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Message started by TheNaughtyLemur on 05/12/17 at 15:25:28

Title: Carb Tuning
Post by TheNaughtyLemur on 05/12/17 at 15:25:28

So I just got the MAC Performance header and exhaust kit put on my bike and I'm looking at rejetting it. I bought Lancer's jetset in preparation for this.

The pain in the ass I am foreseeing is that the California bikes are supposed to come with a #125 main jet, and the smallest jet that comes in Lancer's set is #150. I haven't torn into the bike yet to actually be certain of this, so this could all be unnecessary conjecture.

But to anybody who has a California bike, how do you go about rejetting? Is there a simple mod I can do to the carb to make it more like a non-California bike?

Title: Re: Carb Tuning
Post by verslagen1 on 05/12/17 at 15:53:22

I think the CA on the chart means Canada
If you open it up you'll find 145 main. Don't know anyone who's found a 125.
So don't worry about it just dig into it as told

Title: Re: Carb Tuning
Post by TheNaughtyLemur on 05/12/17 at 16:00:33

Oooooooooooooooh. Classic overthinking. Ill dig into it.

Title: Re: Carb Tuning
Post by norm92de on 05/13/17 at 12:09:02

Don't you have California- I'm from the State and here to help you- types looking over your shoulder? :'(

Title: Re: Carb Tuning
Post by WarriorPoet287 on 03/29/19 at 13:26:36

Super curious about that MAC performance header and exhaust kit... Sounds like you put it on first without any carb change. Did you feel like it affected performance? Did it run OK?

Also wondering what you ended up doing as far as a re-jet. How loud is the MAC exhaust? Is it like "that sounds awesome" or "the neighbors all hate me now"?

Thanks!

Title: Re: Carb Tuning
Post by LANCER on 03/30/19 at 07:47:32

734556564D4B56744B4150161C13240 wrote:

I got a MAC system when a rep from the company came to this site and offered one in a contest which I won. My engine is not stock, nor is my exhaust system. I think it runs pretty good.
I found the system did not work well for me. The muffler had a good sound and is capable of being loud but at idle to cruise settings it had a deep rumble and was not objectionable at all. Get on it hard and it volume definitely increases but in a good way. I liked the muffler.
The header has a 1.75”ID. My header has a 1.6”ID. A stock header has a 1.3”ID. 1.3” is adequate for stock engine with something like a Dyna muffler. For a modified engine you need more, at least 1.5” ID if not 1.6” which works great on mine. 1.75”ID is too large.

Some numbers:

Tube ID Tube area.

(A). 1.3”ID. 1.280” sq.
(B). 1.5”ID. 1.830” sq.
(C). 1.6”ID. 2.142” sq.
(D). 1.75”ID. 2.479” sq.

The area inside the tube increases as follows...A-B 43%; A-C 60%; A-D 76%.
B-C 17%; B-D 35%; C-D 16%.

The percentage increase in the area of the tubes increase dramatically with just seemingly very small increase of tube ID. How much slower must the exhaust travel when the space is enlarged so much ? A lot. The result is poorer performance unless you improve breathing throughout. The more efficiently the air can enter and exhaust exit the engine the more power you can make.
Get too big and results just drop.

Recommended header size for an engine making _____ HP
25-35hp/cyl 1.3”ID
35-50hp/cyl 1.5”ID
45-60hp/cyl 1.6”ID
with some cross over between them.

Title: Re: Carb Tuning
Post by Boberticus on 04/01/19 at 12:39:38

wait, so everything ive read about performance mods say that the header size is too small, but Lancer your saying for what the bike is tuned for from factory its all correct, and it only needs to be enlarged after getting past the ~35hp mark? and by needs, i mean that that is when the size of the header actually starts to become a bottleneck for power?

the motor literally doesn't breath well enough stock to need it?... is this also why people say to not bother with grinding out the exhaust port until after you've done the camshaft swap and wiseco piston mod, because it wont do much if it doesnt need that air to move that fast/quickly/laminar/smoothly...

all this is at sea level, right? does the lower pressure of altitude change the required volume, kinda like how we dont use a single stage rocket to get to orbit? the nozzles dont work right because of the shape of the exhaust bell once you get too high. surely there is a perfect "pressure" for exhaust, does that have to do with ambient pressure, or is it not a factor?

Title: Re: Carb Tuning
Post by batman on 04/01/19 at 22:47:10

The header size (up to 35 hp) isn't the problem it's the shape of the exhaust channel between the exhaust valve and the exhaust header(that's the " bottleneck.") Grinding out the exhaust port (carefully ) should show a slight improvement even on a stock motor.
elevation has to due with jetting ,higher elevation requires smaller jets (less fuel) due to less oxygen , near sea level the opposite.
With the exhaust we are concerned with velocity (flow) rather than pressure. The object is to remove as much of the exhaust gases as quickly as you can from the cylinder ,to allow more room for the incoming fuel/air mix.(more hp).

