School me on Propane carburetion. Small engine needs more.

Working on a scissor lift with a propane engine. Actually dual fuel but I am not messing with the gasoline side right now.

The engine idles fine and will take high idle but sometimes stumbles hard trying to bring up the rpm but I can tickle it and get it up there. However, under load, the engine wants to bog and seems to be lacking power.

Some of the propane stuff has been bastardized to use the small 20lb bottles. There appears to be a couple regs, then a safety solenoid valve, then to the Garretson regulator. The fuel line off the Garretson is about 4-5ft long and is 5/8" heat hose.... Seems a little ridiculous and I am sort of wondering if this large line damps the vacuum required to operate the valving?

Or maybe I have something that needs cleaned and tuned?

Propane inside a 20 LB or a 500 LB cylinder is liquid, except there is a 20% space above the liquid that is propane GAS. The gaseous propane is what is drawn from the upper 20% of the
cylinder, not liquid. The propane gas became liquified when it was put under about 300 PSI of pressure before it was put in the cylinder.. As the gaseous propane is drawn from the upper area
of the cylinder, the internal pressure drops and that allows a portion of the liquid propane to convert back to a gaseous state until all the liquid is gone and the tank pressure is reduced to zero.

In other words, there is no need for a carbeurater, as is used on an engine that consumes gasoline because the propane is already in a gaseous state. By the time it goes through the regulator,
the pressure is reduced from 300 PSI to about one half a PSI. That is why a large diameter hose is used to deliver that low pressure gas to piece of equipment bolted to the intake port of the
engine that also controls how much air enters the combustion chamber.

My guess is that you have an issue with the governor or the governor spring. While that engine does have a carb on it, that carb is there for when you switch over to gasoline. The length of the
propane delivery hose should not matter. Vacuum does not play a part either because the propane gas is under pressure.

Is this a V4 Wisconsin engine?

Propane pressure at 70? F is typically about 125 PSI, but can vary a bit depending upon the exact composition.

If you are messing around with propane at 300 PSI, the tank must be quite uncomfortably HOT!

Ok, from the little education I grabbed on propane fueling, it seems the final regulator (Garrettson) actually requires a bit of vaccum to release propane vapor. The inlet pressure to is only about 6oz so that must be why there are other regs to get this pressure under control. However, there is a short jaunt of fuel line in the 3/8" size or so from the primary regs to the Garrettson reg.


I can certainly grasp the concepts of fueling with Propane, I just need to better understand what I have and how it is metered. With some basic math, I have determined that I could need as much as 250k btu/hr of gas from these little tanks. I am not sure how much they will vaporize. Gas grills seem to be 100K btu and less. Just trying to determine if the tank can even supply the load.


As for the governor, I just cannot go with that. Been building engines way too long and I don't hear an engine bog due to a governor, I hear an engine that drops the hammer, pulls big gulps of air, and no fuel with it.

If Tom has a LP tank with 300# pressure the relief valve on the tank is stuck. I am not familiar with the garrison set up you are talking about. But I have been using and fixing LP tractors since 1957. While the gas flow is propelled by the pressure in the tank the LP part of the carburetor does mix gas and air to the right proportion for combustion. and the rise and fall of vacuum in the intake manifold controls the vaporizer regulator for the amount of fuel required at the time. Check the vacuum line from the intake to the vaporizer. I don't know what your setup looks like, but you shouldn't need two regulators feeding from a 20# cyl. Did it work before with this setup? Did the problem come on all of a sudden or was it gradual? I have seen some setups that have an adjusting screw or valve on the outlet side of the vaporizer.
MMDEL

In rereading your first post you said the last reg was 5' from the carb. so there must not be a vacuum line. I'm not sure how that setup increases the fuel supply to the engine when the load comes on? If it is a common regulator, most have a cap in the center of the reg. that you can unscrew and inside is an adjusting screw that you can change the outlet pressure. You might increase it a little and see if that helps. Mark where it is before you make any changes so you can got back to where it was in case that does not work.
MMDEL

Since I cannot edit, another correction. Since you are taking vapor off of small cylinders. The system does not have a vaporizer. I would go online find Garrison, and find out how many inches of water column is recommended in the line to the carb. Then get yourself a water column gauge and set it right.
MMDEL

OK, here is where I am at. The ENTIRE propane system minus the mixer/venturi on the carb has been bastardized/replaced for some ridiculous reason.

