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Author Topic: Jetting Thread  (Read 24667 times)

Offline Demilus

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Re: Jetting Thread
« Reply #30 on: November 05, 2008, 08:56:47 PM »
I have a '92 GSF400N USA model.  Mikuni carbs.  I just recently rebuilt the carbs (thanks Jay) and put new spark plugs in.  It has stock airbox and *I believe* stock jets and needles.  It currently has a Vance and Hines supersport 4-1 exhaust.  Any suggestions on a good baseline setting to start from?  It runs really rough right now and I'm foreseeing having some trouble tuning it given how it is running now.

Offline gsxr400 racer

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Re: Jetting Thread
« Reply #31 on: November 07, 2008, 02:19:34 PM »
rough as in??? idle, bottom, mid, top end... :yikes:
1988 gsxr 400 sp (sprint bike)
*  SELLER OF THE 442CC BIG BORE PISTON KIT FOR THE BANDIT 400,GSXR400, GK73 and 76.* And carb kits(orings)too. Email me from here.
has been a wera expert #610 lol

Offline Chris H

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Re: Jetting Thread
« Reply #32 on: November 07, 2008, 02:55:27 PM »
Hi all,
was reading your threds on air box tuning and theres abook by John Robinson called motorcycle tuning (4 stroke) second edition which is a good read, it covers bikes of this age and has some interesting reading on air boxes, its worth a look!

Offline tomacGTi

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Re: Jetting Thread
« Reply #33 on: December 06, 2008, 11:34:57 AM »
http://members.optusnet.com.au/sv650-k2/Rejetting_Notes.pdf

Stumbled upon this on a boring, cold rainy day. Thought it was the best written step-by-step for jetting that I've seen yet.

It's written for an SV650 (no surprises there, there are millions of these things) but you should be able to make some judgement calls to suit our bikes.

-Randy

Offline nos

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Re: Jetting Thread
« Reply #34 on: January 10, 2009, 01:03:39 PM »
where can i find a nice kit to fit with 54mm air filters?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=200270085396
can this one fit my 95 japan model?
« Last Edit: January 10, 2009, 08:42:18 PM by nos »
bikes i own:
Bandit 400
GSR500 Racing bike
RS125 Racing bike
1198 Racing bike

Offline tomacGTi

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Re: Jetting Thread
« Reply #35 on: January 11, 2009, 09:34:51 AM »
where can i find a nice kit to fit with 54mm air filters?
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=200270085396
can this one fit my 95 japan model?

Factory pro config 30. You'll have to measure the bellmouth of the carbs to be sure.

Offline tomacGTi

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Re: Jetting Thread
« Reply #36 on: January 11, 2009, 10:14:50 AM »
For those of you stuck with a Dynojet jetkit, the first thing you will notice is that the numbers that others have with the Factory Pro kit will absolutely not jive. With a 97.5 main, my bike would lean surge like hell as soon as it came on the main whereas FP guys say that it works great. Interfuse had posted the needle tapers and similarities somewhere but it is an entirely different needle with a wider tip needing a larger main versus the FP.

If you've got a DJ kit and don't want to spend the money on another jet kit, here are some numbers I've come up with. First off:

-91 Bandit 32mm US carbs
-Unifilter (green foam BF-1 universal sheet, cut to fit)
-modified airbox lid, custom snorkel
-F1S exhaust with 2" baffle, silencer removed in collector
-Tuning done at 50-65*F, low humidity. I may have to jet down a step in the full-blown summertime here in PA as it's vastly different.
-OEM slide springs. The DJ springs are stiffer making the slide a bit more fat than it needs to be. I found the response better with the OE springs YRMV.

All jets are factory Mikuni. I didn't even bother using DJ jets as they're a PIA to source. Also, I used a Uni filter because it was significantly cheaper ($15 at the dealer versus $50+) and flowed just slightly less than a K&N. Expect at least one more jet size up using a K&N.

My modded F1S now flows the same as every other aftermarket slip-on you can buy because of the 2" core, it was 1.75" with louvers before. Changes to the air filter will cause more changes to jetting versus exhaust. Of course they should be tuned together, but that's in a perfect world.

