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2003 50 hp Nissan outboard.

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scavengerpioe

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I have a 50 hp Nissan that is driving me crazy. I work on motors but don't claim to be an outboard mechanic. I know enough to be dangerous. The motor starts right up and I can idol around the lake all day with no problem but from about 1/2 throttle on it starts to fall apart. This is a list of the things I have done. change plugs, 3 new coils, new head gasket, compression check (125,120,125), fuel pump, new cd box, rebuilt all 3 carbs (all ports clean) can't get over 4000rpm new lower pitch prop, the pontoon has a built in gas tank so I stuck the gas line in a fresh tank of gas. I sprayed gas into the carbs while running on the lake at high rpm but it acted like it was flooding out, did not pick up speed. I pulled the plug wires off one at a time while we were moving and it did effect the the rpm's. I pulled the flywheel to make sure there were no loose connections. added clear gas lines to see flow. A lot of this I did because I don't have the tools to do it correctly and didn't want to tie it up in a shop all summer as most shops are packed this time of year. What should I do next?
 
scavengerpioe said:
I have a 50 hp Nissan that is driving me crazy. I work on motors but don't claim to be an outboard mechanic. I know enough to be dangerous. The motor starts right up and I can idol around the lake all day with no problem but from about 1/2 throttle on it starts to fall apart. This is a list of the things I have done. change plugs, 3 new coils, new head gasket, compression check (125,120,125), fuel pump, new cd box, rebuilt all 3 carbs (all ports clean) can't get over 4000rpm new lower pitch prop, the pontoon has a built in gas tank so I stuck the gas line in a fresh tank of gas. I sprayed gas into the carbs while running on the lake at high rpm but it acted like it was flooding out, did not pick up speed. I pulled the plug wires off one at a time while we were moving and it did effect the the rpm's. I pulled the flywheel to make sure there were no loose connections. added clear gas lines to see flow. A lot of this I did because I don't have the tools to do it correctly and didn't want to tie it up in a shop all summer as most shops are packed this time of year. What should I do next?
Click to expand...
 
Need your actual model; year is irrelevant. I usually start mixture screw about 2 turns out and adjust from there per the Factory service manual. What is the prop pitch and the weight of the pontoon boat. Pontoons usually need a pretty low pitch, as they push a lot of water.
 
pvanv said:
Need your actual model; year is irrelevant. I usually start mixture screw about 2 turns out and adjust from there per the Factory service manual. What is the prop pitch and the weight of the pontoon boat. Pontoons usually need a pretty low pitch, as they push a lot of water.
Click to expand...
It is a NS50D2 I installed a new 4 blade 10.8 dia. x 9.9 pitch. It was about the lowest pitch I cold find. Thanks for the info on the adjusting screws!
 
Is this a new to you boat or have you actually seen it do more than 4k rpm?
What size pontoon? Is it possible they might have water in them?
Is the throttle linkage confirmed to be opening the carbs fully?
Can you confirm spark advance is operating properly?
Prop size? As mentioned before, lower pitch on pontoons.
 
Goneagain4 said:
Is this a new to you boat or have you actually seen it do more than 4k rpm?
What size pontoon? Is it possible they might have water in them?
Is the throttle linkage confirmed to be opening the carbs fully?
Can you confirm spark advance is operating properly?
Prop size? As mentioned before, lower pitch on pontoons.
Click to expand...
I have had it for 7 years and up until two years ago it ran fine. I had the same problem last year but just cursed around the lake at low speeds with no problem. I was getting more than 4K from it originally. The linkage is at full open. The prop is about the lowest I could find 9.9. I am questioning the advance. The linkage is moving as it should but I was wondering that where the wiring harness comes out from under the flywheel the wires are flexing at the same place all the time. Could the wires break at that point under the sheath?
 
scavengerpioe said:
I have had it for 7 years and up until two years ago it ran fine. I had the same problem last year but just cursed around the lake at low speeds with no problem. I was getting more than 4K from it originally. The linkage is at full open. The prop is about the lowest I could find 9.9. I am questioning the advance. The linkage is moving as it should but I was wondering that where the wiring harness comes out from under the flywheel the wires are flexing at the same place all the time. Could the wires break at that point under the sheath?
Click to expand...
I did find that when I put the new cid box in that one of the wires going to the #2 coil was wired tied tight and was shorting to the block.The new cid box didn't change anything so I fixed the bear wire and put the original one back on. Could that short have caused other issues under the flywheel?
 
348B641081​
PROP 40C,D-50D (11.4 DIA. X 7.1 PITCH) 4 BLADE​
​
$183.71​
/*FOR VERY HEAVY APPLICATION EX. WORK BOAT OR LARGE PONTOON BOAT*/

What method did you use to clean the carbs?
 
Does this boat plane? Is the top speed the same as it was when you got it or do you notice deterioration in performance?
Does it sit in the water or trailer?
Also, verify the tach is reading true RPM. Neighbor last week had pontoon reading 3K at idle. Yeah, I knew it was idling around 1K from the sound. Wiggled the tach connection and its reading properly now. I've had tach issues before. On one tach I had there was a switch for number of cylinders. Any possibility tach could be wrong?
I've never seen advance wires from under flywheel break but I guess it is possible. I've seen several cases where the conductor inside the insulation is broken but you can't tell by looking at it. Had a front nav light quit working and the conductor was broken in the middle of the run. No stress on it, just broke.
 
pvanv said:
348B641081​
PROP 40C,D-50D (11.4 DIA. X 7.1 PITCH) 4 BLADE​
​
$183.71​
/*FOR VERY HEAVY APPLICATION EX. WORK BOAT OR LARGE PONTOON BOAT*/

What method did you use to clean the carbs?
Click to expand...
Sonic cleaner and ran air and hot water to make sure all the ports were open removed the brass tubes with the holes in and I am confident everything is clean, put in 3 new kits with new floats.
pvanv said:
348B641081​
PROP 40C,D-50D (11.4 DIA. X 7.1 PITCH) 4 BLADE​
​
$183.71​
/*FOR VERY HEAVY APPLICATION EX. WORK BOAT OR LARGE PONTOON BOAT*/

What method did you use to clean the carbs?
Click to expand...
 
Goneagain4 said:
Does this boat plane? Is the top speed the same as it was when you got it or do you notice deterioration in performance?
Does it sit in the water or trailer?
Also, verify the tach is reading true RPM. Neighbor last week had pontoon reading 3K at idle. Yeah, I knew it was idling around 1K from the sound. Wiggled the tach connection and its reading properly now. I've had tach issues before. On one tach I had there was a switch for number of cylinders. Any possibility tach could be wrong?
I've never seen advance wires from under flywheel break but I guess it is possible. I've seen several cases where the conductor inside the insulation is broken but you can't tell by looking at it. Had a front nav light quit working and the conductor was broken in the middle of the run. No stress on it, just broke.
Click to expand...
It is in the water on a lift . I noticed that when it is out of the water running with muffs I do get more RPM's so I think the tack is ok. With the water resistance on the props it just seems like something is holding it back from opening up. I don't think it is gas. It seems more like electronic.
 
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