Nissan 25 fowling plugs

J

Jhawk090108

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I have 2001 25 hp Nissan 2 stroke. I got it about 6 weeks ago. I am having a problem with the boat oil fowling plugs. After long periods of idle or slow trolling the motor runs very rough but clears up after few hundred yards of full throttle running. If I replace the spark plugs it won't do it for a couple tanks of gas. I'm wandering if anyone has an idea of what this is and is it something a shade tree machanic can do? Last time I changed the plugs I leaned up the fuel a little but it did not help.
 
TwoRivers

TwoRivers

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Re: Nissan 25 fowling plugs

Jhawk090108 said:
I have 2001 25 hp Nissan 2 stroke. I got it about 6 weeks ago. I am having a problem with the boat oil fowling plugs. After long periods of idle or slow trolling the motor runs very rough but clears up after few hundred yards of full throttle running. If I replace the spark plugs it won't do it for a couple tanks of gas. I'm wandering if anyone has an idea of what this is and is it something a shade tree machanic can do? Last time I changed the plugs I leaned up the fuel a little but it did not help.
Click to expand...

Welcome Jhawk. Sounds like you're pretty close if your motor will idle for a few hours before stumbling.
Are you familiar with the motor's history? What type of 2 stroke oil did the PO use? What type are you using? Did you check the compression? It could be that the motor needs de-carbed, the carb needs cleaned, the carb air/fuel mix needs adjusted, the timing needs set, the spark is too weak, etc.

When I get a motor (used) I try to go over the the whole thing. Carb, timing, water pump, voltages etc. If you get a factory manual it's not real complicated and you'll learn a lot about your motor and have some fun along the way. These 2 strokes are pretty easy to figure out.
The best part is the confidence you'll have knowing that everything is done right.
Good luck, lot's of people here much smarter than I that will help.
 
Sea Rider

Sea Rider

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Re: Nissan 25 fowling plugs

Jhawk,

2 strokes horses behaves that way, nothing can be done, it's the nature of the beast. If running constantly at idle you could lower a bit the oil ratio bear in mind that the engine will work at idle all the time so to avoid wot runs. Mine doesn't like idling for too long and as I don't fish just go cruising usually go 1/2 to 3/4 throttle with some wot blasts for some minutes which maintains my plugs in near inmaculate state.

To understand fouling issues : At idle for too long time the plug tip won't work as it correct high temp, oil will tend to be deposited on tip and not fully burned and engine will start to miss, the only way to compensate this issue is having the tip working at a high temp only achievable at 1/2 to full open throttle.

Meanwhile, find a Italian Gondolier that acts as a aux engine while singing Italian sing along songs if your boating hobby is fishing or go straight for a 4 strokes engine.

Happy Boating
 
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Jhawk090108

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Re: Nissan 25 fowling plugs

Thanks to everyone for the quick response.
As for the motors history I don't know much about it. I am at least the third owner and the man that had it before me only had for a short time. The motor had just been serviced when I got it.(carb cleaned and plugs changed) I am using mercury quick silver oil and the recommended NGK plugs. Did a compression test before I bought it. Compression is great. Both cylinders showing about 140. I have already leaned up the fuel too. Went from 50:1 to 64:1.
 
J

Jhawk090108

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Re: Nissan 25 fowling plugs

TOHATSU GURU said:
What plugs are you using?
Click to expand...

Thanks to everyone for the quick response.*
As for the motors history I don't know much about it. I am at least the third owner and the man that had it before me only had for a short time. The motor had just been serviced when I got it.(carb cleaned and plugs changed) I am using mercury quick silver oil and the recommended NGK plugs. Did a compression test before I bought it. Compression is great. Both cylinders showing about 140. I have already leaned up the fuel too. Went from 50:1 to 64:1.
 
Sea Rider

Sea Rider

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Re: Nissan 25 fowling plugs

BR7H-10 or B7H-10 are correct, firstly ia a resistor type. 10 ending stands for factory 1.0 mm gapped. Both will perform excellent, but both will be fouled if doing excesive idling when fishing. 50:1 recommended ratio is for prolonged wot runs, you could lean oil ratio and probably match a proper ratio which fouls plugs less, if you find it bear in mind that won't be able to run engine at higher throttle setttings or will seize engine due to poor lubrication.

Theoretically 75:1 to 100:1 will be much better ratio to go for idling, not saying go for it though. It's not same running at 1000-1200 rpm at idle than 5000-6000 at wot with same 50:1 ratio.

Happy Boating
 
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TOHATSU GURU

TOHATSU GURU

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Re: Nissan 25 fowling plugs

Change the plug type to the BP7HS-10, run it for ten hours and then change them again. By then the carbon build up will have dissipated enough for the engine to run without fouling...That is dependent on you running the engine at 64:1.
 
Sea Rider

Sea Rider

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Re: Nissan 25 fowling plugs

Just curious,

On new 2 strokes 25/30 HP engines factory states on owners and service manual using NGK BR7HS-10 or BTHS-10, why would same rebadged models use a different plug type compared to ? have you tested under trial if the same ones with P stands less fouling, assuming will work better or there's a Tohatsu bulletin stating so ?

On 2 strokes motocross motocycles which uses prolonged tip plugs you'll notice that before flag is put down all racers are constanly throttling their engines to high rpm, for same reason, to avoid plug fouling at idle which these 2 strokes motorcycles don't like at all.

Jhawk, try as suggested and if possible report back your findings, have 2 full boxes of P type and haven't tried them...

Happy Boating
 
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pvanv

pvanv

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Re: Nissan 25 fowling plugs

P type is best. Tip runs warmer, while chamber is same temp. Better overall plug for 2-smoke motors.
 
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