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WILLIAMS37

08 yz450f carb/ float bowl question

9 posts in this topic

I can never leave well enough alone and decided to replace the diaphragm in my accelerator pump, after

putting the float bowl back onto the carb I realized that I have no idea how this thing came apart. It took

some wiggling and nudging and it finally popped into place. The bike fired right up but being the good

neighbor that I am, I didn't let it run long or open the throttle at all. The problem is when the bike shut off

the gas started leaking from one of the carb hoses.

I searched the manual and TT with no luck on exactly how to fit the float bowl back onto the carb body.

I checked the float function, (when pushed up doesn't leak, when let down drains gas) but I don't know

why its sticking in the first place. It moves with no resistance when I have the bowl off.

The only thing I can think of is the alignment from this brass (needle?) Is it supposed to go into something?

Does it go into the yellow/off-white plastic piece in center of carb? Just wanted to hear some advice before

I go back down and put it back together.

Here is the needle I am referring to

EAE72D56-3248-4D17-A0F1-3DF138D49D8D-37394-000015590A57AC15.jpg

And this is the yellow/off-white plastic piece

4F8937AE-DA68-44E4-BF13-3AAFECA1FF77-37394-00001558FFA1A7E2.jpg

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The brass standpipe is simply a limiter for how high the float level is allowed to get before it overflows from the drain hose at the center of the float bowl. It doesn't connect to anything inside the carb, just runs up in between things. If the carb overflows, it is for one of 3 reasons:

  • The float is sticking or binding because of incorrect assembly, damage, dirt, gunk, or contact with some other part of the carb in the bowl.

  • Level is set too high.

  • The float needle is worn, damaged, or more likely, just dirty.

Most commonly, it's dirt on the needle seat. The dirt doesn't have to be big, in fact it may not even be visible. It just has to keep the needle up off the seat. With the bowl opened up, and all sources of ignition removed from the area, turn the gas on and let it runs out past the float needle for a second or two, then try again. That may be all it takes.

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Thanks gray, I was hoping you would chime in on this. Just sprayed everything down with car cleaner and a shop towel, gonna give it another shot. Just didn't know if I was missing something to do with that brass post.

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Thanks gray, I was hoping you would chime in on this. Just sprayed everything down with car cleaner and a shop towel, gonna give it another shot. Just didn't know if I was missing something to do with that brass post.

As suggested the brass ''needle'' is the overflow. It just slips up into a hole in the carb. I'm sure if you tried fitting this it would become apparent as to what hole it slots into.

It could be dirty needle & seat..Some have an unseen filter above the needle (inside carby fill line) so blowing it out with an air compressor after removing the float will make sure it's clean.

If the float level is too high as old mate says it will flood- usually only needs adjusting if you bump the float.

The obvious thing with carbs is that the fuel should shut off when the float is level with the carby body.

To check the float level....

To check this attatch the fuel line & remove the bowl. Now lift the float......Does it shut off level with the carb??? If not adjust until it does. Easy.

Edited by Barra8

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This time I got a nice reassuring "click" sound when everything was lined up, tightened it up and it started on the 3rd kick. The whole reason I tore it down in the first place was to replace the diaphraghm in the accelerator pump, but does anyone know why there are 3 different part numbers with varying thickness for the yz450f? or what affect having a thicker or thinner diaphraghm means to the engine characteristics?

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As suggested the brass ''needle'' is the overflow. It just slips up into a hole in the carb. I'm sure if you tried fitting this it would become apparent as to what hole it slots into.

It wasn't a suggestion, and it doesn't "slot into" any hole.

This time I got a nice reassuring "click" sound when everything was lined up, tightened it up and it started on the 3rd kick. The whole reason I tore it down in the first place was to replace the diaphraghm in the accelerator pump, but does anyone know why there are 3 different part numbers with varying thickness for the yz450f? or what affect having a thicker or thinner diaphraghm means to the engine characteristics?

The diaphragms are different as to the length of the stop button on the bottom. This button limits the travel of the AP plunger, and thereby controls the maximum volume delivered with each full shot from the pump. That in turn translates into controlling the duration of the AP squirt. Alternative button lengths are selected when the tuner wants to change the squirt duration. It's important to understand that you can have either too much or too little duration, and bigger ain't always better.

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................................................................................................

It wasn't a suggestion, and it doesn't "slot into" any hole.

.....................................................................................................

How do you figure. That pin is well past the top of the float bowl so it's quite obvious it slots into a hole in the carb. Like any other carb.

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No, it doesn't and it's not a pin, is a pipe. The carb body has the top 50% of the float bowl cast into it, an area large enough to house the entire float assembly. The right side float has some extra clearance cast in so that the standpipe can extend up into the space between the float and the pilot jet boss. Doesn't fit up into any hole.

4025d1280763220-leaking-carb-please-help-141_0707_13_z-keihin_fcr_carb_tech-float_pin.jpg

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Yes well that's better :thumbsup: Makes more sense.

I knew it had to slot into a hole or gap whether it's a hole or gap/pin or pipe is'nt that relavant though ;) .

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