CVX 18 Possible Vapor Lock issue?

[JBD319]

Hello all!

I recently purchased a 1977 CVX 18 that hadn't ran since last fall. It has the original Mercruiser 188/888 302. All the fluids in the motor and lower unit are good, had it looked over by a member and a boat mechanic friend and they basically gave their blessings for sea trials. It has a brand new Holley 2 barrell 350 CFM carb on it, that could probably use some tuning.

Boat fires right up and runs great. Coolant temps run in the 140F at speed, 155F when idling/low speed after warm up. Checked this with a laser temp gun on the risers and temp sending unit housing on the intake manifold.

Twice now about an hour into a river ride, the boat has stalled out and won't restart, had to be towed off the river. However it will fire, then die, if you spray carb cleaner down the carb, so there is still spark. I put a brand new fuel filter on it after the first time, confirmed I can easily pull fuel from the tank with a hand pump so the pickup shouldn't be clogged.

When the stall happened both times it was exactly the same condition. Engine was fully up to temp, had been WOT several times with no incident. After 10-15 minutes cruising in gear just above idle, it would die and not refire. I'm concerned it's heat build up causing vapor lock. My thoughts are to try keeping the engine cover open anytime I'm in that condition to allow engine bay heat to escape.

Besides actually getting the carb tuned, does anyone have experience with this, or an educated opinion given the symptoms? I'm going to change the wire/plugs/distributor cap this week just to eliminate any issues there as I have no idea when it was done last so it can't hurt and they're inexpensive and easy to change.

Thanks ahead of time for any help!

[75starflight]

does the distributer have points or an aftermarket electronic ignition like a pertronix module in it?

I have had issues with a pertronix module doing the same thing.

[JBD319]

does the distributer have points or an aftermarket electronic ignition like a pertronix module in it?

I have had issues with a pertronix module doing the same thing.

I'm not 100% sure but I believe it's an old style distributor with points, but I haven't pulled the cap off yet. Was planning to do that after work today. I attached a photo of my setup.

[thedeuceman]

i would agree with yer assessment on it being a fuel issue.
i have installed a pr gauge in the line to the carb on all my inboards (McMaster Carr has a liquid filled gauge rated for gasolene for about $15)
i have had an issue with water in the fuel on the 1900 we sold to Keisha and Jake (has the same motor)
it seems if the water separator/filter gets a lot of water in it, it stops passing fuel or plugs.

[JBD319]

i would agree with yer assessment on it being a fuel issue.
i have installed a pr gauge in the line to the carb on all my inboards (McMaster Carr has a liquid filled gauge rated for gasolene for about $15)
i have had an issue with water in the fuel on the 1900 we sold to Keisha and Jake (has the same motor)
it seems if the water separator/filter gets a lot of water in it, it stops passing fuel or plugs.

Good to know on the filter. When I drained all the fuel out of the old one to replace it, it seemed like it was all gas. There was no water separating out but I'll empty the new one and see if that happens.

What type of pressure should I be seeing if I install a gauge like that?

[Plugcheck]

What is the fuel line routing from pump, assuming stock mechanical, to the carb?    The majority of fuels sold anymore contain ethanol of some percentage, alcohol "boils" at lower temps, so im wondering if the fuel line is touching or comes close to a heat source?    Next time it happens, run your hand down the line, if you can touch it, its not likely the issue.   I would think normal pressure at the carb should be around 5psi.   

[JBD319]

What is the fuel line routing from pump, assuming stock mechanical, to the carb?    The majority of fuels sold anymore contain ethanol of some percentage, alcohol "boils" at lower temps, so im wondering if the fuel line is touching or comes close to a heat source?    Next time it happens, run your hand down the line, if you can touch it, its not likely the issue.   I would think normal pressure at the carb should be around 5psi.   

Thanks for the great info! It is indeed a stock mechanical fuel pump. The metal portions of the fuel line from the pump to the carb seems to be original routing, then there is a rubber hose joining a short section from the line into the carb.

There is a vaccum line on the carb (300 CFM Marine Holley 2 barrell, brand new) that has a rubber nipple on it. Should I be using that line? I'm definitely new to all of this. I'm skilled enough to understand i'm having a fueling problem, just not sure where to start.

**Also I make sure to use the 91 Non-Oxy gas at my local Kwik Trip**

Pictured below is my carb and you can see the rubber nipple on the side I'm referring to. It's still like that on the boat.

[thedeuceman]

I think that port is to be connected to the vent on the mechanical fuel pump in case the diaphragm fails the leaking fuel will be pumped into the carb (instead of it leaking into the bilge)

[Plugcheck]

I would second Joe's opinion on that port being a "drain" port for a mechanical fuel pump.    Too high on the carb to be full or ported vacuum.    BTW, if you locate the line from the pump and it has any fuel in it, it is a sign the first diaphagm has failed and the pump needs replacement.  Automotive mech pumps just have a hole that will leak fuel on the ground when they fail, ok for cars, bad for boats

[JBD319]

I think that port is to be connected to the vent on the mechanical fuel pump in case the diaphragm fails the leaking fuel will be pumped into the carb (instead of it leaking into the bilge)

Thanks for both replies. I still have the original sight glass on this one. Is it worth switching to a line up to the carb instead?

[thewillets]

Maybe the float sticks closed when the carb is hot.
Try tapping the carb with the handle if a screwdriver to see if it will release and allow fuel flow next time it happens.

[thewillets]

In my youth I have had coils or condensers fail hot then work cold.