470 vapor locking I believe need help correcting, Yes I've searched

[juicebronco]

First let me say this was a motor I picked up that I don't know the history of, I did a bunch of work to get it going prior to installing it as a replacement to my blown 470. I have around 100 miles (no hour meter) so depending in speeds 5-10 hours is my guess.

So I have an 83 470 that seems to be vapor locking. I was out yesterday, stopped for a while, then I went to restart it, it fired up fine, I started driving and it died on me, like it ran out of fuel. SO I check, no fuel getting to the carb, so it's for sure a fuel issue. I checked the filters and blew through the lines and what not, and I couldn't get it go, so I figured it was the pump. I took it apart as far as I could on the boat, and it seemed fine, I put it back together and nothing. I got towed off the lake.

Today, I took it apart, cleaned it up, made sure everything worked good, blew/sucked on it to test the check valves, primed the pump from a separate tank, installed it, and fired it up on the trailer. Seemed to be running good, so I took it out for a test ride. Drove around for 20-30 minutes or so, and shut it off to go swimming, and test the same issue I had yesterday with dying after restart. After sitting half hour or so, I started it up, and it started easy. I went to start driving and it seemed to run out of fuel again. Immediately checked, and no fuel getting to the carb, pulled the line off the intake to the pump and it was dry. My solution was to pull the pump off, bypass the water separator filter, and put the line directly on the tank, and prime it by hand. Once I had fuel in the pump, I hooked it back up, and it started and ran fine, but I headed back home, and started researching.


So Warm engine, restarts, then dies. No fuel in lines. Prime the pump and it works again.


To me it seems like it's vapor locking in the lines, and the pump is losing prime, the engine fires on what is left in the carb, then runs out when that empties.

I've read about idling the motor prior to shut down, and running the blower after shut down for a bit. Opening the doghouse isn't a realistic option to do when people need places to sit.





Maybe related- when I first launch, it tends to want to not open up, I can idle, but if I try and get it up on plane it will start to starve for fuel. cough a little, then i need to work the throttle in neutral to get it running smooth again. I figured it was a cold engine thing, but it did it as well today, after warming it up on the trailer at home, then taking it down to the lake. Once I get it going it runs great with no stumbles. I figure it is a carb issue, but figured I would mention it.

 

[Rick Stephens]

Have you checked the anti-syphon valve on the tank outlet?

When it runs out of fuel, have you opened the filler cap to see if it sucks air, indicating it may have a plugged tank vent?

Have you checked the float height and needle valve?

Fuel pressure from the pump ok?


I have never heard much in the way of vapor locking boat motors. They have unlimited cooling, run so low in temps and route the fuel lines far from anything hot, that it is usually not possible. So probably something else.

 

[Oshkosh1]

Insulate your fuel lines. Use foam pipe insulation and/or insulated ducting tape to wrap them. As the fuel heats it may create enough pressure to overcome the pressure of the float needle seal and it essentially floods the engine with percolating fuel slipping past it. As the engine sits, that fuel evaporates...but does so slowly hence the ability to start after 30 min. I had a similar issue in an old MGB. Insulated the lines in the engine compartment and the hot start/hot idle issues were substantially improved...

 

[stonyloam]

I'm with Rick, chances of vapor lock are slim, something is restricting your fuel, anti siphon or tank vent.

 

[juicebronco]

Thanks for the replies,

I did pull the filler plug, and did not hear any air sucking in.

I also disconnected the tank vent line at the tank and was able to blow through the line, although it seemed as if some fuel was in the line. Which I don't think is uncommon on this boat, often when I fill up, a little will squirt out of the vent.

I haven't checked the anti-siphon valve, I'll have to look into how to do that.

I haven't put a guage on the pump, but once it's primed up, it pushes out good, and if I loosen the top fuel line bolt where it goes into the carb with the engine off, it sprays out as soon as the seal is broke. So the line is for sure pressurized when in good operating condition.

I rebuilt the carb last fall, as it was flooding itself out, so I ordered a rebuild kit and went through it, but I haven't torn it back down since.

 

[wrestling coach]

If you have a Carter fuel pump you have a fuel filter on the top under the bayonet clamp. If not do you have any other in line filters you might have overlooked. Water/Fuel separator?

 

[juicebronco]

It is the carter pump, and I did change the filter that is on the pump.

I didn't replace the water fuel separator filter, but I had replaced it last year, and only went out a handful of times prior to the engine terminating itself. So I figured it was good still when I installed the engine.

 

[juicebronco]

OK, tonight I put a fiberglass mesh heat sleeve (rated for 1800 degrees) over the metal fuel line between the carb and pump, and wrapped that with an aluminum tape to help also reflect heat.

I checked the anti siphon valve by pulling it off and blowing through it, I could only get air to go through one way, so it seems to be working, unless there is a better way to check it.


I ran it on the trailer for 30 minutes or so shut it down for a bit then re-fired it no problem, but I doubt the engine would generate enough heat on the trailer to replicate the issue. I'll be heading out Wednesday for a test run on the lake.

 

[wtg2320]

Did the sleeve and tape work

 

[GA_Boater]

Did the sleeve and tape work

This was 2 years ago. And no complaints since.

Closed.