2004 Nissan 9.8 has a bad idle and throttle, even after a new carburetor

[biederboat]

This outboard was running pretty good since I bought it used about two years ago but just now it's not running well. It starts okay (pretty quick and for a few seconds) but doesn't go down to a steady smooth idle (kind of on & off) and sometimes goes up to high throttle but mostly just stays at a rough/low RPM when trying to get it going at medium/high speed. This is even after a minute or so of keeping the choke on (it seems to stall quickly if you try to let it down after a short time). I cleaned out the carb, was still the same bad run, so I just bought a new carb but it still seems more the same of bad running. I can't say I'm a perfect mechanic but here's what I am pretty sure on:
1. It's very up/down on how it idles, sometimes sounds good, but then goes down and usually stalls. I more have to keep the choke on to keep it running.
2. Trying to get to a higher speed is also on/off. It basically stays at a rough and low RPM when you try.
3. The "low oil pressure" red light comes on but I'm pretty sure when it only gets down to a very low RPM, right before stalling. Oil level is good.
4. I checked the fuel filter and pump (ran it for a bit unconnected to the throttle) and it seemed to dispense fuel at a decent level.
5. The spark plugs are both pretty black (the same on both) but not thickly coated with debris, not sure what would cause this. I'm assuming that's an effect of whatever is not making it run well and that it's not the root cause of the problem.
6. I'm pretty sure my fuel tank and hose are good also, can't see anything bad with them.

Any ideas on what could be causing this? I am thinking of taking it to a mechanic but hoping there's something quick and easy.
Thanks!
Biederboat

 

[airshot]

Is the new carb a factory replacement or a chinese copy from Amazon ? Has the carb been setup and adjusted to the engine? Did you clean out the fuel system, replaced all filters, have an inline filter, and using fresh fuel ?? How good is the fuel line from tank, they only last a few years ??

 

[biederboat]

That's all good questions. I'm pretty sure it's a Nissan carb, but not 100% positive, got it off eBay (picture attached). I did mention that I tested the fuel feed and it looked pretty strong (was coming out just before the carb at higher level than needed, stopped off by the float, correct? I was wondering about the fuel quality. It's been in about a year (small part maybe about 2 years). I did look into the fuel tank and it looked very fresh. I was thinking of getting a new fuel tube and replacing existing fuel with a new filter. I just haven't seen any issues before the carb but I suppose some may be hard to "see" (might look okay but maybe isn't). The fuel line is pretty long, goes under the floor so it's about 12' long. It's probably almost 10 years old. Is there something in particular that goes "bad" on these? I sure don't smell anything that is from it leaking but I suppose something still could not be so good.

 

[racerone]

Most " carburetor issues " turn out to be something else.----What trouble shooting has been done if any?

 

[biederboat]

I'll be doing some more this morning (checking compression as part of it) and getting a new "spare" fuel supply (tank, hose, new filter) which will be good to have as I only have one 3 gallon tank. Will update what happens.

 

[airshot]

That's all good questions. I'm pretty sure it's a Nissan carb, but not 100% positive, got it off eBay (picture attached). I did mention that I tested the fuel feed and it looked pretty strong (was coming out just before the carb at higher level than needed, stopped off by the float, correct? I was wondering about the fuel quality. It's been in about a year (small part maybe about 2 years). I did look into the fuel tank and it looked very fresh. I was thinking of getting a new fuel tube and replacing existing fuel with a new filter. I just haven't seen any issues before the carb but I suppose some may be hard to "see" (might look okay but maybe isn't). The fuel line is pretty long, goes under the floor so it's about 12' long. It's probably almost 10 years old. Is there something in particular that goes "bad" on these? I sure don't smell anything that is from it leaking but I suppose something still could not be so good.

Old fuel looses its power, especially after a year. Fuel lines come apart/ disolve from the inside and contaminate the fuel passing thru it.

 

[biederboat]

Old fuel looses its power, especially after a year. Fuel lines come apart/ disolve from the inside and contaminate the fuel passing thru it.

So if this happens does it usually plug up in the carb, especially the jets?

 

[biederboat]

Also, so I did do my compression test, 90 psi on both, and it looks like that is good (thought it should be higher but looks okay on what I found online). So then I removed the fuel line into the carb, pumped it manually, went very steady and smooth but came out a bit "gold" and I have much newer fuel (needed to run generators due to power outage) and it's very "clear" like water. Is that likely an issue that the fuel is bad?

Thanks again!
Biederboat

 

[airshot]

So if this happens does it usually plug up in the carb, especially the jets?

Yep !!

 

[airshot]

Also, so I did do my compression test, 90 psi on both, and it looks like that is good (thought it should be higher but looks okay on what I found online). So then I removed the fuel line into the carb, pumped it manually, went very steady and smooth but came out a bit "gold" and I have much newer fuel (needed to run generators due to power outage) and it's very "clear" like water. Is that likely an issue that the fuel is bad?

Thanks again!
Biederboat

Yep !

 

[biederboat]

So with the new carb that ran on the likely "bad" gas, I took the old fuel out, pumped the hose out as much as I could, cleaned up the spark plugs a bit, put in new gas and ran it and it seems to be much better. I still may have to clean it, I'll do a full test tomorrow. I do have to say that the gas didn't look "dirty" (just "degenerated") so hopefully it didn't clog up the jets in the new carb. It definitely idled better and ran better at a higher RPM (which I kept a bit low with just hose water). Hope it runs good!

 

[pvanv]

That carb is not a US Tohatsu/Nissan carb. It's the one used on the Merc 9.9 (which is a Tohatsu 9.8)... as evidenced by the accelerator pump.

 

[biederboat]

Well, it does seem to work okay, especially now. I'm 99% certain I got the whole fuel system fixed by just replacing the old fuel with new. I didn't clear out the new carb and it took a while for it to run "clean" because of what was in the float. This is all from a test run near a dock but I ran it at least 15 minutes and it kept getting better over that time and for the last 10 minutes ran very well.

When I bought this carb on eBay, it was listed as what I needed, nothing about a Merc and came with some info about the different functions but just for a Nissan. I can say that it seems to accelerate a bit "slushy" (doesn't stall like it would with the bad fuel) so I may need to do some adjustments and maybe even clean and replace with the original carb.