NR 12 Tuning Problems....

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I have a JAE 12 with a new NR 12 5-port that is giving me trouble. The engine starts easy and responds well to needle changes, but I am having a hard time getting it to run reliable. It will run a 1/2 lap one time and then 13 laps another time. The engine is stock. The carb is modded per Glenn's instructions, the LS needle removed and spray bar cut 90 degrees just after the slot. I did the mods myself. The engine is still tight at the top with probably a 1/2 gallon through the engine. The piston will get stuck and I will need to turn past TDC with a wrench.

When running on the water the engine will stall when the boat hits a few bumps. It also stalls when I turn real tight. This will happen on a full tank. I have pressure checked the tank and lines and there are no leaks.

The engine was converted to air-cooled with removable fins. I am now down to no fins, just the head button, to make sure I get heat in the engine. The first few runs the engine was definitely coming back too cold.

Pipe is a MAC 2.5 cc non-muffled set at 7.5"

Prop is a Zippkit 1440, but I have tried a X438 too with the same results.

Thanks for any input.

 

[Ted buckley]

Craig, What temp. was it outside in N.Y.??? 2 weeks ago, I was helping my Son the day b4 the race and it was above 70degrees - warm. and was running all day with a Back-cut prop. The next day(Race day) it cavitated on the same prop. Condition turned in the 50's - 60's wind/rain/etc. These NR engines will run all-day-long in 80-90 degree days. When you get any type of precip. in the air - you have problems. J.M.O..

 

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I have tried for the past month with outside temps ranging from 50 degrees to 75 degrees.

 

[Mike Byer]

You need to get rid of the pinch, until the pinch is about gone they are hard to deal with.Take it apart and make the piston a little smaller. lower nitro content will make them easier to deal with too. shorten the pipe, the mid point of that pipe should be even with the back edge of the flywheel. Use a small prop and let it turn up.

 

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Try a Hotter Plug

What plugs are you using ?

Greg

The NR plug that came with the engine and an OD Blue Sport. What do you recomend? Thanks.

 

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You need to get rid of the pinch, until the pinch is about gone they are hard to deal with.Take it apart and make the piston a little smaller. lower nitro content will make them easier to deal with too. shorten the pipe, the mid point of that pipe should be even with the back edge of the flywheel. Use a small prop and let it turn up.

I'm running 50% now, how low would you go? Thanks.

 

[RodneyPierce]

Try a Hotter Plug

What plugs are you using ?

Greg

The NR plug that came with the engine and an OD Blue Sport. What do you recomend? Thanks.

O'Donnell red or O'Donnell 77 both are hot plugs that should work.

 

[Glenn Quarles]

Craig, I would just let the motor continue to break in naturally...lapping normally does more harm than good unless you have the right equipment and are very good at it. It sounds like it is too cold and a little too lean. This is common when they are running cold and you try to get it to sound right by squeezing down on the fuel. I would do everything I could to get heat in the motor...remove as much of the head as you can (or just put the water cooled head back on it without any water), shorten the pipe, stinger the pipe one size smaller (this will help build heat very quickly). With only a 1/2 gallon through it, it is still a ways from being broken in to where it will really run. Have patience Grasshopper!

 

[anthony_marquart]

put the water cooled head back on.. drill a 0.05 hole in the top and block the original outlet. run a tank or two through it w/out water, really rich.. I have found that this lets the motor get hot, but still with plenty of oil and fuel,.. it makes the break in much more manageable..

 

[Mike Byer]

30% Odonnel is the best change I ever made with the 12's. use an mc59 or the 1L K&B plug. Put the water jacket back on the head and restrict the water. You will need some water to it when it get fully broken in, despite what you might have heard. You also need to get the spray bar shorter, about .090-.100 off the carb wall not way out in the middle of the barrel

 

[mtruex]

The engine shutting off from hitting wakes or turning sharp has nothing to do with plugs or tight fit etc... Sounds like you have a tank problem to me.

 

[tnrcboatracer]

Or perhaps water ingestion. It only takes a few drops of water in the carb to shut down the plug.

 

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Thanks for all the help guys! I'll let you know how it goes.....