2007 20V Vapor Lock?

[Snowcatt]

Specs: 2007 20V with 340 hp Marine Power and 240 hours. This happened once last summer, but three times this weekend. It starts, accelerates to just above idle, then falls off. If you pull the throttle to idle and try again it generally gives the same result. Sometimes dies, starts again, and same result. Once it died and wouldn't start. After 10-15 minutes it restarted and ran ok. This seems to happen after it has run a good long surfing session, then is shut off for a period of time. It was really hot this weekend as well.

I ordered a new fuel filter/water separator (its' first) but of course it didn't arrive in time to install it prior, so I re-installed the old one. It didn't appear very dirty and was very easy to blow through. I put about 12 gallons of fuel on top of last year's gas.

So, what do y'all think? Vapor lock? Lift pump? High pressure pump? Other?

Thanks for your help.

[Snowcatt]

So, what do y'all think? Is vapor lock likely on this engine or no way? I'm going to install a new fuel filter/water separator, and check the fuel pressure and the backflow preventer. Other ideas?

Thanks,

[chpthril]

In late spring/early summer, vapor lock is a common issue thats due to the fuel, not the engine system. Reason being.

In late summer/early fall, there is a switch from summer gas to winter gas. The basic difference is in the fuel's volatility. Volatility is the point at which fuel ignites. Summer gas has a lower volatility, allowing it to withstand the high summer temps without igniting on its on, as in pre-ignition. Winter gas has a higher volatility that better fits with the colder winter air temps.

How does this relate to you? It common for a boats last fuel tank of the year, to be winter gas. Come spring when the air temps rise, that winter gas with its high volatility, will boil in the lines and turn to a vapor. Vapor cannot be pressurized like liquid fuel. This leaves a symptom of no start or start and stall because the engine is not getting fed with liquid fuel.

The short term fix is to open the engine bay and allow it to cool down. It typically much hotter in the engine bay then the ambient temp. Next, cycle the key a number of times to activate the fuel pump(s). This helps to get cool liquid fuel from the tank up into the fuel system, cooling it an condensing the fuel back into liquid form. Long term is to just burn the winter gas out and get a fresh tank of summer fuel.

There have been some engine designs over the years and models, across all brands, they have experiences abnormal vapor lock issues. The 07 MP 340 is not known for it.

[lancehon]

Just had the same problem on my boat, sucked all the winter gas out, put new 90 ethanol free in and the boat has never run so good

[Snowcatt]

Thanks a lot guys. I'll add draining the gas tank to my list of "to-do's". I appreciate your input.

[Snowcatt]

I drained the gas, replaced the spark plugs and fuel filter/water separator, and tried it a few weeks ago. It worked pretty well but hesitated slightly when opening the throttle while cold. On one occasion after having run several hours and then shut off for a couple hours, when opening the throttle about 1/4 while still cold it rev'd up but then fell on it's face but didn't die. Idled back and repeated with same result. Then throttled up to about 3/4, it hesitated then ran fine. The boat has done this the past couple seasons but did not prior to that. Ideas?

[lee]

Check to make both wire are connected to the low pressure pump. Have you looked inside your distributor cap to see if it is clean?

[Snowcatt]

Ok, finally found the problem and thought I'd report back. The low pressure pump had some foreign matter in the check valve and the check valve on the tank was leaking. The dealers wanted $3-400 for the pump but with only a little research I figured out the same pump (identical down to the numbers) is sold at auto parts stores for about $70. I replaced the pump and tank check valve, installed an inline filter between the tank and pump, and it's been running perfectly all summer. HooHah!