1983 johnson 7.5 problems.

[derwood]

I am haveing problems with two things on this motor.<br /><br />1#....I started up the motor after a 2 months and found that the weep hole is spitting water but not alot and it's very hot....I changed the impeller and it did not help....There is lots of water squirting out from the seam between the lower foot and the shaft....There was no gasket there but it sure looks like it needs one, It's comming out like a lawn sprinkler.....the impeller is the right one and I put it in right so whats left???<br /><br />2#....When the PINHEAD at the marina fixed The rivets on my jon boat and replaced the coil on one plug....He said that he adjusted the mixture screw to where it's supposed to be, but It does not run as fast as it did, it has more carbon on the plugs now and it smokes way more than it did....How do I get the R.P.M.s of a 2 cylinder motor....I have tach's, but they are for cars and only have 4, 6 and 8 cylinder settings....I used to do it by ear and get it to run smoothly at as low an R.P.M as I could....Don't know if I should do that anymore.<br /><br />Thanks for your help.<br /><br />Derwood.

 

[Bob in Calif.]

Re: 1983 johnson 7.5 problems.

derwood..... Your water pick up tube might not have been properly seated in the water pump housing or the base of the power head. That would cause your over heating. Or you could have a clogged water passage in the power head.<br />Correct your water problem before you run it long enough to adjust your carb. It is best to adjust the carb at running tempature, AFTER the water is circulating thru your motor. Another check is the condition of the thermostat and passages in the "stat" housing. Make sure you have a new gasket. <br />If you use your engine in salt water and the stat hasn't been changed in a while, even with proper flushing, they can "freeze shut", thus causing over heating. I would start with the easy check of the thermostat first.<br />One question, was the old impeller complete or in pieces when you removed it? If it was in pieces, chances are good you have an "impeller impeedment" in your cooling system<br /> .....Bob in Calif....

 

[derwood]

Re: 1983 johnson 7.5 problems.

Alright....after I burnt up a brand new impeller putting it in backwards....It was a piece of trash in the power head. <br /><br />I am glad it was'nt in pieces....I had to put it back in <br /><br />There is no T.stat. in this engin....I'm sure that there is supposed to be one....maybe in the plastic cover over the plugs....It did'nt have one when I bought it....found that out later.<br /><br />I let it run for awhile before I go anywhere that way it gets warmed up a bit and I can check the weep.<br /><br />It also does'nt have a gasket between the foot and the main shaft....should it?<br /><br />I would still like to know how to get the R.P.M.s of a 2 cylinder engin.<br /><br />Derwood.

 

[rickdb1boat]

Re: 1983 johnson 7.5 problems.

Derwood,<br />There is no gasket between the foot and the "Main Shaft", but there should be an "O" ring on the drive shaft. If there isn't, you need one. Also, make sure the driveshaft is properly installed into the Water Pump grommet(Did you change the grommet??). That should cure your Water problem. As for the RPM's, you just need a plain old marine Tach avalible at Teleflex and others. You could try yours in the "6" position, but I'm not sure it would read correctly. Here's a link to the Tachs. and troublshooting them.<br /><br /> Tach

 

[rickdb1boat]

Re: 1983 johnson 7.5 problems.

Then again, check out part # 14 on page below(Click on it to enlarge). Does not show this in my manual!!?? What is your Model Number?<br /><br /> web page

 

[Bob in Calif.]

Re: 1983 johnson 7.5 problems.

Howdy again derwood.........I am looking at my 1983 Jonnyrude shop manual and it shows you do have the provision for a thermostat. It is located at the top, to the rear of your power head, above and to the left of your spark plugs. The stat cover has three (3) bolts in a triangler configeration. Remove the three bolts,the cover and the stat, etc. If there is no stat in place, you should have one to allow the engine to warm and operate in it's normal 4500 to 5500 rpm range. It is not good to run an outboard with out a (working) thermostat. After you have the cooling problem solved, your idle speed should be 6oo rpm in forward gear. It's best to adjust your low speed and high speed settings while the the engine is in use,that is when your boat and motor are in the water, as it will have the back pressure it needs to run properly.<br />While you have the stat cover off and the stat out, don't forget to check the water passeges for blockage. Once you get into it, this will be easier than it sounds. (for real) ...Bob in Calif...

 

[derwood]

Re: 1983 johnson 7.5 problems.

Thanks guys....I have been all through the water system now and its working good....I don't know why I did'nt go to the water plate first....I had to do the same thing to my 1952 Johnson 3hp light twin.<br /><br />I did'nt see a tack for my motor but you got the modle no# right....the parts skimatic will help alot....Thanks.<br /><br />Why can'yt you run a OB motor without a thermostate if you let it warm up first?<br /><br />That is where the thermo. is at....not that I understand why they made it plastic....When I go to replace some more parts I'll get a thermo. and a new cover plate....among lots of other stuff.<br /><br />What's the srl modle?<br /><br />Also what's the diffrence between the two sizes of props listed there and in what direction are they getting those measurements?<br /><br />I need a new prop....I have whats called around here as a "redfish prop"....Its not to bad yet but it's on its way.<br /><br />Derwood.