Engine too hot? Engine troubleshooting help

[jaxracer]

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.

 

[Danny King]

Change the bearings.

 

[John Beardslee]

Look in the exhaust port and see if the piston looks good. If you cooked it you probably would see evidence on the side of the piston.

 

[Kris Flynn]

did you try running it without water again, or restrict alot again to get it hot and see if it just liked being hot?

 

[Wasted wages]

What % fuel are you running?

 

[jaxracer]

Hey Kris, I have not yet but that was my next step was going to be remove water again and see what happens. It's odd that prior to it being hot, it had no issues. It's a Nelson outboard, not sure if that makes any difference.

And Frank it's 60%, same fuel jug and percentage that we have been running on that and all our motors.

I'll check on that John, what exactly would I be looking for? Like I mentioned, it starts up fine on the stand and sounds good until it hits the water.

Danny, thoughts on why you would say bearings? I just had them replaced the night before and had run them throughout the day without issues. Would heat wreck a new set?

Thanks for all the help guys!

 

[James Schmidt]

What Kris said!!! You will need some water’ but Iif you fixed your water pick up and are running your cooling full bore, it cools engine to much and you can’t burn the nitro fuel mixture you had before fixing it. Other than reversing your water fix, try leaning it if it gets better then go back to your richer setting and restrict your cooling.

I used to run full water too, but guys like John Beardslee turned me on to water restoration a few years back. Now it’s as important to me as getting a needle

Good luck

Jim

 

[James Schmidt]

And yes, if your bearings have some time on them change them

 

[Danny King]

Yes the hot run can wipe out the bearings. Also check the holes on EACH END OF THE ROD. to be sure they didn’t wear out.

 

[Kris Flynn]

Nelsons do like to run fairly warm...well mine does.

Guys above have good suggestions and know more than me about bearing and such.

I know it ran fine and all before, but are you running a large fuel line to the pipe and larger tubes into the fuel tank? I had a nelson starving for fuel after a few laps at full song and worked out it just wasn't getting enough fuel to the carby/pressure to the tank. large fuel line fixed that.

How do you know it was not running hot for a few runs prior to when you found the issue? ie did you see water coming from the hear on the previous runs prior to finding the broken fitting?

Kris

 

[Jeff Lutz]

What Kris said!!! You will need some water’ but Iif you fixed your water pick up and are running your cooling full bore, it cools engine to much and you can’t burn the nitro fuel mixture you had before fixing it. Other than reversing your water fix, try leaning it if it gets better then go back to your richer setting and restrict your cooling.

I used to run full water too, but guys like John Beardslee turned me on to water restoration a few years back. Now it’s as important to me as getting a needle

Good luck

Jim

Tell us more about your above mentioned “ water restoration “ . Lol

 

[James Schmidt]

Ok lol!! It was a typo, I ment restriction.
Dam dictation

 

[James Schmidt]

Not even a typo, just darn dictation

 

[Wasted wages]

can you feel any pinch at the top when you rotate the motor by hand ?
I bet it expanded the sleeve to the point the fit is gone... just my past experience once they get hot..

do you have lots of time on the piston/liner ?

 

[ALLAN YUEN]

Maybe fuel filter inside dirt? Or bad tank cause brass tube cracked ?Or crankshaft was cracked line ?

 

[jaxracer]

So bearings are brand new as of the day before the run, ran fine on the new bearings until the motor got hot. I already restrict the water to a pinhole stream out of the cap because yes more heat, more fuel, more power.
Yes, motor still has good pinch and rolls over and feel super smooth.
Needle was cleaned and put on a flow meter and is where we run it normally.
Kris we noticed no water to the engine on the run that it had no water I’m pretty sure. My brother picked it up out of the water and was like “Hey isn’t this supposed to be attached?” and was just the fuel tubing attached to the motor with the water pickup zip tied to it dangling off the side
We’re using large fuel tubing on both the carb and pressure lines. My only other thought is that maybe something happened with the tank that I’m missing? But I don’t see any air bubbles to the carb with it started on the stand so almost want to throw that option out too.

 

[Steve White]

What Kris said!!! You will need some water’ but Iif you fixed your water pick up and are running your cooling full bore, it cools engine to much and you can’t burn the nitro fuel mixture you had before fixing it. Other than reversing your water fix, try leaning it if it gets better then go back to your richer setting and restrict your cooling.

I used to run full water too, but guys like John Beardslee turned me on to water restoration a few years back. Now it’s as important to me as getting a needle

Good luck

Jim

Overcooling causes all kinds of strange things. Back when I discovered that, up until then full water cooling. Had an outrigger that would just die for no reason when running. Finally figured out the engine was way under optimum temperature.

I use small jewelers screwdrivers as the gauge, different sizes and pinch the pickup together from side to side. Not sure how I'll work it out with the rudder pickups - but, temperature management is a must.

 

[Ken Retallick]

Mitch, Check all engine bolts for tightness. A hot engine expands, and when cools down bolts will not be as tight as they should.
Especially head bolts.

 

[Wasted wages]

Mitch, Check all engine bolts for tightness. A hot engine expands, and when cools down bolts will not be as tight as they should.
Especially head bolts.

Good call... I would also check the fit of the crank to the housing bore... carb o-ring etc.

 

[jaxracer]

Thanks for the input fellas. Plan of attack, check the head bolts and make sure everything is tight, pull the water back completely off, and if neither of those work, I’m going to swap out the tank. (Really avoiding this bearing thing as new bearings were justt put in there). It won’t be for a few weeks before I go run again but I’ll keep you guys posted what I find.
Thanks!