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Carbs - Educate me.

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ThatDippyTwat
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PostPosted: 20:04 - 18 Jun 2017    Post subject: Carbs - Educate me. Reply with quote

I suspect I have a carb problem. Difficult to start when hot, won't pull properly, stutters when trying to get the rev's up. Bike stood for 2+ years.

Now, I can balance carbs easily enough with syringes, food dye and fish-tank air tube, but that's about it. I know nothing about them. They've always "just worked".

Any good links for me to educate myself? Starting point to attack it from? It's a Keihin CVK30 from what I can find out.
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temeluchus
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PostPosted: 20:20 - 18 Jun 2017    Post subject: Reply with quote

Usually it's a worn float needle(s) or some O-ring or other worn out. Fuel leaks past, runs rich so you get shite running when hot.

https://www.myural.com/keihin_32cvk_disassembly.htm

useful link, most CV carbs mikuni, keihin etc are pretty similar.
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pompousporcup...
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PostPosted: 21:55 - 18 Jun 2017    Post subject: Reply with quote

What do you need to know?
Bike stood for 2 years. If fuel was in the bowls it would have turned into a right old mess. When you ran the bike you ended up blocking the jets with the fuel mess

If it was running before being laid up, you will need to take them apart and clean the bejebus out of them.
It's prolly easier to just buy jets but things like needles and diaphrams can push costs right up, depending on the bike


On that note, what bike?
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bamt
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PostPosted: 22:45 - 18 Jun 2017    Post subject: Reply with quote

Also, how long have you run it for since putting it back on the road?
If you've only done a few miles, then bear in mind that sometimes (if you are lucky) just giving it a decent blast with some fresh fuel can be enough to get things running nicely.
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chris-red
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PostPosted: 11:10 - 19 Jun 2017    Post subject: Reply with quote

Clean it thoroughly, use an ultra-sonic cleaner if possible, if it has a lot of miles on it a carb rebuild kit is well worth it. I rebuilt the carb on my RXS and it made an huge difference. Rebuilt kits are typically ~£15 per carb.
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ThatDippyTwat
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PostPosted: 17:13 - 19 Jun 2017    Post subject: Reply with quote

Bike is only a 125 used for work, far too much vibration to ride any further. It's a Derbi, Mulhacen Cafe 125.

It's a bit better after a "spirited" (for a 125) ride to and from work, but it's still a git to start when hot, I don't trust it to idle at a junction, and it's still not pulling like it should.

I'll look for a float needle in the UK for now, as a rebuild kit only seems to be available from Taiwan. I'll order it if it's the right one, but I can't see it being here within the fortnight.
https://www.ebay.co.uk/itm/OKO-SERVICE-KIT-for-CVK-CARB-CARBURETTOR-30mm-GENUINE-PARTS-/261699230968?hash=item3cee7d5cf8:m:mkhE3F1CX6OcYKuAqrngBPA
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chris-red
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PostPosted: 17:18 - 19 Jun 2017    Post subject: Reply with quote

Is it due a valve check? tight clearances could cause these issues too.
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ThatDippyTwat
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PostPosted: 17:34 - 19 Jun 2017    Post subject: Reply with quote

It's only just past 10K(miles), It's not due until 15K. I can do it if needs be, but I'm fairly certain it's a carb issue.

If it's any help to anyone, it's the same engine in a Derbi GPR 125 4T, & Aprilia RS4 125.

Looks like I can get "copy" replacement carbs for about £40. Are these (generally) any good. These all mention a GY6 engine, and seem to be quite plentiful. The stock item is, I think, a genuine Keihin.
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ThatDippyTwat
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PostPosted: 19:09 - 25 Jun 2017    Post subject: Reply with quote

The float needle valve thingmy has arrived. However... while I'm in there

I'm debating binning the stock airbox and chucking a cone filter on it. I know I'll need to alter the jets, but how much? Stock values are 35 idle, 100 main.

I think these are the correct jets...
https://www.amazon.co.uk/Hrph-Carburetor-Main-Pilot-Keihin/dp/B071Y67719/ref=sr_1_cc_2?s=aps&ie=UTF8&qid=1498412799&sr=1-2-catcorr&keywords=CVK+main+jet

Any idea's?
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