F20 startup issue +video

[panasonic]

The seat is BRASS or similar.
Look at picture number 6 please, use zoom.
link to pictures, scroll down to picture number 6 and click it: https://imgur.com/a/LXaUD

If my eyes are not deceiving me, which they very well may be, it almost looks like the needle seat has migrated up out of the bore slightly....that would explain this whole thing. Can you take another close up picture of it for us?

You guys look at it closely and tell me what you see....zoom in.

[pstephens46]

Could it be that the needle was replaced with one that is too short?

[panasonic]

Could it be that the needle was replaced with one that is too short?

He says no parts have been replaced in the past, as far as he knows.

It would be to long, if anything, to make the float raise up high. I thinks the seat has moved...could be wrong, hard to see in the pic.

Hopefully he will take yet another good close up picture of the needle seat.

[TownsendsFJR1300]

He says no parts have been replaced in the past, as far as he knows.

It would be to long, if anything, to make the float raise up high. I thinks the seat has moved...could be wrong, hard to see in the pic.

Hopefully he will take yet another good close up picture of the needle seat.

As I posted in post #68, with no other parts changed, that seat moved outward taking the needle and float with it..

I never had to change a seat, I assume gentle tapping with the correct socket (largest as possible) would re-set it deeper(back to normal)?

That OR buy the correct needle (which would be possibly shorter) in case someone DID dink with it in the past.

But yes, that seat (with the gauge on it, isn't very deep at all).

For the OP, does the needle go FULLY INTO THE BORE??
The edges of the needle should not be visible when fully seated..

[99yam40]

If my eyes are not deceiving me, which they very well may be, it almost looks like the needle seat has migrated up out of the bore slightly....that would explain this whole thing. Can you take another close up picture of it for us?

You guys look at it closely and tell me what you see....zoom in.

My guess is the seat has a shoulder and is seated all the way to the shoulder in that pic

this still does not make any sense to me.

if the float/needle&seat allows fuel into the bowl when primed, why will it not let fuel in when running?

[merc200dalarna]

He says no parts have been replaced in the past, as far as he knows.

It would be to long, if anything, to make the float raise up high. I thinks the seat has moved...could be wrong, hard to see in the pic.

Hopefully he will take yet another good close up picture of the needle seat.

The seat has probably moved up a bit, I took new pictures as close as I could with my phone.
If I remove the needle and use only the pin and float, it seats fine. But as soon as the needle goes in the seat it starts to pivot on the needle instead of the pin. That is why I have to unscrew the screw to compensate. Perhaps you guys have a link to a good picture of another similar yamaha/keihin carb?
I will google around some.
I do not dare to apply force to the seat until I know how far it should be seated down.
~8 new pics: https://imgur.com/a/4uUHC

[merc200dalarna]

As I posted in post #68, with no other parts changed, that seat moved outward taking the needle and float with it..

I never had to change a seat, I assume gentle tapping with the correct socket (largest as possible) would re-set it deeper(back to normal)?

That OR buy the correct needle (which would be possibly shorter) in case someone DID dink with it in the past.

But yes, that seat (with the gauge on it, isn't very deep at all).

For the OP, does the needle go FULLY INTO THE BORE??
The edges of the needle should not be visible when fully seated..

Yes the needle is fully down, but most likely the seat has come up a little bit somehow. Because the whole thing balances on the needle now, not the "pivot-pin" as it should. I need a pic of an original before I dare to push down (with tools) on the seat. My thumb alone did not move it.

[merc200dalarna]

My guess is the seat has a shoulder and is seated all the way to the shoulder in that pic

this still does not make any sense to me.

if the float/needle&seat allows fuel into the bowl when primed, why will it not let fuel in when running?

I can't quite rationalize the behaviour either, but it all points to the seat isn't in its proper position. Look at the pics and you will see how tilted sideways it becomes for me to compensate. There is also pics of the needle alone. Also the seat alone, from two angles, and no caliper in the way. It is still around "0.078" protruding. New pics are in one of my answers above. Thank you.

[pstephens46]

This is crazy. Can you put a flat piece of metal over it and press down a tad harder? Where is the Moto X previous owner? Could you ask if he ever touched that carb? Are those seats generally just pressed it? Any sealant?

