Carburetor tuning cb450

[Leetillman351]

Ya they are VM32's, and I've heard those restrict a lot of performance so I'll order some different one today.

If I take out the jets will it say what size it is on the jet itself?? That's the only way I will be able to identify them.

 

[teazer]

Yes. All mikuni jets are stamped with the square inside a square (Mikuni trademark) and the size. Needle jets also have the series e.g. 159 P-0, Main jets will be Large Hex and will be something like 190. Pilot jets will be something like 32.5 and teh needle will read something like 6DP5 and will have the E clip in the center slot of the 5 grooves.

Fortunately the carbs come off easily and take all of about 5 minutes to strip. FYI, to get the needle jet out, remove the main jet and washer and then screw the main jet back in without teh washer and tap it upwards out of the top of the carb (take the slide out first)

 

[Leetillman351]

Excellent, I've torn them apart a few times for cleaning and have never paid anted attention to the labeling. I'll tear them apart today and try to post this afternoon. Thanks teazer!

 

[cxman]

its not just the jet sizes

you need to look at the throttle slide it has a number that is needed

when you undo the main jet lift the jet needle (brass tube)out and get the number off it

then take a pic of the inside of your pod filter and post that as well

then

then take the needle out of the throttle slide and see what groove the clip is in and what size the needle is

remove the pilot jet and tell us that sizes as well

then in the 6 oclock position from the air filter side of the carb there is a hole

look down it and if there is a small brass air correct jet in there remove it and post the size for it as well

32s are a great size for the 450

 

[Leetillman351]

Had an audience

 

[cxman]

ok so now how is it running??

do you have a caliper can you measure the bore they look like 30mm not 32 but it could be the angle my crappy old eyes

from the jetting and slide it would seem to me it would be rich at idle pull fairly well but with a little cackling till about

half throttle then fall off a bit or even bog till you get to 7/8/wide open

 

[Leetillman351]

You're spot on. That's exactly how it's running. Also the left cylinder is a bit weak and seems to run much richer than the right cylinder. And there is a slight mis fire while at low RPMs on the left cylinder. Adjusted the valves and points and both are within spec with new plugs, so it may go into a shop here soon.

When I decide to chop my exhaust and run a baffle, the back pressure will be reduced so I'll need I rejet it.

Judging by the jets I have in there now, what would you recommend would be a good starting point to begin rejetting?

 

[Leetillman351]

And yes they are 32's

 

[cxman]

one more bit of info that will help what needle do you have and what groove was the clip in the needle in

 

[surffly]

14.7:1 is the only real answer to your question.
How to get there is reliant on a million different factors that only you can acount for.

You need to buy a few sets of jets in different sizes and then take them ride/feel/dyno the bike.
There is zero "this is what you need" that will come from the Internet.

 

[cxman]

well since the experts have jumped in on this post with there words of wisdom and rays of sunshine

if i can be of any more help just pm me with the needle numbers

 

[Leetillman351]

If I'm am going to free up the air flow immensely, what combination would be a decent starting point as far as jet sizes go? Like I said fellas I'm new to this, ANY guidance would be greatly appreciated as I am going to start fabbing the exhaust tomorrow, I would like to order a few different sizes of jets.

Thanks again guys! ;D

 

[Leetillman351]

I'll get that needle groove number and setting as soon as I get it back home

 

[cxman]

i sent you a pm

 

[Leetillman351]

Plan on chopping it right where the muffler starts

 

[teazer]

What diameter are the headers and the secondary pipe? It's probably an optical illusion, but the secondary (after the collector) doesn't look any larger than the headers.

 

[Leetillman351]

From what I've observed, it's 1 1/2 the whole exhaust. Which I believe is spec

 

[Leetillman351]

6DH7

 

[teazer]

I'll let CXMan chime in on your carbs. He sounds like he has a good idea as to what is needed.

The pipes are interesting though. Rule of thumb for a 2 into 1 is that the area of the secondary pipe (after the collector) should be 1.5 - 1.75 times the area of the primary (header). So a 1.5" header should work best with a tailpipe of 1 5/8 to 2" diameter. Of course we need to know the actual bore of those pipes and not the OD to do that calculation properly, but a twin trying to exhaust through a single 1.5" tailpipe is likely to be restricted at higher revs/load. Go with a short mid section and shorter muffler or maybe a DANMOTO motoGP style if they have one in that size.

Without a muffler the thing will be obnoxiously loud and won't run well at all.

Megs/Coneeng list a couple of alternatives 1.5 to 1.875, 1.5 to 1.75 and 1.5 to 2.0 outlet. Go with their CL2-15175-MS in mild steel and add a 1.75" tail pipe which you can buy as bends or get your local muffler shop to bend up for you. Just be very careful if you weld zinc plated pipes - they send off toxic gas.

 

[Leetillman351]

I was planning on putting a 8inch baffle wrapped in fiberglass packing in the existing tubing (may need to lengthen it a little bit though)

Would that serve the same purpose as a standard muffler?

Thanks for all the info, you know much more than I do!