SL125 carb issue

[Laava]

I have a std carb that I cleaned meticulously and put a kit in, all new jets gaskets etc. i have adjusted the float level to what it says in the manual, which is a bit ambiguous, but basically set it at where it seems right and it runs as if, to my limited experience, the idle circuit is not working. It basically will only idle with the idle screw in as far as it will go, at which point it is probabaly idling on the main jet only. Then if I turn the fuel off it will get to a point where it starts to rev up a bit and then if you give any throttle the revs will hang high and very shortly die altogether as the fuel gets too low.
So I have tried it running on about 4 different settings with basically the same result. I have used the clear hose method as well with the fuel level anywhere from 3-0mm below gasket surface.
OK, so I have tried a different carb, as I have 2 bikes the same, a brand new chinese one on the bike and it ran perfect. The original carb ran the same way on the other bike so I am convinced it is neither fuel or ignition. Any ideas or should I just give up and buy another chinese carb? Seems a shame as I was hoping to keep it as original as possible. Thanks in advance, Al

[F5 Dave]

So you have compressed air? When you remove the pilot jet and blow through, does it spray out into the throat? It is serious tiny. You may have to block the air jet at face of carb as there 3 holes to create 2 hole thus pressure in and out.

[Laava]

I threw the carb into a water tank for a month before I started and have run carb cleaner and compressed air thru it multiple times. It seems my options now are try what you suggested, or replacement. But what you said makes sense…bit late now, don't want to wake the missus up!

[husaberg]

I threw the carb into a water tank for a month before I started and have run carb cleaner and compressed air thru it multiple times. It seems my options now are try what you suggested, or replacement. But what you said makes sense…bit late now, don't want to wake the missus up!

If you are quick you can get most of the way through before she wakes up.........but on the subject of the carb I am with Dave use compressed air on everything you can also use plastics brush bristles out of a gong bush to push into the carbs crevice's on most jets and orifices.

.
I would also confirm the new kit parts are the right parts.

The hanging throttle normally means pilot circuit is too lean. but if you are turning off the fuel that's to be expected.

if its too rich it will start too easy from cold sans choke.
it will blubber. in response to thottle
make sure your needle is in the correct position as that can be ambiguous so put it in the middle

Honda float levels are set like this

https://www.hondatwins.net/attachmen...ent-jpg.40872/

i have heard of new float needles never working but you will have fuel leaking out normally

pm me you address i have a CB100 or sl carb somewhere and some bits and bobs.
i guess the spare SL can be modified and tuned?

[Laava]

Thanks Husa, will work thru that lot. I did check all the jet sizes when I rebuilt the carb a couple months ago and did a static needle valve check with a bowl full of fuel before fitting. The accepted norm with the clear tube check seems to be 1-2mm below gasket mating surface of carb body. The workshop manual shows the carb being on it's side but following that diagram, the float is hanging freely not even in contact with the needle valve and cannot be adjusted. I did it upside down which makes more sense. Is frustrating me as the carb really couldn't be any more basic. I hope it is just an insanely stubborn blockage!

[husaberg]

Thanks Husa, will work thru that lot. I did check all the jet sizes when I rebuilt the carb a couple months ago and did a static needle valve check with a bowl full of fuel before fitting. The accepted norm with the clear tube check seems to be 1-2mm below gasket mating surface of carb body. The workshop manual shows the carb being on it's side but following that diagram, the float is hanging freely not even in contact with the needle valve and cannot be adjusted. I did it upside down which makes more sense. Is frustrating me as the carb really couldn't be any more basic. I hope it is just an insanely stubborn blockage!

My experience is you measure the float with it sitting on a 90 angle. Maybe i have always done it wrong?

[Laava]

My experience is you measure the float with it sitting on a 90 angle. Maybe i have always done it wrong?

