Keihin Carb mystery
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Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Sun Nov 22, 2020 4:01 am quote
I've been off the road now for about 6 weeks. Bike will only run with a little throttle and dies with any more. Have removed carb and cleaned but found nothing to concern me. Have read 18 pages of advice here and still I'm beat! Replaced fuel tap, filter, fuel pump, plug and coil. All fuel/vac pipes are sound. My question is: should there be a "collar" 16017 between the needle jet(emulsion tube?) and the needle? I may have washed something out when I stripped it first time. Have had carb off 7 times now. Saw this "collar" on an exploded view of a CVK34 on a kawasaki forum. I've been crawling round the garage floor with a torch and I may not have to. Anyone any experience of these carbs or could recommend anyone who has?
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gts 300
Joined: 20 Nov 2020
Posts: 4
Location: west michigan
Sun Nov 22, 2020 7:28 am quote
Absolutely. I bought a 16 year old Kymco 250 with 158 miles - didn't run well. Several cleanings were of no use. I couldn't figure out why it was running so rich and poorly.

A Youtube video on cleaning a Harley CVK carb explained how when the emulsion tube is removed, the small brass "needle jet" (which is held into the carg throat by the emulsion tube) often falls out un-noticed. I removed my carb again, looked down the throat, and didn't see the small brass protrusion where the needle enters the lower carb body. Bingo! I waited for one to come from Kymco parts - intstalled it and now the scoot runs perfectly.

At the time, I found very little info on this on the web, so it was a fluke that I caught it while watching the video. Over time, I have found the Kehin CVK carb has been used in a number of bikes, and the internal parts are apparently the same.

You should be able to source the needle jet (I don't believe there are different sizes or numbers) from Vespa. I got mine from a Buddy (PGO) 125, they are in Harley CVK, Kymco 250, Burgmans, and others.

It is so tiny, I doubt if you would ever find it on the floor. Good Luck!
Addicted
GTS 250ie Super, Italjet Velocifero, Scarabeo 150, S50, ET4, ET2
Joined: 22 Nov 2016
Posts: 555
Location: Winston-Salem, NC
Sun Nov 22, 2020 11:04 am quote
Pictures are always helpful.
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Sun Nov 22, 2020 1:07 pm quote
Thanks Dan. I see you've just joined the group. I'm glad you did because you have really helped me. Ebay here I come.
I'm not sure that we can post photos on here but I'm sure nobody wants to see my garage floor anyway:)
Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: 21 Oct 2005
Posts: 8100
Location: The state of insanity, SoCal
Sun Nov 22, 2020 2:18 pm quote
Pinkscooter wrote:
Pictures are always helpful.
Hold plz...

-g
Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: 21 Oct 2005
Posts: 8100
Location: The state of insanity, SoCal
Sun Nov 22, 2020 6:31 pm quote
here's the stack
top to bottom: needle, main, diffuser, needle guide

needle guide (or needle jet?) goes into carb body, diffuser screws into carb body- specifically the the guide goes in with the flat side into the body and the convex side toward the diffuser and then main screws into the diffuser.

diffuser and guide

here's a detailed shot of the ends of each that go together- convex and concave. to note, the needle guide will go in either way. just, like, fyi

here's the other side of the guide

this is the side that goes into the carb body, you'll note that it does not fit cleanly into the diffuser end.

hth

-g
Member
Vespa LX50
Joined: 30 Oct 2020
Posts: 15
Location: Honolulu
Sun Nov 22, 2020 7:37 pm quote
I am not sure this helps for the 125 carb that the OP but the latest awesome pics posted reminded me that I did have a diagram that is like the carb on my LX50. Maybe it can help?

Keihin-CVK-Carb-Settings.jpg

Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Mon Nov 23, 2020 4:59 am quote
Kevin T wrote:
I am not sure this helps for the 125 carb that the OP but the latest awesome pics posted reminded me that I did have a diagram that is like the carb on my LX50. Maybe it can help?
That's the pic that started the panic Kevin. I didn't remember seeing the "collar". Read about being easily lost and decided that's why my bike won't run. Turns out mine was brass and was still stuck in the carb body. Do you have "Numpties" over there. Well if you do, I'm one!!!
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Mon Nov 23, 2020 5:03 am quote
, the small brass "needle jet" (which is held into the carg throat by the emulsion tube) often falls out un-noticed.

