What makes the motor sneeze/cough, snuff out!?

[wlbolerdo]

I've got a 2005 yamaha 70tlr. About a year ago the motor was skipping and missing through the midrange and wide open throttle, It idled great. I pulled the carbs apart and cleaned them, it ran great. Recently it has run crappy through the midrange and wide open throttle again. I bought kits and rebuilt. Now it runs crappy at idle and great every where else. I pulled a suspect carb off and cleaned it again, same thing. Idle seems too low now and it has that coughing/sneezing at idle.
Any help would be greatful
Wayne

 

[rodbolt]

Re: What makes the motor sneeze/cough, snuff out!?

coughing is a lean backfire in the crankcase.
left unchecked it can break reeds,shear flywheel keys and blow fuel pump diaphrams.
its caused by lean fuel mix.
did you carefully clean the pilot fuel jet and have you removed the brass plugs covering the fuel mixture screws?

 

[wlbolerdo]

Re: What makes the motor sneeze/cough, snuff out!?

I did not remove the brass plugs at all, I didn't want to mess with the idle screws. I need a little help

 

[wlbolerdo]

Re: What makes the motor sneeze/cough, snuff out!?

I soaked each carb in parts cleaner. Each carb was completely broke down except for the brass plug and the mixture screw. I used torch tip cleaners and compressed air to completely clean and dry everything.
I can put my hand over the top two carbs and snuff out the motor. When I do this to the bottom carb there is no change in the motor, this would tell me I have a problem with this carb and it may be my coughing problem as well.
I'm leaving for the Keys Wednesday for a fishing trip and would love to have this boat right.
Should I pull the brass plug and adjust on it or is there some other problem?
Wayne

 

[rodbolt]

Re: What makes the motor sneeze/cough, snuff out!?

clean the carbs again and chek/replace the fuel pump.
I use a 9/64th drill and drill a hole in the plug and use a #10 self tapping screw and pliers to pull out the plugs.
if you allow the drill to hit the screw it drives he screw in so dont let it happen.
if it does start with an initial setting of 1 1/4 out.

 

[wlbolerdo]

Re: What makes the motor sneeze/cough, snuff out!?

Carbs have been pulled apart again, soaked, rinsed and blow-dried. They're back on the motor. Pulled fuel pump apart, it looks fine. Got the brass plugs out so now I can adjust the carbs.
Here's a dumb question, when we back the mixture screw out 1 1/4 turns is that like the slot is facing north and south and you back it out north around one complete turn back to north or half a turn to south? I'm sorry but I want to be clear on this. Anyone, Rodbolt?
Wayne

 

[Triton II]

Re: What makes the motor sneeze/cough, snuff out!?

Here's a dumb question, when we back the mixture screw out 1 1/4 turns is that like the slot is facing north and south and you back it out north around one complete turn back to north or half a turn to south? I'm sorry but I want to be clear on this. Anyone, Rodbolt?
Wayne

Wayne. With the mixture screw fully in (clockwise until the screw won't turn anymore) note the position of the slot. Then turn the screw anti-clockwise through 450 degrees, i.e One complete turn until the slot is in the same orientation as it was fully screwed in, and then a further 90 degrees in the same direction. As Rodbolt was saying, if you have not rotated the screws when pulling the plugs, the screws should still be in their correct position and you won't have to adjust them. Good luck and enjoy your fishing trip.

TII

 

[wlbolerdo]

Re: What makes the motor sneeze/cough, snuff out!?

I got it now. I'll go do that and see what happens. I'm tired of this friggin thing!

 

[Triton II]

Re: What makes the motor sneeze/cough, snuff out!?

I got it now. I'll go do that and see what happens. I'm tired of this friggin thing!

OK. Let us know how you go. Best of luck, once it's running right you'll be a happier fisho!

TII

 

[wlbolerdo]

Re: What makes the motor sneeze/cough, snuff out!?

Good morning everyone, the motor is running as I type this to let it warm up. I have it in a test tank to create back-pressure but wont be able to put it in gear. I drilled out the brass plugs to get to the mixture screws and set them 1 1/4 turns out, also pulled and cleaned carbs again.
Whats the procedure for adjusting/tweeking the carbs to get the max out of them now?
Wayne

 

[Triton II]

Re: What makes the motor sneeze/cough, snuff out!?

Good morning everyone, the motor is running as I type this to let it warm up. I have it in a test tank to create back-pressure but wont be able to put it in gear. I drilled out the brass plugs to get to the mixture screws and set them 1 1/4 turns out, also pulled and cleaned carbs again.
Whats the procedure for adjusting/tweeking the carbs to get the max out of them now?
Wayne

I can only give you the basics, and Rodbolt's advice is a lot better than mine. I suggest you run the engine as is (with all three mixture screws 1.25 turns out from fully in) for your first fishing trip. After putting a few hours on the motor, motor gently back to the dock for ten minutes or so then pull each plug and check for fouling and colour. The plugs' centre electrodes should be a dark grey colour. Black sooty deposits indicate that carb is too rich and a whitish grey electrode indicates running lean. Turning the mixture screws in leans out that carburettor and turning them out richens the carb.

But remember, the mixture screw is for low throttle settings only - from about a third throttle all the way to WOT makes the carbs run on the main jet and idle throttle runs the pilot jet. As I said before, I'm just an amateur who's tinkered with a few engines over many years, however maybe the best advice of all is to wait for Rodbolt to answer your question. Good luck.

TII

 

[99yam40]

Re: What makes the motor sneeze/cough, snuff out!?

also pulled and cleaned carbs again.
Whats the procedure for adjusting/tweeking the carbs to get the max out of them now?
Wayne

Did you know that your manual has a link and sync procedure you need to follow each time you reinstall them?