If you mean with the carb upside down, then that is what I have done and it makes the most sense. Maybe the manual is just a bad translation…

[F5 Dave]

If you spray some brake cleaner in the pilot cct, block the airjet entry and blow air through it should blow the spray out to the throat where you can see it (through safety glasses) . No pathway, no idle cct.

[Laava]

Right so the bowl gasket in the rebuild kit is non petrol resistant.
The passages are all clear, I am unsure why this is an issue, I am going to try to lower the fuel level a mm at a time, aware that there is a point where it becomes so low that the float is basically touching the bowl so no petrol can come in at all.
The photo shows it with the original, prob 50yr old, gasket. Which I am back to using...
Also showing the carb upside down with the vernier sitting in the notched sections. My understanding is that it is always measured from gasket mating surface unless it has these notches?

[Laava]

My other thought was that the fuel level setting is predominantly for the main jet right? And on all the bikes I have had, they will continue to idle way after you have turned the fuel tap off. So it has me flumoxed, it should be working, even if badly, but no.

[F5 Dave]

You should be able to remove the main jet and not tell the difference until you are at about 1/2 throttle.

[F5 Dave]

You've tried another carb so the likelihood of an airleak is low. But think about the interface.

[Laava]

Is not an airleak, I sprayed start ya bastard about to check, is not a choked up air filter, is not ignition, I have spent 3 hrs on it today and got nowhere. Unbelievable. I am just going to buy another chinese carb, although I will interchange with the one I got just to check…but it ran and rode perfectly with it(chinese) the other day…does my fucking head in this kind of shit
I have bent the float tab so many times now trying different levels, it must be suffering from fatigue!
I have an older shittier Mikuni that I could quickly clean up and put on just to try but I might be just wasting more time

[Black Knight]

Hi Al-I have a the same or very similar carb on one of my bikes,Honda S90,I have had it on and off the bike so many times I can now do it blindfolded.
I have found that the overseas kits can have the wrong idle screw,too short and have no effect on the idle revs-The correct length is 32mm-If you look into the carb at the intake end you can see the throttle valve,it has an angled slot on the RH side which the idle screw goes into.With the correct size screw you will note that as you screw this in it raises the throttle valve.At rest and with the throttle cable adjusted correctly,the gap at the bottom of the valve is around 3mm.Once started and warmed up you can then play with the screw to get a decent idle.
You can now play with the idle air screw to adjust the fuel ratio once you have a decent idle-my base is one and one eighth turns out-in for richer out for leaner-until the motor runs smooth,do this adjustment gently.
I needed a new idle jet,my bike has #38 which is tiny and easily blocked,these are unobtainable but Botany Honda has a close aftermarket which i got and cut 7mm off the length.
If you need a correct length idle screw I have a spare here you can have if you want a quick ride up the back road to collect.
Cheers-Chris

[Laava]

Hi Al-I have a the same or very similar carb on one of my bikes,Honda S90,I have had it on and off the bike so many times I can now do it blindfolded.
I have found that the overseas kits can have the wrong idle screw,too short and have no effect on the idle revs-The correct length is 32mm-If you look into the carb at the intake end you can see the throttle valve,it has an angled slot on the RH side which the idle screw goes into.With the correct size screw you will note that as you screw this in it raises the throttle valve.At rest and with the throttle cable adjusted correctly,the gap at the bottom of the valve is around 3mm.Once started and warmed up you can then play with the screw to get a decent idle.
You can now play with the idle air screw to adjust the fuel ratio once you have a decent idle-my base is one and one eighth turns out-in for richer out for leaner-until the motor runs smooth,do this adjustment gently.
I needed a new idle jet,my bike has #38 which is tiny and easily blocked,these are unobtainable but Botany Honda has a close aftermarket which i got and cut 7mm off the length.
If you need a correct length idle screw I have a spare here you can have if you want a quick ride up the back road to collect.
Cheers-Chris

That is bizarre! I will check that next time I am inspired to go into the garage! That would certainly explain why it started well on a part throttle too…cheers Chris!