1975 75 hp johnson

[cooper0720]

Im hoping someone can help me. i bought a 19' aluminum landau boat with a 75 hp johnson. i was told it ran about 35 with no problems in arizona. I live in colorado and took it out and it wont run worth a crap. So i replaced the plugs checked the timing rebuilt the carbs ran all new fuel line. What the boat does is wen your at a dead stop you can floor the throttle and it acts like it is loading up and just bogs down, but it will eventually get out of the water and run like 27 mph at 5200 rpm does anyone know what else to do it has a 15 degree prop does thast need to be changed???? I also took the low and high speed jet out and they are right for the altitude.. Please help

 

[fishin1789]

Re: 1975 75 hp johnson

First, get a Clymer manual and make sure all the linkages are set properly. Just one bad linkage setting will drive you nuts trying to fix it! Make sure the carbs open at the same time and are opening fully, choke is not closed, timing advance is operating as it shoud, etc. Good luck!

 

[Al-53]

Re: 1975 75 hp johnson

dont get a clymer manual....worthless.....get a OMC manual...

when you changed all the fuel lines..to use use the OMC ties or the rachet ones to secure the fuel lines ..just a shot in the dark as you may be sucking some air is all....

others with more knowledge should come in soon to help....

Al

 

[cooper0720]

Re: 1975 75 hp johnson

thanks for the replys i bought a seloc manual and all the linkages are right the auto choke doesnt work so the motor is set on manual choke everything is opening as is should the spark advance seems to be working right i dont no how to check max spark advance i used zip ties to seal the lines to the carbs since there isnt clamps small enough for 3/16s line

 

[cooper0720]

Re: 1975 75 hp johnson

also another question my motor has 3 carbs fuel feeds in the middle carb and then over flows into the top an bottom carbs would it be better to split the fuel line form the fuel pump and run seperate lines to each carb

 

[Bifflefan]

Re: 1975 75 hp johnson

thanks for the replys i bought a seloc manual and all the linkages are right the auto choke doesnt work so the motor is set on manual choke everything is opening as is should the spark advance seems to be working right i dont no how to check max spark advance i used zip ties to seal the lines to the carbs since there isnt clamps small enough for 3/16s line

A 15 pitch prop is what you have?
You should be able to run a 17p with not problem and a 19p when running lite. altho the hole shot will suffer a bit with the 19p.

Im guessing that you have a power pack issue, or a bad coil, its possible you have weak spark. You need a spark box to check this.

As for the WOT timing. Take out the plugs, ground the plug wires, then have a buddy crank the engine while you read the timing and advance the throttle to WOT. set the timing about 2 degs short of the recomended WOT timing and you should be good.

You really dont want the auto choke to work. There was a factory bulletin to disconnect it anyway.
When its running good (in the water) you should only have to hold the choke to start it and then bump it a couple times to keep it running when it cold, after that you dont need it at all.

I would take it to a dealer and spend the $$$ to get it running right, then enjoy it. Then you can learn as you go and not have to worry about it leaving you stranded and rowing.

And no matter what you hear about seloc, they are fine manuals. they are just like the rest and photo copied out of the factory manual.

 

[jimdd810]

Re: 1975 75 hp johnson

Just a question that hit me what is the elevation you are at? Could use different jets. Call your local omc parts and service and find out what they are doing for motors? Just a thought.