Another Keihin 31mm CR Carbs Question

[tubarney]

Does anyone know if these carbs are round slide or flat slide? Had a look in the threads about them but couldn't find it anywhere.

[Racer x]

Round

[tubarney]

Thanks Racerx, the keihin website is rubbish. What carbs do you have on your bike?

My tuner told me to get flat slides to maximise the gains from the cylinder head porting, he recommended mikuni so I'm going to see if one of their models fit tomorrow. Will let you know how I go.

[Racer x]

Mikuni makes the flat slide carb. I have 31mm CR Specials by Sudco. I absolutely love them. Jeff at Carb Parts Warehouse sells them at a good price. He can help you will tuning and all the parts. He just helped me convert my carbs to E85.

[tubarney]

I will be getting myself a pair of those if the mikuni's won't fit.

You might be interested in this. I spoked to my builder (http://www.ramsheadservice.com.au/) today and he said theres no chance of getting custom valve springs in Australia, unless I want 400! He did say that for him figuring out spring pressure is easy. He is going to do it for me and tell me if there is an engine I can get some out of. He seemed confident and says he even puts car valve springs in these things. If you want his help once you've figured out your cam and valve specs I will be happy to talk to him on your behalf.

He also told me everyone in Australia uses web cam camshaft so I'm going to give them a shot also. Have you looked into valvetrain modifications in the past?

[Racer x]

Thanks..my builder has one of those computer operated milling machines to do head porting.
I am having cams made at megacycle. I think you can use 600 springs. I will find out what year.

[tubarney]

Do these guys work with new cams or the stock ones? Are you thinking about going with a longer duration cam?

[Racer x]

Megacycle only works from original cams. No blanks.

My builder is going to increase valve size, lift and duration.

[tubarney]

I'm planning on doing the same. Please post what your builder chooses to go with when you get around to it. I know your experimenting with e85 at the moment. I'll post what I end up doing as well.

[HKr1]

Originally Posted by Racer x

Round

And Smooth Bore.

[Racer x]

Yes, round slide and smooth bore. you can change the bore size also. And they are not vacuum operated slides. Fully mechanical.

[tubarney]

Do they have a pump accelerator? I was told by a supplier that CR specials do not.

Mikuni 33mm are a no go. There isn't enough room in the frame to fit them. Not to mention the price with custom cables is more than double the Keihin's. The 33's are designed to run on single engines so the way they have mounted the accelerator creates a lot more width, also running two pump accelerators with 33 mm carbs is a bit of overkill on this engine (so I was told).

[tubarney]

Racerx, find out what year model the 600 valve springs come from. My tuner said he has heaps and will give them to me for nothing. Even the new 636 springs. Will post you some if want to pay postage, which is something like 10 bucks to you guys in the states.

[Racer x]

You will like the CRs. But they don't have a pump. You don't need one. The throttle response is great. Unlike CV carbs you just have to be careful opening the throttle. Not a big deal.

The throttle cables are tough . You can use the stock 250 ninja cables . But they are tight around the hose coming from the head.