Outboard help

[Matthew Marsha]

All:
For the last couple months I have been working to get my Leecraft with 3.5cc NR back in racing form. I am still having issues with the motor dying after shortly after launch and there must be something I am over looking. Occasionally, will run several laps never faster than 25-30 full throttle. Running 40% nitro. To date I have:

Replaced and pressure tested fuel lines, filter and tank (no hopper, never had issue previously)
Replaced all bearings
Cleaned and checked lines, needle, tank numerous times

One thing I am questioning is the carb, seems to have play and drawing air? I know I am forgetting details to help diagnose and apologize. Any advise from those way more knowledgeable than I will be much appreciated.

Just to add, got a Lynx (Thanks Ron and Carl) for boat two and have it painted and radio box finished. Sure to have some future questions as well.

 

[Grimracer]

Matthew,

Good going.. lets review a few basics

You have good bearings.. that #1
You have a good piston fit..? we dont know that.. remember.. saying its "new" or not used much really does not always tell the condition. (I would over rock TDC) it should compress the same air 15 times OR MORE.. if its less... then its how much less.. I have seen motors run at 6 BUT.. they are hard to launch.

I would VERY much doubt the carb is your issue.

Check the piston fit.. and lets go from there...


Grim

 

[Mike Crawford]

Rotate the carb barrel the other direction and see if that works MC

 

[Carl Van Houten]

Are you water cooling your engine? I have had that problem and found that my water pickup was dumping too much water on the head and the engine would not make it to the center of the pond and die. I restricted the water and boom...ran great from then on. Over cooling the engine is not good for it.

 

[john v]

make sure you are not lean on the fuel , start out really rich and start to lean it down until it starts to clean out. make sure the glow plug is good also. i have had a good glow on the plug and found the center electrode was loose and loosing compression

 

[Carl Van Houten]

Use fresh fuel when you are trouble shooting too. Drop down to a light pitch prop like a little M440 (at least until you get it making laps) and replace tanks and all tubing. Check your flex shaft for kinks too.

 

[Mark Poole ModVP]

One more thing to check. Not sure about NR but I have seen it on KB's. Use carb cleaner (spray) to degrease and clean the powerhead. Use a magnifying glass to inspect for hairline cracks anywhere...around bolts, the carb hole, intake, upper bearing and around the case. This will cause frustrating lean out issues.

 

[Carl Van Houten]

Mark brings up a good point. If you are running the turbo head we had one to crack and ran us CRAZY until we spotted it. The area around the plug hole is thin and can split easily and it is very hard to spot.
-Carl

 

[Kevin Burns]

Dito on everything everyone already stated. Now let's look at a few other things like;
Is the crank cracked or bent? A cracked/bent crank will kill an engine every time much like your saying.

The crack can be located at the corner of the cranks intake opening, just a hairline crack will do what your saying simply from to much friction acting like a brake in layman's terms. .
How about the flex shaft/or prop shaft, are they binding? maybe a bad thrust washer spacing (Is the drive dog being forced into the lower unit?)
Even a cracked fuel line inside the tank will cause a engine to die.

At wide open a leaky carb will have no ill effects, a leaking carb will have ill effects at the lower openings of the barrel or low rpm range.

Less looked at things is, prop, prop depth, and angle of attack. Are you placing to much stress on the engine.
I'm not saying you are.
Me, I always run dead level to the water line and straight back. I balance my boats a different way.
I run my tunnels wet so when the water gets choppy I'm still stable, but that's just me.