Outboard making me lose my mind

mrgnstrn

Super Anarchist
1,375
4
Herring Bay, MD
howdy y'all.  I need some help with my sanity.

I have an older Nissan outboard that will not run without choke on. and even then only at idle.

particulars: 1996 Nissan 3.5 hp - 2 stroke with internal fuel tank.

engine is based on a Tohatsu, also same as the 3.3 hp 2-stroke Mercury.

Carb has been fully rebuilt, and what wasn't replaced was cleaned with brake cleaner.

Here is what has been cleaned: tank, fuel filter, fuel valve, fuel hose.
also replaced the hose clamps on the hose, and the o-ring between the carb and the intake.
cleaned and checked the tank vent.

The only thing in the fuel system that wasnt replaced was the main jet, which got the brake cleaner treatment, and is back to bare metal. no varnish or other gunk.

It starts reliably with choke, and will only run for ~5 seconds with choke off.
it will run roughly with choke, but it wont die, but on in idle. any higher speed and it dies.

It has all the signs of "not enough fuel" but there is no obstruction as far as I can tell. fuel drains quickly thru the valve, the fuel bowl, etc, so it seems like everything up to the main jet is good.

There is only one jet. it is not adjustable as far as I can tell.

I can get it to run in idle with choke off, but only for 5 seconds, and if I switch back to choke for 2-3 seconds, it will last another 5 seconds with choke off.

the main jet is clean, but doesnt act it. i am losing my mind. help!!

-M

 

bacq2bacq

Anarchist
603
254
Ottawa
I have a 4hp 2-stroke Merc, but it's been good to me, first pull (with a can of quick-start) this year. 

How beat is the engine: piston slap, rings?  If it got cooked, it might not run right again until at least honed or more.

I've started using a bit of seafoam in my gas.  It does sound like insufficient gas, but I'd think if you can't open the throttle at all without it dying, and it won't take load, then, yeah, I don't think you are nuts, you might still have a fuel-delivery issue.  I screwed up the re-assembly of a 4-stroke generator carb once.  Mis-assembled the float valve putting on the bowl, couldn't see my mistake.  How many times have you done all that final assembly to make sure it wasn't something stupid?  Air-leak post-carb could do it too.

 

Zonker

Super Anarchist
9,268
5,196
Canada
cheap and easy ideas:

replaced the plug?

checked plug wire for good connector?

replaced the gas?

checked for good spark against the block?

checked float height?

(I agree it's likely a fuel issue but check easy stuff first)

Maybe:

find somebody else with same 3.3/3.5 motor and ask to swap carbs. 

expensive:

buy a new carb

 

mrgnstrn

Super Anarchist
1,375
4
Herring Bay, MD
I have a 4hp 2-stroke Merc, but it's been good to me, first pull (with a can of quick-start) this year. 

How beat is the engine: piston slap, rings?  If it got cooked, it might not run right again until at least honed or more.

I've started using a bit of seafoam in my gas.  It does sound like insufficient gas, but I'd think if you can't open the throttle at all without it dying, and it won't take load, then, yeah, I don't think you are nuts, you might still have a fuel-delivery issue.  I screwed up the re-assembly of a 4-stroke generator carb once.  Mis-assembled the float valve putting on the bowl, couldn't see my mistake.  How many times have you done all that final assembly to make sure it wasn't something stupid?  Air-leak post-carb could do it too.
The engine is in really good shape. and runs with choke....but never without anymore.

I have disassembled and reassembled the carb about 50 times by this point. i doubt i am so consistent to screw it up in the same way every time, so i doubt that is the cause...

but thanks for helping me narrow down what it is and isnt.

 
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mrgnstrn

Super Anarchist
1,375
4
Herring Bay, MD
cheap and easy ideas:

replaced the plug?

checked plug wire for good connector?

replaced the gas?

checked for good spark against the block?

checked float height?

(I agree it's likely a fuel issue but check easy stuff first)

Maybe:

find somebody else with same 3.3/3.5 motor and ask to swap carbs. 

expensive:

buy a new carb
I have not directly checked spark, but I have run it for 5 minutes at a shot, by alternating the choke on and off. I deduce if I had shitty spark, I could not do that. I did pull the plug and didn’t notice anything really amiss. 

For fuel, I tried some of that “tru fuel” pre mixed for chainsaws and the like.  It doesn’t have any ethanol. No better performance. I’m trying a third source tomorrow. 

How does one check the float height with the bowl installed?

ive already replaced all the internals of the carb, my wife will kill me if I have to buy another freakin carb. 

Ill see if someone even has this motor to swap carbs; I don’t  hold any hope for that. 

Any other ideas?

m

 

See Level

Working to overcome my inner peace
With the motor upright take the bowl off, the float should drop allowing fuel to flow, lift the float and see if it stops the flow.

Edit

Float should be level when it's shuts off the needle valve.

 
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olaf hart

Super Anarchist
Had the same issue with an Austrian built Makita chain saw, the carby manifold was warped, you might want to check with a straight edge next time you have it off.

Sent the repair shop guy nuts till he figured it out....

 

Zonker

Super Anarchist
9,268
5,196
Canada
You do open up the carb and see... Never mind - you google and find the Service Manual :)

https://www.sv-zanshin.com/r/manuals/tohatsu_service_manual2005-2.pdf

(38.5 MB file)

> There is no fuel pump on this - it's gravity fed so no fuel pump diaphragm

> change the spark plug even if it looks fine. Keep the old one as a spare. It costs very little but eliminates one item.

> Leave gas cap off. Eliminates the chance of vent being partly plugged.

Did you try this?

Unscrew the gas tank valve - it might have a mesh screen in it. It could be partly clogged.

"For the 2.5, 3.5 and 5B engines, the in-tank pickup filter is the only fuel filter used. This filter is part of the fuel cock, and if clogged or damaged, it must be replaced with a new fuel cock assembly."  Is this the filter you cleaned or replaced?

"tru fuel” pre mixed for chainsaws and the like
Ooops. Maybe not a good idea. Their website says "TruFuel can be used in all air-cooled, 2-cycle equipment. Leaf blowers, line trimmers and chainsaws are the most common, but snow blowers, small generators and air-cooled outboard engines"

I would use a marine TCW3 2 stroke oil with at least a mid grade gas. If it's fresh having ethanol doesn't matter. If the gas is several weeks old the ethanol sucks.

 

TQA

Super Anarchist
1,208
35
Caribbean
Sure sounds like a full or partial blockage in the main jet system to me.

Take the carb off and blow through the main jet while it is in the carb but use a high pressure compressed air line.

A known issue if you have been running fuel with an ethanol $ is the fuel line from tank to carb degrading. Worth changing just in case. 

 

Rain Man

Super Anarchist
7,033
1,947
Wet coast.
Sometimes when they  rebuild carbs they get some gasket-sealing compound or dirt loose in  the bowl which then stuffs up the jets.  Only solution is another cleaning.  Your symptoms sound a lot like carb.

 
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mikegt4

New member
44
15
ohio
I have had good luck cleaning carbs using an ultrasonic cleaner. It can break up clogs in the tiny passages better than solvents or compressed air. Most good lawnmower repair shops will have an ultrasonic cleaner and will clean your carb for a modest fee

 
Had a similar issue with a Honda. Actually bought a new carb. Since i'm at altitude, I checked to see what main jet I had been using, found it to be marked the same as the new one but had some sort of non-dissolvable deposit neatly within the bore. Put the new jet in the original carb. Motor works like new.

Buy a new main jet !

 
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