QUESTION FOR THE EXPERIENCED WRENCHES

[Stu_Weisenheimer]

My 5 hp Nissan (2 stroke) is going to be a great motor once I get the bugs out. It's a 1998 model which was seldom used by the Captain I bought it from.<br /><br />It's starts OK and runs fine at top end. The problem seems to be from just above idle speed until it reaches it's top end speed. It starts out as rough spot and as it throttles up will hesitate (sometimes) until it reaches full throttle where it runs just fine until I throttle it down and then it gets rough running again.<br /><br />Here's what I tried.<br />1) Change and regap the spark plug<br />2) Remove and clean the fuel tank <br />3) Remove and clean carb (three times)<br />4) Had a problem with clutch which was fixed<br /><br />All educated guesses are welcomed!

 

[JB]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Hi, Stu.<br /><br />My first thought is the intermediate speed jets in the carb. They are often overlooked. These are usually an orifice in the carb throat between the high and low speed jet orifices. Because you have "done" the carb, this seems unlikely.<br /><br />I am not familiar with your engine, but on many small outboards a spring advances the timing as the throttle is opened or the throttle plate as the stator is advanced. You may have a sticking part in that linkage.<br /><br />Good luck.

 

[Yepblaze]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

The "intermediate speed jets" might also be reffered to as pilot jets, and may just need a probing to loosen hardened deposits. Also it may have an emusion tube above the main jet that could be suffering the same hardened deposits.<br /><br />Just my 2 cents

 

[Stu_Weisenheimer]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Thanks for the tips guys! I am really thinking about that "pilot screw" right now. Clymer doesn't even list one on the 5 hp, but it sure has one. I have been guessing at the setting and it seems to work best around 1/2 to 5/8 turn out. But, if the jet is partially obstructed that might change if I clear the obstruction. Even though I took the carb down 3 times maybe I missed something there. I will get a broomstraw and work it over a bit and blow some more compressed air thru.<br /><br />I will have to study up a bit more on the timing advance issue before I jump into that if the 4th carb cleaning doesn't solve the problem.<br /><br />The motor wants to run so I feel it's got to be something minor.

 

[flydangler]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Hey Stu,<br /><br />Anything new to report? Inquiring minds want to know.

 

[jim dozier]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

I think the guys above are on the right track with the jets. You wouldn't be the first person to do an incomplete carb cleaning/rebuild. Go back in and completely disassemble the carb and clean the jets with carb cleaner and compressed air. You can probe the jets with monofilament fishing line. Remember cleaning the carb is not a beauty pageant, its not the outside that counts, its the inside of the jets and orifices that counts. Then put it back together and make sure the synchronization of the throttle with the ignition timing is correct.

 

[Stu_Weisenheimer]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

OK here's an update. I emailed Nissan Marine and they gave me the setting for the pilot screw. The guy said it was 2 1/2 turnouts from the lightly seated position. <br /><br />Tried it and tested the motor at the local lake this afternoon. Definately some improvement but there is still a roughness that wants to kick in at low and medium speed. <br /><br />The funny thing is when I run the motor hard for a time and slow down it seems to run pretty good for a minute or two before resorting to the rough operation. It will alternate from smooth to rough. There is definately a difference in the sound and vibration when it is running rough. Some slight stalling when throttling up from the rough running mode. <br /><br />I just feel it can't be much wrong.

 

[Salmon Tub]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Stu, the 2.5 out is a starting point, sounds like you are still a little lean, meaning that at high speeds, it is getting the right mixture since it runs off the jets, then, as it idles, the actual mixture inside the crankcase dilutes back to a little lean. Next time, once it gets rough again, try choking the engine just a hair, if lean, the engine should smooth out a little.

 

[Stu_Weisenheimer]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

OK, I noticed when the motor is running rough it is smoking quite a bit. When it kicks back into smooth mode the smoking stops. So, when the roughness started I tried choking it and it dies. So, I think I have a rich or flooding condition. I tried all kinds of settings with the pilot screw to no avail.<br /><br />If I run the motor at high speed for quite a while when I throttle down it keeps it smooth running mode for a while. Then if I bring it down to idle and up again the roughness, excessive smoking starts all over again. Then as I throttle up to plane the boat the motor will hesitate a bit then as the rpm's come up it will clear and run just fine at near top speed.<br /><br />Took the jets out and cleaned the carb well yesterday and put it back together. Same condition as before when I ran it. Starts OK, rough idle, rough low speed and intermediate speed, some hesitation until it gets near top speed then runs OK.<br /><br />I am tempted to buy a new carburetor, but, just my luck it would turn out to be an ignition problem, lol.

 

[45_red]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

With the engine not running, does the bulb firm up? If it does,can you-have you tried setting the throttle plate to open a bit more? The only danger with that is possibly making it too lean(too much air) at full throttle.