[panasonic]

I can't quite rationalize the behaviour either, but it all points to the seat isn't in its proper position. Look at the pics and you will see how tilted sideways it becomes for me to compensate. There is also pics of the needle alone. Also the seat alone, from two angles, and no caliper in the way. It is still around "0.078" protruding. New pics are in one of my answers above. Thank you.

OK there is one of two things going here:

1 The needle is to long..but it is the one that came with the engine. But that does not mean it is the correct one (somebody may have put the wrong one in there) The only way to know for sure is get a new one and compare...simple as that.

2 The needle seat has moved. There are a couple of different brass needle seats on the go. There is the press in type, with or without an O-ring on them. And the screw in type which usually have a hex head or a screwdriver slot for installing or removing them (but not always)

Seeing that the parts break down doesn't show the seat as a replaceable part... I would say yours is a press in type. it is not meant to be removed after installation.


First try to contact the person who sold it to you and see if he fooled with the carb.(changed any parts)

If it was my carb (do at your own peril) I would first try to turn it with a pair of pliers.

If it does not turn, I would get a socket that is approx the same diameter as the seat, support the carb solidly and gently tap on the seat and see if it moves...measure with your calipers to see any difference. All the carbs I have seen with pressed in seats are just pushed in until they bottom out in the bore.

Note: seats in pics are not from your carb

Good Luck

[merc200dalarna]

This is crazy. Can you put a flat piece of metal over it and press down a tad harder? Where is the Moto X previous owner? Could you ask if he ever touched that carb? Are those seats generally just pressed it? Any sealant?

I don't have any phone number for the previous owner, lol, we made the deal at a local gasstation. (haha, I had the motor checked by yamaha sweden for insurance issues and what not, it was bought by that dude.) I checked a video by "eric edic" on youtube disasembling a yamaha carb, I can almost see that my seat has moved out compared to the video. But I still want a measurement before I press down harder. I could use a vice or similar, but i don't want it out of spec the other way instead.

[merc200dalarna]

OK there is one of two things going here:

1 The needle is to long..but it is the one that came with the engine. But that does not mean it is the correct one (somebody may have put the wrong one in there) The only way to know for sure is get a new one and compare...simple as that.

2 The needle seat has moved. There are a couple of different brass needle seats on the go. There is the press in type, with or without an O-ring on them. And the screw in type which usually have a hex head or a screwdriver slot for installing or removing them (but not always)

Seeing that the parts break down doesn't show the seat as a replaceable part... I would say yours is a press in type. it is not meant to be removed after installation.


First try to contact the person who sold it to you and see if he fooled with the carb.(changed any parts)

If it was my carb (do at your own peril) I would first try to turn it with a pair of pliers.

If it does not turn, I would get a socket that is approx the same diameter as the seat, support the carb solidly and gently tap on the seat and see if it moves...measure with your calipers to see any difference. All the carbs I have seen with pressed in seats are just pushed in until they bottom out in the bore.

Note: seats in pics are not from your carb

Good Luck

Nice pictures, so basicly, the seat can move on the o-ring, I mean the o-ring is soft and pliable.... If I only knew that the seat should bottom out? Can I be sure it should? Because if it bottoms out at the right height, I would dare to push it in??? EDIT# I still believe there is an o-ring on my seat too, because I can see a small gap around the edges.

[merc200dalarna]

Hell, I took a gamble and pushed the seat in about 1 mm. The pivot pin and the screw are flush now, the screw is tightened. (unfortunately the float isn't according to spec, but I will have to go with it and hope it works)

[TownsendsFJR1300]

Technically, you SHOULD NOT have been able to push the seat in further..

That seat SHOULD bottom out in the carb housing... Is it fitting snug in the body??

Is the float (seam) NOW about parallel with the carb body?? (as if you adjusted with the mounting screw like before)

How it moved is beyond me...

*If Yamaha wanted/allowed any adjustment, it would have been engineered into the FLOAT itself (usually a metal tab)...

[pstephens46]

It's only about 10 or 11pm at night in Sweden. How about a moonlight cruise to test it?