Hot exhaust pipe means what??

[shockerfd]

I know, simple question right? Hot exhaust might usually point to a failing cooling system. The reason I ask is that after 3 blown engines, I'm beginning to wonder. Yes, carbs have been rebuilt and gone back over by Seadoo. Boat has been switched to premix. When things were running well and after running, the exhaust was cool enough to touch. Normal. Boat runs normal temp and rich looking plugs. Then another time out boat runs lean and exhaust is sizzling. Everytime the engines seized, the exhaust pipe was too hot to touch. Now I have seen water flowing out the tell-tale on land and in water, so I'm assuming all is well there. Now, can a lean condition be caused by cooling system not working or do I still have a fuel problem that's blowing my engines? Will a lean condition cause the exhaust to run hot? thanks

 

[seadoodude1]

Cooling has no significant effect on running lean. It's a fuel problem or air leak. Yes running lean will overheat exhaust and can also melt the aluminum pistons, this blowing your engines. Have you checked or rebuilt carbs lately? Fuel restriction somewhere or weak fuel pump or tank vent not allowing fuel to flow.

What boat and engine we talking about here? Three blown engines, something is wrong.

 

[kcr357]

Partially blocked exhaust?

 

[CypherAZ]

Partially blocked exhaust?

Thats what I wasw thinking something jammed in the exhaust piping.

 

[shockerfd]

This is the 787 enigne on the 97 challenger. Carbs have been rebuilt and gone over by Seadoo with pop-off pressures checked and set to specs. That carb went on the engine and I made it to the 50% throttle break in point before "boom". 150psi on Pto and now 120 on Mag. As mentioned in earlier post, I ws constantly pulling plugs and checking and they were looking fine. Last trip out it seized just from cruising through the wakezone. Please indulge me with a little more info on the possibility of the exhaust being blocked. Is this a simple check? But I guess it doesn't seem logical that it would cause a cylinder to go lean.

 

[kcr357]

I am not up on the exhaust mechanism of the boats, that was just a guess. Maybe someone with more exp will chime in. You could also start the boat, and spray starting fluid around(not in) the carbs and intake manifold. If the engine surges or anything, that indicates a leak. What did the plugs look like after running hot?

 

[cobra5007]

Mine was doing the same thing and it ended up being the water regulator on the exhaust. The spring in mine broke and that made the water pressure and seal leak. Just a little info that may help.

 

[shockerfd]

Mine was doing the same thing and it ended up being the water regulator on the exhaust. The spring in mine broke and that made the water pressure and seal leak. Just a little info that may help.

Did this cause any engine damage or just run hot? Did it cause your engine to overheat? I'm apparently not getting an overheating issue, hence no warning beeps or the color change on that little "sticker" SBT puts on engines. I'm getting water flow that I can see so I'm assuming that it's working correctly. I talked to SBT today and without seeing the engine yet they still think there is a fuel issue somewhere. Soooo, I guess I'm going to suck out old fuel and go through fuel lines and make sure there are no blockages.

 

[seadoosnipe]

Air leak?

I know, simple question right? Hot exhaust might usually point to a failing cooling system. The reason I ask is that after 3 blown engines, I'm beginning to wonder. Yes, carbs have been rebuilt and gone back over by Seadoo. Boat has been switched to premix. When things were running well and after running, the exhaust was cool enough to touch. Normal. Boat runs normal temp and rich looking plugs. Then another time out boat runs lean and exhaust is sizzling. Everytime the engines seized, the exhaust pipe was too hot to touch. Now I have seen water flowing out the tell-tale on land and in water, so I'm assuming all is well there. Now, can a lean condition be caused by cooling system not working or do I still have a fuel problem that's blowing my engines? Will a lean condition cause the exhaust to run hot? thanks

If you've gone through that many motors, chances are, it's a sub component causing the problem and not something to do with the engine.

The water coming in from the pump goes straight across the top of the head cover and crosses over to the tuned exhaust, where it travels around in circles being preheated before going into the water jacket of the enigne. Then, the water travels up through the the water jacket and out the top head cover nipple on the right. If you see water from the tell tale, then your engine is flooded with water. That's not the problem.

You said the carbs have been gone through so I'll assume your low speed screws are set properly.

So, that leaves me to believe you have one problem. What causes a "lean" condition? To much air. If all the above is adjusted out right, then something between the carb and engine is out of spec or a gasket is not doing it's job. You would probably best be served to do a pressure test on these components in question. And most important, check your clearance on your rotary cover.

The clearance between the rotary valve and the cover must be .30 +/- .05". If the clearance is below 0.25", this WILL create an overheating condition, over .035 creates a hard starting situation. You'll need 45* feeler gages to check this and your carbs will need to be removed so you can see and turn the rotary by hand. Take out your plugs so the engine is easy to turn over.

With your issues explained above, I feel pretty certain (99.9%) that your problem is rotary clearance; which is one thing everyone replacing an engine takes for granted..................Good luck!:cheers:

 

[shockerfd]

Thanks for chiming in snipe. I've been out messing with the boat and came in to check the forum. I took the old engine back out of the box and checked the clearance like you said. If I read your post correctly, below .25 will cause overheating, thus making it run lean?? Or is that overheating from friction? .30 is a bigger gap allowing more air and wouldn't that be making it leaner? Using my old school spark plug feeler guages, I was able to squeeze .25 in there. It was a tight fit but it went. The o ring is new. I hoping I'm making sense of this. If not, please lead me down the right path. lol This has been one frustrating nightmare. The plugs looked fine, by the way. Color was tan. The piston is scarred like there was debris in the cylinder.