Topic: Pd42b fuel mix screws not seating

[Jrev04]

Long time listener, first time caller.

Been putting these carbs back together, and 1,3, and 4 needles go in fine all the way down, but the needle for bowl 2 stops about 1.5 turns out.

I'm not sure if this is standard for that carb, kinda like how you sync to the number 2 carb or what.

There isn't a washer down in there or ring, and the threads on the needle still look good, so should I just match the other needles to where that is now (1.5 turns)

Bike has original airbox with kn filter, and 4-1

Thanks

[flybox1]

there are no such thing as pilot needles.  are you trying to describe the fuel (mixture) screw right next to the bowl?
under the fuel screw, there is a spring, oring and washer.  be sure there isnt one lodged down in there.

yes, the #2 carb is the slave carb, which the other three are set to.

[Jrev04]

I don't have much experience with these bikes or any for that matter, but I was going off terminology I read on someone who did a quick write up of these keyhole carbs in another thread.  They refered to them as pilot jets/needle

Any way, I'm positive there is nothing down in that hole. I've used some thin wire and air to see if anything would fall out and it hasnt. Looks identical to the other 3

They should all seat in all the way right? That #2 seats in exactly 1.5 turns out compared to the other 3, so I might just leave it at that

 

[CB650CPastor]

How do you know it's 1.5 turns out if it's stopping before it bottoms? How do you know that it's not bottomed? Not sure I understand your problem...

[harisuluv]

Sounds like he means mixture screws but you make a great point cb650cpastor.

If we are talking about mixture screws, no they go all the way in and all the way out.  There is no stopping mechanism to any of the carbs.  The #2 carb others are synced to is really only related to the slide set sync.  #2 has no adjustment, so all the other slides are adjusted to #2.  That is the only thing that is different.

So.. if you're suspecting some kind of thread problem, the first thing I would do is simply try a different thread, i.e. one of the other carbs which you seem to have already verified the threads are good.  If it screws into another carb fine, it's the #4 body threads, if it doesn't, try a different screw in the #4 body.  Catch my drift?

[Jrev04]

How do you know it's 1.5 turns out if it's stopping before it bottoms? How do you know that it's not bottomed? Not sure I understand your problem...

When all 3 screws are in, I can back them out 1.5 turns and they equal the same height as the screw in the #2 carb.

I've taken that screw out and put it in the other carb bodies and it fully seats.  I've also taken the other 3 screws and they all stop about 1.5 turns out in that #2 carb

I can't tell if the threads on the carb are mashed up or not, so I guess I'll try once again and see if something is in fact in there

[Jrev04]

This is a pic of the number 2 and 3 carbs. See how the screw in number 2 is sitting out further than 3? It's about 1.5 turns out. Tried doing it without the spring washer or oring and it's still 1 5 turns out

[Jrev04]

Couple of notes, this is the page I used when I refered to then as pilot needles.http://forums.sohc4.net/index.php/topic,48858.0.html

Secondly, they are Pd42b carbs, not a

[flybox1]

If you call it a (fuel) mixture screw, everyone here will know what you are referring to.

Did you try another one in its place and get the same result?

[Jrev04]

I've tried all 4 screws in there, along with trying one without the washer, ring, and spring. Still stops about 1.5 turns out compared to the other 3 screws.


I've fished around in there to find a left over oring or washer, and I'm certain there is nothing in there. It looks exactly the same as the other 3 carbs by the naked eye.

[CB650CPastor]

Is it possible that someone broke the tip off a mixture screw in the past by bottoming it too hard? If they did that, the piece may still be lodged in the hole and not allowing the new screw to turn all the way in as far as the others. Did you verify that the passage is open by spraying carb cleaner though it?

[Jrev04]

Is it possible that someone broke the tip off a mixture screw in the past by bottoming it too hard? If they did that, the piece may still be lodged in the hole and not allowing the new screw to turn all the way in as far as the others. Did you verify that the passage is open by spraying carb cleaner though it?

I'll check with some cleaner in a few mins.

Visually it looked just as clear as the other 3, but I'll find out

[Jrev04]

Shot some cleaner through it, and it flows very well, exactly the same as the other 3.

Not sure what to do next.....besides a bench sync these carbs are ready to go.

Since that one screw is seated 1.5 turns out more than the other 3, I might just leave it and see what happens when fuel and air starts going through it

[harisuluv]

I don't really have a solution for you, but it seems like all you really need is some pointers in troubleshooting.

-As suggested you have tried swapping out the needles and bodies to isolate the problem to the #2 carb body somewhere. 
-So now you explore the #2 and see WHY it's not seating like the others
-Try a screw (M5 I think?) bolt and see if it goes down smoothly or gets caught, the threads could be damaged.  The screw isolates the thread issue from bottoming out otherwise.
-You can measure the exact depth from where the oring and washer would seat to the top of the tube, compare that with the others.
-When you seat the mixture screw you will be able to feel the tip in the throat just peaking out.  See if you can, then compare this to the other carbs.  If you can't feel it, you need to figure out why.
-You said you sprayed cleaner into the hole and it came out clean.  From WHERE??  That's not just a one way in, one way out circuit.

It is quite apparent you have a high quality high res camera.  It's an asset that you're not using and you have even pinipointed the problem to #2 seat/threads/screw in point. 

[Jrev04]

Here's some more pics.  They are the best I can do at the moment with my cell phone camera

[Jrev04]

Top is number 4 carb body, and bottom is #2 which is the carb body in question.

Camera sure does highlight the crap in those tubes....looked alot better by eye

[flybox1]

yes, but it does look clear   
if you have a dial caliper, measure the depth of each, and with an appropriately sized screw, check that the screw reaches the same depth of each, just as harisuluv suggested.