1967 FD21R Flooding

[bennyfran]

Looking for some help/information on a Johnson FD21R. Last summer I purchased a 16' 1964 StarCraft aluminum boat with a 1967 FD21R and a 1969 25R69D, and trailer for $650 (off a family friend a few camps down). I know I got a steal, especially because after fresh gas, new spark plugs, about a half a can of carb cleaner and starter fluid, we got the FD21R running. I use the boat for bass fishing so I mainly use the motor to run to spots, then kill it and run a trolling motor. My issues comes when I attempt to restart the motor after less than 30ish minutes of using just the trolling motor. When I stop the motor either by turning the handle to Stop, or hitting the stop button, I hear what sounds like a suction of fluid and dripping. If I pull the motor to start right then, it will start right up, but if I let it sit for less than about 30 minutes, it won't start no matter how much I pull. I have had some success starting up in less time by pulling the gas line off the motor about 100 yards from where I plan to fish, or if I let the motor sit for about 30 minutes with the gas connected. I am assuming that when I just kill the motor, there's still suction pulling in gas and flooding the cylinders. Would this be correct? Also, anyone have any suggestions on how to use this motor in the scenario I plan on using it? Any suggestions/advice is welcome, thanks!

-Ben

 

[fdrgator]

Well, I suppose it is possible that pressure in the tank is flooding the cylinders. But. the first thing I would check are the magneto coils. The symptoms you describe certainly fit those for old, cracked coils. Notorious in motors from that era, unless they have already been replaced.

 

[racerone]

Check the venting of your fuel tank.----Check / replace fuel pump diaphragm ( $10 or less ) ------Inspect float valve and float in carburetor.-----Wrong to assume there is " suction " causing this issue.----Also test spark, should jump a gap of 1/4" on a test device.

 

[timguy]

Agree with Gator and Racer. If the fuel tank is building pressure, it may be enough to push past the float needle valve, then flooding the motor. The fuel will pool up behind the carb and into the chamber holding the reed valves. In many cases, the reed valves will let the pooled fuel leak into the crankcase, and/or, it will get an "overdose" of fuel when you first pull it over to start. This will cause hard starting. If the tank is still the original steel tank, you can crack open the fuel cap and see if there is pressure built up after that 30 minutes of fishing in the sun. If the little pin is not doing its job, there where the coupling clips on the tank, that is fairly common on older tanks, and you can remove and clean the vent valve with a good spray cleaner and compressed air. The other little pin, to the right, is a valve that opens the suction tube to allow fuel passage. If the tank is building pressure out in the sun, then it will also cause stress on the fuel pump to suck the fuel on a cloudy, or cooler day. Does the motor start okay on a cloudy, cool day? If you have a plastic tank, then you have other things to consider, regarding venting. Newer style plastic tanks do not have a manual vent and they are supposed to just blow up and build pressure in the sun, therefore relying on a good strong float needle valve to stop any fuel flow that is not wanted to enter the motor. The problem with that idea is in the event you decide to pull to the shore and tilt up the motor it can pressurize and dump quite a bit of extra fuel into the boat or the lake, more so if you park in the sun. So if you have a plastic tank then it is best to have one with a manual vent valve, that can breathe in BOTH directions.

 

[bennyfran]

Hey everyone, thanks for the advice! I have a shop manual coming so magneto coils and fuel pump diagram will be on the list along with cleaning out the carb. Sounds like I need to by a spark tester as well, any suggestions? Do you know the spec for the plug gaps?
As for the gas tank. It's a red plastic one that the guy I bought everything from included. I know it's not new, but no idea how old it is. I don't keep the tank in the boat, but have noticed after running for a while the tank will almost seem sucked in. When I first head out, the motor starts first or second pull each time. I'll inspect the tank to see if there is a valve, might just replace the tank with one that has a manual valve.
Also, as I said, I have a 25R69D as well that currently doesn't run. My plan is to use this a learning motor to tear down before really breaking into the other. Are they similar enough that this is a good plan? Thanks again for all the advice!