Vapor Lock?

[fast94impala]

96 5.7 Merc w/Thunderbolt V. Running great for weeks. Ran it hard for several hours Sat and again on Sunday. Late afternoon took a 40 minute slow cruise (25mph) through choppy water stopped on island for 1 hour. Started up but had little power. Idled OK, but would only rev to 1500 rpm at WOT. 30-40 seconds and all of a sudden the boat comes back to life and has been fine since. Was down to about 6 gallons of gas (28 gallon tank) Don't believe it was ignition because it would not have kept running with WOT fuel pouring in. Thinking some form of fuel starvation. Fuel pump going out? or vapor lock? Clogged filter?<br /><br />Any help appreciated.<br /><br />Thanks,<br /><br />Mark

 

[tommays]

Re: Vapor Lock?

dont no the care that the boat has recieved but fuel filters are easy fast and cheep to replace and then see how it runs at that point <br /><br />dont forget the small carb filter<br /><br />tommays

 

[qaztwo]

Re: Vapor Lock?

When my engine vapor locks it will not start. I normally have to raise the engine cover and let the engine cool off. If it has a fuel/water fillter would start there.

 

[qaztwo]

Re: Vapor Lock?

Your engine is a 96, is it fuel injected or carb. Fuel injected won't vapor lock.

 

[DaveM]

Re: Vapor Lock?

I would check the antisiphon valve. No, actually I would just replace it, especially if it is one of those aluminum jobs. They like to react badly to heat after the age a few years.

 

[fast94impala]

Re: Vapor Lock?

Qaztwo - It's carburated. Encountered flooding problem with 2bbl in June. Perfect excuse to slap a 4 bbl on it. Went with Edelbrock intake and 600 cfm 4 bbl carb. Has been running great since. Tops out at 54 now!<br /><br />Juan - Where is the anti-siphon valve located? Original is 8 years old!<br /><br />All - Only recent change was new coil a few days ago. Wasn't getting any spark to distributer so I spent $40 and replaced original coil. Dumb *** mechanic (me) soon discovered no spark was actually caused by safety switch (in off position) duh!! It's OEM and number identical to original.<br /><br />Thanks

 

[alternative]

Re: Vapor Lock?

i have the same problem my OMC 305 keeps flooding and dont know wh??? should i change carbs?

 

[fast94impala]

Re: Vapor Lock?

alternative - if its carburated, it's most likely one of 3 things. Accell pump, floats sticking or bad needle/seat. I first tried to salvage the 2bbl and had it rebuilt. Problem just got worse. New Merc 2 bbl was $400. 4 bbl conversion cost me $600 in parts. I installed it myself and glad I did!

 

[DaveM]

Re: Vapor Lock?

Impala,<br /><br />The anti-siphon valve is located at the fuel feed from the tank. Typically it is between the tank to the fuel line. An anti-siphon valve is about 2" long and has a spring and a steel ball inside. When it wears out the ball gets sucked into the line and cuts fuel flow. They can also get junk to clog them. They cost about $15 and cause major frustration. Been there, got towed in.

 

[Chris611]

Re: Vapor Lock?

Fast94Impala, sorry, don't mean to hyjack your post, but I couldn't figure out how to email you direct. I also have a '96 5.7L that came with the 2 bbl. The well plugs leaked and I replaced it with new 4 bbl and intake. You say you noticed an increase in performance on the top end. Were you able to obtain this with just bolting on or did you have to tinker with the carb? I have an Edelbrock #1409 and I haven't seen any improvement in the top end. Engine still runs 4600 RPM with 23 pitch prop, same as with 2 bbl. Wonder if the carb isn't adjusted right? What are your thoughts.<br /><br />Thanks <br />Chris

 

[DHPMARINE]

Re: Vapor Lock?

With only 6 gallons of gas rolling around a 28 gallon tank,I'd expect fuel starvation problems.Chances are you have a shallow tank located in the center of the boat,maybe 20 to 24 inches wide,and probable 3 to 4 feet long.now add choppy water,you'll probably get fuel starvation.<br />DHP

 

[trebor0301]

Re: Vapor Lock?

I had a similar problemwhen I cruised around slow for awhile.I found that little air would be getting into the engine compartment thru the vents while idling around.Running the blower and or opening the motor hatch up corrected my problem.

 

[fast94impala]

Re: Vapor Lock?

Chris_P - Simply bolted #1409 on. No metering rod changes. Only tweak was advancing timing a few extra degrees. 20 Ft Maxum ran 49 with 2bbl. 54 with 4 bbl. Noticable difference from 2000-WOT.

 

[fast94impala]

Re: Vapor Lock?

Thanks Juan - I'll replace it while IVAN is in town for the remainder of the week .<br /><br />DHP - I encountered the problem in smooth water.

 

[highaltitude]

Re: Vapor Lock?

i would tend to agree with juan cool and dhp. an alternative to replacing the anti-siphon valve might be adding a pint of 2 cycle oil to a full tank of gas to lube the valve-cheap way to test-especially if you are not mechinacally inclined to replace the valve. a primer bulb and crescent wrench can be valuable tools to test vapor lock.

 

[deputydawg]

Re: Vapor Lock?

Don't rule out vapor lock even with feul injection. If the fuel line was moved during your conversion to 4bbl, check where it is run now. If it is running too close to engine or exhaust you could be heating the feul in the feul line. This will boil it inside the line, turn it to vapor insie of the line and cause it to have a sort of air pocket. Vapor lock will usually starve the engine until it stalls. Check feul filters like everyone here said. It might have had just the right conditions such as engine temp, feul temp, engine compartment temp and circulation to flood the engine. After a few seconds or a minute at WOT you burned the gas until enerything stabilized and it ran good again.

 

[fast94impala]

Re: Vapor Lock?

Thanks all. As a precaution, I changed out the fuel filter and then put some gas treatment in a filled up the tank. Didn't experience any problems this weekend. However, the boat didn't sit after a 1+hr run like last time either.<br /><br />Deputy - I took a look at the fuel line and noticed that it is pretty close to the new intake manifold. Need to get custom Stainless steel one made anyway. Have been using old 2 bbl line/w 4" rubber section after the 4 bbl mod.<br /><br />And for those of you who are contemplating the 2-4bbl mod on your 5.7. Plan on going through an extra 6 pack when customizing ALL the brackets (on Maxum anyway)! The Edelbrock sits higher and required hack sawing and filing.

 

[jimmythekid]

Re: Vapor Lock?

could it have been sand or weeds on the prop??