replacing carb vacuum piston diaphragm Keihin ?

[lostforawhile]

Ok I've discovered that vacuum piston assemblies for the genuine Keihin carbs, apparently don't exist, the standard assembly with the needle retained by a screw, the piston diameter is too big for a Keihin. The Keihin has an adjustable needle, retained by a plastic cap,which is retained by the spring. The vacuum ports in the Keihin are  also different, the Keihin has one, the standard Chinese knockoff carb, has two, This video shows how to replace the diaphragm on a Keihin twin power carb,    but the process should work the same, You can remove the diaphragm from the  18mm cvk the same way, the retainer groove pops out. The construction looks close, so it should go back in the same, or with the dental floss trick .  www.youtube.com/watch?v=H0GOExal_VA

[ThaiGyro]

I am not a CV carb fan...on my big bikes I replace them. That said, Keihin has multiple factories here in Thailand. Their scooter, small bore carbs factory is only 25 minutes from our home.

Maybe they still have replacement parts...lots of new and old scooters here. Get me some model numbers/part numbers and I can check fairly easily.

[lostforawhile]

I'll try and get a part number its just the standard keihin 18mm cvk carb,the same one used on all kinds of scooters,it's a pretty new carb

[tocoo]

Feb 7, 2018 20:58:46 GMT -5 ThaiGyro said:

I am not a CV carb fan...on my big bikes I replace them. That said, Keihin has multiple factories here in Thailand. Their scooter, small bore carbs factory is only 25 minutes from our home.

Maybe they still have replacement parts...lots of new and old scooters here. Get me some model numbers/part numbers and I can check fairly easily.

Do you know a website who ships genuine Keihin carbs to europe ?

[ThaiGyro]

I will ask...I know they do R&D in Germany for over 10 years. Must be parts too, but that never means that you can locally purchase the same stuff as SE Asia.

We do not really have the same EPA/EEA laws as the States or Europe. We can do anything to carbs and FI systems here.

For example: We have a 2014 Ford Focus. It does not exist on paper. It is a basic Focus S, but has traction control and ABS, like a North American ST...but no turbo. Plus, it dyno's near 170 hp on 95 octane @ 5% gasohol. The US model has maybe 155. Why? We can alter fuel systems...like VW.

[lostforawhile]

Ok it looks like swapping the diaphram from the wrong part to the keihin piston assembly will work, I'll know more later,I made a tool from a small zip tie,and smoothed the end,to push the retaining lip into the groove on the piston,pictures later

[lostforawhile]

I also found a piece of sharp plastic on the retainer under the diaphram,I smoothed it with fine scotchbrite, it may have caused the damage

[lostforawhile]

Ok the diaphragm was able to be switched, this means that for those with an 18mm keihin, which has no replacement for the diaphragm, piston assembly, the diaphragm for the more common assemblies can be removed,  and  installed. PFS also sells just the diaphragm. On the white plastic retainer, there is also a molding seam, mine had a very sharp edge,and a piece of plastic sticking out. I suspect this is what put the hole in mine. 





 

 







the diaphragm

once you remove the old diaphragm, you place the new one right side up, and stretch is onto the retainers,so the lip is between the two retainers, then you take a blunt very thin object, and start to push  it between the retainers, so the lip locks in the groove, I rounded off a 1/8 zip tie, and used it, or you can start to wrap dental floss around the groove, which forced the lip between the two. 

 

The two pistons, the larger diameter one is the one that fits most cheap no name carbs, the needle is retained by a screw and retainer, it also has two vacuum ports , the Keihin has one vacuum port, and the needle is retained by a plastic cap on top of it, that the spring fits on. I have called every scooter parts place I can find and the Keihin piston is not available, this was an expensive genuine carb, and a basic part doesn't exist