REFLECTOR:Rough Rider

[Chuck Jensen]

I have an engine issue that two mechanics have looked at...and that's all
they've done.  I wondered if anyone has ideas on avenues of
investigation/solution.  I'm running a 540 with mag/EI combo.  The engine,
particularly after a long flight (less so after starting cold), runs rough
at ramp speed (1,000 rpm).  Here are the symptoms with a hot engine after
flight:

As long as the booster pump is on, runs smooth as glass.  VM-100 indicates
30 psi (from another post, is that way too high??) and approx. 4.0 gph @1000
rpm.  If the booster pump is secured, fuel pressure drops to 28 psi, fuel
flow shows 1.7 and engine bounces between 650-700 and just barely stays
running.  Turn the boost back on, and it immediately goes back to smooth
operations with the first set of values.  Turn the boost off, and it's right
back in the dumps.

At cruise or high power operations, the boost pump on/off makes no
difference in fuel pressure, fuel flow or smoothness of operations.

One mechanic suggested that the idle speed needed to be increased.  ??
Seems he was missing the point.  I'm intentionally setting it at 1,000 rpm
with the booster, then engine goes in the toilet when the booster is cut.

The second mechanic increased the richness setting which may have been too
lean since I did not get a temporary rpm increase when cutting off the
mixture, but the reliance on the booster pump did not change for smooth ramp
operations (especially when hot).

Induction plenum has been checked thoroughly but that would seem to be
unrelated to the observed symptoms.

Questions:  1) are my fuel pressure values way out of line (earlier post
talked about 5-6 psi)?  		2) if my numbers are bogus, do I
have a bad fuel pressure sensor or ground?  
		3) what do others run for fuel pressure/flow at 1,000 rpm on
a 540?   
		4) is the main fuel pump going in the crapper? (its been
this way for a long time 				with no further
degradation/change)  
		5) is this type of poor low power performance characteristic
of deterioration of the 			positive displacement type
fuel pump?
		6) is there a way to check the main fuel pump performance?

I was in the camp that the main fuel pump is going downhill but I don't
understand why, if it is putting out that much pressure, why the fuel flow
should fall so much when the booster pump is secured.

By all rights, these questions should be investigated and fixed by a good
mechanic (which exempts me), but since that avenue has been unproductive, I
thought I'd check out the collective wisdom/experience of the Reflectorites.
Best idea wins an official Atta Boy award; redeemable wherever good ideas
are sold.

chuck
N27GV