Fuel Pressure Reading

[Steevo]

Hi All,

Just wondered if anyone has a fuel pressure gauge fitted to their 2200 engine. If so, what readings are you getting on just the mechanical pump at idle power.

I have been chasing a potential problem for a while now that I am beginning to think isn’t a problem and just how it is.

Now Jabiru state in their manuals that fuel pressure should not be less than 0.75psi and not more than 3psi from the mechanical pump. They also state that the electric pump should fulfill the flow requirement and pressure but they point you to an electric pump that is rated at 4.5psi after saying that the carb can flood at 4psi.

The reason I ask is that my Jab is never less than 4psi on the mechanical pump and I have verified that with both an electronic and manual gauge. Sometimes it will go up to close to 5psi.

Now Rotax use the same carb (32mm version but the specs are the same with most jets and valves interchangeable). They specify their fuel pressure range as 2.2psi to 5.8psi. Also, Jabiru use a different float valve with a stiffer spring than Rotax so it should be more tolerant of fuel pressure not less.

I am involved with a few Jabs and none of them have a fuel pressure below 3. I have just fitted the version 2 mechanical pump and didn’t have a fuel pressure gauge on there before. I have not flown it yet with this pump fitted but at idle power I am getting in the high 4psi range.

I am not sure what the difference is between the version 1 and version 2 mechanical pump except that it requires a slightly different push rod. I believe the push rod is 1mm longer. Was this designed to run at a lower pressure or higher pressure?

I have checked that the breather hose is clear and everything else is normal. Plus the carb is definitely not flooding or any engine problems. Most people I speak to don’t have a fuel pressure gauge fitted so it’s been very hard getting first hand information, but the ones I have seen have all been over 3psi.

[Garyo]

Stevo, I would remove the gauge and go flying, less to think about.