Carburetor tuning cb450

[Leetillman351]

Hey all! I gotta question about my mikuni carbs. I got a 72' cb450 k5 a few weeks ago and I'm in the process of getting her running, and have done a lot to get to this point. It has mikuni carbs and a 2 into 1 exhaust. What is a general setup for the fuel to air mixture that I should start off with? How many turns out for the fuel screw and how many turns out for the air screw? Not exactly, just a general setup to get the tuning process started. Sorry for the lack of detail, and lack of knowledge: this is my first build.

Any help is appreciated, and Thanks in advance!

 

[cxman]

need to know which (size) mikunis you have air screws should start at 1.5 turns

 

[Leetillman351]

Unfortunately I cannot determine the size. I bought the bike used and have no knowledge. The best I can do is a picture

 

[cxman]

first those pod filters suck and will restrict the air flow to your carbs toss them they have a big rubber lip on the inside

that will make the carbs run rich

remove one of the carbs and measure tghe inside bore of the throat of the carb that will tell us the size

next you have water pipe tubing and valves on your bike carrying fuel

not to be a snot but that can kill you take it off the bike and get proper fuel line

 

[Leetillman351]

The valves are very temporary and they are there so I can take the tank off and on with ease ease for now until I get all the wiring completed. There was one black hose connecting the two drain holes on the bottom of the tank. And the lines connecting to the carbs are temporary, just figuring out the proper length and routing. What filters do you recommend getting to replace the current ones?

 

[xb33bsa]

the size should be stamped in the side flat spot casting on the carb body by the clamp where it is on the rubber flange to the engine thingy

 

[xb33bsa]

cxman is the man I think he may agree to these babies, wotsay murray ?

 

[Leetillman351]

The part of the carb that attaches to the engine is 35mm, hopefully that helps!

 

[cxman]

well if its 35mm then you have 28 mm mikunis

those are a little small for that engine i run 32s on mine

i might even consider selling / swapping those for at least 30s with someone that bought some to big

28 will choke you out at higher rpm they will work good on a cb350 cb360 kz 400 tx 400 ect

 

[Leetillman351]

It was a 35mm inside diameter

 

[Leetillman351]

Hopefully this will help!

Im new to this if you can't tell, so please bare with me! 8)

 

[cxman]

you need a caliper but they look like 32s

yes if you look at the stamped number they are 32s

 

[cxman]

my 1973 cb450 is stock except for ignition and harley mufflers

i have iridium plugs so this may be a bit rich for you but i run 32s on mine with this setup

PJ: 37.5
NJ: 6DP17
JN: 159-Q6
AJ: 2.0
Slide: 3.0
MJ: 150
Air screw: 2.5 turns out

you will still have to tweak the needle i run mine in the second from the top

 

[Leetillman351]

Awesome. I'm shooting to have it started and running tomorrow so that helps a lot!

 

[cxman]

you will need to set your timing and valves to verify them before trying t tune your carbs

also start with fresh plugs

 

[Leetillman351]

I just needed a general idea of what the air and fuel screws should be at to get it started. Then I'm doing my timing

 

[cxman]

do you know what jets throttle slide or anything is in the carbs? that is what decides positions and jet settings

 

[Leetillman351]

I tore it apart and cleaned it, but am not sure the jet sizes. I need to buy a full rebuild kit and start from scratch, but until then I'm just trying to get it running and idling. Further adjustments after that.

 

[Leetillman351]

Reviving the thread here: I got it idling and running great, however my rearsets won't mount properly with that huge exhaust in the way. So I'm chopping it off and having a short GP style exhaust that is straight pipes with an 8 inch baffle in it. Keep in mind I'm running mikuni carbs. Top picture is the bike currently, bottom picture is the type of exhaust I'm going to run.

What size main and pilot should I start with ordering? I'm thinking about just ordering 2 jets of 5 or 6 different sizes but that would get pricey. I know it is going to free up air flow a lot, so bigger jets are a must. The only problem is that I don't know the sizes I'm currently running, they came on the bike already. Any help is greatly appreciated!!

Thanks, lee ;D

 

[teazer]

You need to list all the jets inside those carbs and the needle and work from there. Forget about rebuild kits. They look like VM Mikunis with very small pods. If those are Emgo pods, they will restrict performance.