Essex fuel priming pump/rich running

[jongat]

We've just acquired an RV6 in the UK. It is c8 years old and has done only 140 hours, with very little flying over the last two years. The Lycoming 180hp engine has just been fully overhauled prior to our purchase and seems to be running very rich, indeed we've had a few backfires whilst taxiing. We've been told we may have a problem with the priming pump that's contributing to this - can anyone please enlighten me as to whether this is a credible explanation, why it would be the case and most importantly give some advice on fixing it?
Thanks

 

[rvbuilder2002]

We've just acquired an RV6 in the UK. It is c8 years old and has done only 140 hours, with very little flying over the last two years. The Lycoming 180hp engine has just been fully overhauled prior to our purchase and seems to be running very rich, indeed we've had a few backfires whilst taxiing. We've been told we may have a problem with the priming pump that's contributing to this - can anyone please enlighten me as to whether this is a credible explanation, why it would be the case and most importantly give some advice on fixing it?
Thanks

It is possible.
There are check valves in the primer pump that can stick open. The engine can then draw fuel through the primer nozzles.
It would not be difficult to temporarily disconnect the primer system from the primer pump and plug the lines, and then run the engine.

There are a number of different things that could cause the engine to be rich so testing is in order, but this is one possibility that would be easy to verify.

 

[Bob Martin]

No primer pump

It is possible.
There are check valves in the primer pump that can stick open. The engine can then draw fuel through the primer nozzles.

To be clear, in the Van's primer system, there is no "primer pump".
The solenoid is just a valve that opens and closes electrically.
The fuel is pressurized by the electric boost pump in the fuel delivery system,
and delivered to the primer system via the port/plug on the top of the
gascolator. As stated already, it is an easy job to isolate the primer system
by removing the line from the top of the gascolator, plugging the top
of the gascolator and capping the primer lines so they don't suck air
while running and causing a lean mixture.
Good Luck.

 

[rvbuilder2002]

To be clear, in the Van's primer system, there is no "primer pump".
The solenoid is just a valve that opens and closes electrically.
The fuel is pressurized by the electric boost pump in the fuel delivery system,
and delivered to the primer system via the port/plug on the top of the
gascolator. As stated already, it is an easy job to isolate the primer system
by removing the line from the top of the gascolator, plugging the top
of the gascolator and capping the primer lines so they don't suck air
while running and causing a lean mixture.
Good Luck.

Bob,
He specifically started his post with Essex fuel primer pump.
Essex is one of the common brands of primer pump (plungers) used on certificated aircraft, so he must have a different primer system that what Van's supplies parts for.

That is one of the problems with the transmission of tips and advice on a forum such as this. There is no standard on how RV's get built.

 

[GrayHawk]

Older RV-6A with the Essex Primer Pump:

For whatever reason, I had the pump come apart on me at a remote airport. Not having the technical data at hand, I incorrectly reassembled it. The engine ran rough, very rich, drawing fuel through the pump. Quicky shut down, disassembled, checked, and reassembled correctly. Everything back to normal.

 

[jongat]

Scott/Bob/Grayhawk,
Thank you all for the replies - much appreciated. Now we know the diagnosis for the rough running is credible we'll tackle the primer as suggested and see what we find.