CB900C custom carb fitting help.

[HeadsTooBig]

Hello! I have a 1982 Honda CB900C I picked up that didn't have carbs. I bought a set of what I think are 1982-ish KZ1000 carbs, and they also fit into the stock engine side intake boots, and the airbox boots. My problem is that I'd like to run the stock airbox that came with the CB900, but the boots are destroyed, and any boots you do find cost an arm and a leg. Is it possible that the airbox boots off of a CB750 might fit, such as these 1982 CB750C boots, or is it possible that 1982 KZ1000 LTD/CSR/Police boots or what you have you, such as these 1982 KZ1000 airbox boots, could slot into the box? I've read about tuning issues with pods, and I also already have the airbox, and it's probably just better all the way around in terms of actual filtering and performance.

 

[Biebs]

Your going to have to custom build something or motorcycle junkyard or eBay.

Lots of options but you have the right idea.

Are the Kz carbs CV carbs?? If not you can use pods.

 

[HeadsTooBig]

Yes, they are CV carbs. This is my first really getting into a motorcycle with carbs that wasn't an old dirt bike. Why can't you run these CV carbs with pods? What do people usually do in this scenario, or what is the best course of action here?

 

[Biebs]

CV= constant velocity - air box helps keep a constant velocity.

Pods create a pulsing for each cylinder defeating the CV carb design.

 

[HeadsTooBig]

All right. So by the sound of it, it might not ever run "right" with pods, but yet fixing this airbox might also be challenging. I see on Vintage CB750 that they have CB900 boots that are about $80, but when I put the carbs up it looks like the spacing isn't quite right on the inner carbs. A KZ1000 airbox and boots is double that easily. Maybe some of the boots are offset, or can be squeezed into place with the OEM 900? I guess if I knew the KZ stuff might fit, the CB900 has a airbox I.D. of 57 mm on the bare housing, 54 mm air filter side on the carbs. Really just brainstorming on it.

 

[Biebs]

it will run with pods but it will be hard to get the idle below 1000rpm

 

[HeadsTooBig]

it will run with pods but it will be hard to get the idle below 1000rpm

I can deal with a weird idle rpm as long as its runs well and has good power honestly.

 

[brettp]

Keep in mind an idle too low affects the oil pump from pumping efficiently. I believe idle is set to 1100RPM + or - 100.

 

[HeadsTooBig]

That's excellent information to know. I also ended up ditching the KZ1000 carbs as everything just does not fit without extensive modification. By the grace of God found a really nice Keihin VB42 rack for 124 bucks on eBay, somehow. I believe they are for a cb750, but I read in a few places where they are the same size? I'll be finding out soon enough lol.

 

[brettp]

You might need different jets, though. Look up your stock jet size.

 

[HeadsTooBig]

Where is the bike going to suffer in terms of jetting potentially? Also, this bike hasn't ran in a very long time, and it sat outdoors in the sun for most of it. Is there a specific thing about this bike that has to be right or I'll suffer catastrophic damages kind of scenario?

 

[brettp]

Because the combustion chamber of a 900cc bike is bigger than a 750cc, the carbs from a 750 will have jets for a 750cc engine. So, given the amount of fuel a 750cc jetting provides, those jets might be too small for the amount of air in a larger engine. And therefore, your 900 could run lean, and too hot.
But I say that without knowing for sure. After you get the carbs on the bike, check your plugs after running it to see what they look like.

 

[HeadsTooBig]

Carbs have arrived! I will say the difference in quality from the Mikuni -- I think they are BS34's or something like that, and the Keihin's is pretty dramatic. Finally got the right carbs spacing wise, and these airbox boots would complete the airbox if I had the entire left side and cap lol. So I suppose it's buy another, ditch the chrome and just stick the plate on there, or make one? Now it's just getting the inch of rust out of the tank, unseizing the rear master cylinder, and rebuilding the front one.

 

[Exponent]

How are you gonna do the tank?

 

[HeadsTooBig]

My first plan is electrolytic rust removal using an old battery charger I picked up off eBay. If that doesn't work I'll soak it in muriatic acid, and seal it with the POR-15 stuff after whichever one does the job. I've never actually done it before so I really have no idea how well it's going to work.

 

[Exponent]

My first plan is electrolytic rust removal using an old battery charger I picked up off eBay. If that doesn't work I'll soak it in muriatic acid, and seal it with the POR-15 stuff after whichever one does the job. I've never actually done it before so I really have no idea how well it's going to work.

good ideas, anyone near you do those processes professionally? I just had mine done and they patched a hole as well

 

[HeadsTooBig]

I'm sure they do, and I seriously considered it, but I want to see how well this can work first. I literally found the bike underneath a pile of scrap steel, pipe, and wood with the gas tank open for who knows how long, and open inlets to the cylinders, but it was free lol. I can't believe the CDI boxes and the regulator still work. The wiring was so bad that the harness was actually shorting through every plug from the extreme corrosion.