Basic fuel questions

[SteveVT]

I have three basic questions re. simple 2 cycle small hp outboard troubleshooting. I know the answers should be obvious, but maybe my understanding is incorrect, so I just want you to make sure I'm not assuming something wrongly:

1.) If a fuel feed problem is due to the fuel pump not supplying enough fuel to carb, would squeezing the inline fuel bulb temporarily bypass that problem by manually feeding the carb?

2.) If the inline squeeze bulb remains pumped up hard when the engine quits for lack of fuel does it mean that the fuel pump is supplying fuel, assuming that the carb needle is not stuck closed?

3.) If a fuel feed problem was due to the carb float needle sticking, would applying the choke allow the engine to start temporarily? In other words can choking ever bypass the fact that the carb bowl is empty?

These questions relate to my problem thread posted yesterday, but there were no answers, maybe because it wasn't direct questions -- just an account of a problem outing. I hope this one will just quickly clear up some basic questions that I have.

 

[Scott Danforth]

1 - yes
2 - maybe
3 - no

 

[Sea Rider]

1 yes, 2 a fuel bulb will only remain firm when primming it, once the motor is running the bulb will remain less firn, not soft though. 3 a stuck needle won't allow fuel to fill the carb's bowl and will spill fuel through the carb's side...

Happy Boating​

 

[SteveVT]

Wow, that was quick. Thank you Scott Danforth and Sea Rider. Here's present the situation:

1.) I just took apart and cleaned the carb
2.) Inline bulb is pumped, I can hear fuel fill the empty bowl and then stop.
3.) I pull out choke knob. And pull start cord.
4.) Engine runs briefly then slows to 4 cycle, then I push in choke. Engine speeds to 2 cycle, then stops.
5.) Bulb is still hard
6.) Engine will start again if I pull out choke, and repeat 3 thru 5 above.
7.) Engine will continue running if after choking, I push in choke about an eighth of an inch, but the range of choke where it will sustain is extremely narrow
8.) Idle mix screw is at 2 turns out. Turning it further out makes no difference to the above. ie 3 turns out, same problem.
From what has been said, it seems that the float needle is not blocking fuel, and the fuel pump is working.

 

[Sea Rider]

When cleaning carbs specially if being 2 stroke ones it's a must check with a flashlight the internal needle's seat to see its current condition, the seat must be cleaned shinny as when the motor was taken out of the box for trouble free carb operation..

Happy Boating​

 

[SteveVT]

Thanks Sea Rider, I'll take it apart again.

Did you mean the float needle seat, particularly....or the idle mix needle seat?

 

[SteveVT]

Also for cleaning and polishing the float needle valve seat, would toothpaste and a Q-Tip be okay, or do you have another way?

 

[flyingscott]

You need to clean your whole carb. What motor are we talking about here? Does it have a choke or a primer? It sounds like your idle circuit or main jet is still plugged.

 

[SteveVT]

Thanks Flying Scot, I will be cleaning the whole carb again (3rd time) and this time also polishing the float needle seat per Sea Rider's comment above. I also suspect the idle circuit could be plugged again after getting the answers to my 3 questions above. I will also check the float height this time (should be .78")
It's an '86 8hp 6G1 Mariner 2-cyc (Yamaha under the hood). Full description of what the symptoms were when this started is here:

1986 Mariner 8hp 6G1 won't idle without choke

I just cleaned up my low hours 1986 Mariner 8hp 6G1 manual shift (Yamaha block, I believe) after 30 years of storage. Taking off the scratched cowl, the engine looks new inside. I replaced the waterpump (though the impeller actually looked good). I took off the carb, cleaned it -- all parts...

forums.iboats.com

 

[Scott Danforth]

4.) Engine runs briefly then slows to 4 cycle, then I push in choke. Engine speeds to 2 cycle, then stops.

Huh?

 

[SteveVT]

Sorry, let me rephrase that: Pull choke out, Pull starter rope. Engine starts then gradually bogs down from too much choke. Push in choke, engine picks up revs then leans out and dies.

I think of the sound of 2 cycle motor running over-rich as "4 cycling", but maybe that's wrong, and apologies for any confusion. It comes from building model airplanes 60 years ago as a kid and tuning the needle valve, when you could definitely hear it go from 4-cycling to 2 as you leaned them. That's what we used to call it anyway.

 

[Faztbullet]

Scott is dead on......and if a needle is stuck shut not allowing fuel in bowl it WILL NOT spill from side.

 

[SteveVT]

Will polish the seat, for sure.

 

[Sea Rider]

Also for cleaning and polishing the float needle valve seat, would toothpaste and a Q-Tip be okay, or do you have another way?

Yep, micropolish it in circular motion with toothpaste and a sushi wooden stick with cotton rolled tip dampened in water which does not flexes as a Q-tip till the needle's seat looks shiny cleaned...​

Happy Boating

 

[dwco5051]

I agree that it most likely needs a good carb cleaning. If that motor has sat for 30 years or so I would then check the fuel tank to be squeaky clean and check or replace the fuel hoses. No sense starting with a clean carb and bring more crud into the system. The passages is those small engines are also very small.

 

[SteveVT]

Thanks Sea Rider. Just did it!

Anybody know the float height setting?
(1986 Mariner 8M (Yamaha) 6G1

Carb is a 6G1-100AH26

I found one reference that said .78" but that seems way too high (float is quite angled at rest) . As found it was at .625" and looked relatively level.

 

[SteveVT]

Carb disassembly, cleaning and polishing completed. I went back to .625" on the float. Turns out the manual I have shows the wrong (or a different) carb for the 8hp Mariner, so the .78" float height doesn't apply.

The engine runs really well in the tank - 1 pull start. Running great at all speeds. I did need to screw in the idle mixture needle a little for best idle, but that puts it in the expected range, rather than the 2 turns it was at before.

Next test on the water. Thanks to all who helped!

ps. dwc5051 -- I'd already done all that, but thanks for contributing.