Aftermarket exhausts and re-jetting?

[NDORFN]

Should I be alarmed when I'm told by an agent for aftermarket exhausts that the carbs won't need re-jetting despite the fact that the airflow is considerably increased? It seems a big fat oxymoron (is that the word for it?) to me.

[SARGE]

STOLEN FROM THE INTERNET....




Here is a simple set of jetting guidelines that have worked for me. For those considering jet changes, this might help select a starting point.

1 jet size for custom 4 into 2 exhaust

2 jet sizes for 4 into 1 exhaust

1 jet size for K&N filter (single inside airbox)

1 jet size for drilling out the bottom of the airbox

2 jet sizes for both single K&N and drilled airbox

2 jet sizes for individual filters

2 jet sizes for no muffler (open header)

1 pilot jet size for every 3 main jet size increase

Add up all the jet size increases and subtract one. (Remember they go in steps of 2.5 for each jet size)

Under a mismatch condition, like individual filters and stock exhaust or 4 into 1 header with stock filter and air box, subtract an additional 1 jet size.

Check plug color often, sync carbs after each jet change, make sure the floats are set correctly, and seriously consider purchasing a Color Tune. (See "Color tuning Carburetors" in the Maintenance Section).

Make sure your carbs are in perfect working order before making jet changes.

Example from my '79 XS1100 F:
Stock main jets: 137.5

Stock pilot jets: 42.5

2 sizes for 4:1 exhaust (Jardine)

1 size for single K&N

1 size for drilled air box

4 (main sizes) - 1 = 3 or 137.5 + (2.5 * 3) = 145.0
1 (pilot jet size) or 42.5 + (2.5 * 1) = 45.0

With this jet configuration I get 32-38 mpg on the open road, Smooth idle, very strong acceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 65K mile on it, of which I have put 33K with this jet configuration.

Happy Jetting
Additional info: Decrease main jet size one step per 2000' above sea level. Decrease pilot jet every 6000' above sea level



learn it .. know it .. live it

[YellowDog]

Good steal.

Thanks Sarge.

[awayatc]

to be able to burn more fuel, oxygen is the limiting factor.
(thats why there are turbochargers/superchargers)
So just giving it more petrol is not necessarily what your bike needs with new exhausts.....
Adjusting air/fuel mixture screw (further out is more more fuel)
and shortening the needle in carb(s)(lowering the clip on needle makes it shorter=richer) will give you a good indication if your bike runs better with a bit more fuel.
Dyno is good to find out where your bike is at......
Good luck

[SARGE]

This information was submitted by various people. I assume no responsibility and am not at fault if YOU screw it up.
________________________________________


Follow steps in order:
1. Top end (full throttle / 7.5k to redline) - Best Main Jet must be selected before starting step 2!
Select Best Main Jet
To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm.

A. If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large.
Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.

B. If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small. In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use! Do not pay too much attention to the low end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low end / cruise later - after step 2.
2. Midrange (full throttle /5k-7k)
Select best needle clip position
To get the best power at full throttle at 5k-7k rpm, after you have already selected the best main jet.

A. If the engine pulls better on a full throttle roll-on starting at greater than 3k, when cool but soft when at full operating temperature, it is too rich in the midrange and the needle should be lowered.

B. If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.

If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set. Do not pay too much attention to the low end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets that produce the best power at high rpm. You will deal with the low end / cruise next.
3. Low end (full throttle / 2k-3k)
Float height (AKA fuel level & how to..)
To get best low end power, set float height so that the engine will accept full throttle in 2nd gear from 2.5k to 3k rpm at minimum. Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.

A. If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm).
This will lower the fuel level, making full throttle / 2k-3k rpm leaner.

B. If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level. Example: change float height from 15mm to 14mm to richen up that area.

REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting. Warning: If the engine is left with the fuel level too high, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.

Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm. Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!

