125cc Carb Diaphragm Replacement - now rev problem

[MarauderGian]

Hello!

I am new here so please forgive me if i have posted in the wrong place.

So, i have a Suzuki Gz125 and i just replaced the carb (mikuni) diaphragm because it had around 7 small holes in it and now the bike starts and idles just fine but bogs down when triyng to rev it up. If i am patient and careful and i get it over that bad spot on the throtlle i can redline it but once i go beneath it happends again. I think it might be running rich. How i can fix this? Adjusting the needle jet?

Thank you!

[ThePhatomfart]

Hi , could be a few things , but take a look at this and tell us at what throttle position the problem is

[fastbob]

I would begin by checking and returning every setting to standard including needle height and pilot air screw turns out.I see there's a position sensor as well , is it properly connected? Have you remembered the fuel tap vacuum pipe? If you're going to be fiddling, making notes is a good idea.Good luck!

[MarauderGian]

When i replaced the diaphragm i also cleaned the carb but i didn't mess up with the air/fuel screw. I just cleaned the main and pilot but they are just screwed all the way in. What i noticed is that the TPS doesn't do any difference (connected or not) the same for the air filter.

I have moved the clip on the needle one position up (original on the lowest) but it didn't make any difference...

[ThePhatomfart]

Worth doing a test on the TPS

[MarauderGian]

I checked the TPS following that diagram and i got for test A = 1.113k and for B= 5.10k. I think it's just busted because when i action the throttle it goes through numbers quite strange, going up and down without any sense. Is any way i can fix it or i should just buy one?

Thank you all!

[ThePhatomfart]

You could try undoing the 2 screws that hold the TPS in place, just so you can move it slightly and take another reading, if they are no different to the first maybe then have a look at another TPS

[MarauderGian]

Unfortunatelly one of the screws is striped but i managed to find some ways to test the TPS and i've seen that it works decent, it just have a dead spot right before fully open.

I start to think that is not the TPS, one because of the reading and second because of the fact that the bike runs the same with or without the TPS connected.

Tomorrow i will give it another try with the clip on the needle. I think the previous owner tuned the carb with that broken diaphragm or for the after market exhaust or for both and now that i replaced the diaphragm the settings are all wrong.

[MarauderGian]

Hi , could be a few things , but take a look at this and tell us at what throttle position the problem is

At first the problem was around 1/4 and now after moving the clip up is just at the finest touch of the throttle.

[Stu]

Check the choke works right too

a nice trick is to stick a bit of choke on and see if the problem is still there

Have you checked the main jet size too? no one has put a larger or smaller one in have they

[ThePhatomfart]

Hi , could be a few things , but take a look at this and tell us at what throttle position the problem is

At first the problem was around 1/4 and now after moving the clip up is just at the finest touch of the throttle.

The mixture screw should be just above one and a half turns out from bottom, could be an idea to check that first

[MarauderGian]

Hi , could be a few things , but take a look at this and tell us at what throttle position the problem is

At first the problem was around 1/4 and now after moving the clip up is just at the finest touch of the throttle.

The mixture screw should be just above one and a half turns out fromhttps://themotorbikeforum.co.uk/posting.php?mode=quote&f=5&p=980464&sid=2d841969d58105b27557f5b4b2487bab# bottom, could be an idea to check that first

 

No luck as the mixture screw is screwed (striped) .

[MarauderGian]

Check the choke works right too

a nice trick is to stick a bit of choke on and see if the problem is still there

Have you checked the main jet size too? no one has put a larger or smaller one in have they

 

The choke works strange, no change before half and from that it just goes crazy. But with some choke the problem seems to be diminished.

I will upload a video in 5 minutes

[ThePhatomfart]

Could be part of the problem, previous owner could have tried to set up everything else around the mixture screw

[Stu]

Check the choke works right too

a nice trick is to stick a bit of choke on and see if the problem is still there

Have you checked the main jet size too? no one has put a larger or smaller one in have they

 

The choke works strange, no change before half and from that it just goes crazy. But with some choke the problem seems to be diminished.

I will upload a video in 5 minutes

 

That to me suggests it's running lean

I would be tempted to strip that carb and ensure everything is spotless and set to stock including the main jet and air screw set as per manual too

Start from how it should be from the factory

And make sure you have no splits in the intake rubber

[MarauderGian]

https://www.youtube.com/watch?v=P0-rdWwMsEE

Here you have a clip with the bike running. I will take the carb down again, drill the mixture screw, buy another one (i coudn't find it on ebay, so maybe you guys know a website where i can find one ), reset to factory everything and hope for the best.

