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View Full Version : Chopping stock 4-4 pipes, and adding lollipop baffles?[cb900c]



FSUCREW
08-17-2016, 5:02 PM
Looking for some quick input before my bored broke ass does some chopping.

Running stock carbs, stock jetting, and stock airbox.

How bad would my bike run if I chopped the pipes right before the muffler, and added some lollipop baffles for a little backpressure?

Could I just adjust the idle screw to compensate for the A/F mixture being too lean?

Chrome on the pipes is wrecked btw, and I have two more sets in good condition.

What do?

FSUCREW
08-17-2016, 8:37 PM
Well I went ahead and gave em the ol' chopparoo.

Loud as hell, and I love it.
Probably not the best exhaust tone you could go for, but it sounds cool!

As for performance, it got up to 90 about as quick as it normally would.
Noticed a slight decrease in mid range torque, but still peppy as hell.

cheers.

Will update when my exhaust valves are toast.

farmall
08-18-2016, 11:47 AM
Will update when my exhaust valves are toast.

It ain't shit to slightly richen da carbs if required. You idle speed screw is a throttle stop and doesn't richen mixture.

Get set of #60 thru #80 drill bits for almost nothing online.

Remove low speed jets. Insert SHANK of drill bits into jet until you find the largest shank which fits. Then take the next number size drill bit and grab shank with vise grips. Spin jet between thumb and forefinger until drill goes thru jet.
Stroke three or four times without spinning to deburr. Inspect under bright light, then reinstall. Works with stock exhausts too since everything was EPA-lean from da factory.

Low speed jets account for a good chunk of midrange performance. We used to do it on every budget bike that came thru the shop which needed de-leaning. Many people replace mains when the low speed jet answers their problem, and for some odd reason more mains were offered than low speeds. They were drilled in production so I've no problem drilling oversize. Never use a power drill on jets. Mentor who taught me the trick has used it since the 1950s.

While you are at it, remove the EPA idle fuel mixture screw flags or plugs. I usually snip off the flags with side cutters but some people heat them to loosen the adhesive.

https://www.youtube.com/watch?v=ZpMy4W6yx3Q

You'll get some fuel adjustment with the idle fuel mixture screws but I suggest drilling the jets.

CarloFreeze
08-18-2016, 3:59 PM
You can always try getting some of these baffles to get a little more midrange.

71579

FSUCREW
08-19-2016, 4:13 PM
So whenever you go up a size in jets, it's just a bigger passage for fuel?
I'd never looked in to it, but I always thought they got longer for some reason.

Also If I end up too rich, can I really just fill it in with copper solder and re"drill" the hole?

Man, If I'd asked over at the cb750c forums I wouldve gotten responses telling me to spend $100 on new jets.

FSUCREW
08-19-2016, 4:14 PM
where could I find those? and how do they affect the sound?

Tattooo
08-19-2016, 4:25 PM
where could I find those? and how do they affect the sound?

They will make it quieter........