exhaust is overheating after repair

[Scubadave16]

OK, I am back after a short break. So the boat exhaust is still overheating. wasn;t a big deal if I kept the RPM under 6K and only went short distances. But I took 3 friends out and had to run it harder than usual and burnt through the exhaust coupler. more on that later.

So I did something radical; and I want to know if it will screw something up. I bypassed the water regulator valve completely and just ran the hose from the "T" to the stinger pipe. And guess what??? it WORKED. the thing runs fine. the pipe is warm, but not burning up and the boat gets up on plane. maybe not quite as fast as it was and only gets up to about 6500 rpm at WOT, but I can live with that for the 7 weeks remaining in the season. So all you experts... what is the down side of this? doesnt the water from the stinger pipe wind up in the water box and muffler anyway?

 

[2x2smoke]

I'm no expert but there are two scenarios.

your water regulator system is not working properly as discussed above. Your bypass might not hurt much but top end performance. The manual describes engine damage if you tamper with the water regulator. Maybe dumping too much water into the tuned pipe at full throttle restricts exhaust flow to the point of overheating the top end? I've read there is a specific way to bypass the water regulator with jets that control the water flow instead of the bellows. 96 racing manual?

Second scenario is that your water regulator is functioning but there is something wrong with your engine or fuel mixture that is superheating the exhaust. Your bypass might be masking a more serious problem . I guess this is less likely if the engine seems to carburate smoothly with good power. What do the spark plugs tell you?

 

[Lumps]

I still thing there is a partial blockage in the cooling lines of the pipe

 

[Scubadave16]

I, too, think a blockage would explain things, but I have pulled off every hose and water just pours out. when I took off the tuned pipe and connected it to a garden hose water flowed freely through it. I even thought of a blockage in the heads themselves, but the water flowing out of the block/head is warm and at a pretty good stream. visually about the same as the stream that is going into the head when i pull the hose off. and the tuned pipe is relatively cool, only the stinger pipe is hot. from what I can see the only cooling the stinger gets is the direct water injection.

interesting that 2x2smoke mentions that the problem could be from the engine running too hot, rather than the exhaust not being cooled. not sure how I could test that, except at all times the engine block/heads are cool enough I can put my hand on them. only the pipe is hot. could unburnt fuel be going past the engine and igniting in the pipe? The boat mixes fuel and oil so I don't have any control over that. it does smoke a tiny bit, but the plugs look kinda normal when I pulled them.

so kinda back to the beginning meaning I have know idea what is wrong. since only 6-7 weeks left in the season here I will just keep doing what I am doing. I am still open to any ideas to test/fix/adjust it.

 

[2x2smoke]

Check the manual but I think it says the water regulator should deliver .4 gallons per minute at open throttle. It doesn't specifically say but that should mean .4 gallons to the cone pipe at WOT. That is a value you can actually test and adjust towards (since they provide it)

Make a test rig: Get a long length of tubing to go from the water regulator valve to a spot convenient for you to monitor as you sit in the cockpit. Get a clear gallon jug and mark it for .1 gallon increments to measure the output of the regulator valve.

get a timer person and get to the center of the lake where you can go varying speeds and WOT for 15 or 30 seconds. Hook up your test rig and see what is going on. It should be flowing more than .4 GPM at low speeds and taper off as speed increases. Look for .1 gallons in 15 seconds WOT. Screw down the adjuster to get more flow. Once you see that there is actually any flow at WOT, you can get more precise on the actual output.

Get a cheap IR temperature gun to monitor component temps if you like for further information. 15 second bursts shouldnt hurt your exhaust coupler but watch it and let it cool while testing if necessary.