High fuel pressure reading at idle and low RPM

[bjmauldin]

I have a Rotax 912 ULS on a 2008 Flight Design CTLS. My mechanic did the annual in April, with 5 year hose change, new fuel pump and new rebuilt carburetor with the newer designed floats.

There has been issues with the fuel pressure and RPM every since the annual. On lift off and climb out I can get an additional 200 rpm by applying carb heat.  After 20 minutes of flight, in level flight, without carb heat on I can see 5000 rpm with a lot of throttle movement left.  I think something is unusual with the carbs or the air flow system since the annual. At taxi 1800 RPM the fuel pressure on the Dynon reads higher than normal - 5.7 to 6 PSI, yellow band to red line.  At takeoff and cruise about 2.5 PSI, normal reading.

 

I am seeing 4800 RPM when applying full power on take-off out of a 6200" airport, normal, but starting the climb it drops to about 4600 RPM. I can't remember if it used to do that before the annual, or if I'm being super sensitive to problems. Your opinions please 

[Al Downs]

Almost acting like carb heat is on, you should get 53-5400 on take off.

[Ed Cesnalis]

Check your float bowls for rubber debris from the hose change.  Seriously

 

Did you pay him to adjust your prop pitch too? (higher RPM result from flattening the pitch which is a common need)

[Ed Cesnalis]

31 minutes ago, Al Downs said:

Almost acting like carb heat is on, you should get 53-5400 on take off.

You need to know his elevation and prop pitch to say that.  Most are optimized for something close to best speed and don't see such numbers on take off.   just sayin

[Tip]

The carb heat cable may have an issue causing it to be on all the time. Or, your mechanic may have crossed the CEET tubes on the back of the air box which is easily done.

[sandpiper]

20 hours ago, Al Downs said:

Almost acting like carb heat is on, you should get 53-5400 on take off.

How do you get that high of an RPM??  I get about 5100 on climb and my prop is pitched to give 5600 flat out and level at 3500MSL.

[Al Downs]

I am pretty sure 5800 wide open is correct and the should get 5400 max at cruise. Could be wrong

[Ed Cesnalis]

1 hour ago, Al Downs said:

I am pretty sure 5800 wide open is correct and the should get 5400 max at cruise. Could be wrong

There is no 'correct'.  We all have adjustable props and there is no effort to prevent us from optimizing our pitch.  Everyone's numbers are going to be different but in a range.

5800 is the redline for climbing with a 5 minute maximum.  We go with coarser pitches for better speed and you will find few CTs that can achieve 5800.