 

[jim dozier]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Not clear from your description but here's a thought. If the carburetion is OK, sometimes a leaking fuel pump diaphragm will inject fuel directly into the intake port (where the fuel pump gets its vacuum pulse) causing the cylinder to which the fuel pump is attached to run rich. Its a simple and cheap fix to replace the fuel pump diaphragm on most motors. Since you've been through the carbs, you may want to check the fuel pump before you pull any more hair out. Good luck

 

[Stu_Weisenheimer]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

OK guys,<br />The 5 hp has an internal fuel tank so there isn't any primer bulb. And, the throttle cable runs directly to the carb with no linkage elseware.<br /><br />I took the fuel pump apart and the diaphram/s look OK. No splits or cracks. But that sounded like a good idea anyways, thanks.

 

[45_red]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Yup, my bad

 

[Christopher A. Boody]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

OK, I noticed when the motor is running rough it is smoking quite a bit. When it kicks back into smooth mode the smoking stops. So, when the roughness started I tried choking it and it dies. So, I think I have a rich or flooding condition. I tried all kinds of settings with the pilot screw to no avail.<br /><br />If I run the motor at high speed for quite a while when I throttle down it keeps it smooth running mode for a while. Then if I bring it down to idle and up again the roughness, excessive smoking starts all over again. Then as I throttle up to plane the boat the motor will hesitate a bit then as the rpm's come up it will clear and run just fine at near top speed.<br /><br />Took the jets out and cleaned the carb well yesterday and put it back together. Same condition as before when I ran it. Starts OK, rough idle, rough low speed and intermediate speed, some hesitation until it gets near top speed then runs OK.<br /><br />I am tempted to buy a new carburetor, but, just my luck it would turn out to be an ignition problem, lol.

I hate to hy-jack this guys thread, but it seems like it has been Idle for some time... I have 1998 15 horsepower nissan, and this is EXACTLY what I am experiencing.. she runs so very smooth and strong at over half throttle that I cannot imagine there is anything internally wrong, but at slower speeds/ idling and trolling speeds up the about 1/3 throttle, it seems like it is running very rich and possibly only on one cylinder. I have to get this fixed, because the lakes I run on, are 'slow speed no wake' areas... I would love to know what this guy found to be wrong with his 5hp before I go any farther,... any body have any ideas?

 

[Sea Rider]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

If it's the 5 HP model that comes with a spare 3 gal red tank, check if both gas filters are obstructed, a small one is located inside gas selector bowl the bigger one towards left, both are small and obstructs easily. If your gas tank hose is one that has double layer, probably the inner one has rotten in small parts and obstructing primer bulb, had this issue many years ago and drove me cracy for some time until discovering the fault. This issue is common in Mariner gray plastic hose, don't know if this issue has been corrected replacing for black Tohatsu hose.

Happy Boating

 

[TOHATSU GURU]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

"it seems like it is running very rich and possibly only on one cylinder"

You have to run through the engine troubleshoot list, as found in the service manual, before you start looking for fixes. IE Screwing with the carburetor would be pointless if you are loosing spark or replacing electrical items would be pointless if you have block issue.

 

[Christopher A. Boody]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

T.G.

I Got the service manual as suggested,

I took the carburetor apart, and found no obstructions at all on the idle side, however it does look like at some time, someone stuck something into the carburetor from the back side, and tried to push out the main jet... in doing so, it looks like a bit of the nozzle was crimped down a little bit,... not noticable from the choke side but visible from the intake side... In your opinion, will this cause the motor to run too rich to idle?

My compression is 105 on both cylinders, and I do have spark when the throttle is at idle position.

someone has definitely been into this carburetor before, but the previous owner claims he has never had any work done to it.... I am suspicious that this has been a long term problem with this motor.... the previous owner lived on the water and ran the motor just about every day...

 

[TOHATSU GURU]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

I don't see how that would make it run too rich, but it could cause the nozzle to "clump" fuel which would prevent it from being atomized correctly. You should change it out before you do anything else as that could cause a pooling of unburned fuel which might mimic a "rich" incorrect air mixture.

 

[pvanv]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

OK, looks like this thread is trying to address two completely different motors... a 5-hp and a 15-hp.

In reviewing the posts...

1- I don't see where the carb for Stu's 5 was ever disassembled and soaked in carb dip. Probably prudent. Spray-can cleaners are not adequate for dissolving hard-varnish carb deposits. A de-carbon treatment might not hurt either.

2- Christopher's 15 definitely should have the physical damage to the carb repaired, possibly with a different carb, since, as Elvin pointed out, atomization will definitely be inconsistent.

Perhaps this thread should be split into two different problems...

 

[Christopher A. Boody]

Re: QUESTION FOR THE EXPERIENCED WRENCHES

Stu has not been back with his 5 horse since 2004- I jumped onto this thread because I noticed the sympoms were so very similiar, but there was never a resolution posted.

I am going to purchase a new carb and investigate the possibility of new reeds... I know this motor was run almost daily for several years. The shift interlock has also been removed, and I guess I have to consider that might have fouled up the timing mechanism somehow.?