VRO: Minimum Compression to Run the Air Pump

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
hazzman
Posts: 1
Joined: Thu Jul 14, 2016 11:08 am

VRO: Minimum Compression to Run the Air Pump

Postby hazzman » Thu Jul 14, 2016 11:21 am

I have been wrestling with my 2002 Johnson 175 for a few weeks now. I just completed a [cylinder pressure measurement] test and the results are 104-105-105-104-102-95-PSI for cylinders 1 to 6.

[The 2002 Johnson 175] runs good at idle and mid-range but starves for fuel at higher RPM's and WOT. If I pump the primer bulb all symptoms clear up until it uses all the primer pumped fuel again. Then the engine begins to misfire again due to lack of fuel.

I have rebuilt the VRO with the two diaphragm kits, I have checked and or replaced all of the fuel lines and primer bulb, I have checked and changed the fuel filter.

I know from doing the research that cylinder-6 is the cylinder that sends the pulse to the VRO for operation of the air pump. Is it possible that 95-PSI is not enough to run the VRO efficiently?

Should I replace the VRO with a new one?

Thanks for any input or assistance--hazzman

OldKenT
Posts: 91
Joined: Sun Mar 06, 2016 1:18 pm

Re: VRO: Minimum Compression to Run the Air Pump

Postby OldKenT » Thu Jul 14, 2016 9:29 pm

Two possibilities come to mind before changing the VRO pump:

--clean and rebuild the carburetors, and focus on the high speed orifice and the pickup tube. The slightest blockage could be the cause of the fuel shortage;

--remove and clean by back flushing or replace the pulse limiter. If it has any deposits, it will not work properly, and it controls how quickly the VRO pump increases fuel supply.
1985 Newport 17
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flymo
Posts: 189
Joined: Thu Oct 22, 2015 2:58 pm

Re: VRO: Minimum Compression to Run the Air Pump

Postby flymo » Fri Jul 15, 2016 7:40 am

Your experiment pumping the fuel bulb tends to rule out a blockage in the carburetors themselves.

The idea to clean or replace the pulse limiter is a good one, and while you're at it, replace the pulse line itself. It may have gotten soft over time, or perhaps someone replaced it with a piece of more flexible tubing that won't transmit the pulse efficiently.

Other than that, re-check your VRO pump rebuild. All it takes is a hair or piece of fuzz in one of the valves and it won't pump well.

Flymo