Datsun/Nissan forklift w/propane problems.

I have an old (1970's) 3 ton Datsun/Nissan forklift that starts and run poorly. It will start and run as long as the accelerator pedal is pushed, but does not want to idle. I suspect fuel problems, but not sure. I worked years ago (50) as a auto and truck mechanic before I started my apprenticeship. I understand the gasoline systems, but never got into propane carbs. Can anyone point me in the right direction (online) to get up to speed on troubleshooting propane systems?

JH

The relevant part for liquid cooled engines starts on page 24. This should give you some familiarity with the components.

http://www.propane.com/uploadedFile...tainingRepairing PropaneStationaryEngines.pdf

Edit: A few more things to help understand propane systems.

http://www.rrc.state.tx.us/media/8562/7stepimpcosystem_fl-troubleshooting.pdf

This isn't a direct answer, but I chased a problem on my little datsun for quite awhile and I thought it was fuel related, even swapped the carb/regulator thing and it finally quit for good and made me trouble shoot it properly. Turned out the points were burnt, I filed them and reset the gap and it has ran perfectly for 2 years now. I'd check that and other ignition system components as well. The propane makes any deficiencies in the ignition show up much quicker and worse than on gasoline.

Most fuel related problems lead to the vaporizer (some people call it a regulator). The carb on most propane lifts is nothing more than a throttle butterfly, all fuel metering is controlled by the vaporizer. Vaporizers work off manifold vacuum to tell how much fuel to send.

macgyver said:

This isn't a direct answer, but I chased a problem on my little datsun for quite awhile and I thought it was fuel related, even swapped the carb/regulator thing and it finally quit for good and made me trouble shoot it properly. Turned out the points were burnt, I filed them and reset the gap and it has ran perfectly for 2 years now. I'd check that and other ignition system components as well. The propane makes any deficiencies in the ignition show up much quicker and worse than on gasoline.

Click to expand...

Macgyver: I have not yet delved into the engine compartment other than a cursory glance. Monday morning, the first order of business is to do a tune up and other checks. It's been about 4 years since i have done anything serious under the hood. I want to eliminate anything other than propane related first. Several years ago, I did a tuneup, coil, plug wires, dist. cap and rotor, points and condenser and compression check. Nothing lasts forever, but want to eliminate the easy stuff first. Thanks.

JH

m16ty said:

Most fuel related problems lead to the vaporizer (some people call it a regulator). The carb on most propane lifts is nothing more than a throttle butterfly, all fuel metering is controlled by the vaporizer. Vaporizers work off manifold vacuum to tell how much fuel to send.

Click to expand...

m16ty: Thanks, that makes it easier. Most appreciated.

JH

scottl: Thanks for the links. I do appreciate the help, sorta feeling myself thru the woods at night.

JH

m16ty said:

Most fuel related problems lead to the vaporizer (some people call it a regulator). The carb on most propane lifts is nothing more than a throttle butterfly, all fuel metering is controlled by the vaporizer. Vaporizers work off manifold vacuum to tell how much fuel to send.

Click to expand...

That's entirely incorrect.

Vaporizers do exactly as the name suggests: They evaporate liquid propane, into gaseous. Vaporizers are also called 'coverters' or 'evaporators'.

Manifold vacuum is NOT used to determine 'how much' fuel to send, as it is actually OPPOSITE of demand. Think about this: When engine is running fast, and you close the throttle, manifold vacuum skyrockets, and fuel demand actually goes to nothing. When manifold vacuum is low, either the throttle is open wide, and the engine is heavily loaded, or the engine's not running. Manifold vacuum on a gaseous system is only used for one purpose: Fuel lockoff... meaning... shutting OFF the fuel. A vacuum-fuel lockoff is a fuel shutoff valve that opens only when vacuum is present.

