Hey guys, I have a propane powered air cooled generac guardian 14kw from 2010 (GT-990 Engine) and beginning of the year it started taking longer (more crank cycles) to start up on its weekly test run until in around may when it constantly ran into overcrank. 

the following was done already by generac service, they couldn’t find anything wrong with the machine:
valve lash checked
spark plugs changed 
airbox unit replaced
gas supply checked
new battery
gas regulator checked by gas provider

now they suggest I start replacing more parts as a trial and error but this kind of an expensive game. 

any idea what could be going on?

fuel plenum was replaced beginning of the year as a generac recall and I feel it has gotten worse since then

you can get the machine to start if you try forever (sometimes 30+ crank cycles) and once it runs it runs fine, I went through this a week ago as we had annoutage and in ran for 30 hours, no problems. 

it’s just the starting that is difficult. I feel it has problems pulling the fuel somehow. If I have it cranking with the airbox open and I cover the air intakes with something I can get it to start sometimes. 

what could be the reason it is not pulling fuel? Any other ideas?
as said , propane company checked fuel supply already and they said it is right where it should be (12psi or something? Don’t remember exactly...)

thanks in advance your help is much appreciated!!

Hi Matty, my first suspect would be the valve lash is not correct. If the lash is too tight and the valves can't seat then it won't open the demand regulator to allow fuel in. The next thing I would do is raise the LP pressure on the secondary regulator to 13.5" w.c. static, this is the regulator outside of the generator but downstream of the tank mounted regulator. The next suspect would be thatthe ignition magneto's are failing and not providing a strong spark. Have you tried giving it a shot of starting fluid in the throttle bores when it's cranking?

78buckshot , thanks for the fast reply. So would you recommend having the valve lash rather on the loose side of the tolerance (manual says 0.002“-0.004“)?  

as far as the gas pressure goes, the propane guy said he played around with putting the pressure up and down a little bit didn’t have any different result...I guess I could try this myself again to see what happens, just have to get a gauge..

I didn’t try starting fluid through the throttle yet. So you’re saying if it won’t start even if I put starting fluid through it may be the magnetos? But wouldn’t that mean that it’d have a hard time running in general? As said, once I get it to fire up it runs smooth...

thanks again!

Ya, I keep the valves .003" go and .005" no go, but as long as you have some clearance it should open the demand reg. The mags are a little finicky on these, try closing the spark plug gap to .020" and see if it improves starting. If it starts with either (starting fluid) but not on it's own the we still have a fuel issue.