1 merc. 700 keeps vaporlocking
#12
Registered
The absolute fix for the problem is to run the fuel return back to the tank, instead of back to the filter head like it currently does.
Eddie
#14
Although vapor lock is a likely culprit there is one other condition that can cause similar symptoms. The diaphragm in the VST can go bad allowing fuel to bleed through and out the secondary vapor line to the throttle body. Check this line to see if its percolating. If so it will actually flood the engine forcing you to go to flood clear mode to get it started but will appear to be vapor lock.
#15
Banned
iTrader: (9)
Those VST are problem childs to begin with even the O-ring seal can be hard to install after removal. That fuel set up did not stay around long for Merc and there was reason for it as in problems. Also there was a reason starting with Gen II cool fuel systems to the current Gen III as of fuel & cooler components moved to the bottom of the engine area. It brings it closer to the bilge area in which stays cooler plus the lake water underside of the hull keeps that area cooler as well.
Also for Gen II cool fuel systems Merc added a Boost pump in which helps against vapor lock. Merc also had a couple of Service Bulletin's about vapor lock back in 1997 and a revised issue in 1999 if I remember correctly because many black productions motors were experiencing vapor lock right out of the box back then.
Also the fuel you use can cause vapor lock. If you read up about RVP = Reid Vapor Pressure that can explain a lot. Its value changes in places of the US up to 7 times depending on the weather conditions for a period of time. We experience this here in Texas in the marine end because a customer filled up his boat on the 4th of July and never use the boat again - then we get it to winterize at freezing temps. The (summer gas blend ) does not work very well in temps below 40 degrees. It has to do with RVP of the fuel itself. RVP and specific gravity of fuel can make your engine run not so great sometimes.
Also for Gen II cool fuel systems Merc added a Boost pump in which helps against vapor lock. Merc also had a couple of Service Bulletin's about vapor lock back in 1997 and a revised issue in 1999 if I remember correctly because many black productions motors were experiencing vapor lock right out of the box back then.
Also the fuel you use can cause vapor lock. If you read up about RVP = Reid Vapor Pressure that can explain a lot. Its value changes in places of the US up to 7 times depending on the weather conditions for a period of time. We experience this here in Texas in the marine end because a customer filled up his boat on the 4th of July and never use the boat again - then we get it to winterize at freezing temps. The (summer gas blend ) does not work very well in temps below 40 degrees. It has to do with RVP of the fuel itself. RVP and specific gravity of fuel can make your engine run not so great sometimes.
Last edited by BUP; 06-30-2014 at 07:46 PM.