Engine too hot? Engine troubleshooting help

[Richard Dahlheimer]

Hello Mitch, if your problem continues check motor compression as soon as motor dies. Just turn motor over by turning prop, and see if motor has compression when still hot. This happened to us twice before. Turned out piston and liner were shot. Good luck. Richard

 

[Bill Eilers]

Hey guys,

Posting this problem to see if anyone might have suggestions on how to solve it. I ran my .45 size tunnel in open water and finally got the boat dialed in on the needle and running well. On and off the throttle without issue. I brought the boat in and noticed that the water pickup had broken off of the lower unit so the engine wasn't receiving any water. Not a big deal I thought as the boat ran good and made it back to the dock so I just put a water pickup back on it. Next day went to go run the boat and it would die somewhere in the first turn, or a couple times I got it to light off and make some good laps but as soon as I got off of the throttle and went to get back in it, it would die again. Boat fires up on the stand easy, no air bubbles to the carb and sounds great getting into the throttle on the stand.

I have: change ALL fuel lines, pulled the pipe off and pressure tested for leaks, double checked the carb, adjusted the needle both really rich and really lean, recently replaced bearings, dumped the fuel tank thinking it might have water in it and replaced with fresh fuel and still nothing.

I have not adjust pipe length, setup or prop because it was literally running perfect the day prior and days prior exactly how the boat sits.

The only thing I can think of is that one hot run where it ran great and came back to the dock. Could that have "cooked" the motor or could it have expanded the motor just enough that now I have to run it without water? I'm beyond frustrated trying to figure this thing out at this point.

Any other thoughts here for something else to check would be much appreciated.

 

[Bill Eilers]

Everything hase been mentioned except. To much moisture in your fuel. If you haven't already always start with what is called clean methanol nitro mix. (Dry fule)

 

[Brian Sorgente]

Heres a few things I’d check.

Check compression for “bump”. With the glow plug in, and a couple drops of oil or fuel in the cylinder (it just shouldn’t be dry) roll the motor over TDC with the glow plug in and you will feel the compression push the piston back down down or “bump”. Now without letting the piston open the exhaust port rotate it the opposite way for another bump. Keep doing this until all of the pressure in the cylinder is gone. If you only get a couple before its gone, your fit is gone. If you get 10+ then you’re good.

Pull the head off. If you run a tight head clearance and blow plugs now and then, you could have plug elements embedded in the squish band or piston. These can create hot spots while running and make the engine go lean and die.

After that, I’d pull the motor apart. If you actually overheated the engine you could have cooked an o-ring. Replace them all, even the little ones around the carb neck screw if it has them.

While it’s apart, you might as well check the bearings and the rest of the parts to make sure everything looks good.

Make sure your pipe coupler isn’t loose or has a hole.

Check your fuel filter. Swapping the tank like you said is a good idea but it’s weird that it went from running great to bad after the fuel line issue…

Does it have a remote needle? Could the o-rings be shot? I’ve seen those k-type needles leak a lot when the plastic threads wear out. Sometimes the nipples themselves get loose and leak around where they attach. Woth a couple fuel lines attached, blow in one side while blocking the other with the needle under water in a sink. If you see bubbles coming out, thats a leak.

Let is know how you make out.

Brian

 

[Bradley Maglinger]

Have you changed bearings?

 

[jaxracer]

Hey guys, a little bit of an old thread but I swapped to a backup engine and it runs flawlessly. Still not real sure what was wrong with engine #1 but it’s in a box right now. Cylinder looks good, bearings feel good (they were just replaced maybe 1/4 gallon prior), all bolts were tight and everything was sealed. Who knows, I may revisit later but in the meantime the backup engine is running well.

 

[Daniel's Racing]

Cap the intake and the exhaust and introduce air to the plug hole and submerge the whole thing look for leaks.

 

[Bill Eilers]

Cap the intake and the exhaust and introduce air to the plug hole and submerge the whole thing look for leaks.

Brian is on track. It's happened to most of us. For me it's always been the motor is sucking air from somewhere it's not supposed to. But take the possibility of wet fuel out of the mix

 

[SayMikey]

How bad were the orginal bearings? If the crank rubs the crankcase it could ruin the crankcase"loose the seal"