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16kw generac stby generator 990 LP engine not starting

Fast eddie

Hi guys, my generac generator model #0058240 won't start unless I manually open the lever in the fuel regulator behind the diaphragm using a small screw driver, or spraying a small amount of quick start in the mixer box. When it starts it operates perfectly in all load modes. My lp fuel pressure is 11.5 in/H2O at the outlet of the regulator, compression test on both cylinders is 210 psi, and pressure holding 210psi for 10 mins. The generac tech said the regulator was bad, I replaced it but engine still did not start unless I manually opened the lever or use quick start. Does anyone know of a test, or is there a vacuum from the intake that assist the diaphragm to open the lever to.


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Eddie- first off- never manually operate the regulator in any way other than the way it was intended- using a screwdriver, etc., to push it open will damage the diaphragm, bend the lever, etc., and render it unsafe and inaccurate.

Next... I believe by your description, that the regulator you're referring to is the Demand Regulator (first one before the mixer) there should NOT be need for any vacuum or manual operator to get the regulator to properly meter fuel... the demand regulator's design makes it sensitive to demand (venturi) vacuum, it meters fuel based on airflow through that venturi... and it should be sensitive enough to respond to airflow at starting speeds.

First thing to check, is for a nice, snappy-mean-hot spark... your engine has lots of compression, and with a gaseous fuel that's rather lean, it requires lots of spark energy to light the mix.

Next thing, is to make sure your exhaust is not partially obstructed. Not uncommon for rodents, wasps, etc., to restrict the exhaust enough to alter vacuum signal during cranking. Same goes for intake air supply restrictions (air cleaner).

Fast eddie

Morning all, got it running, found the vacuum leak at the rubber sleeves on the intake manifold where it is attached to the mixing box. Replaced them and the generator started up within 5 seconds of cranking. It was a tricky one, thanks for your advice.

Fast Eddie

Billy J Shafer

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It is always the simple things that get you.I was working on a transfer switch that would not transfer. Spent some time on it. Then noticed the transfer motor switch was OFF. But it all back together. Told the customer no charge and left. I felt like an idiot.