O-320 H2AD quits if G meter reads less than +0.7

[RonRV8]

I have an RV-8 with an O-320 H2AD engine and if I push over so the G meter reads +0.7 G or less, the engine cuts out. If I pull back so the G meter reads +0.8 G or more, it runs fine. The fuel pressure never changes (5 psi.) when the engine cuts out. It feels like a loss of fuel flow because when I pull to increase the G load, the engine comes back on smoothly ? no back fire. I had my mechanic check the carburetor float level and look for any other possible cause, he found nothing wrong. It seems to me the engine should keep running as long as the G meter is reading a positive value (greater then than zero). My current theory is there is something wrong with the carburetor. Has anyone else had this problem with the O-320 H2AD engine?

[AltonD]

does it happen with the boost pump on?

[RonRV8]

This happens with the boost pump on. The fuel pressure stays steady at 5 psi. I have experimented with this problem and it seems to be closely related to the G reading and the response to the change in G reading is very quick. Push to +0.7 and it cuts out, pull slightly back and the engine comes back to life smoothly. In level flight at full power I get enough full flow to be 125 to 150 degrees rich of peak with good smooth power. I first discovered this problem when doing a departure stall and noticed the loss of power correlated to the lower G reading.

Thanks for the reply.

[Kevin Horton]

Originally Posted by RonRV8

I have an RV-8 with an O-320 H2AD engine and if I push over so the G meter reads +0.7 G or less, the engine cuts out. If I pull back so the G meter reads +0.8 G or more, it runs fine. The fuel pressure never changes (5 psi.) when the engine cuts out. It feels like a loss of fuel flow because when I pull to increase the G load, the engine comes back on smoothly ? no back fire. I had my mechanic check the carburetor float level and look for any other possible cause, he found nothing wrong. It seems to me the engine should keep running as long as the G meter is reading a positive value (greater then than zero). My current theory is there is something wrong with the carburetor. Has anyone else had this problem with the O-320 H2AD engine?

One hypothetical explanation is a combination of the following:

• A g-meter that is somewhat in error, such that the actual g is closer to zero than it says. E.g. it really is 0.3g when it reads 0.7g.
• When you have a nose down pitch rate, like when you are wings level with less than one g, the actual g at any given location will be less and less as you move further forward. I.e. the actual g at the carb will be less than it is in the cockpit.

[RonRV8]

Good point, but... I happen to have a spare G meter, so I tried my spare, and it gave the same readings. Not being satisfied with that experiment, a friend offered try the ?pushing over the hill? test in his 172 (O-320 E2D). He did the flying, I held the spare G meter on top of the panel. In a series of tests increasing the push over by about 0.1 G each time, we eventually got to zero G push overs. His engine never hesitated, smooth power every time. We thought it best to stop the experiment at zero G. It was obvious that my engine cut out when his engine did not.

[Geico266]

I know you said the A&P looked at the floats, but it sure sounds like floats set wrong to me.

Good luck!