What jets to use with K&N pod filters?

[Greg Good]

I'm trying to get the jetting right on my 79 XS1100 Special. The exhaust is stock and I just switched over to K&N pod filters. Has anyone come up with a combination that works? My supply of jets is growing but I haven't landed on the right combo yet. Thanks, Greg

[GTXS1100]

Jetting Recommendations

--------------------------------------------------------------------------------

Jetting Recommendations
by Denny Zander

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

3 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 Colour Tune. (See "Colortuning 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 exceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 76K mile on it, of which I have put 44K with this jet configuration.

I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.


here are jet pictures for reference

a air jet - b main jet - c pilot jet (some have different # of holes)
d various needle jets (emulsion tubes) - e two styles of float needle valves and float needles

(note: there are several styles of Mikuni main jets - the ones of interest to us are the 'large round' style)


Needle (jet needle)


Happy Jetting

[Rasputin]

Jetting Recommendations

--------------------------------------------------------------------------------

Jetting Recommendations
by Denny Zander

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

3 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 Colour Tune. (See "Colortuning 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 exceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 76K mile on it, of which I have put 44K with this jet configuration.

I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.


here are jet pictures for reference

a air jet - b main jet - c pilot jet (some have different # of holes)
d various needle jets (emulsion tubes) - e two styles of float needle valves and float needles

(note: there are several styles of Mikuni main jets - the ones of interest to us are the 'large round' style)


Needle (jet needle)


Happy Jetting

From any experience I have had with jetting this is bunk! Try 1 size up (Idle/air) for Pods and 1 size (Mains) up for pipes. After that it is a colortune/plug check at idle or a high speed chop at WOT which will determine where to go. I have tried to follow the jetting recommendations a few times and have done nothing but spend money on extra jets. Keep in mind that I am 3200 ft in elevation or close to it. Thing is that every bike has it's happy point and you have to find it.

[jetmechmarty]

Jetting Recommendations

--------------------------------------------------------------------------------

Jetting Recommendations
by Denny Zander

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

3 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 Colour Tune. (See "Colortuning 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 exceleration from off idle to 80+ mph, and steady pull past 120 mph. My "F" has 76K mile on it, of which I have put 44K with this jet configuration.

I have applied this to the '78-'79 carb set with great success. These guidelines should work for the '80-'81 carbs also. The only part I have not tested is pilot jet changing on the second generation carbs.


here are jet pictures for reference

a air jet - b main jet - c pilot jet (some have different # of holes)
d various needle jets (emulsion tubes) - e two styles of float needle valves and float needles

(note: there are several styles of Mikuni main jets - the ones of interest to us are the 'large round' style)


Needle (jet needle)


Happy Jetting

HMMMM..... I have a K&N filter in my unmolested airbox. I have a 4 into 1 exhaust. My jetting is stock. All indications are that it's properly jetted.

Just sayin'

[mharrington]

I like the jetting guide posted by GTX. I do know however is just a reference and one must really add whatever jets it takes to be optimal with THEIR bike. Jets are not too expensive but when you have four carbs that test and tune period can get pricey. As much as Id love some bigger individual K&Ns or UNIs Im sticking with the box as Im just not motivated to play with 4 carbs. MY XS650 twin however may get some individual filters.

[JasonRedbeard]

My '79SF with 4-2 turnouts and pods runs beautifully on 45 pilots and 145 mains. Stock exhaust is great so probably very little difference there. I'd start with either 45/145 or 45/142.5 jets. (42.5/137.5 is stock)

[GTXS1100]

Jets jets jets

Any one know of a place to ge a master set of jets for these bikes. Id like to fine tune mine better and dont want to have to buy them individualy. Right now i have 6 bike im trying to keep going (3 mine and 3 for friends). It would benifit me to have an intire kit on hand to tune with.

[motoman]

All good as long as they are Genuine Mikuni and not stamped K&L or RD on topside of jet. K&L and RD jets do not use same method of measuring fuel flow, therefore have a larger orfice....not good, and you'll NEVER get engine tuned properly.

[motoman]

All good as long as they are Genuine Mikuni and not stamped K&L or RD on topside of jet. K&L and RD jets do not use same method of measuring fuel flow, therefore have a larger orfice....not good, and you'll NEVER get engine tuned properly.

.....reason being, Mikuni/Yamaha still holds the patent on ALL internal parts(jets,metering rods,etc.) of Mikuni carbs. Therefore, they CANNOT be copied exactly. Same goes for Honda/Kiehn carbs. Just something to consider.

[GTXS1100]

Good to know but does mukuni make a kit with different size jets that i can but without getting every size individually.

[skids]

Be careful if you decide to buy main jets at bikebandit. I had to return a set because, although they were mikunis, they were the wrong threaded diameter.

[donebysunday]

Be careful if you decide to buy main jets at bikebandit. I had to return a set because, although they were mikunis, they were the wrong threaded diameter.

I've never heard of this before ?
Was there ever a determination as to why the threads were different, what were they made for ? What carbs were they supposed to fit ?

[BA80]

Try it with stock jetting before you change anything. You might end up chasing a problem you created.

[bikerphil]

does mukuni make a kit with different size jets that i can buy without getting every size individually.

I have never heard of or seen such a thing, I do remember the dynojet kits would come with several size jets. I haven't seen those available in a while. Do a google search, you never know what you may find. I think most of us here are probably too cheap to buy a large box of jets.

[Ranger_xs1100]

I have never heard of or seen such a thing, I do remember the dynojet kits would come with several size jets. I haven't seen those available in a while. Do a google search, you never know what you may find. I think most of us here are probably too cheap to buy a large box of jets.

I have a couple of spare dynojet kits here with instruction sheets if you need more info about them. I think they have 3 different size jets, as well as a set of needles, but they are not mikuni jets.