Propane generator won't stay primed

[Jammer]

Also, you have to hold the "prime" switch down at the same time you are pushing the "start" for it to do anything.  It's not like a gas engine where you prime first then crank.

 

[rsalhus]

Since Shonrt's generator starts occasionally and runs fine once started, I would imagine that either the "prime" switch or the wiring connecting it to the solenoid has failed.  The fact that the generator starts easily when warm is probably due to the higher cranking speed with warm oil making the vacuum switch more likely to close.

Why would one think the "prime" buton has anything to do with problems on a propane generator?  I scanned through the Owner's Manual for this generator and I didn't see anything in the manual about using the "prime" button for anything, including holding it down at the same time as the "start" button.  The "prime" button comes on all Generac control panels but is only used for priming a gasoline generator that has a fuel pump.

Maybe the wiring from the start switch to the propane solenoid valve is faulty, but I doubt that the "prime" button has anything to do with Shonrt1's problem.

 

[Gary RV_Wizard]

The NP666LPG manual at this location

http://gen-parts.com/Manuals/A4081.pdf
Shows a Primer Switch on the generator panel and gives instructions for using it on  a"cold engine", which it says means "has not been started in more than two weeks". No mention of a primer switch on the remote start panel.

 

[rsalhus]

http://gen-parts.com/Manuals/A4081.pdf Shows a Primer Switch on the generator panel and gives instructions for using it on  a"cold engine", which it says means "has not been started in more than two weeks". No mention of a primer switch on the remote start panel.

What it also says in that paragraph of  the manual is that "you must press this switch to bring fuel from the tank to the fuel regulator".  I didn't think this applied to propane, but now I'm not real certain, as they do show in this (propane only) generator manual a gaseous fuel regulator and a gaseous fuel solenoid in the exploded view of the carburetor.  (I didn't think propane generators used carburetors either so maybe the "primer" button really has a useful function in a propane generator, like opening a solenoid as Jammer suggested.  Unfortunately, this manual doesn't show or describe that function as existing.)

 

[Gary RV_Wizard]

Propane generators do have a carb of a sort - still has to mix air and fuel for combustion. It's a much simpler carb than a gas engine, though.  This Generac runs on propane vapor rather than liquid LPG, so about all that is needed is a place to let some air mix with the propane vapor. And some sort of throttle valve to control the flow. There would have to be a shutdown valve/solenoid, though, or propane would leak out all the time, right? Maybe that's what the fuel regulator does - controls flow from zero at "engine off" to whatever flow is needed under load.  I don't have much of any experience with propane gensets, so I'm guessing just like you.

 

[Gary RV_Wizard]

Paul Demars is here with me and he has some propane genset experience (non-rv). Says this sounds like a fuel delivery problem, maybe a leak in/around the feed line or carb/regulator. Spraying soapy water as a leak test is always one good way to attack this sort of problem. Leaks in fuel intake can give all kinds of odd symptoms.

You should also check the fuel inlet solenoid to make sure it is energizing. Lay a screwdriver right on the regulator solenoid to see if it gets magnetized (it will if the solenoid has pulled in). It apparently is working ok at times or it would never run at all, but it may not be working every time or may be weak.

 

[Jammer]

The way they work is they have a zero-pressure regulator and a venturi.  The venturi produces suction (Bernoulli effect) which draws propane from the zero-pressure regulator.  There is a butterfly valve throttle between the venturi and the intake manifold just as on a gasoline carburetor.  Since propane is a gas at the temperatures at which the generators are intended to work, the various problems related to metering and vaporization of a liquid which make gasoline carburetors so complicated don't exist.

 

[John From Detroit]

As to why they would put a primer switch on a propane generator.... Well.

In many cases they make basically one generator with several carbarators

And the gasoline models need a primer

That said.. It appears from what others are saying that the generator in question

Might not be propane after all.. And my earlier comments were specific to PROPANE or Natural Gas fueled generators. NOT Gasoline/Diesel  fuel generators.

 

[rsalhus]

.. It appears from what others are saying that the generator in question

Might not be propane after all..

No, it's definitely a propane generator.  The facts are that it's a DP and the owner says it doesn't have a gasoline tank, so it's almost got to be a propane generator.  The insignia that says it's a Generac NP-66G Mobile Generator is actually a label on the outside cover of the air cleaner.  If another air cleaner cover was put on from a  gasoline generator, then that would explain why it looks like it's a gasoline generator when in fact it is a propane generator.

Another thing, it appears this Generac Model 9734-3 was initially manufactured before 1997 because the generator manual revision 1 was published 9/18/97.  The other picture attached by Shonrt1 contained a label warning that is titled "IN USA USE PROPANE FUEL ONLY".  This  label also reads "THIS ENGINE CONFORMS TO US EPA PHASE 1 AND 1995 TO 1999 CALIFORNIA EMISSION REGULATIONS FOR ULGE ENGINES".  I take this to mean that this generator was manufactured in 1999.  Shonrt1's motorhome is a 2001, the same year as our motorhome, and the label on our propane generator reads "....2000 to 2001 CALIFORNIA EMISSION REGULATIONS....".  This makes me think that this generator was probably not the original generator that came with the new motorhome, and could be in fact, a 1999 model that replaced the original generator.  Would National put a 1999 Generac generator on a new 2001 motorhome?  I don't think so, but I've been wrong before. 

 

[Gary RV_Wizard]

Thanks for the explanation, Jammer. That makes perfect sense.

 

[RedT]

Shonrt1, there is a genset expert on USNET that will be happy to help you. He (Alan Robinson) usually posts on "alt.rv" and on "rec.outdoors.rv-travel". Post your question there, or Ping him and I'm sure he will help you.

I experienced a similar problem with an Onan liquid propane genset and he helped resolve the problem. (was a small hole in the fuel delivery line from the regulator to the mixing chamber - it was sucking air during the start cycle, resulting in a hard-to-start situation)

 

[John From Detroit]

Well if it is deffently a propane generator then the primer switch is because the only difference between a Propane and Gasoline motor is the carb.  So why build two control systems.

Now, most DP's have a Diesel generator  Just so you know  but I have seen some with propane generators so I won't argue the point.. (And I've not seen all that many RV's but I've seen some with Propane generators)

I will say again, Propane fuel systems are under constant pressure. so long as you don't disconnect the line they should NEVER need priming, there is no fuel pump. the fuel itself does the "Pumping"


Just a thought.... Where did you last buy propane, and how cold is it where you are parked now?

In some parts of the country they call it propane. but the the actual product is not propane, it's butane if I recall correctly

Propane's vapor temp is about (this is not exact) 40 below zero.

Butane's vapor temp is closer to freezing (32 f or 0c)

When the generator starts sucking gas,  The liquid gets colder. FAST since a generator vaporises a lot of liquid when it's running (don't matter if it's propane, gasoline or diesel on that one, it vaporises a lot of liquid and that makes the liquid colder)

It may be you just need genuine propane.

 

[Jammer]

Usually a failure to vaporize due to cold temps manifests itself with the propane appliance working for a few minutes then running out of gas.