Topic: carb choices

[rooky]

hi
I've been a member of this forum for ages and all I have done is soak up other peoples knowledge which has been very educational.
At last I have a real question
If you were going to put together a non standard 750 - different air filter-k&n replacement for the honda demand non standard exhaust, would you rather use K7 carbs with the accelerator pump but press in jets or the earlier carbs with screw in jets.
Also does anyone know just how much wider the driveline is on the K7 than on earlier models.
what I'm trying to do is build something along the lines of the "gentleman's express" without going over the top.
I'm 50+ stiff and fat and I really don't see myself looking good on a balls out cafe racer.
As far as the handling is concerned that's all taken care of as the engine is going in a rickman cr frame that has sat in my garage for an embarrassingly long time

[gnarlycharlie4u]

I personally prefer the later carbs, the press in jets aren't really a problem for me despite being a pain in the butt.
They're a LOT more complicated and involved when rebuilding them though. The early ones are cake compared to the PD's (later model carbs)

However, it's going to be impossible for you to find the later model carb insulator boots if you don't have them already.

I'm not sure what you mean by how much the K7's "driveline" is compared to earlier models.
The K0-K6 used a 530 chain and sprocket combo while the later K and F bikes used a 630. This spaced the front countershaft sprocket out more. Maybe that's what you're referring to?

The K0-K6, K7, and F2 all have different swingarms. The K7-8 have a longer and wider swingarm than the K0-K6. The 77-78 F has an even LONGER swingarm than it's K counterpart iirc.
Here's some differences between the early, later, and DOHC swingarms.
I suggest you do some research on them before swapping as adding width or length will change the way your bike handles and tracks.

[rooky]

As far as the carbs are cocerned, is there noticably better performance from the later ones.
I just checked cms and they list boots 1 and 3 which i guess would also fit 2 and 4.

I was under the impression that the sprocket was further away from the centreline of the engine on the later models and obviously it is for the reason you stated, i just wondered how much.

I think we're ok as far as swinging arms are concerned but the link was really useful since one of those three is going to be my choice as i have box section versions of the shortest and longest.

What i want to do is run an f1 rear hub so i can have a spoked wheel with a disc brake and a cush drive
but the standard f1 swinging arm won't fit in the frame.

As we are building this thing from scratch we need to start from something which is fixed and i think the best one to use is the drive chain as we can play about with spacers, possibly machining the hub or sprocket carrier and possibly offsetting the rim to make everything else line up

I also have another question, is it a good idea to increase rim width and if so what size is recommended

[gnarlycharlie4u]

As far as the carbs are cocerned, is there noticably better performance from the later ones.
I just checked cms and they list boots 1 and 3 which i guess would also fit 2 and 4

Like I said, unlike the early carbs that only use 2 boots (2 inner and 2 outer), there are 4 different boots for the later PD carbs.
I THINK the later boots might have a slight angle that may prevent you from just flipping them over and having them fit perfectly.

[rooky]

well that would make quite a good argument for using the earlier carbs thanks for the info

[mrrch]

Flipping the boots 1 & 3 will work, not perfect but they will work just fine.

[gnarlycharlie4u]

As far as the carbs are cocerned, is there noticably better performance from the later ones.
I just checked cms and they list boots 1 and 3 which i guess would also fit 2 and 4.

I was under the impression that the sprocket was further away from the centreline of the engine on the later models and obviously it is for the reason you stated, i just wondered how much.

I think we're ok as far as swinging arms are concerned but the link was really useful since one of those three is going to be my choice as i have box section versions of the shortest and longest.

What i want to do is run an f1 rear hub so i can have a spoked wheel with a disc brake and a cush drive
but the standard f1 swinging arm won't fit in the frame.

As we are building this thing from scratch we need to start from something which is fixed and i think the best one to use is the drive chain as we can play about with spacers, possibly machining the hub or sprocket carrier and possibly offsetting the rim to make everything else line up

I also have another question, is it a good idea to increase rim width and if so what size is recommended

What year CB do you have?

The early bikes had a 18x2.15" rear rim and the F2 and K7-8 had a 17x2.5" rim.
The extra length and width of the later model swingarm allows you to run the wider rim/tires but note that the rim diameter was also reduced in order to do so.
I'm not entirely sure if you can fit a 2.5" rim and appropriately sized tire on the stock early swingarm.

[I Zombie]

You can use boot's 1&3 for 2&4. lil bit more fun to get em all lined up but doable.