I was looking for something silver in colour until I read this. I managed to find mine after all. It was in the carb. Sorry for the false alarm. Don't think I'll make that mistake again. Oh no hold on............I'm at that age!
Member
Vespa LX50
Joined: 30 Oct 2020
Posts: 15
Location: Honolulu
Mon Nov 23, 2020 9:11 am quote
Rustybike wrote:
Kevin T wrote:
I am not sure this helps for the 125 carb that the OP but the latest awesome pics posted reminded me that I did have a diagram that is like the carb on my LX50. Maybe it can help?
That's the pic that started the panic Kevin. I didn't remember seeing the "collar". Read about being easily lost and decided that's why my bike won't run. Turns out mine was brass and was still stuck in the carb body. Do you have "Numpties" over there. Well if you do, I'm one!!!
???

https://www.youtube.com/watch?v=VLop79w2LuQ
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Mon Nov 23, 2020 10:29 am quote
Do you have "Numpties" over there. Well if you do, I'm one!!![/quote]

???

https://www.youtube.com/watch?v=VLop79w2LuQ[/quote]

Yip, that it the work of a Numpty. Someone who is prone to doing foolish things. Same thing as "eejit" here in Ireland. Here endith the lesson:)
Enthusiast
BV250, BV500
Joined: 10 Mar 2018
Posts: 87
Location: SFBay
Mon Nov 23, 2020 10:29 am quote
On my 2007 BV250, has a carburetor, it wouldn't idle and only ran if I kept the throttle open enough that at stop signs I had to hold the brakes to keep from going. After lots of exploring I found that a brass vacuum tube that was supposed to be secured into the rubber intake manifold was loose and leaked air around the sides. I couldn't find an adhesive that would work so I replaced the intake manifold.
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Mon Nov 23, 2020 10:33 am quote
After lots of exploring I found that a brass vacuum tube that was supposed to be secured into the rubber intake manifold was loose and leaked air around the sides.

Well spotted."Robot" suggests spraying carb cleaner around this area while listening to tickover speed. I tried this but it made no difference.
Enthusiast
BV250, BV500
Joined: 10 Mar 2018
Posts: 87
Location: SFBay
Mon Nov 23, 2020 6:08 pm quote
If your scooter has this fitting I'd just lightly pull on it to see if it moves. If it does, deal with it. If not, move on. The other thing, which was already mentioned I think, is a float level set wrong. Are you using the original air cleaner? Is the filter clean?
Sergeant at Arms
Weird 80's Vespas & Cool Vintage Lambrettas
Joined: 21 Oct 2005
Posts: 8100
Location: The state of insanity, SoCal
Mon Nov 23, 2020 6:54 pm quote
When you pulled the carb to “wash” it did you pull the idle jet and soak it as well? Did you pull the air/fuel mix screw and clean that passage as well?

Basically, did you just hose it all down and call it done or did you fully disassemble and soak the parts, clean them and then verify with compressed air and/or cleaner that all is open for business?

Because if not, you now know you need to.

-g
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Tue Nov 24, 2020 3:08 am quote
greasy125 wrote:
When you pulled the carb to “wash” it did you pull the idle jet and soak it as well? Did you pull the air/fuel mix screw and clean that passage as well?

Basically, did you just hose it all down and call it done or did you fully disassemble and soak the parts, clean them and then verify with compressed air and/or cleaner that all is open for business?

Because if not, you now know you need to.

-g
Well g to be honest, I did pull out the idle jet and mixture screw and gave them a quick squirt. Pilot fuel and airways got carb cleaner squirted through to ensure no restriction however I may have replaced the mixture screw without spending much time on it as I believe it effects low speed more. (I did lose the spring for a while,typical me). I'll do as you say because carb is on bench for 8th time.
Hard to know what is going on with diaphragm but sometimes when I operate the slide, it sounds and feels like the rubber is bunching up (sorry, can't really describe it). The slide had heavy black deposits and the rubber was coated in black oily substance. This may have gotten in through the vent to atmosphere as the filter was pure black too. I'll fire up the compressor and give everything a blow out. I believe I can test the slide operation with low pressure too.
Member
GT125
Joined: 09 Nov 2020
Posts: 13
Location: Ireland
Tue Nov 24, 2020 5:12 am quote
Well I am shocked. I did have black crud on tip of mixture screw. Wonder how that got there? Better out than in I suppose. Washed out again with carb cleaner and airline too. Don't try this at home kids unless you're wearing safety glasses. Carb cleaner really stings your eyes:(
Member
Vespa LX50
Joined: 30 Oct 2020
Posts: 15
Location: Honolulu
Tue Nov 24, 2020 8:01 am quote
Sounds like you are on the right path but I wanted to mention that I had similar symptoms on mine that were related to the smallest particle clogging the pilot jet. I don't have the best eyes but it was small, like a dust particle small! So check it again before buttoning it back up. I used a copper wire to ream it out and then compressed air from a can to get there.
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