1974 7.5 mercury dies after 45 min

[lilbuddy1]

I have this 74 Merc for trolling and ran into a problem trolling this weekend. Motor will run for 30 to 45 minutes and then sputter out. reprime , choke & it will start back up again with a few tries. Any ideas on why? Have replaced float, gaskets etc on carb with no improvement. Seems to be an intermittant problem.

 

[huntin dawg]

Re: 1974 7.5 mercury dies after 45 min

Is the vent open on your fuel tank? Sounds like vapor lock.

HD

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Motor is attached to the main gas tank of boat. Tank is vented.

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Any more thoughts?

 

[huntin dawg]

Re: 1974 7.5 mercury dies after 45 min

Overheating?

HD

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Nope. Cool as a cucumber. cooling well. Can squeeze bulb and choke & will fire back up.

 

[huntin dawg]

Re: 1974 7.5 mercury dies after 45 min

Still sounds like a vapor lock or loss of fuel. Have you run it on it's own tank and not on the boats main tank? That's what I would try.

HD

 

[pointandshoot]

Re: 1974 7.5 mercury dies after 45 min

is this a kicker motor or is it the only motor on the boat?

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Kicker Motor. Running only for trolling. Main is 115 Merc.

 

[Wingedwheel]

Re: 1974 7.5 mercury dies after 45 min

Does it have its own bulb? Perhaps the prime is leaking down.

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

I had that thought too. The bulb is the same line as the main motor, but I have thought it might be a problem. Would a small air leak in bulb cause this? It doesn't seem to effect the operation of the 115, but that might just be because of size.

 

[huntin dawg]

Re: 1974 7.5 mercury dies after 45 min

It should have it's own line and bulb. Yes, an air leak anywhere in the line can cause your symptoms.

HD

 

[Wingedwheel]

Re: 1974 7.5 mercury dies after 45 min

If you say you can pump the bulb and its soft, I'd start there. Thats an inexpensive fix if thats the problem, however its right that you should put in a tee or valve to give your kicker its own supply line.

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Well..... All replaced lines, started, and ran well... then about an hour later .... no sputter, just died???? What the heck???

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Is it possible that the tank is located too low in proximity to the motor? How far can a motor pull fuel ?

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Well, I'm hoping someone can shed some light still on this. The last time out, motor ran well for about the same amount of time. Then without sputtering, just shut off. From reading around thinking this might be a switchbox or coil problem. While trying to find the part numbers for coil & switchbox, my sierra book does not list my combination. The motor is a 1974 7.5 merc with a part number 3801856. Any help or input would be greatly appreciated. I'm missing out on some good fishing... Thx

 

[SC1650]

Re: 1974 7.5 mercury dies after 45 min

If you have the original fuel cell for the 7.5 you should be able to isolate the problem. If not, maybe you can borrow one. Just fill it with the mixed fuel and try running it. If it keeps running with the extra tank then you know it is something to do with the fuel delivery from your boats tank. If it stalls as it did before, then it is in the motor itself.

 

[Mi duckdown]

Re: 1974 7.5 mercury dies after 45 min

You are correct. Those smaller motors do not like to draw fuel from a long distance. Try, Borrow, a known Good spare 3/6 gallon tank. even though you have six feet of line wrapped around the tank.??? Then go from there. Fuel pump?

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Update.... Only been running on 1 cyl. (bad coil). switched coil wires and still (1) coil doesn't fire. P/N on coil is 339-5288. Is this 3395288T2 from Seloc a replacement coil that will work? S/N motor is 3801856 - 1974 Mercury 7.5hp. Please let me know so I can get this on order asap.

 

[lilbuddy1]

Re: 1974 7.5 mercury dies after 45 min

Can anyone help with this Part Number?