Sticking diaphragm needle - consequences?

The backstory: my 82 Seca 650 wouldn't start and I found gasoline in the oil. Also there was a small amount of gas coming out the carb>airbox boots. After checking the sparks and the cylinders (for flooding), I decided to clean out the carbs and look for some culprit.

Well, the float heights checked out OK, but I've discovered the #2 and #3 diaphragm needles are sticking in the "up" position. The #3 won't even come down if I pull on it. I think it's the plastic washers attached to the needles. Is there a cheap-o way to fix this or do I have to spring for a couple of carb rebuild kits? Maybe sand-down the washer?

 

First off, it sounds like you are talking about the float needles. Flooding the carbs and getting gas in the oil happen when the needle/seat/float/float pin are rusty, gum covered, varnished, unclean, ETC. They should work as if they are loose, and polished. They should be bench tested wet- - necessary to set the level anyway.

But when you say diaphragm needles, this implies the piston sliders.
Not in the float bowls, but in the center of the carb. Engine vacuum draws the slider up (freely, no sticking) to meet the engine's needs, and the big needle varies the size of the main jet/emulsion tube.

You have many things to clean, polish and adjust.

http://www.xjbikes.com/Forums/viewtopic/t=14692.html

 

No, the sliders are fine, as are everything in the bottom of the carb. I'm talking about the long needle that's held within the sliders that can move up and down independently of the sliders. It's attached to a spring and plastic washer within the slider.

On two of the carbs, this needle is not being pushed down as far as the other two. It's stuck in the "up" position, and I believe it's due to the plastic washers rubbing against the inside of the pistion. I was wondering if this could contribute to the flooding because its the ONLY thing that isn't right about these carbs.

 

I bought a rack of 650 carbs off the "bay ( for $7.00) and I see the needle will move about 1/4 inch. I don't know exactly why the needle would need some relative motion, but it looks like a big flat blade would dis-assemble it for cleaning.

Regardles- - this metering needle is above the fuel level in the bowl.
The flooding you described comes from the needle/seat.
If your bike is together, get a piece of clear tubing, put your bike on centerstand, check your float level using the drain screw.
Gas should come to within 3 MM of the bowl gasket.
Not at or above the gasket. Not below the screw head.
Doing this test running is more accurate than stopped.
Take all appropriate safety precautions. . .
Then polish the seat with a golf tee and wipe the rubber tip gently with 1500 grit. This dresses your old needle/seat/
Then roll a bit of the 1500 grit to go into where the float hinge pin goes,
You polish the inside of this pivot point.
You did polish the pin. . .

 

TIME is right, the needles move when the slides move, not independently (although there is some allowable "play.")

The slides need to move freely (search "clunk test") and the float heights need to be verified using the method outlined above.

 

i just looked at one and the only thing i can think of is somethings under the plastic "hat" on top of the needle
when you look down in the slide theres a plastic cap with a hex hole in it,(10mm ?) right?
under the cap is a spring, then the "hat" on the top of the needle
the spring should fit in the cap and hold itself there, the other end of the spring should press down on the "hat"
theres a pin in the bottom of the well where the needle goes that makes the needle set crooked, don't know why
the needle should spin easily when it's all together
maybe the spring got under the "hat" instead of over it ?
no way it'll work like that, midrange would be real rich and if the needle comes out of the emulsion tube the main jet would pour out gas

 

Yea, the needle in the piston has some play of its own (about half a cm of travel up and down). It was stuck in the up position so I sanded the plastic washer that holds it in place. Now it moves up and down freely.

BTW, this is all AFTER a thorough cleaning. I've cleaned many Mikuni carbs, so I'm well aware of how to properly clean and adjust a carburetor. This is just one instance of a piece of hardware that doesn't translate from Mikuni > Hitachi so well. I've also adjusted the float heights.

Anyways, this bike is still refusing to start after the cleaning. Even with Quick Starting fluid, there isn't any combustion:

-The starter turns
-The motor turns
-the plugs are fine and offer plenty of spark
-the cylinders are not flooding
-the float heights are fine
-I bench-synced the carbs
-butterfly valves adjusted to offer plenty of idle air
-the petcock works fine
-tried with or without air filter

There is one clue as to what's going on: when one spark plug is removed, and the hole left open, the engine gets much closer to starting. It could be any plug.

Any thoughts?

 

Time to fire it up- - let's cheat !
First, double check your coil low tension wires, orange to orange.
They can get swapped.
Pull all4 plugs, tape to cover, let's see all 4 spark.
Squirt a very small amount of oil in each CYl, just to boost compression.
Hook up a 10 amp battery charger, bring things up to 14 Volts.
Unplug headlight / pull fuse. Check voltage drop while cranking, looking for at least 12.8 or so. Sometimes while cranking there is NO spark.

Example = My 900 starts when I let OFF the button. (sometimes)
My fix is to clean out my starter, or just bolt on my TURBO starter.

Plugs back in, add just a whiff of starter fluid.(optional), crank with throttle closed. That should do it. You could also try bump starting it on a hill.

 

I might give the starter a going-over. My bike does get closer to starting when I let off the starter button.

 

That to me sounds like the battery voltage is dropping too low during cranking.

When you're checking spark, are you doing it by pulling one plug and grounding it with the cap on, or by using a 5th plug (leaving all four screwed in to the head)?

Can you try push/bump starting instead?

 

I checked each plug by grounding it against the engine w/ the cap on.

 

Right. So each time you were checking plugs, you had one open spark plug hole, thus reducing the load the starter has to turn when cranking. When you were trying to start it, though, you had all the plugs in, so more load on the starter, which means less voltage for the ignition system.

Did you try a push start?

 

Not yet. It's sounding more and more like it's the starter. I'll try a push start when I put it back together.

Thanks for the tips guys

 

Replaced the brushes in the starter and it STARTED! Hurray!

Ran it for about 4 minutes but it was running quite rough, with some backfiring. Hopefully it just needs a sync after being cleaned. Also the oil level dropped drastically (about 1/3 from the bottom of the glass port) after I ran it. I find that kind of odd considering there is no smoke coming out the exhaust and no visible leaks or pools. I just changed the oil and it should have 2.5 fresh quarts in it. Oil reading is supposed to be done after running the bike a bit correct?