VRO Test

[flounderpounder225]

2004 90HP Johnson (BRP Carb'd motor)
I have been having a problem with fuel accumulating in the carb throats after running the engine, next day I will have nasty stuff running down the mid section (posted this before) traced it back to dripping from port side carb assy. throttle plate shaft as it protrudes through the carb housing.  First instinct was the needle/seat was not sealing, and with a pontoon fuel tank above the enginel, I had flow which was causing this.  Installed an inline manual fuel shut off, seemed to stop the problem.  However, I also have performance issues, runs great starts easy cold, after sitting a while after running it starts but doesn't want to stay running.  

I pulled the carb assys the other day, took to the shop for a rebuild, the mechanic says could also be the vro(OMS) fuel side causing the fuel accumulation (and rich mix when starting hot), so I will get to the question: to test the air motor of the VRO and make sure fuel is not seeping through the diaphram and into the crankcase, I was going to use my vacuum gun to pull a small vacuum on the pulse side of the VRO and see what happens, if it will not hold a vacuum the diaphram is bad?? That is my theory?  I know I should have a pressure/vacuum device to thoroughly check the VRO operation, but I just want to know if I have a blown diaphram??  what say ya'll
Marc

[flounderpounder225]

Ok, went out there, put the vacuum gun on the "air motor" male fitting on the OMS (VRO) unit, slowly applied 10 inches of vacuum, it held steady, no drop, and fuel started coming out of the fuel rails where they would normally be inserted into the sides of the carb assemblies.  To me, that tells me the diaphram on the fuel side of the air motor is good, which is what the mech told me could cause gas to flow into #4 if that diaphram was bad, plus cause starting issues.  I think I am back at the carbs for the culprit??  

[flounderpounder225]

Fitz,
Here is the outcome as of now on the BRP 90.  Had the carbs professionally rebuilt at the Dealer, 45 year shop here in Pcola.  No more fuel crap coming down the mid section, but that could be the valve I installed.  Took it out last weekend, pretty much same thing.  Starts great cold at the house on the house, at the ramp, purrs like a kitten running.  Then go set up for an hour or so, and it doesn't want to stay running when started.  Have to juice it up with the high-idle a few times, and then get it in gear and go.... otherwise it wants to stall.  I will try opening the idle air adjustment screws 1/4 turn as the mechanic told me to try?? Dunno...   maybe I'll post over on THT to see what opinions I get over there also?  
Marc

[fitz73222]

It sounds like classic vapor lock. The fuel is just evaporating or bubbling out of the carbs or fuel pump and the engine is lean on start up after a hard run and sitting. Engines can heat up another 30-40 degrees when shut down after a hard run. This was such a problem on older Mercs that they actually had water cooled fuel pumps to keep the fuel from bubbling out of the pump and into the purge line opening and spilling into the bottom cylinder or the engine had to be reprimed in order to refill the fuel pump.This might sound really dumb but try taking a big wet rag and wrap the fuel pump with it and try to see if stops the problem. If it works, now what do you do? There is probably a TSB on this issue but year dealer should be able to help.