Marinette Boat Forum

I have had my 1972 28' Express, single 318 on the water for 3 months and could not get it to run right. Temp gage never would read over 110 degrees so figured the gauge was bad as had confirmed that a thermostat was installed. Finally followed Fast Jeffs advice and bought a Laser thermometer at Lowes (on sale for $ 19.95) and started checking. Found out that the thermostat was defective so once again followed Jeffs advice and rather than buy the $ 105.00 + SH thermostat, made my own. I found a 142 degree Mercruiser thermo at Napa for $ 22.00 and made my stainless plate from stuff I had at home. Installed and couldn't believe how much better she ran. Since I finally got a working tach, with my GPS I could finally determine how well she was doing. Max rpm I could pull at WOT was 3,000 With a top speed of 26 mph. I know the prop is a 14/10 as checked it while on the trailer. Since I have the original delivery sheet, I know this is what she was delivered with new. I believe I should be pulling more rpm and wondering if anyone might have any suggestions.

Timing maybe I have the same boat and working on the same thing my new distributor is not giving me as many rpm as the old one but it could be my coil I changed it from a flame thrower to a super coil and I need to but the ft back in and check. Does your spec sheet tell the max rpm or top speed? Do you have trim tabs?

I have 73 with 318s & I seldom go to above 3000 rpms considering the engines are over 40 years old .The question is how fast is fast enough? Enjoy the the trip.
Wayne

ANy thing over 2000 RPM and I can not hear the Radio!! but I would like to figure out what the best prop for the 2000 RPM range is.

I don't want to go fast, just trying to get an indication as to whether I'm were I need to be. Sweet spot seems to be at 2500, 16-17 mph. A fellow boater rode with me an said he thought I would use less fuel at this setting than 2,000 rpm at 11-12mph. I have huge trim tabs, Bennett 11 x 42 that came with the boat.

That 3,000 rpms is a mite low. I'd check to see if the distributor advance is working correctly with a timing light that has an adjustable scale--you can buy one from Harbor Freight (or maybe borrow one from Auto Zone). To use it, run the engine up until the mark stops moving, then center it with the dial. Finally, read the amount of total advance on the scale (of the timing light). Should be something around 25 to 30 degrees.

It's common for the advance systems to stick with age.

Jeff

Check that all ignition wires are on the correct plug. They are easy to cross. Been there... Done that I'm no expert like Jeff, but I don't see how a boat that size with a small single engine.. Loaded down.. Dirty bottom could pull out much more rpms.