Help Needed With Johnson 75

[ALLAN DENNIS]

Hi All.. My son has just put a 75 on his F3 tunnel boat but it wants to do only 1 lap before dying.Give it 5 seconds and restart and it usually completes the race. It will run forever on the trailer at the ramp. Have tried a new Fuelpump,checked all the fuel lines Carbs Etc.
Any advice would be appreciated..
Thankyou
Allan Dennis

[Jeff_G]

If you are running an electric fuel pump check that you aren't running too much pressure. Secondly check the float levels if it dies while in a turn or shortly after.

[mercclassic]

What year is the motor and does it still have any of the originall electronics on it?

[outrace]

I had a similar problem years ago found it to be the powerpack, don't know why it did it but I did all the things you have as well as changing head gasket pulled gearbox off to see if any loose exhaust manifolds and then in desperation borrowed a pack and the problem never occured again.
Not saying this is the same for yours but it fixed my one.

[mercclassic]

This problem usually occured after the motor had warmed up. If u let it cool off it would start again.

[ALLAN DENNIS]

Hi Guys ..thanks for your suggestions..It does seem to die just after it has turned the first corner to the left..running 3 pound pressure on a holley pump with a new regulator.Have tried another power pack..The packs are of the Old metal type..should I be trying one of the new Plastic Black ones?Have changed the needles in the carbs,and set the float levels to parallell.

After letting the motor sit for a few seconds, it starts again and seems to keep going most of the time but NOT allways.

Could this be a fuel tank problem?

Many thanks

[Mark1]

Yes it could be a fuel tank problem. Sometimes old tanks get rusty and debris collects at the bottom of the tank, especially around the pickup as it the lowest point. Debris then of course goes in the fuel line and clogs things up, this can worsened by all of the bouncing around of the boat of course.

Just another avenue to look into

[LightNBug]

If you are using the metal case packs they are very old. Are they new? I would get a new or known good pack to try before looking for any other problem. It has the symptoms of a bad pack. If that doesn't correct the problem, try disconnecting the kill wire from the pack for a test run. Remember that when you do this the engine will not shut off with the kill switch. Bad safety switches cause many hard to diagnos problems.