The 20# tank is feeding vapor to a reg, then a solenoid lockoff, then the Garretson fuel reg. However, I believe I have determined that the vaporizing capacity of the 20# tank is WAY off the mark for providing enough vapor to properly feed the engine. I am sure the factory system was a liquid system and unless you can direct me otherwise, I am thinking the only way to get this fixed on propane is to convert back to liquid.

However, it seems that the vaporizing ability of the Propane is a function of its temperature so the vaporizers are either heated with engine coolant or next to a hot exhaust. It would seem logical that the entire 20# tank could be heated to perform the same but I am sure that would not be wise or thermally efficient.

What I am trying to determine at this point is what components I will need to convert this to liquid. Can th high pressure liquid go right to the converter/vaporizer? Will the vaporizer work the same as the Garretson by not flowing gas unless there is vacuum on the outside side? So the venturi vacuum from the carb modulates how much gas it gets just the same as it is now?

The way I understand the function of the vaporizer is instead of heating a large volume of liquid like the tank, it brings in a small amount of liquid, heats it to vaporize it faster, then provides what is needed to the engine?

Everything you said is pretty much right. First off how large is your engine? Small lawn mower type engines use a system like you have, just the vapor and a reg, Larger engines that need more fuel run liquid from the tank and vaporize it with a vaporizer-regulator. A vapor-regulator has two diaphragms. On the inlet side is a diaphragm and a valve that regulates the amount of fuel coming in. Then the fuel passes through the area where the hot water is flowing. Usually with water from the cooling system. Is vaporized and the amount of fuel to the carb is controlled buy another diaphragm. A line from the upper carb called a balance line. Or on a Century system linkage from the throttle shaft to a valve in the passage of fuel from the reg to the carb. However I have 80HP tractors that I can run all day on light to medium loads on vapor. Why don't you try a 30# or a 100# cyl on the unit and see if that makes a difference before you go to a lot of work changing everything? The only other thing I might do is remove the first reg from your setup. I see no purpose in a double reg. Maybe the guy that messed this up was a furnace man. on those setups there is a reg on the large supply tank outside the house and another reg closer to the furnace to further reduce the pressure. Again I ask did this setup work for you for a while and get worse, or did it quit all of a sudden? Or didn't it work for you at all????
MMDEL

I bought the machine not running right and knew it was engine related and nothing else.

I decided to dump the old reg and install two BBQ style regs with dual tanks. That took care of that problem and I am now trying to tune it better. It wants to be lean at idle yet a little rich under full throttle and only one valve to tune it. Just have to try to hit the middle.


I am now stuck with other issues. Seems the drive motors don't have much power and hits a relief valve pretty quick so I suspect the relief is in need of help. Everything else pulls the engine hard but the drive motors do not. Just goes to the relief.

What I am VERY frustrated with is the hydro diagrams I have really SUCK! no port diagram at all so I am stuck guessing which relief it is.

I'm reading through all of this. I am by no means a LP guru but I have ran a few engines with it.
First I am wondering if these "new" opd style 20# tanks are limiting your amount of flow out. I'm pretty sure they shut down with too much flow. I have ran my 4 cyl. willys jeep engine and a 4 cyl. Waukesha fork lift engine just fine off an old style 20# tank before with just gas and no liquid and one regulator.
You also should get hose made to handle LP as many break down and can put bits into your gas.

Actually, with my dual tank setup, it seems to be working great. However, I think I am now fighting a minor rich condition when power is demanded. I can tune back the only needle jet there is for the propane and my idle then sounds lean.


I am wondering if anyone has ever tuned on the fuel regulator (Garretson) to make it more sensitive at idle to help that? It seems amazing that only one jet handles it all.

I could be just not pulling enough vacuum at idle but I tend to think we can find a way to tune around it.

I am now stuck with other issues. Seems the drive motors don't have much power and hits a relief valve pretty quick so I suspect the relief is in need of help. Everything else pulls the engine hard but the drive motors do not. Just goes to the relief.
What I am VERY frustrated with is the hydro diagrams I have really SUCK! no port diagram at all so I am stuck guessing which relief it is.[/quote]


I have worked on all sorts of lifts, many have a valve you can turn to allow the unit to be towed/pushed.
Good chance if you find the valve a couple of turns will restore your drive power.