2005 115 Johnson PLSOR fffffffffrustration... (still dies off idle)

[Harkonnen]

So I am still trying to find out what my problem is: it almost feels like the motor is fuel starved AND runs rich at the same time. Starts fine, but when you give it throttle, sputters and dies.

So far:
Carbs rebuilt (gaskets, needles and seats) + new bowls (jets moved from old). Hope I did not screw them up worse than they were, but at least it cured excessive smoke problem. Plastic gasket thingies between needle seats and upper bodies removed per earlier @racerone suggestion, float heights readjusted per Seloc manual.

New plugs.

Ignition tested, all cylinders fire.

Compression tested, low end of acceptable, but consistently so across all cylinders (+/-2%, IIRC)

Fuel pump pumps.

The only other thing I can think of is fuel pump diaphragm leaking. Is there a good way to troubleshoot for it?

Any other things I might be overlooking?

Thanks!

Video, if it attaches, is of a more or less typical example.

New video; old was too large.

 

[racerone]

Have you had fuel pump apart for inspection ?-----Tested the check valves in the fuel pump air motor housing ?-----Checked the pulse limiter for blockage ?

 

[Harkonnen]

Have you had fuel pump apart for inspection ?-----Tested the check valves in the fuel pump air motor housing ?-----Checked the pulse limiter for blockage ?

No on all three. What do I look for when I tear it down? Thanks!

 

[Harkonnen]

Pulled the pump.

So there are three hoses: gas supply from the engine fuel filter, oil supply for injection (plugged off by the previous owner - running pre-mix), pulse hose to the crankcase, and there is also a fitting to the vapor separator that sends the gas to fuel manifolds on each side of the block. Naturally, it is a non-serviceable unit (at $600, yikes!) with a lot of fancy security screws.

Fair amount of gas came out the pulse hose. Is it normal or is it a sign of busted diaphragm? Gently pressurized the supply hose with a spare primer bulb - no leaks. I am puzzled here.

 

[racerone]

The pulse hose could have a bit of fuel in it.-----There should be no gas coming out of the pump to the pulse limiter / pressure hose.-----There is a repair kit available for this pump.

 

[Harkonnen]

The pulse hose could have a bit of fuel in it.-----There should be no gas coming out of the pump to the pulse limiter / pressure hose.-----There is a repair kit available for this pump.

The pump seems functional, then. What else I might be overlooking?

 

[racerone]

Some folks are afraid of these simple pumps.----Sorry---I have many of them and I consider them to be simple.-----I would look at the fuel piston diaphragm.

 

[Harkonnen]

fuel piston diaphragm.

What is that? Thx.

 

[racerone]

Post #1 says that you feel it is fuel starved and running rich.----Can you elaborate on that theory.----Explain why you think this is so.

 

[Harkonnen]

feel it is fuel starved and running rich

It smokes too much even for a two-stroke, backfires occasionally, and there is more raw fuel in exhaust than I am comfortable with - sounds like rich, right? Yet, open the throttle, it sputters and dies, as if it were not enough gas. Why I am getting both of those symptoms at the same time is what puzzles me.

 

[racerone]

Perhaps it is just as simple as throttle plates opening too early.-----That stops most 2 strokes the way yours is acting.

 

[Harkonnen]

throttle plates opening too early

What do you mean by that? What do I look for?

 

[racerone]

Something called ------idle timing------It is the point where throttle plates open.-----About 50 years ago I checked tuned a Johnson 28 HP 1963 model.-----Had it running perfect in shop tank.------Then on the weekend I visited the local launch ramp.-----Saw this same motor with hood off.-----Wandered over to have a look.-----Owner said it would not idle.------I tried to adjust carburetor , no results.-----I then noticed an adjustment.-----I asked the owner if he touched it.-----Why off course he said.-----When I put it on the boat it is the first thing I changed because you guys at the DEALER did not know what you are doing !!-----So I changed that adjustment back to how it left the shop.-----Motor ran perfect again.---------LONG , LONG story I know.----I see the puzzlement on websites regularly.----But it proves that today folks still do not understand.------That adjustment is correct , but it looks wrong to the tinkerer.-----Sorry , but that is how I see it !

 

[Harkonnen]

Fair enough, but I didn't mess with any adjustments.

Alright, this may be weird, but when I pop off the float chamber, it feels dry, as if there was no gas in it. There is gas draining from the carb, though. Something to explore, or is my paranoia getting to me?

 

[racerone]

Sorry----Best to visit your local BRP experienced shop.