The device which modulates fuel delivery, is called by several names: "negative regulator", "Zero Governor", or "Fuel Controller", and the principle is simple:

A common liquid-fuel carbeurator consists of a passage where incoming airflow is constricted through a narrow venturi. As the airflow approches the narrow spot (the convergent side), airspeed MUST increase. on the other side of the venturi, is a divergent segment. As air coming through the constriction enters the divergent zone, airflow slows down, and in the process, there is a PRESSURE DIFFERENTIAL between exterior (atmosphere) and the venturi divergent zone. This happens to be the point where a little suction tube drops down into a float bowl, and because of the difference between venturi-divergent pressure (top of the tube) and atmospheric (in the bowl), there's a natural suction of liquid fuel up into the tube. Just downstream of the divergent zone is a throttle plate, and with all this in place, the suction in that tube... aka 'fuel demand'... changes with respect to two things: THROTTLE POSITION and MANIFOLD VACUUM.

Imagine for a moment, that instead of drawing up liquid fuel, you draw up gaseous fuel. To do that, you'd need a special fuel-pressure regulator...

Consider the pressure regulator on your air compressor, torch tank... whatever. Let's say you've got somewhere between 80psi and 2500psi in the tank, but you need to feed out at no more than 20psi... you grab the handle, twist it backwards, which relieves pressure on a spring, and the OUTPUT PRESSURE Gauge drops to 20psi... now your hose only blows to 20psi. IF you put your thumb over it, and squeeze strong, you'll hold back that 20psi, right?

Now dial it down MORE. Dial it all the way down to ZERO. It won't flow at all.

Now put your lips over the hose and SUCK ON IT. It'll flow, because you're applying LESS THAN ZERO to it's output... and the reg is set to ZERO.

A ZERO GOVERNOR is exactly that: It regulates fuel gas pressure to zero. Actually, to slightly negative pressure... so slightly, that it's not measured in PSI... it's measured in INCHES OF WATER COLUMN... "-W.C. For propane and natural gas fueling, the general standard is 11" of water column... that's 0.397psi.

The biggest catch of the zero-governor... is that when the engine is off, it HAS TO STOP FUEL FLOW. When the engine is cranking, there ain't much of a demand signal, but the zero governor's gotta be sensitive enough to respond and flow a little fuel. Many people make a mistake of taking a screwdriver to the zero-gov, and after messing with it, don't realize that it's LEAKING FUEL... hour later, the shop roof flies into the neighbor's back forty.

The gaseous carb 'mixer', can be something as simple as a venturi with a 'spud'... a tube to connect to the zero governor. The 'spud' is an equivalent to the demand point of a liquid fuel carb, and in fact, many propane conversion systems consist of a 'spud' adapter that one simply removes the bowl, float, etc., and the main jet, slips the 'spud' into where the jet WAS, and connects a few draw hose from spud to the zero-governor valve.

Back to the vaporizer... the evaporator. A liquid withdrawl propane system is common to forklifts and other machines that have high fuel demand, but SMALL tanks. Propane assumes liquid form at any temperature below -35F or so... and in liquid state, you can pour yourself a quart of it, and throw it on a fire, and it will SNUFF OUT the fire. Why? Because LIQUID PROPANE doesn't burn.

Even when warm, it will not assume gaseous state unless it's given enough volume to expand, and sufficient time and latent heat, to expand and evaporate. After withdrawing liquid from the tank, it must be turned into vapor, and that's done by passing it through an orfice, into a heated area where it can expand. The evaporator is either mounted to something hot (air cooled engines) or fed warm water from the cooling system (liquid cooled) or in some cases, hydraulic fluid (from hydraulic machines with air-cooled engines) to provide heat.

Of all the propane-fueled engine problems I've resolved, I've found that most propane systems are a result of insufficient understanding of propane systems by a person. Everything from simply not having the bottle facing the right way (liquid withdrawl tube facing up, means no liquid, just vapor), or someone tinkering with the regulator, mixer, or evaporator when they should have been reading the book first.

It's very important to remember that a very quick and easy way to kill everyone within nintey feet of you, is to mess around with a gaseous fuel system while lacking the most important tool: Knowledge.

Impco, Garretson, and others have quite a bit of good information posted online, and you'll also find documents like the Propane Serviceman's Handbook... all good reads. Other excellent sources of information: Any antique tractor manuals from the 50's to '70's, as they show plumbing for early gaseous fuel systems by Ensign, Zenith, Beam, Garretson, and many others.