If there are low end richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, also check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs.
4. Idle and low rpm cruise
Fuel Screw setting (AKA mixture screws)
There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs use a special "D" shaped driver, usually supplied in the carb recal kit. Set mixture screws at recommended settings, as a starting point.

For smoothest idle, 2nd gear 4000 rpm steady state cruise, and 1/8 throttle high rpm operation:
Pilot fuel mixture screw settings, float level AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.

A. If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments.
Alternative pilot jets are supplied when normally required.

Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers.

B. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem. NOTE: A rich problem gets worse as the engine heats up.

C. If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture. NOTE: A lean problem gets better as the engine heats up.

D. If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen the mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm!



carbs are p piece of piss ..i can tune a set faster than most people can tune FI.. grab / buy / rent/ borrow a set of balancing gauges

[Cary]

to be able to burn more fuel, oxygen is the limiting factor.
(thats why there are turbochargers/superchargers)
So just giving it more petrol is not necessarily what your bike needs with new exhausts.....

Dyno is good to find out where your bike is at......

Have now got Termignoni muffler and have removed Cat converter from mid pipe of Ducati so am going to get it tested on dyno next week to see if it's running lean etc.

Expect i'll need Power Commander to alter it but i'm informed this is the best way to find out. Cost of this is $163/hour

[TripleZee Dyno]

Have now got Termignoni muffler and have removed Cat converter from mid pipe of Ducati so am going to get it tested on dyno next week to see if it's running lean etc.

Expect i'll need Power Commander to alter it but i'm informed this is the best way to find out. Cost of this is $163/hour
Flate rate of $120 for check runs. Depending on outcome you may find you dont actually need a Power Commander. It is likely that your bike would be "optimised" with a PC and tuning, but is it so far off that it "needs" to be tuned?
A lot of bikes with minor mods dont actually "need" retuning so getting it checked before shelling out 1200 for a PC and tune is a wise move.
If you do get a PC dont use a DJ downloaded map unless you have no choice. 99% of them overfuel to some extent.
If done in the states its a fair chance they have been done using oxygenated fuels
cheers

[TripleZee Dyno]

Should I be alarmed when I'm told by an agent for aftermarket exhausts that the carbs won't need re-jetting despite the fact that the airflow is considerably increased? It seems a big fat oxymoron (is that the word for it?) to me.

If you are tuning your EX250 and you are in Matamata you can tune the old way.
Get a bit of straight road, still air conditions, and see how fast it goes. Turn around and do it again. (accounts for wind and road conditions) average the 2 speeds. change your main jet and do it all again. the jet that gives the best speed and pulls the best is the one to keep.
Otherwise follow the carb tuning procedure (original + more info available on factorypro.com) already posted and you should be right.
If its not an EX250 but some big monster bandit or something, stick it on the dyno. You'll live longer.

[Cary]

Flate rate of $120 for check runs. Depending on outcome you may find you dont actually need a Power Commander. It is likely that your bike would be "optimised" with a PC and tuning, but is it so far off that it "needs" to be tuned?
A lot of bikes with minor mods dont actually "need" retuning so getting it checked before shelling out 1200 for a PC and tune is a wise move.

Good to know.

The $163 was quoted from AMPS for a check run. The only reason i'd get a PC is for engine health, not increased power (has enough for me!)

[imdying]

carbs are p piece of piss ..i can tune a set faster than most people can tune FI.. grab / buy / rent/ borrow a set of balancing gaugesHahahaha, you crack me up. I can have a new map loaded from my SD card before you've even put the bike on a stand :rofl:

[vifferman]

Should I be alarmed when I'm told by an agent for aftermarket exhausts that the carbs won't need re-jetting despite the fact that the airflow is considerably increased? It seems a big fat oxymoron (is that the word for it?) to me.
Despite the very good posts by Sarge et al, there is a very good chance that the agent is right. OEM mufflers are actually pretty well designed, so don't flow that much less gas than aftermarket ones, plus bikes tend to be set up jetted a little rich from the factory anyway (apart from at the revs that emissions testing is done). I don't know why this is, but I suspect they err on the side of caution (better rich than lean and overheating), possibly to allow for owners fitting aftermarket zorsts and/or filters and then getting pissy when their bike leans out and craps out. Of the last two carbed bikes I've owned with modified airfilters and zorst, all that was required was a shim under the carb needles to stop some popping on deceleration, and a tweak of the idle mixture.