With Uni air filter in modified box (2" inlet)
-110 main, 107.5 when it gets hotter.
-3.5 turns on the screws
-1 shim

With stock element in modified box (2" inlet)
-105 main
-3.25 turns
-1 shim

I know the airbox topic has been beaten to death in here but I have found that with a snorkel, the midrange is more rideable at throttle openings below WFO. I have two lids, one with an inlet bellmouth and no snorkel and one with a length I figured in to start resonating at 8k and the snorkel has a smoother roll-on everytime. Both are the same size opening, difference being one is 4cm to clear the front hump in the lid and one is 15cm tuned to resonate.

Try it for yourselves if you want, I posted on how to make one not too long ago. Since the openings are the same size and just the length changes, no need to rejet.

Also, using this guide I found as well (I don't remember where, FJ forums I think) helped a great deal and is fairly accurate even with our bikes. Starting jetting point would be 102.5 Mikuni:

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.

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


Hope this helps someone out.

-Randy


« Last Edit: January 11, 2009, 01:45:13 PM by tomacGTi »

Offline gsxr400 racer

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Re: Jetting Thread
« Reply #37 on: January 20, 2009, 03:58:44 PM »
good stuff Randy :beers:
1988 gsxr 400 sp (sprint bike)
*  SELLER OF THE 442CC BIG BORE PISTON KIT FOR THE BANDIT 400,GSXR400, GK73 and 76.* And carb kits(orings)too. Email me from here.
has been a wera expert #610 lol

Offline tomacGTi

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Re: Jetting Thread
« Reply #38 on: May 30, 2010, 03:02:29 PM »
Work in progress:

-Vance and Hines 4-1 supersport pipe w/different muffler (F1s with 2" perf'd core)

-120 main
-3.25 turns
-3rd clip DJ needles 1 shim (better roll-on, too lean before)
-Uni filter in factory box with 55mm snorkel.

-90* and humid

Pulls like a freight train from 8k on up, bit softer in the middle in comparison to modified stock header with same muffler. Definitely better up top but softer from 5-7k.

Comes off of idle well but the lean spot that all Bandits have is still there and worse if you're lugging the motor. Have to be on the pipe all the time to get the max out of the setup.

« Last Edit: May 31, 2010, 01:35:04 PM by tomacGTi »

Offline canyonbreeze

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Re: Jetting Thread
« Reply #39 on: May 08, 2011, 09:38:20 PM »
I'm trying to figure out what is in my carbs and how to get it somewhat leaner.  My mileage could be better and there is still some soot accumulating on the exhaust.  When I bought the bike a year ago it was already 20 years old and changed hands an unknown amount of times.  The people I bought it from had it 9 years but barely used it.  I've put twice the miles on it in the 9 months I've had it.  

The bike had an unknown make 4-1 header with a Yamaha muffler when I bought it.  I put it back to a stock pipe.  Airbox is stock foam with some large holes right above the snorkel.  

Altitude is just shy of 6 feet above sea level when I'm standing up (near the beach).  The highest mountains near me are about 5,000 feet.  I've had the bike up to ~9,000 feet near Yosemite and it was very unhappy about that.

I have an extra set of rusty carbs I got cheaply for extra parts.  The main jets in them are marked 102.5, the needle jets are brass in color with no adjustment steps.  

The carbs that came in the bike have main jets marked 96 and the needle jets are steel/aluminum color with adjustment steps for the C clip, currently on second from end.

Neither of the main jet markings matches the Mikuni numbers in the chart on the previous page of this thread.  Maybe it currently has a DynoJet kit?

Width(thousands)------Kehein # -- DynoJets # -- Mikuni #
...
0,0370----              97,5--------- 96----------- 90,0
...
0,0390----              102,5------- 100---------- 93,8

The carb kit I bought had the wrong float needles and the bike flooded.  The needles from the rusted carbs look better condition than the ones that were in there so I used those when I put it back together again.  Now it's no longer leaking out but is still flooding a bit from the smell, the acceleration sucks and it won't hold a steady idle.  I used stock float level and maybe that isn't right with the jetting kit.  Also some of the linkage may be sticking up a bit.

I replaced the two o-rings on the float plastics and the tiny o-ring by the diaphragm with Viton ones.

I didn't do any adjustments to the mixture levels since it idled well before cleaning and no jets were changed.  The plugs were gone so someone somewhere did when they did the jet kit.