A liquid propane fueling system consists of:
Liquid-withdrawl tank ->fuel lockoff->filter->evaporator->first stage regulator (10psi or 2psi) regulator (11" w.c.)->zero governor->Mixer

A gaseous withdrawl system consists of:
Tank -> first-stage regulator (10psi or 2psi) -> seconds stage regulator (11" w.c.) -> zero governor -> Mixer.

In liquid withdrawl systems, it's not unusual to see the fuel lockoff and filter combined as one component. The Impco VFF-30 as an example. It is also not unusual to see the first and second stage regulator combined into the evaporator body as a 'converter unit', like the Impco J or Cobra.

An excellent example of a zero governor, is the Garretson KN. Look these up, read about 'em, and look at the prices for replacement units, and then look at the prices for rebuild kits, then ask yourself wether it's worth the peace of mind to save a few bucks on the rebuild kit.

A great explanation of the propane system. Very different from the way a gasoline system works.

One issue, the low pressure is in the narrow portion of the convergent/divergent section. It is really counter intuitive, but the faster the air moves, the lower the pressure. Same thing as on an airplane wing.

Here's an explanation:

http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html

Yes, because it's accellerating. It would have been great to be a fly on the wall in Bernoulli and Boyle's workspace.

To define equivalents:

The float valve's function in a liquid fuel carbeurator prevents fuel from overflowing. In a propane system, this is the Fuel Lockoff's function.

The main jet in a carbeurator venturi is the equivalent of a mixer's 'spud'. Most gaseous fuel mixers have an adjustment device that looks like a large screw, but instead of a sharp point (like a carb needle) it's typically rounded on the end. This is usually referred to as the 'power adjustment'.

The relationship between main jet and fuel draw point in carb bowl (including the fuel LEVEL) is demand metering... that's the job of the Zero Governor / Negative Regulator. The demand imposed by the relationship of venturi pressure vs. atmospheric pressure is where the 11" w.c. regulation lines up.

The Evaporator... this is the cool part:
As I noted above- liquid fuel doesn't burn... only the vapors burn. In a liquid fuel system, liquid is drawn into the venturi, through the throttle plate, into the manifold, down the runner, through the valve, and somewhere along the way, that liquid is SUPPOSED to evaporate. Most of it does, unless it's really cold, then only a little bit does... because when air flows, restrictions along that pathway (like the venturi and throttle plate) cause low pressure... they GET COLD. The lower-pressure areas absorb heat. Now, if the fuel is warm, it provides some heat as it evaporates, but usually nowhere near enough, and it's cold enough so that fuel droplets simply will not get enough TIME to evaporate, so they tumble through the engine, and go out the tailpipe as half-burned black crud.

To make up for the lame atomization, we close the carbeurator's CHOKE... that causes a much stronger vacuum in the venturi, enrichening the mixture... so that there's more vapor, albeit at a large addition of non-burning liquid, but it gets the job done. We also pipe exhaust heat through the intake manifold, and we do other fancy things like 'heat risers' to block off part of one exhaust manifold to 'force' exhaust gasses through the manifold. It's brute force simple solutions to basic physics problems.

With gaseous fuel, this simply does NOT happen... it's already evaporated, ready to go... so there's no NEED for a 'choke' on a propane or natural gas system. There's no need for manifold heat, no need for a heat-riser. The only place we have to worry about evaporation, is in a liquid-withdrawl system... the evaporator, which is up the line a ways. It's got an orfice in it, where liquid propane flows in, and expands. It'll expand all on it's own for a while, but the evaporator body starts to chill, and as it does, will not be as effective, so piping some engine heat through it solves the heat input issue. As long as the fuel is clean, it'll be dandy.

Here's some other important things to know:

Liquid fuel engines perpetually deal with contaminated fuel. It's a liquid, you pour it into a partially-vented can from a dispenser which was filled from a truck on a rainy day, and sits in another vented tank through all sorts of weather, eventually to be pumped through a filter into the carb bowl which is SUPPOSEDLY at atmospheric pressure.

