454 7.4 MPI Vapor Locking

[asa400ex]

I am wondering if any of the RDPers that have a 7.4 MPI have ever had vapor locking issues. I read online that Mercruiser has a serve bulletin out on vapor locking. My issue is when I come to a complete stop after running the motor for some time (Topock to channel) and shut the motor off for 20-30 mins, it will not start.

Has anybody solved the vapor locking issue in their 7.4?

Here is the link to the service bulletin.
http://www.boatfix.com/merc/Bullet/99/99_07.pdf

What do you all do to keep your engine compartment cool? Should I add another blower motor to get the heat out?

 

[RiverDave]

I am wondering if any of the RDPers that have a 7.4 MPI have ever had vapor locking issues. I read online that Mercruiser has a serve bulletin out on vapor locking. My issue is when I come to a complete stop after running the motor for some time (Topock to channel) and shut the motor off for 20-30 mins, it will not start.

Has anybody solved the vapor locking issue in their 7.4?

Here is the link to the service bulletin.
http://www.boatfix.com/merc/Bullet/99/99_07.pdf

What do you all do to keep your engine compartment cool? Should I add another blower motor to get the heat out?

I know some guys that crack the engine hatch when they stop to help prevent that. I think they actually rerouted the fuel lines away from the exhaust manifolds as a permanent fix? I'd have to call AJ or Aaron to find out for sure.

RD

 

[Outdrive1]

Crack your hatch and open your throttle body wide open when your parked.

Higher octane fuel also has a higher boiling point.

You can run a fuel pump with a bypass regulator also. That's a permanent fix. It's also really pricey to do.

I've had more customers with this problem this year than any other year. I think the blend or quality of fuel is bad this summer.

 

[Runs2rch]

I know some guys that crack the engine hatch when they stop to help prevent that. I think they actually rerouted the fuel lines away from the exhaust manifolds as a permanent fix? I'd have to call AJ or Aaron to find out for sure.

RD

This. Single tank or dual tanks? Single tank it is easy to run the return line to the tank.

 

[OCMerrill]

Blower - Run it constantly and maybe even get a bigger blower. You can also try wrapping the fuel line with a DEI product. That's my .02. Great suggestions in this thread. It's hot under those covers.

 

[Racey]

Crack your hatch and open your throttle body wide open when your parked.

Higher octane fuel also has a higher boiling point.

You can run a fuel pump with a bypass regulator also. That's a permanent fix. It's also really pricey to do.

I've had more customers with this problem this year than any other year. I think the blend or quality of fuel is bad this summer.

This exactly right here. 100% spot on.

If you are in a pinch and need to get it started if the fuel rail has the fuel pressure gauge schraeder fitting cycle the key on and off to build up some pressure in the rail, then take a rag and hold it over the schrader while you press it in to burp it (like letting air out of a tire), just for a split second. it will let the vapor escape and liquid fuel into the rail.

Disclaimer Do not do this if you are not mechanically savy, you can easily start a fire as you are releasing fuel vapor/liquid out and it will spray!!!!

 

[bobbytheboozer]

My buddy had the same problem in his magic magician with the same engine. We ran from havasu springs to copper canyon. Floated around and drank some beers for about 25 minutes, Went to fire the boat and it was locked.

 

[asa400ex]

Dual tanks. It's a 28 Sleek Enforcer.

 

[Deja_Vu]

My 7.4L is carburated and I swear we had this same issue.
We ended up removing the check valves that were integral with the fuel tank outlet fittings and replaced them with regular 90 degree elbows.
Haven't had an issue since.

 

[asa400ex]

Crack your hatch and open your throttle body wide open when your parked.

Higher octane fuel also has a higher boiling point.

You can run a fuel pump with a bypass regulator also. That's a permanent fix. It's also really pricey to do.

I've had more customers with this problem this year than any other year. I think the blend or quality of fuel is bad this summer.

When you say open your throttle body wide open, do you mean after you shut the motor off, put the throttle at 100%?

 

[Brian]

When you say open your throttle body wide open, do you mean after you shut the motor off, put the throttle at 100%?

Yes. It helps let the hot air out of the intake manifold and prevent the manifold from heat soaking and warming up the fuel rail. If you do this, just remember to bring the stick back closed before you start cranking again.

 

[Dettom]

My 7.4L is carburated and I swear we had this same issue.
We ended up removing the check valves that were integral with the fuel tank outlet fittings and replaced them with regular 90 degree elbows.
Haven't had an issue since.

Same problem with my 21 Advantage. Same motor. I ended up wrapping all the fuel line with air hose to keep it cool. Problem solved but it took years of pulling hair out, changing fuel pumps, getting rid of tank switch over valves to figure it out. Never thought of 90 deg. elbows on fuel tank though.

 

[LB247XS]

I had this happen last summer at MEAD.I BLED out the fuel rail at the shrader valve.started right up and just cracked the hatch when kicking back.i would like to fix it so I can leave the hatch closed since the wife and kids are always lounging on it

 

[TCHB]

Had the same exact problem with our Howard.

Solved the issue with a electric fuel pump from the tanks to the engine.

 

[Outdrive1]

When you say open your throttle body wide open, do you mean after you shut the motor off, put the throttle at 100%?

Yes. So air gets in the intake.

 

[TCHB]

The problem is the height of the engine, fuel tank location, amount of fuel in the tanks, warm gasoline temp, and a hot engine compartment.

When you add the fuel pump from the tanks to the engine you keep a constant pressure on that line which solves the problems.

Mercury has a bulletin on this issue.

 

[Deja_Vu]

Same problem with my 21 Advantage. Same motor. I ended up wrapping all the fuel line with air hose to keep it cool. Problem solved but it took years of pulling hair out, changing fuel pumps, getting rid of tank switch over valves to figure it out. Never thought of 90 deg. elbows on fuel tank though.

Glad you found something that works!
I like the electric fuel pump idea also to keep up the line pressure.
I might have to add that when its time to replace all my fuel lines...which is probably soon.