Any other comments or suggestions on this?  Thanks all and happy mothers day (in the US).  :thanks:

EDIT:  Tearing it all apart again this evening found the mixture screws were out 4 turns, seems a bit much.  Replaced those o-rings and put them to 2 1/2 turns.  Will re-set the float levels and put it all back together tomorrow.

EDIT AGAIN:  Got it back together with the correct float needles.  No more gas leakage but it idles like crap.  Runs up to 5~6k RPM then very slowly drops down and dies.  High speed seems decent but quite a few flat spots in acceleration.  Will put the mixture screws back to 4 turns where they were and make sure the slides are moving freely.  Float levels are set to 15mm on the highest float, they don't sit evenly.  The o-rings are seated ok.  Any other suggestions on why it would do this?  

FINAL EDIT:  Just to not leave it hanging... The symptoms I had pointed to a vacuum leak.  I put the idle mixtures back to 4 turns.  Then meticulously cleaned and assembled the diaphragms, needles, covers, etc, and put it all back together.  Made extra sure to fully seat the carbs into the intake manifold and the airbox onto the carbs.   Added clamps to most of the hoses.  Started up rough but slowly got better over a ~5 mile ride at high RPM/Speed.  Now seems ok except for a bit less 'off the line' acceleration than it had before.  I'm assuming that may be helped by syncing the carbs.
« Last Edit: May 13, 2011, 01:07:08 AM by canyonbreeze »

Offline Chris H

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Re: Jetting Thread
« Reply #40 on: May 10, 2011, 11:27:19 AM »
Hi, are you sure the carbs are not from a gsxr400 as some of them have 96 mains and no bungs in the pilot jets.
I have a dyno jet kit and the needles are much finer than the B4 ones which are a very thick needle compared to most bikes.
Im sure the dyno jet kit came with 100 or 102 mains.

Offline canyonbreeze

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Re: Jetting Thread
« Reply #41 on: May 10, 2011, 11:45:31 AM »
I can't be sure as the bike was 20 years old when I got it.  The needles are single taper, very pointy, with 5 slots for the C clip.  I don't think those are stock.  Everything else in the carbs is identical to the other set I have.

The company I got the carb kit from on eBay, Sirius Consolidated (www.siriusconinc.com), is overnighting the correct float valves at no cost.  Very good service as I bought the kits about 3 months ago.  

I looked up the DynoJet kit on their website and it comes with 96 and 100 main jets.  This matches all the parts listed in their kit.
« Last Edit: May 11, 2011, 06:43:29 PM by canyonbreeze »

Offline Squishy

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Re: Jetting Thread
« Reply #42 on: October 04, 2011, 06:21:14 AM »
Did any of you here had to install bigger jets after installing an aftermarket exhaust or will changing the throttle needle suffice?

Offline andrewsw

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Re: Jetting Thread
« Reply #43 on: May 07, 2012, 11:32:48 PM »
Quote
I didn't get a real good test run (no traffic, hence no low rev cruising ;)

What a damn shame.  I have plenty of great of great opportunities to try out pilot jet riding here,... you're welcome to come by and test....
« Last Edit: May 08, 2012, 01:45:37 AM by stormi »

Offline Nickelodeon

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Re: Jetting Thread
« Reply #44 on: June 08, 2012, 04:13:24 PM »
91' Bandit (MFG June 90'):

Stock Exhaust
32mm BST's (Rebuilt w/ new o-ring kits)
Factory Pro 1.0 kit
Alt: ~ 360ft

Setup:

180 deg. CBR F3 Thermostat(idle hunts a little less)
Stock airbox(well sealed, had to use tape due to warpage), K&N filter and stock exhaust
95 MJ (tried 97.5 for a bit, it was too rich)
Needle Clip #3 position from top(Factory Pro needle)
Fuel Screws 2-1/4" turns out

Carburates PERFECTLY through rev. range, but still hits the wall @ 110 mph...not sure yet if it's electronic restriction or stock header/muffler restriction...sent a message to Jay and hopefully he can illuminate...but it runs like a scalded dog up to around 90mph or so.

Just did a carb sync before my last shakedown yesterday(and a valve adjustment), so everything is in "spec".

« Last Edit: December 22, 2012, 01:50:29 PM by Nickelodeon »

 

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