The simple presence of atmosphere allows moisture (humidity) to enter the fuel at every point from the distillation tower to your carb bowl. In ethanol-mixes, there's even more, because Ethanol is naturally hygroscopic- it's a moisture sponge. Take a sample of E10 in a glass jar, put a lid on it, punch a small hole in the lid, and set it on a shelf for eight months, and look at it every couple weeks. You'll see it settle into layers, first with the gasoline rising to the top, the ethanol migrating to the bottom, and a 'funny' looking layer in the ethanol down at the bottom. Eventually, you'll have water at the bottom, saturated ethanol, then heavier fractions of petroleum, with lighter on top, and the lightest fractions (most flammable) will have evaporated off. If you toss a couple strips of various metals in there vertically, you can see what the fuel mix does to metals, too (fun experiment)
Imagine what happens in a carb on a cold morning, when you've got that moisture drawn up through the venturi, into an area that's frosty cold... what do you get? Snow, cold ethanol, and the heaviest fractions of fuel. Think it'll wanna burn? Not really. Wanna start a cold engine, on a cold day? Take your hand-held propane torch, crack the valve (don't light it) and wave it in front of the carb as you crank her... more than likely fire up long enough to draw something more ingestible than the goo down in the bowl.

I digress... back to 'clean'...
A propane tank, by concept, is sealed. On a -45F day, a pressure gauge will read zero... meaning, ambient. You could unscrew the valve, and liquid propane will roll around in that can, pour into a coffee cup, and stay there. Carry that coffee cup into your house, set it on the table, and it will start to boil... into propane gas. (please don't do this, though...)

On a zero degree day, I'll expect to see that gauge reads around 25psi or so... at 30F, around 50ish, 60 I'll see 95, and 150 at 90F... of course, if you're in a higher elevation, the pressure will be higher, and at sea level it's a pound or two lower.

If you were to compare propane to water, just adjust the temperature scale... Where propane boils at -43ish, water boils at 212. Same general idea... it's called 'phase change'.

Now, since it's in a well-sealed pressure vessel, it's REALLY HARD for moisture to get in. A little bit can, but such a small amount that it will have no detectable appearance in the system.

Unlike gasoline, Propane is NOT a 'mixture' of formulations. There's no magic 'additives' mix to help keep your engine clean, or satisfy governmental economic or environmental mandates... it's C3H8, in a closed can. Doesn't matter how big or small the can is, eighty years from now, it'll still be C3H8, and the inside of that can will be basically unchanged from the day it was filled.

A filter is only necessary to stop the crud that could get in during filling or changing of tanks. The worst thing that can happen with a gaseous fuel system, is to have debris foul a regulator or the fuel controller. This will cause it to flow when it shouldn't, and flood an area with fuel gas.

End notes:
For several reasons, engines with gaseous fuel systems run different ignition base timing and benefit from more aggressive curve. It's not unusual for someone to service an ignition system, even change a distributor, and not realize that the systems are set up differently. You do NOT want the advance to be so high as to cause preignition under ANY circumstances.

Another note- It's easiet to set up a propane fueling system using an exhaust gas monitor... but not too many guys carry one around in their glove-box. When tuning 'by ear', realize that when running 'lean', a gaseous system acts like a liquid system running 'rich', and when running rich, a propane system acts like a gasoline system running lean.

Well, better late than never, but I finally got around to finishing the fork truck. Rebuilt the evaporator and the fuel lock, a kit in each. The little engine is running smooth as a kitten. The best in years. Guess it needed help for a while. I want to thank everyone that contributed to the quest, particularly DaveKamp. Very knowledgeable.

JH

Glad you were able to get your lift truck back up and running James.

And thanks to DaveKamp for such a detailed and nuanced overview of propane systems.

I figured I'd post this link that I found online concerning troubleshooting forklift propane systems.

Lots of basic but important information that anyone can try if they find themselves with a troublesome LP forklift.

Forklift Propane Fuel System Troubleshooting: A Step-By-Step Guide - Conger Industries Inc.

Cheers!