Title: Re: Carb Tuning
Post by DragBikeMike on 04/02/19 at 11:58:11

Lemur! I run that Mac Header pipe with a modified stock muffler. I agree that at 1.79" the ID of the header is too big. I never even tried to run it with the 1.79" ID. I reduced the ID by inserting an 18" section of flexible exhaust tubing into the header. It was tricky but it went in. It works fine and the engine seems to like it. You end up with a stepped header. The first 18" is 1.5" ID and then it steps up to 1.79". If you install the Mac system and find that your low end power goes in the toilet, all is not lost.

Title: Re: Carb Tuning
Post by DragBikeMike on 04/02/19 at 12:03:17

The flex pipe is inexpensive and can be purchased at any auto parts store. It has a 1.5" ID and the OD is just the right size to allow it to be slipped into your 1.79" ID header. You have to exercise it a bit to loosen it up prior to insertion. As you are feeding it in it will start to bind a bit. Each time it starts to hang up you simply pull out on it a little and then continue feeding it in. Lube it up with some anti-seize prior to insertion.

Title: Re: Carb Tuning
Post by DragBikeMike on 04/02/19 at 12:10:00

Once it is almost all the way in, while there is still a small amount protruding, seal up the joint between the header ID and the flex pipe OD with some of this JB Weld "Extreme Heat" putty. Shove it home, clean up any excess putty, and let it sit overnight. It should be ready to rock-n-roll. I plan on pulling my system off in the near future to take a look at the joint between the flex pipe and the header to see how the "Extreme Heat" putty is holding up. Currently, I probably have about 1000 miles on the pipe and it runs fine with no outward sign of any sort of problem. I will fill you in when I do the inspection.

Title: Re: Carb Tuning
Post by DragBikeMike on 04/07/19 at 17:45:41

Well, I did the inspection...….and......this is tough to report......my flexible pipe ran away. That sucker migrated a few inches down the header. I am sorry to report that I got flummoxed when I saw that flex pipe down inside the header. I was majorly concerned about retrieving it and lost sight of why I had the pipe off in the first place. I started digging around trying to snag the flex pipe before I got any good photos of the extreme heat filler. I can tell you that a lot of the filler was gone, so I am not thrilled with the inspection. How's this flex pipe look?

Title: Re: Carb Tuning
Post by DragBikeMike on 04/07/19 at 17:49:31

Every cloud has a silver lining. Now I know I can get one out if I decide to install another one. In the event that I do install another flex pipe, I won't cheap out and only get the readily available 18" section off the shelf in the auto parts store, I will get at least 36" so I can run it through the entire header and capture it on both ends. For reference purposes, here is what the flex pipe looked like on the initial installation.

Title: Re: Carb Tuning
Post by DragBikeMike on 04/07/19 at 17:51:51

Here's a shot of the little bit of filler that remained after I finished my ballistic removal procedure. It's a dirty job but somebody's gotta do it.

Title: Re: Carb Tuning
Post by DragBikeMike on 04/07/19 at 18:02:17

Just to put things in perspective. When I shoved that pipe into the header I had everything all slathered up with anti-seize. The slippery stuff was all over the place. The interior of the pipe in way of the flange is chrome plated, and I did absolutely no prep (anchor grinding, sanding, etc.), and I did my best to clean things but there was a pipe inside of a pipe, so access was like almost zero. The fact that any of the extreme heat filler was still in place borders on miraculous. Hey, it's a learning thing, right?

Hey Lemur! Take note of this fiasco. If you go the flex pipe route install it for the entire header length, don't short change it like I did.

I went for a nice long ride this morning pushing exhaust gas through a 1.79" ID header. I can report with confidence that I hardly noticed any difference. The S40 ran fine with that big header hooked up to my modified stock muffler. There might have been a barely discernable loss on the bottom with a barely discernable little kick about 4200 to 4500 rpm or so. But seat-o-da-pants could hardly perceive any change.

Title: Re: Carb Tuning
Post by Fast 650 on 04/08/19 at 09:41:06

5855585F484E53594F493A0 wrote:

The stock port and exhaust will provide acceptable performance if you are a new rider, or if you don't accelerate hard or ride at higher speeds. Judging by the number of posts from people who are modifying theirs, a good portion of us like more oomph from our bikes. A good porting job and better flowing exhaust will make a noticeable improvement even on a stock engine. Even with only a rejet and a Dyna muffler you will feel a difference in performance.

Lancer's chart sizes exhaust by the HP. I figure pipe diameter by gas velocity, and we end up with similar sizing. His chart says 1.3" is near the limit for a stock engine, and that 1.5" ID is just a hair big for it. My numbers say 1.3" is too small and that 1.5" would be a better choice. I don't know if his chart uses HP at the crank or at the wheel though. If it is at the crank, then his chart matches up spot on with my method of calculating size by gas velocity. Either method will give acceptable pipe diameter recommendations for normal street riding.

Going to a larger bore and/or hotter cam is when the porting and pipe size will show the biggest benefits. The LS engine suffers from chronic asthma so anything that improves breathing will reap rewards.

Title: Re: Carb Tuning
Post by LANCER on 04/08/19 at 10:48:20

The pipe size chart for the header is based upon HP at the rear wheel.

Title: Re: Carb Tuning
Post by Fast 650 on 04/08/19 at 11:25:48

Okay. That means that there is just some wiggle room in how the two methods calculate pipe diameter then. They still come out pretty close, good enough for most cases.