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Quick one about changing carb diaphragms

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MarkGoy
Borekit Bruiser



Joined: 26 Jan 2017
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PostPosted: 18:38 - 06 Apr 2017    Post subject: Quick one about changing carb diaphragms Reply with quote

I'm pretty sure something isn't right here.

But I can't work out what it is....

Steps..

1) Take diaphragm and slide out of carb.
2) Remove diaphragm from slide.
3) Inspect diaphragm for damage.
4) Re-attach diaphragm in correct orientation, the right way round to the slide
5) Re-insert diaphragm and slide into carb, making sure diaphragm lip is inside recess and diaphragm tab is in its own recess on carb body
6) Re-place spring and lid, tighten down.

But no dice.... I made a video of me doing the whole process start to finish.

Help?

https://www.youtube.com/watch?v=S-b5jC5D9O4&feature=youtu.be

Thank you.
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Isj0321
Two Stroke Sniffer



Joined: 04 Apr 2017
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PostPosted: 18:59 - 06 Apr 2017    Post subject: Reply with quote

Well you could havd had the curtains beforehand, and could have switched a light on. Other than that.. i have no idea what your problem is.
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Suntan Sid
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PostPosted: 19:33 - 06 Apr 2017    Post subject: Re: Quick one about changing carb diaphragms Reply with quote

MarkGoy wrote:
I'm pretty sure something isn't right here.

But I can't work out what it is....


What's the problem?
Do you think the carb's not working properly?
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MarkGoy
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Joined: 26 Jan 2017
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PostPosted: 20:04 - 06 Apr 2017    Post subject: Reply with quote

From my limited knowledge about the functionality of a diaphragm.

I understand what its for and how it works, not so much how its meant to move.

Its going down too fast isn't it? the diaphragm should (to my understanding) slow its descent ?

My engine appears to be running lean. I have no air leaks, I checked physically and by spraying carb cleaner on the rubber seals.
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Isj0321
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PostPosted: 20:33 - 06 Apr 2017    Post subject: Reply with quote

Absolutely nothing wrong with the operation of that slide, its sprung and assisted by gravity, its meant to go down fast.
What are the lean running symptoms you have identified?
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ADSrox0r
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PostPosted: 21:32 - 06 Apr 2017    Post subject: Reply with quote

If it seats right, which is often the tricky bit if they've warped (experience: don't disassemble carbs then leave them in the 'project' pile and expect the rubber not to do a number on you) then it should be fine. As already stated the slide is just gravity/pressure.
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MarkGoy
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Joined: 26 Jan 2017
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PostPosted: 23:05 - 06 Apr 2017    Post subject: Reply with quote

Aaaah i see, thank you very much for clearing that up.

//

Symptoms :

* white spark plug.
* Being a pig to start cold
* unstable idle speed, prone to stalling
* lack of power in mid rev range

I put a brand new plug in, held the bike in its low power state for about 30 seconds... this is what it looks like.

Oh its a GZ125
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Isj0321
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PostPosted: 23:12 - 06 Apr 2017    Post subject: Reply with quote

Checked your fuel filters?
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MarkGoy
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PostPosted: 23:15 - 06 Apr 2017    Post subject: Reply with quote

No......

I have an engine oil filter and an air filter, ive not seen a fuel filter

Its gravity fed from the tank to the carb.
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Isj0321
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PostPosted: 23:36 - 06 Apr 2017    Post subject: Reply with quote

Youd have seen an inline filter between tank and carb but there may be one in the petcock, there may be one in the carb also.
Worth a check. Another thing to check if you havnt already would be carb jets, any blockages there.
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MarkGoy
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PostPosted: 23:54 - 06 Apr 2017    Post subject: Reply with quote

I'll take a look, but as far as I know this bike doesn't have one?

Also Jets have been cleaned by mechanic
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jaffa90
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PostPosted: 23:57 - 06 Apr 2017    Post subject: Reply with quote

PostPosted: 02:01 - 24 Mar 2017 Rating: Good (Helpful) Post subject: Reply with quote Edit/Delete this post
Pic 1 is weak enough but passible, would be better with a biscuit colour on the white bit (insulator). I`m surprised there`s a c.v. carb fitted and not a direct cable lifting the carb piston / slide.
If the fuel level is correct then it`s possible that the carb slide is not lifting high enough under vaccuum. The diaphragm rubber has to be sealed around the edges and puncture free to operate.
A simple test is to lift the carb slide manually and watch it slowly going back to rest.

Slide operation video,
https://www.youtube.com/watch?v=lY-jnf7m_NM


Last edited by jaffa90 on 00:10 - 07 Apr 2017; edited 1 time in total
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Isj0321
Two Stroke Sniffer



Joined: 04 Apr 2017
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PostPosted: 00:09 - 07 Apr 2017    Post subject: Reply with quote

MarkGoy wrote:
I'll take a look, but as far as I know this bike doesn't have one?

Also Jets have been cleaned by mechanic


If your gonna be doing your own work on yhe bike id advise getting a haynes or a clymer manual. Well worth the money, will answer many of your questions and save you a lot of time.
Seems you can find the workshop manual here https://www.bikechatforums.com/viewtopic.php?p=1261261
Hope this helps
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MarkGoy
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PostPosted: 01:54 - 07 Apr 2017    Post subject: Reply with quote

Yeah Jaffa, I remember, hence why I was asking for help diagnosing what I was doing wrong while fitting.

To my understanding I'm fitting the diaphragm the way I'm meant to... but its not working?

//

I have a Haynes manual, don't know where I've put it though....

I find the book not to be detailed enough and even wrong/missing information in parts.

I'll find my book, sit down and read what it has to say on fitting new diaphragms and opperation.
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kramdra
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PostPosted: 08:13 - 08 Apr 2017    Post subject: Reply with quote

MarkGoy wrote:
and by spraying carb cleaner on the rubber seals.


Carb cleaner will eat through rubber very quickly. It is designed to remove hardened petrol.
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Devlin
Two Stroke Sniffer



Joined: 04 Feb 2016
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PostPosted: 08:38 - 08 Apr 2017    Post subject: Reply with quote

Is that a new diaphragm or are you fitting the floppy old one ??, with a new one fitted and assembled without the spring the slide will sit above its normal position, try fitting the old one without the spring and if it hits bottom its shagged
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MarkGoy
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PostPosted: 11:19 - 08 Apr 2017    Post subject: Reply with quote

Kramdra : Oops, I won't be doing that again, I saw someone do it..., not that that is an excuse.

Devlin : my book didn't mention that, it is a new diaphragm but I will check as soon as.

Thanks.
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Devlin
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PostPosted: 11:28 - 08 Apr 2017    Post subject: Reply with quote

I have seen slides flutter up and down due to floppy diaphragms with the result the engine gets varying fuel delivery
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MarkGoy
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PostPosted: 13:00 - 08 Apr 2017    Post subject: Reply with quote

OK, it sits at the same level, with or without the spring, right at the bottom.

The old diaphragm is tough and stiff, this one is flexible, I assumed that was the way it's meant to be..

It's not a cheap thing, it cost me £30.

I'm going to keep reading.
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Devlin
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PostPosted: 13:32 - 08 Apr 2017    Post subject: Reply with quote

I would have though there should be a gap otherwise air cannot pass to enable fuel to be sucked and hence fuel from the top of the needle jet check the book for settings,
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Robby
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PostPosted: 16:49 - 08 Apr 2017    Post subject: Reply with quote

Did you ever check the O-ring between the inlet rubber and the head?
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