Topic: Question for those with stock 4 into 4 exhaust system,

[seanbarney41]

don't go up at all until you need to...120's are usually all that is needed

[754]

Give it what it asks for, it looks a tad lean , imo... Each step is 5 .
 What I was trying to say before, if you try it try just that, then if you pull baffles , that US another test..
 Easier one thingar a time..

Back in 75 I had a 72 with a Hooked header and pods. It ran good but my buddy who was a lot lighter had a 74 and he was always a bit ahead of me.... we tried many times. Finally I bumped  up a jet size and it ran stronger, kept up or even pulled on him a bit.. felt good.. About 2 day's later , we totalled both bikes.. hit each other at a stupid speed difference. .
 I think I had gone from 120 to 125..mot sure..it's been 45 years.

They do seem to vary, not all want that much, and big bore...oddly does not always need more.. and after a good bunch of miles, at times we have found we could go down a size....
 There is no formula, trust the plugs...

[DesertKyorugi]

Well, my butt dyno tells me it can run a little richer than 120anove 5000rpm. And this is running with the diffusers in my HM341s.

I imagine if I am running without the diffusers I would definitely need to up the main jets

[754]

Real good chance of that... you probably got a pretty good  one...

[PeWe]

Tricky with A/F check on dyno with diffusers in.
The Dyno guys here stick a copper pipe as deep in as possible. An external device with lambda.

My K2 on dyno with no numbers got no A/F since bike felt OK, needles and mains found by road tests. Dyno guy agreed, bike felt right.
 (Too rich needles or mains can be verified by slowly repeat increasing-decreasing throttle at around 100-140kmh for needles, faster for mains. You hear and feel when slowly decelerate if too rich. Good to repeat that from 100kmh- full speed.

I did that last summer on my K6, often in the 140-200kmh area which sometimes was risky when too focused on engine.

My K6with same No numbers 4-4 a few years ago got A/F check without diffusers. Power checked with and without.
Same with the Lotus Root pipes.

Hindle 4-2-1 does not have such restriction, a wide hole all the way in!   (Easy for Dyno A/F copper pipe.)
It muffles the sound surprisingly well when cruising.

[DesertKyorugi]

Tricky with A/F check on dyno with diffusers in.
The Dyno guys here stick a copper pipe as deep in as possible. An external device with lambda.

My K2 on dyno with no numbers got no A/F since bike felt OK, needles and mains found by road tests. Dyno guy agreed, bike felt right.
 (Too rich needles or mains can be verified by slowly repeat increasing-decreasing throttle at around 100-140kmh for needles, faster for mains. You hear and feel when slowly decelerate if too rich. Good to repeat that from 100kmh- full speed.

I did that last summer on my K6, often in the 140-200kmh area which sometimes was risky when too focused on engine.

My K6with same No numbers 4-4 a few years ago got A/F check without diffusers. Power checked with and without.
Same with the Lotus Root pipes.

Hindle 4-2-1 does not have such restriction, a wide hole all the way in!   (Easy for Dyno A/F copper pipe.)
It muffles the sound surprisingly well when cruising.

Unfortunately, all I have to go by is my butt dyno. It's been decades since my racing days and my Shoei's soundproofing is a little too good for listening to deceleration. The only comparison tool I had was my newer sportbikes.

[PeWe]

You will feel it more than hear it. My helmet also reduce sound rather well. Schuberth C3 Pro.

You'll get the feeling for it when riding that specific bike and exhaust for a longer ride or 3.

[DesertKyorugi]

Is "butt dyno" not a term used for motorcycles as well? I am pretty sure it is not strictly a car term 😅😂

[PeWe]

Butt dyno mentioned on many threads!

[JLeather]

The last bike I had with stock exhaust I ran without the diffusers.  I really liked the sound.  Surprisingly louder than with the diffusers in, also throatier with more of a "pop".  May have cost me a little HP but I didn't care.  I recall having to bump up the needles a click and I think I ended up at 42 idle jets on that bike...

[DesertKyorugi]

The last bike I had with stock exhaust I ran without the diffusers.  I really liked the sound.  Surprisingly louder than with the diffusers in, also throatier with more of a "pop".  May have cost me a little HP but I didn't care.  I recall having to bump up the needles a click and I think I ended up at 42 idle jets on that bike...

What year is your CB? My K1 with HM341 s idling a little rich with the stock 1 turn on the air mixture screw. The bike runs great below 4000 rpm and as you can see from the spark plugs, it is quite acceptable but I am just being picky due to my butt dyno telling me the performance can be better above 5000rpm.

I will be testing for sound difference with or without diffusers soon and will report back

[JLeather]

It was a '76, the most detuned bike to ever run 341 exhaust stock   I also had a K7 with the ends of the pipes cut out (same as removing the diffusers) and it was awesome sounding.

[DesertKyorugi]

Had a little bit of time today so I did a little sound test at idle at 1500rpm. With diffusers, it is averaging 81db. Without diffusers, it is averaging 90db.

A quick spin around the block, my butt dyno says quicker response and more eager to rev. I did not have time to go for a real ride so I will have to wait for another day so I can do a plug chop as well to see how much leaner it is running without diffusers.

I also want to confirm what you guys are saying, all the diffusers were wet with condensations. I decided not to put them back in.