Jet and needle setup

[TheBogo]

Hi there,

just a question, is there any possibility of a List or spreadsheet where you can find or calculate the best jet/needle setup for different exhausts, Stage kits or engine-setups?

 

[Fire-medic]

Refer to the factory specs for the Mikunis, and the specs for the exhaust you wish to use. Slip-ons usually don't need mods, they're designed to work with the stock jetting. Full exhausts, with larger tubing from cyl heads to the canister(s) will probably require re-jetting for optimal function. Because of differences in altitude a Kerker 4/1 and a Dynojet Stage 7 kit will be leaner in Denver than in Miami. Richer is safer than leaner, in-that a too-lean carb can cause holed pistons, in an extreme scenario. Detonation ('pinging') is dangerous in that the cyl temps become much-higher, as the fuel charge is ignited ahead of when the spark plug fires.

I know this isn't what you asked-for, but following the manufacturer's directions gets you in the ballpark, and then experience of making changes is your best guide. How does it run after making changes? Using an exhaust gas 'sniffer' is probably the most-scientific way to get data, for most people that means dyno time.

A lot of people including myself have found that going a step or two leaner on the main jet can help, but if you're in Denver, your jetting should be leaner to begin with because of the lesser oxygen density at that altitude. The commonly-expressed delta for air density, from sea level (Miami) to Denver (CO) is 15%. Also, as temperature increases, air density decreases. You can understand why it is very important to prevent going too-lean, as combustion temperatures can spike, causing the fuel to ignite prematurely, (detonation) causing overheating of the piston crown and ring lands, and catastrophic engine component failure.

 

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https://www.vmaxforum.net/threads/oem-carbs-post-your-setup.16981/

No spreadsheet but there is a good bit of data in this thread.

 

[TheBogo]

Thanks for the link.

Yes there is a lot of data, but the quastion is, is it GOOD data, if you know what i mean.

I thougt that there is any other option then just to run to a Dyno-Station every time i changed the Jets or something to find THE perfect setup for my bike.

 

[Fire-medic]

Since you're only 338 ft above sea level, not-even 100 meters, you don't have the height of Denver Colorado ("the Mile-High City" 1560-1730 meters) to worry-about. If you want the best info, deal with the best data acquisition method, a tailpipe sniffer, and chart-across your rev-range, see what the readings are and alter your jetting from there. Depending upon how-precise you want to-be, you could take readings from each header pipe, and adjust accordingly.

 

[MaxMidnight]

Yes there is a lot of data, but the quastion is, is it GOOD data, if you know what i mean.

I thougt that there is any other option then just to run to a Dyno-Station every time i changed the Jets or something to find THE perfect setup for my bike.

The only way to get good data for your bike would be to do a dyno run and look at the data.
IMO there is no perfect set-up...carburetors aren't perfect and changes in ambient air temperature and pressure will alter the fueling requirements.
The most you can expect is the best compromise.

 

[caseyjones955]

The method I used is one I learned here, which is (with carbs synched up and floats set) to tune from the top down. I'm not near a dyno or a sniffer so I got to do it seat-of-the-pants. Mine is a 99, stock other than a Kerker 4-2-1 and Seans Jet Kit (money well spent btw). Sean and others were kind enough to get me to a good jumping off point RE jet sizes and settings. I ended up with mains of 147.5 and I think my low speed jets are stock size. I live at 4000' and only ride upwards from here. The second time I changed the main jets it was down to a <15 minute process. I spent more time on needle shims than anything else.

Once I found the jets that made me have to hang onto the bike and be very careful not to overrev (no rev limiter on a Gen1). I felt just a little bog with the leaner ones and it just lacked that crisp snappy zip when too rich. The 147.5 was definitely the jet that gave me the sharpest WOT passes, so from there I went to positioning and shimming the needles then the low speed jets. It took an afternoon of goofing around but I'm infinitely pleased with how she runs. Obviously if your at sea level my settings are completely useless to you, so I use it only as an example. When I get moved I'll be over 8000' and I'll retune it the same way, I bought a few sets of jets just so that I could tune it this way.

Also noteworthy is that DJ (Dynajet) and Mikuni jets do not use the same numbering system and are not the same. A quick search will turn up conversion charts all over the net. I know a sniffer/dyno is best but if you know your not going to do that then you might consider this. It worked for me, YMMV.

 

[TheBogo]

okay, first of all, thx for the answers.

With the different numbering system of the mikuni and DJ jets I already knew.

SOrry for maybe not using the correct terms, but i am from germany and don´t know the exact words in english.

But isn´t there any file or something what you can use as a Manual. Like what Jets (The Upper ones, ones on the sides or the inner Jets) and changing them with larger or smaller diameter has which effect on the bike. Same with the Needle Level.

I Drive 2 Vmaxs. One just modified by myself, and the other one re-constucted and build completely just started with the frame.

Carb cleaning is also no Problem, did this on Both already.

Both have a Stage1, and I have the Dyna3000 and the COPS.

Just different exhaustes. One Marving and one DAM.

And now I just try to optimize my bikes and want to unterstand how exactly the Carbs are working and what effects the changing of different things have.

 

[Fire-medic]

Do you know what manufacturer the Stage 1 kit is? Many people on-here have had difficulty w/the Dynojet Stage 1 kit, getting the bike to run well. It seems that staying stock is the best path to-take (Stage 1 vs. stock jetting), given the difficulty of getting the Stage 1 to work well. Sounds like you may have had better luck w/the Stage 1?

I have a Dynojet Stage 7, I kept functional VBoost, a K&N drop-in air filter, a 4/1, and the only other engine mod is COPS. It runs well throughout the rev band, I use 147.5 mains, and am at sea level.

 

[sdt354]

Dynojet stage 1 made some good top end power for me,but milage was awful. Traumahawk is one of the few tuners that got the stage 1 to work well, that I know of. Stage 7/Morley kits work well. And the milage can be much better than OEM.

 

[Traumahawk]

Dynojet stage 1 made some good top end power for me,but milage was awful. Traumahawk is one of the few tuners that got the stage 1 to work well, that I know of. Stage 7/Morley kits work well. And the milage can be much better than OEM.

The only way that I got the stage 1 kit to work was to throw the directions out of the window. I went with a little bit leaner on the mains than stock and went very lean on the needles. I stayed with the stock air jets and used the stage 1/7 springs. Hp was ok.....and a little bit better than stock. Mileage was comparable to stock. For the time and effort....you get a better bang for your buck going with Sean's kit....or something along those lines. A stage 1 kit can be made to run if you set it up leaner than the directions.

 

[sandy klock]

Hey Brother TheBogo; It appears you have knowledge needed for modding bikes so I would suggest a wideband o2 sensor and guage. That will get ya exactly where you want to be. I'm not familiar with your exhaust so no idea what ya need. There are plenty of directions on tuning the cv carbs. Good luck and welcome to forum.