Author Topic: Carb question  (Read 5367 times)

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March 17, 2016, 03:25:54 PMReply #15 on

Offline BruKen

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Float height is non-adjustable, the plastic floats and lever that closes the needle valve are moulded as one and have to be replaced if there is any wear.

As I can't do anything to it in the next couple of weeks the owner is taking it back today and her dad is going to have a look at it.

As the bike has been standing for a while and presumeably with the carb dry I'm wondering if the plastic hasn't shrunk / expanded as is plastic's want when exposed to fuels  :^_^ Certainly parts for the CG are dirt cheap (see below) and it has to be worth a go. Putting in bigger main jets as Mustang suggested is certainly an option but would only complicate an already rocky road if the float height was off.

http://www.wemoto.com/bikes/honda/cg_125_br-f_j/85-91/

Complete carb repair kit - £15
New carb - £52

March 17, 2016, 04:34:46 PMReply #16 on

Offline JayDub

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Ethanol degradation... always gets to the seals, and builds up a 'varnish. layer whilst in storage - unless you use an additive and/or drain the carb(s)
I do both now  :nod
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March 18, 2016, 08:02:07 AMReply #17 on

Offline Bixxer Bob (OP)

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I know what you're saying, but I don't think they had Ethanol in fuel in the UK when this was put away.

It's gone anyway, her dad's problem now.  Thanks again everyone.
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April 14, 2016, 06:18:04 PMReply #18 on

Offline Bixxer Bob (OP)

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Ok, it's back again for me to fit a rack and top box and I have it for a week while she's gone home to Lithuania to visit family.  With some use aparrently it's running better but not perfect so today I had the carb off again.  I found two things that I missed the first time:

Firstly,  I checked the accelerator pump was working last time but neglected to identify the gallery that takes that spurt of neat fuel to the venturi.  It was blocked, hence the feeling it was lean - because it was.

After blowing that through it still bogged before picking up when blipped and would even stop if I didn't back off the throttle to catch it and instead kept it wide open.  This time though it felt decidedly rich so I messed around with pilot jet settings and accelerator pump adjustment for a bit but nothing made a great deal of difference so I whipped it off again (little bikes are so easy, less than 5 minutes to have it off and in bits).  I checked the spec in the Haynes and this model (with Kehin carb) should have a 90 or 95 main jet.  This one has a 110 so I'm going to order the smaller one and see what happens.  It might be that somewhere along the line it's been into a shop to cure the bogging caused by the blocked gallery and they've upped the main in the hope that it might cure it, but only guessing.
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April 14, 2016, 08:02:11 PMReply #19 on

Offline Sin_Tiger

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That certainly fits with the evidence you're seeing  :thumbsup
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May 19, 2016, 03:40:15 PMReply #20 on

Offline threepot

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Bob,I'm wondering if you sorted that issue? My daughters xr125 has similar. She bought it 2yrs ago,but not used it. Now she wants to sell,and pay for repairs to her car(thats anotherstory..bloody VW's!!!) Anyway,I've checked the carb,and its clean. But it dies when you open the throttle,until it warms up,then its fine! Float height can't be adjusted,and I'm not sure what size main jet it has? Should I start there? Don't think this carb has accelerator pump as mentioned?
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May 19, 2016, 03:57:36 PMReply #21 on

Offline Bixxer Bob (OP)

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No, I've not completely sorted it yet although it's a lot better.  I can only get at it occasionally as she's using it now.

So far I've blown all the orifices through twice with high pressure air fter soaking in carb cleaner.  the tiny hole that bleeds air into the venturi at the intake end was blocked and clearing it made most of the difference.

I've also spent ages on the idle screw, the tickover screw and the accelerator pump so it now picks up cleanly unless you really blip it hard.

At the moment it's got a 110 main jet but should have a 95 or 100 so that's next. Although I think that will simply release a bit more top end power (I use the word laughingly) I don't think it's anything to do with the pick up.  MY next plan is to increase the fuel injected by the accelerator pump and how early it does it because I think it dies beacause it's not getting enough fuel. 
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June 15, 2016, 05:58:28 PMReply #22 on

Offline Bixxer Bob (OP)

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FINALLY!!!!!

It runs well.  Manual says 95 main, it had a 110 so dropped it to 100.  Pulled really well but plug was white so put the 110 back in, faffed around with the needle, it likes second down from top best.  Mixture screw 1 3/4 turns works well, but the bogging if the throttle was blipped still remained.

Although everything looked ok, and after coming across the idea on a forum, I changed the very small O ring round the air bleed.  It's not the idle jet, it's a tiny airway at the back of the float bowl.  Anyway, it worked.  And it now runs like a sewing machine.  You can get it to bog very slightly if you give it  very sharp blip so Imight have a bit more play with the mixture screw.  But the O ring leaking seems to have been the issue.
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