1979 40hp 2cyl serial 5483525 thermostat stuck open

I have had a weak tell tale stream and was worried about overheating. When I replace the impeller I had a bunch of chunks in the housing area. I also had some weird looking worms in the end of my telltale. I removed the stat and it's stuck open. So I ordered a new gasket and stat. But I was wondering how the stat and poppet work? I also replaced imp and the top imp housing. I'm trying figure out where to insert a zip tie or some other tool to try and clean out any old impeller bits and pieces. Also I read that a person can remove the water tube from the bottom left of the block that runs to my fuel pump on the starboard side to aid in cooling. I'm not going to do that unless I understand how everything works. Any help or good explanation would be appreciated.

I ended up removing the lower unit and blowing air up the h2o tube while putting a vacuum on top of the thermo stat holes. I also put a big air duct zip tie down the thermo stat and poppet holes to dislodge any chunks. I placed an old Tshirt inside my shop vac to see what I could see. no big chunks of old impeller came out only some dust. I put the stat and gaskets in and it still hasn't increased my tell tale stream. i let it run for about fifiteen minutes and the tell tale stream never did heat up. should the stream of water be warm as it comes out? Any reply would be great.

As long as the left exhaust plate on the block never gets so hot you can't hold your hand on it, then you are okay. The Tell Tale stream tends to stay fairly cool while running at idle.

Jeff

Great! thanks Jeff. I've cooked a few motors over the years and as a result I'm always paranoid about high temps. Do you know how the water circulates thru the power head and what role the poppet and thermostat play?

I have a theory. The usual impeller design (like yours) is a positive displacement pump, meaning it can not be throttled back (like when the t-stat is closed). The water pressure has to go somewhere, so the poppet acts like a relief valve, shunting the water around the power head until the t-stat opens. Some later impeller designs (like Yamaha 9.9s and 15 hp) have long, spindly vane impellers (vs. short and stiff). These can 'bend back' to avoid over pressuring the system while the t-stat closed.

Jeff

Thanks Jeff. Everything seemed good the water jacket was cool and there wasn't a spot that I couldn't touch where it was really hot. Now I'm dealing with a poor idle. I just rebuilt the carburetor and when doing this I relived the idle set screw and tried to remove the main jet to clean and inspect it but my screw driver wasn't big enough and I couldn't remove the jet and in the process stripped the top of the jet slightly. Would this be enough to cause a rough idle? Also anyone know how many volts from the switch box to the coils. I've went thru everything new coils, tested and replaced stator and trigger, fuel pump and new rectifier. I swear it ran a little better before I redid the carb. I can barely get it to idle below 800rpm. I have an appointment with a guy on Wednesday if he can fit me in. But I really wanted to get this myself also I'd like to save $50 an hour. Anymore input be appreciated. Thank you

The main jet being striped won't bother the idle (and, since gas flows through it from the rear) it won't change the WOT operation.

Proper idle adjustment can only be done in gear, with the motor warmed up.

The stator puts out 200 to 350 volts, so be careful.

Jeff