1973 115hp Johnson low WOT RPM

Hedhunter · #1 (**permalink**) 09-10-2011, 10:08 PM

I have a 1973 115hp Johnson. Ran boat on water and engine would only hit 4000 rpm. Sprayed fuel into carbs and RPM went up so I cleaned both carbs. Put boat back in water and it ran fine, getting over 5000 rpm. While running that day I got the over temp alarm so shut down and got towed in. Replaced water pump and tried boat again. It would not go over 4000 rpm agaain so I pulled carbs again and cleaned them and also replaced all fuel lines. Tried boat again and still will not go over 4000 rpm. It does not help to spray gas in carbs. What can it be?
Thanks,
Hedhunter

boats.net · #2 (**permalink**) 09-12-2011, 03:58 PM

Need to check compression and check for spark at spark plugs.

Rebel Sympathy · #3 (**permalink**) 12-11-2011, 07:56 PM

Quote:

Originally Posted by Hedhunter

I have a 1973 115hp Johnson. Ran boat on water and engine would only hit 4000 rpm. Sprayed fuel into carbs and RPM went up so I cleaned both carbs. Put boat back in water and it ran fine, getting over 5000 rpm. While running that day I got the over temp alarm so shut down and got towed in. Replaced water pump and tried boat again. It would not go over 4000 rpm agaain so I pulled carbs again and cleaned them and also replaced all fuel lines. Tried boat again and still will not go over 4000 rpm. It does not help to spray gas in carbs. What can it be?
Thanks,
Hedhunter

Usually an alarm at 5000 rpm tells you that you have just fried your engine. Seriously, by the time a temp alarm goes off on an older motor running at 5000, the damage has usually already been done.......
If you are spraying gas in carbs, then you are leaning out the oil ratio. You should be spraying a gas/oil mix into carbs. You may have scored your cylinder walls as a result. I hope not. Also, if you have been running motor at wide open with fuel starvation, that is an very good way to burn a piston or two. The heat from that will set off temp alarm. But, it is too late......