Do you think the mixture screw can be off now after replacing the diaphragm? I don't want to risk ruining the carb trying to drill that mixture screw out for nothing.

Also, what i forgot to specify is that in the old broken diaphragm from that 7-8 holes i noticed that 2 are man made, they are tiny squares, the rest are just rips.

Why someone should do that?

[ThePhatomfart]

Hi,is your carb the Mikuni BS26SS

[MarauderGian]

Hi,is your carb the Mikuni BS26SS

 

I don't know, i measured the intake port and it's 26mm so i think you are correct.

Here you have some pictures of it:

First one is with the spark - obvious running way to rich

And you have also the stripped mixture screw

[ThePhatomfart]

Hi, that mixture screw looks mauled ,and the plug is black, yes your running really rich there, could do with getting that mixture screw out,if previous owner hasn't drove it all the way in it could come out, maybe a tiny ezee out could do it but have to be careful

[Northern Biker]

That carb looks paggered mate, i'd be surprised if you can get that mixture screw out without damaging the carb. Looks like it's been screwed right in as tight as possible and it's snapped the head off. It's only a brass screw, so very soft metal and easily damaged.

Also it looks as though the TPS has been messed with, it has 2 different screws and both of them have been butchered.

You don't know who has done what to that carb so i'd be looking for another second hand one if it was my bike.

The way the bike revs better when the choke is on suggests your problems are fuel related (weak mixture) but the choke will be sooting up your plug, so a good second hand carb could go a long way to fixing it.

[MarauderGian]

That carb looks paggered mate, i'd be surprised if you can get that mixture screw out without damaging the carb. Looks like it's been screwed right in as tight as possible and it's snapped the head off. It's only a brass screw, so very soft metal and easily damaged.

Also it looks as though the TPS has been messed with, it has 2 different screws and both of them have been butchered.

You don't know who has done what to that carb so i'd be looking for another second hand one if it was my bike.

The way the bike revs better when the choke is on suggests your problems are fuel related (weak mixture) but the choke will be sooting up your plug, so a good second hand carb could go a long way to fixing it.

 

I took the screw out eventually but with alot of damage to the carb, i think i still can use it if i improvise somehow the tread back. The thing i need to know is: the mixture screw is doing its job only with the tip? Or the mixture its adjusted with the help of a bigger protion of the screw?

From this image i understood that only the tip does the mix...

https://tse1.mm.bing.net/th?id=OIP.4hJnLexbz4nvGLrLwKwEWQEsEc&pid=15.1&P=0&w=166&h=158

In other hand, as a replacement I found this but i think i will not be able to put the TPS on it... Can the bike run just fine without it?

http://www.ebay.co.uk/itm/Heavy-Duty-Suzuki-GZ125-Marauder-GN125-GS125-EN125-Carb-Carburettor-Choke-/142047114772?hash=item2112aaf614:g:o1AAAOSwzJ5XfSmk

[ThePhatomfart]

Have you got a Workshop manual, yes it's more of the end of the screw that does it for you, thats why when setting it up you should only screw it in till it touches bottom with no pressure on the screw, as regards TPS ,that relays throttle position to the CDI/ECU , though at the moment you say either way on or off it doesnt make much difference ,that would change with a good set-up

[Northern Biker]

Why bodge it? If you want it to run properly get the correct carb for the bike.

[MarauderGian]

Have you got a Workshop manual, yes it's more of the end of the screw that does it for you, thats why when setting it up you should only screw it in till it touches bottom with no pressure on the screw, as regards TPS ,that relays throttle position to the CDI/ECU , though at the moment you say either way on or off it doesnt make much difference ,that would change with a good set-up

 

So i just need another carb now . Can you tell me where i can find one or if i can put any other 26mm carb ? I cannot find one exactly for my Gz125...

Thank you all for your help!

[ThePhatomfart]

Hi, is the carb you got beyond repair or can you fix that hole where the mixture screw sits, I have been looking for a second hand one, and their as rare as hens teeth, here's the workshop manual, and I'll check again for the carb

https://www.dropbox.com/s/pjhga7bmb5fb8s1/Suzuki%20gs-gn-gz-dr125-manual-eng-copy.pdf?dl=1