Dave,
Sure sounds like a fuel issue. The governor does not restrict flow, it
sets the rotation of the plungers in the HP pump which controls how much
fuel in delivered to the injectors. The fuel not used or which leaks by
the pump plungers is what returns to the tank. Under light load you'll
hardly see any return fuel, more as the load goes up.
The governor works by a balance between a spring and flyweights, the
throttle lever adjusts the spring tension and engine speed sets the
flyweight position. A quick look at the M20 tech manual shows the
governor is right in the HP pump assembly, it's possible the governor is
sticking and causing slow response but it may also be worn fuel pump.
You'd have to pull the whole assembly and send for rebuild. Cost me
about $700 for that on an M3-20B engine last year on my club launch.
Before that extreme, however, let me ask the more obvious questions
(don't mean to offend, just asking): any water in the fuel? That could
give a slow response, or maybe an air leak on the fuel supply hoses,
though it sounds like you've checked that?
Neil Gallagher
Weatherly 35-1
Glen Cove, NY
On 9/7/2021 9:16 PM, Dave via CnC-List wrote:
Evening all. Trying to help a neighbour here with a diesel issue.
His engine will rev freely at idle but with the transmission engaged
in either forward or reverse, revs increase very slowly and only to
1800-2000 RPM on the tach. (whether tach is accurate or not, RPM
under load is much lower than no-load, and RPM increases quite slowly.)
We have verified that neither the exhaust system nor the fuel supply
to the high pressure pump is obstructed. Air Intake is clear. The
speed lever works smoothly to its full travel. The compression
release is not engaged. The engine runs a new facet electric fuel
pump with plenty of flow.
When the engine is running, no fuel returns to the tank via the return
line. The return line is not blocked, at least not downstream from
the return barb at the injector. I am not sure under what
circumstances the fuel should return to the tank in a diesel, as the
return occurs after the high pressure pump.
All This leads me to suspect a fuel (volume) problem but i am not
exactly sure where to look next. I believe all that’s left are
injectors and high pressure pump. The high pressure pump has a
governor, not sure if that functions by restricting fuel flow.
Any thoughts?
Many thanks! Dave 33-2
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Thanks to all of the subscribers that contributed to the list to help with the
costs involved. If you want to show your support to the list - use PayPal to
send contribution -- https://www.paypal.me/stumurray Thanks - Stu
