1 merc. 700 keeps vaporlocking
 

My friend has a 42 Outerlimits with 700 mercs. and only the port side engine the forward engine vapor locks. Now its hot ass hell 92 deg. but this seems to be getting worse. I think its odd that it only the engine every time.

Any ideas?

I have a friend with 700 s in a 39. Cig and it vapor locks everytime he turn it off on a hot day .they told
Him to open the motor hatch to let air in while ur stopped . It does work but why should u have to do that...
A bunch of bull.... Merc fix the problem......

We do that every time we stop. But wy just that engine and not both its always just the forward one.

I would do a fuel vacuum test on that motor as it is showing a problem by itself. Also change all fuel filters, make sure all your fuel system has tight connections (do not over tighten fittings) with no leaks including air leaks. If your fuel vacuum test shows more than 2 Hg that indicates a fuel restriction, or a form of a leak. Merc max spec is 2 Hg for fuel vacuum testing.

Also it is important to make sure you have the proper fuel pressure so check that as well. If not that can cause a fuel delivery problems - weak / bad fuel pump(s) and or fuel restrictions - These 2 tests I would do first to see if those specs are met beforehand.

You could have weak fuel pumps(s) and or the that motor is running hotter than normal. Next look into the area of the COOL FUEL system - make sure no water leaks or air leaks or restrictions.

I always open my engine hatches when I stop, whether it's the 388, the Talon, hell, after I take the wife's Viper for a little run, I open the hood and let her cool off. Heat is the death of any engine...

The fuel rail are hot as hell! I had the same issue with a 390 velocity. I installed scoops on the hatch and it never vapor locked again. I think one problem is that these boats don't get enough fresh air. Especially the front engine. The air inlet is on the side towards the back of the engine compartment. But I also agree with a fuel system issue. We checked the smart craft and it showed we had good fuel pres. Thanks for all the great info.

Believe it or not this one is easy. Run 89 non-ethanol fuel and your problem is solved. It's that easy.

I agree with 39Ultd!

We just went to orange beach and it was the first time I put ethanol in my boat. I already ran return lines back to tank but after the first run and shutting down without giving extra time to cool off caused some issues.

Both cranked but would not rev till a minute or so till I got fuel back up there.

Gave additional 5 minutes of idling fixed my minor vapor lock symptoms!

I have the problem with vapor lock (2000) 7.4mpi bravo iii only when I run jip-joint gas. As long as I stay with 89 octane from shell, mobil or bp - NO ISSUES. It was very hot today in northern Indiana and I was running quite hard - what I do is idle the boat for a minute or two prior to shut off and just open the engine cover and let it cool.

3pointstar

My carb'd engines don't vapor lock.

LOL.

Just some EFI vs Carb elbow jabbing.

leave your bilge blowers on...just a suggestion. I know my boat gained 2mph when I cracked the hatch at full throttle. I added a scoop and hole sawed vents it the back of the hatch.

That is extremely common, believe it or not. Usually, the port engine is the one that vapor locks. Merc puts the fuel filter on the port side of the engine on just about every engine they build. Because of that, the port engine's fuel filter gets heat from not only the engine it's mounted to, but from the starboard engine as well. The starboard engine's filter is on the outside of the boat. It's not receiving heat from the other engine. Also, there are usually vents on the outside of the boat, so it ends up getting a little more cooler air, stopping it from vapor locking.

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

duplicate

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.

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.