250 Grandvista top speed issue

[windwheeler]

I thought I had a picture of my ex G/V of the engine under the seat, but I don't.  Please search the internet, I am sure there is a pic on the engine.  Also a PDF service Manual is available on the net, just search for it.

Picture #1 seems to be the recycle/emissions hose that needs to be hooked up somewhere; and where it isn't it may draw false air.

Picture #2 is incorrect to be plugged up; it IS open.


I am sorry to say, if you "sprayed the carb outside (?) with Seafoam" what good should that be???  No, you need to take it apart and clean all out, especially the jets.  If that is over your head,  then be honest to yourself and let a scooter shop do that, and at the same time let them hook up the vacuum hoses correctly.

[windwheeler]

Any late news Mr. tonyode?

[mrbios]

Pic of house out of carb.

BTW, I put screws in each end of hose so to be able to identify.

Take that hose off.  The place where it is attached is not supposed to have anything (I checked my GV250 as a reference).

Now, remove the top cover on the carb - two screws.  Verify that the Main jet needle is installed correctly: Vacuum Diaphram / piston, Main Jet needle, Needle holder prongs (4) down, spring, lid, two holding screws for metal cover.  More than likely the diaphragm needs grease in the groove to help it seal and get rid of the vacuum leak.  This is what is preventing the main jet from operating because the slide is not going up all the way.  The bad news is that the OEM part is $40!

I tried and don't recommend the aftermarket Keihin CVK30 (30mm) carb which costs around $80. 

http://www.motorcycle-superstore.com/14/71/988/22862/ITEM/Permatex-High-Tack-Gasket-Sealant.aspx?SiteID=Google_PLA988&WT.mc_ID=10012&esvt=0-GOUSC&esvadt=9-0-3886819-1&esvaid=30548&kw=%7Bkeyword%7D&gclid=COvB89HdzLkCFe1_QgodzlEAjw

http://www.motopartsoutlet.com/keihin-cvk-carburetor-keihin-30mm-carburetor-p-2703.html?utm_campaign=export_feed&utm_medium=cse&utm_source=googlebase&gclid=CL6K3PXdzLkCFa9fQgodBm0AMA

[windwheeler]

It would be good Mr. Tonyode if you can give us an update of the situation right now what you discovered and accomplished so far.

[tanuki]

Fast Forward to August 2014
These are exactly the same vacuum lines/hoses I am trying to make sense of on my 2004 GV.

Symptom: wont rev past 5/6 k

Air filter is fine
Removed and cleaned the carb float bowl and jets
The jets are not clogged in any way, ok so they are not ultra shiny new as some would suggest they need to be but they are unrestricted.

The question remains: where does the hose with the U shaped bend go?
I understand its some sort of exhaust recirculation bit, my question is where does it physically attach?
To the carb intake manifold? Ive looked all over in there with a bright light, still don't see anything.
It does seem to be drawing air when the engine is running.

[mrbios]

Fast Forward to August 2014
These are exactly the same vacuum lines/hoses I am trying to make sense of on my 2004 GV.

Symptom: wont rev past 5/6 k

The question remains: where does the hose with the U shaped bend go?

The hose should point to the ground and does not go anywhere.  The purpose is to allow gas to come out if the scooter overturns.  I followed it and it comes out in the "ceiling" of the carb float chamber.  Most motorcycle carbs have something similar. 

The problem is most likely the vacuum diaphragm is leaking which prevents the plastic slide from going up all the way.  Watch my videos and and you see a simple test that works on ALL CV type carbs:

Part II deals specifically with the diaphragm test:

Kymco Grandvista / Grand Dink:


Carburetor Cleaning & Theory three part series:

[tanuki]

Mr Bios, First things first...THANKS for your timely input, I am determined to get this scooter running by tomorrow for a couple of days of vacation..riding rather than wrenching.

Spent some more time in the garage today trying to figure it out.
The slide seems to function fine, lift it up let it drop and it drops slowly while sucking air.
I did take the top off the carb and gently lube the diaghram.

As an experiment I grabbed the air intake tube and squeezed it to restrict air while it was running and sure enough the revs came up under throttle. Let go of the air intake and the revs fall and it wont rev past 5 thou.
I need to go to work now but Im not going to stop thinking about this. I will check back here after work, 3 AM or so, I really want to be riding this scooter soon.
Do you know where I can find a "map" of the carb hoses..fuel intake, float bowl overflow and such, any CLEAR pics that show where the various carb hoses connect would be great. I looked at the online Kymco manual and didn't see anything very useful just a shot from above that has no detailed routing.

Thanks again
Phil
I want to make sure they are all in the right place.

[mrbios]

Mr Bios, First things first...THANKS for your timely input, ...

Do you know where I can find a "map" of the carb hoses..fuel intake, float bowl overflow and such, any CLEAR pics that show where the various carb hoses connect would be great.

Phil,
I have been in your shoes.  When something is not right with my scoot it plagues my mind.  I have all the passages mapped on the carb click the link below containing all my pictures of the oem Keihin CVK30 OEM carburetor.  Inside you find every port / hole etc mapped as you you requested.  Also, contains links to after market jets and extensive technical notes as I worked through my carb problems.

To the 'elders' on this forum or anyone that enjoys helping others - please feel free to download and share the info freely to wherever it might be needed.

Warning file size is 250 Megabytes!:
http://www.wecandobetter.com/dnload/Scooters/Kymco/Carburetor_Clean_Keihin_CVK30(web).zip

[BettinANDlosing]

That U house it's actually the vent tube for the float bowl and it NEEDS to be open!!!!!! The vent needs to be there for gas to flow in and out of the float chamber. If your squeeze the intake and the revs go up you need a larger main jet. You should be able to rev the piss out of it on the center stand not 5k that's too low.

[windwheeler]

Correct about the vent, if you don't get enough gas in there you starve the carburetor with fuel, such it would act "like a rev limiter".  NOT GOOD! 

Also the OEM specified float bowl level is very important. 

I disagree about the blank statement "put in a bigger jet", if it is a fuel supply issue it would bring nothing.

Let's assume it is an original main jet that is installed, which you should verify if you still have the problem after sorting the fuel supply situation.  Make also sure your vacuum fuel pump works properly and no filter restricts the fuel supply to the carburetor..