1976 15hp 15604A Idle and lower unit problems

[brianteel]

I picked this motor up cheap and like anything else that is cheap things never run right. I pulled the lower unit off and it had salt build up by the shift shaft. I did not feel like cleaning right now so i got another lower unit off of ebay. It is a 1992 lower unit. With that unit off it will shift into forward reverse and neutral no problem. I bolted it onto the motor and now it will go into forward and neutral and sometimes reverse. Is it possible that when i bolted it on i did something wrong or could there be a problem with the lower unit.

My second problem is the idle/ misfire. I took the card apart because it was not starting and I figured that had to be the problem. I found that the float was bad and it was gummed up a bit. I cleaned it out and put it back together. I got it started in 1 pull but it is running really bad. It is misfiring and and can not get it to idle down with the choke off. I cleaned the plugs and they do not look like they are fowling. I am not sure of the age of the plugs but I am going to get new ones anyway. I do not know much about the small engines like this and how old they are but can trouble shoot most problems. The coils look newer and there is strong spark coming off both plugs. There are not broken wires. I am not really sure where to go from here. I think i might need to check the points to make sure they are in good working order.

Side note how do I replace the thermostat in the engine or at least check it.

 

[OptsyEagle]

Re: 1976 15hp 15604A Idle and lower unit problems

OK. I do not know if the 1992 LU is interchangable to the 1976 so I cannot help you there. You need to put the motor in Forward and ensure that the screw that connects the shift rod is in the indent of the upper shift rod. If not you will have shifting problems and of course will strip your screw.

When you cleaned your carb did you adjust the idle adjust (rich/lean knob). It sounds like you are running too lean by evidence of your mis-fire and your necessity to choke (choke just enriches the fuel mixture). Use this method to adjust your carb.

http://forums.iboats.com/showthread.php?t=167352

If that doesn't work you may need to clean your carb again.

You said you had strong spark. Is that using an external spark tester and getting it to jump at least a 3/8" gap. If it does, it seems to me that your points are fine. Never hurts cleaning them, but I doubt it is your problem. If you are just seeing a spark on the plug, then that doesn't guarantee strong enough spark for ignition.

Your T-stat is in the cylinder head at the bottom. You need to remove about 8 to 10 bolts to remove it. You will probably have to remove the hood lock to take it out. If you order one make sure to order a seal with it. You would think it would come with one, but you would be surprised. Sometimes they do and sometimes they don't. There is a gasket in that water jacket you will be removing (you do not need to remove the cylinder head to remove the water jacket that houses the T-stat) and if you damage it you may want to order another one.

If you have the LU off and haven't already done so, you should change the impeller for the water pump. Even if it looks goods, these need to be changed at least every 5 years. They also have to be changed when they look good, because waiting to change them after they look bad usually requires you to buy a replacement powerhead since you just overheated this one. Impellers are only about $15.

 

[brianteel]

Re: 1976 15hp 15604A Idle and lower unit problems

I did not check the spark like you said. I think i need to check the points and pull the flywheel off.

any idea what the gap is for the plugs that year?

 

[OptsyEagle]

Re: 1976 15hp 15604A Idle and lower unit problems

The spark plug gap is 0.030". I prefer using the NGK B7HS spark plugs on that motor. The point gap is 0.020".