Vapor Lock?

I've been having an issue with my '75 Nautique with the 351W that seems to be heat related. The boat runs very well for about 45 minutes or so and then it dies as if the fuel supply is shut off. I'm almost certain that the problem is that there is a vapor lock in the steel fuel line from the filter to the carb. The water temperature never goes above 180 degrees. After letting the line cool for a few minutes with the doghouse open, the boat cranks right up after a couple of squirts from the accelerator pump. It has been doing this for as long as I have had it and I just recently changed the entire ignition over, so I'm almost certain that it is fuel related. I'll verify the spark next time with a timing light when it happens. Has anyone else experienced this problem? I tried a piece of rubber hose, but had the same issue. Maybe the fuel is boiling in the bowl? Do I need a heat isolator for the carb? The last time that this happened was when I got up to around 4000 rpm for a few moments. It always seems to be starved for fuel at that rpm. I probably need a different power valve, but that is probably a different issue- and I hardly ever run the motor to 4000 anyway. Any ideas or experiences with vapor lock or boiling fuel?

Anthony

If its vapor just cut the line from the pump and insert a piece of rubber hose, This will stop vapor lock, if infact that is the problem.

Additionally,
There could also be a collaping fuel (soft) line, or a clogged fuel inlet screen set within the dip tube's fittings

I doubt it is vapor lock also. I think your coil might be breaking down,or if the timing is advanced too much, it will run, but after a few minutes above a certain rpms, it can advance itself and it will die.

Thanks everyone for the replies. I don't have an electric fuel pump, just the standard mechanical one. I tried replacing the steel line with rubber hose, but that didn't change anything. As many of you said, it's probably not vapor lock due to the fact that the fuel is flowing when it happens. I really think that the issue is heat related due to the fact that it happens consistently after running the boat for 45 minutes or so, and definitely when I open the rpms up for a short time. I could make it happen by riding around the lake for 45 minutes and then pushing the motor to 4k for 10 seconds or less. It happens every time like that. Even though it seems like a coil issue, it can't be because I just replaced the entire ignition and distributor and the problem is the same as before. I now have a $500 distributor with gm HEI that has a simple 2 wire hookup. After reading some other posts, I think that my problem might possibly be a resistor of some sort under the plate on the back of the motor where the voltage regulator and switch are located. Even though I did remove a ballast resistor near the coil when I converted to HEI, I might still have another one under the plate if that's what that is back there. I don't know why my boat would have had 2 ballast resistors, but it may be possible due to the fact that someone had converted to mallory electric eye ignition from points. I need to check and see if I get 12 v at the distributor. That resistor could be heating up and cutting power. That's my theory for today. I'll check it this weekend. Does anyone agree with me on this theory? Or does anyone know if in fact that is a ballast resistor under the plate at the back of the motor?

If the boat already had a Mallory unit most likely a ylu554cv model you really wasted your money on the HEI unit, not that the HEI unit is bad or anything, Try running hard or over 4k just after its warmed up say after 10-15 minutes and see if you have the same problem and if so I would look at the fuel system like low fuel pressure you should have atleast 5 lbs of pressure, if the pressure is good then you may need to rebuild the carb or replace the secondary diaphram or power valve the power valve should be 6.5.

Thanks to everyone for the replies. I think that I found the problem. The little resistor under the plate on the back of the intake was in fact wired in with the ignition wiring. I was only getting 9 volts to my coil with a cold motor and probably less with a warmed up motor. I bypassed the resistor and I now get full battery voltage at the coil. A test run at the lake showed no problems at all. The conclusion is this:

Apparently the original ignition resistor is indeed the one under the plate on the back of the intake. It was used with the original points to keep them from burning up. The previous owner converted the system to electronic ignition with a Mallory setup with an electric eye. Yet another resistor was added with that setup because the electric eye doesn't like full battery voltage either. Apparently the previous owner did not know of the original resistor and felt the need to add another one. So, I had two of them. I took all that Mallory and Prestolite junk off when I installed my HEI setup. I removed the new resistor, but not the old one. The old one kept cutting my voltage when the motor heated up. The HEI distributor from performancedistributors.com is a very nice unit. Yes, it is pricey at nearly $500, but I will never have to worry about all that points, electric eye, external coil, spagetti wiring, and resistor junk. The unit is all one piece with two, yes only two wires to hook up. One for 12v and one for the tach. It is basically a GM style distributor with the coil in the cap. It has a powerful coil that allows me to open up the gap on my plugs to .055 or so which cuts down on plug fouling. The timing has a much smoother advance curve unlike the original Prestolite or Mallory or whatever that junk is. It is well worth the money in my opinion.