[Motig]

Probably depends on the pipe. When I was dreaming of an aftermarket muffler for the GSX and investigating different makes there were various models available within the brand. It all depended on what you were doing with the rest of the bike - ie full race system you'd have to do the rest of the motor but if you just wanted a bit more noise and minimal increase in power you could get the muffler with a lower state of tune so to speak and engine could be left stock. Look up the well known aftermarket makers on the web- yoshi etc they'll give you the info.

[CookMySock]

Get a bit of straight road, still air conditions, and see how fast it goes. Turn around and do it again. (accounts for wind and road conditions) average the 2 speeds. change your main jet and do it all again.This is how we used to set the ignition timing in the old days with our cars. Theres no way we could tell by the seat of our pants, but the stopwatch revealed all. This is not to be underestimated.

My guess is, modern bikes are set up rich as hell, just for maximum responsiveness. Unless you are going to run them at sustained full-power for some minutes (impossible?) I doubt you will overtemp anything, unless radical changes are made.

Steve

[TripleZee Dyno]

Good to know.

The $163 was quoted from AMPS for a check run. The only reason i'd get a PC is for engine health, not increased power (has enough for me!)
I think electricity is dearer in town. And they have more phones.

As regards engine health vs more power, they are not mutually exclusive. All things being equal, a healthy engine will run better, be more efficient, and a byproduct of this will be "more power".
Which is why we tune to "power" rather than an AFR. If at a certain throttle setting and rpm the engine is producing the max power it can, it means it is converting fuel and air into heat most efficiently, which means the AFR is correct (whatever it is)
How much power an engine produces is a very good indicator of the engines health.
I'm not talking about modifying an engine/bike to get more power but rather tuning what you have to get it running the best it can.
Truth be known 99% of the time fooling around with the exhaust, changing mufflers, removing valves etc, will cost as much power as it gains. Not only full throttle but part throttle response, cruise etc etc
A decent tune will minimise the losses and maximise the gains.
all very interesting but I have to get back to work
cheers

[vifferman]

My guess is, modern bikes are set up rich as hell, just for maximum responsiveness.
What?
So... I should change all those negatives on my Power Commander map to pluses, so I can maximise its responsiveness?
Thanks for that helpful info! :niceone:

I guess lots of hundreds'n'thousands on top is very rich and makes for maximum responsiveness too, huh?

[t3mp0r4ry nzr]

its quite possibley correct, but ultimately depends on its usage.
a commuter road bike MAY get away with no changes, or raising the needle a clip and turning the fuel screw out 1/8th turn.also depends on the base jetting. you will only know by putting the new pipe on and seeing how it goes.

[Cary]

I think electricity is dearer in town. And they have more phones.

As regards engine health vs more power, they are not mutually exclusive. All things being equal, a healthy engine will run better, be more efficient, and a byproduct of this will be "more power".

all very interesting but I have to get back to work
cheers

You could be right, re costs :clap:

The only reason I changed muffler was for sound & cause I could afford to. I mean, why have a Ducati thats sooo muffled :devil2:

True, get back to work and check your e-mails.......:niceone:

[SARGE]

hahahaha, you crack me up. I can have a new map loaded from my sd card before you've even put the bike on a stand :rofl:

i wasnt being literal poindexter

[imdying]

i wasnt being literal poindexterSo.... just talking shit then? :Pokey:

[SARGE]

So.... just talking shit then? :Pokey:



YEA ..


JUST TRYING TO FIT IN :blank: