and tend to last longer than the gas versions. On the downside, it is a lot more difficult to keep contained and transported. It takes a bunch of special equipment to be worth while, even on the refilling side. On commercial forklifts for indoor and outdoor use, they use changeable fuel cannisters that are supplied by a service, not cheap but safer than on site refueling for the average employee. That and most insurance carriers require it. These small units don't draw much and therefore vapor withdrawl is adequate. On larger engines that are under heavy work they use liquid withdrawl and the regulator converts it to a vapor for the engine so as to prevent the tank from frosting up. The liquid needs heated water from the engine in the regulator to convert fast enough to keep up with demand.
 

EMU

Registered
Could I remove the mixer and screw in a Vaporizer, then connect propane line then in that line install a regulator . Say to a 9 kg propane / lpg bottle .
 
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