The Infamous Viking Mod
 

Originally from the guys over in sweden..
i've gotten more than one request for details and i figured when people google or search the site this will come up.. i know the mod is good for all carbureted blades from 92 to 99.
i also want to point out that i have found between three different forums that guys try this mod and cant figure it out and their bikes run like crap until they put everything back to the way it was and give up.. i will be honest and say i was almost one of these guys, well no not really. i'm somewhat too hard headed for that.. i knew all along i was missing something but didn't know what!!!
so i want to remind everybody reading and attempting this!! to follow my instructions to the letter or it wont work..

1)
well first goto jetsrus.com (thank u Conrice)and buy four 140 mains (and yes you can buy the cheap ones)and install them into your carbs. next flip the carbs over to the needle/slide side and pull your needles out of the needle holder, you can use one of the 3 screws that hold the cap on, to get a grip on the needle holder and gently pull out.. if you already have a jet kit in, put the clip on the third slot down from the top.
if you dont have a jet kit, there are two ways of bringing up the Stock needles. you can goto radio shack and they sell a box of assorted washers and the smaller sized washers (m3) you'll need for this.
anyway slide three washers on including the washer you'll find when you open the needle holder.. so thats four washers all together..
or go onto amazon and buy a 100 pack of m3 washers and fit them the way i've described..just make sure the fourth washer you put on is the one you found in the needle holder, that goes on last.
skip to 2 if you already have a jet kit installed and you put the clip on the third notch.. if you dont have a jet kit already installed please keep reading this is for you!
before putting the needles back you need to drill out the two holes that flank the needle. with a 1/16th drill bit.. then put the needle and holder back and be careful sliding them back in place.. the last thing you'll need to do is take all four springs and count two rings down and then clip.its roughly a 1/4" off the original springs..
now that you have just did the poor mans jet kit, you are def committed and better listen to the rest of what i write or you'll be ebaying parts later this afternoon..

2) still on the carbs and this will be the last adjustment before reinstalling them.. the idol fuel screw or air/fuel screws, what ever you want to call them are on the opposite side of the slides, so turn the sucker over and sink them all the way in.. this is the spot where you need the special tool or a dremel so you can use a flat head screw driver instead.. i prefer the flat head screw driver, only because its easier to count the turns..
now back them out 4 turns from lightly seated, dont worry your going to do a idol drop test later, to get them just right and most likely they be turned in a little bit more..

Ok, you are now finished with the carburetors.. Reinstall!!! this part is really important, our bikes are getting up there in age and a lot of the parts are old.. make sure the slides all move up and down more or less the same.. if you have die electric grease, you can coat the rubber diaphragm on top of the needle. just dont man handle it.. apply it really gently, this will help keep them fresh and pliable. to move freely up and down..
also if you notice one or any of the needles just plung right down too fast, that means its not seated right and you need to reopen it and make sure it seated right, before tightening the cap back down..

3) and the single most important part, no not really, but really important.. The air box.. you need to drill three ten millimeter holes or half inch holes on the front. towards the outside (not the middle of the box!!)
you basically split the air box. unscrew the flapper stuff and remove. next get your dremel back out and start to remove the partition "but not all of it!! or if you remove too much you'll have to duct tape the giant slice of a hole you can make if done wrong!!
now personally i just got my grinder out and did use duct tape in the end..
i just found it easier and faster..plus its under the tank.. no one can see it..
back to the holes.. these holes will obviously be drilled on the top half of the air box.. and actually now that i think about it, the location of these holes are critical. this was part of the reason i couldn't at first get everything to work..
ok, put the air box together dont bother with the screws just put it in place and then put the tank on in place, don't screw that down either ..
now, part of this mod you have to raise your tank at least a half inch or more.. when you look between the frame and tank, thats where you should be able to see the holes your going to make in the top part of the box.. use a marker make a mark remove the tank, split the air box again and drill away.. so long as you have line of sight, your box will get fresh air and not whats just coming from the radiator.. now speaking of the radiator.. just in front of that is your factory horn.. remove it!! number 12 metric socket, and unplug.. use a zip tie to keep the wires together with the rest of the harness, you'll obviously need that later.. but do not put it back in that spot, it messes with fresh air getting into the box from the scoop that rests on top of the radiator..
and one last thing with this box, i'm basing all my information on the fact you have a aftermarket air filter, most likely a k/n. on the top of the k/n's there is also a removable divider built in.. maker sure you leave that ON.. that helps break the fresh air from whooshing straight into the carbs,, you want as much fresh air you can get into the box, but you need that piece on top .. i also noticed on the original swedish directions, they dremeled a 1/4" inch off the the outside of the K/N divider.. i didn't have to do that to mine, so i'm not going to suggest it here, i'm only mentioning it, because there are other threads which people may read and combine, well dont!!
i plan on editing this with pictures all week and any questions just ask them here, because it will most likely answer the same question for some one else later down the line..
i have to say, when i did this mod. i was shocked at just how much raw power the bike has with just a little bit more of fuel and air.. its also smooth, silky smooth..this was single handedly the best MOD i have done to my 95 cbr900 so far..
i have a d.d exhaust, plus four degrees advance, sprockets and K/N filter.
and by far the fastest nine i've ever driven, it even feels faster than my 97 919.

like i said stayed tuned for pictures and a explanation of the drop test method later today or tomorrow, i need to get to work or i would keep going..
one last thing, if you can clean and sync your carbs first that would be wicked smart.

cant wait to see those pics JC i got mine tore aprat right now would be a great time to do this mod.

yep, sorry i've had a couple of very long days.. finishing a bathroom for a customer.
anyway..
here are some pics of what your air box should look like before and after gutting it out.. where the holes are positioned is the most critical component of the whole mod.

Attachment 28679

after
Attachment 28680
another after:
Attachment 28681
this is after the tank is put back on and what you should see from a straight on shot..
Attachment 28682
this is what some have done to their filters, the divider has to stay in but if you notice the very outside edge was dremeled off by about a quarter inch..
Attachment 28683
this is a good little lead on cheap gaskets just for the bowls.. usually people get roped into buying the entire rebuild kit, when you really done dont it.
Attachment 28684

ok, so this covers the air box, later ill add pictures of the carbs.. and add some info on fine tuning.
i also wanted to add one last picture, this is half of my carb parts collection, the other half is down in my garage. before doing this particular mod, i've played with different size pilots, i've been up and down on the needles.. this is been quite an experience this year just on carb setups. this one by far is the best..
Attachment 28685

Nice write up, wish I had a 900rr to do this to. I wonder if something like this could be done to a 600 F2.

Good write up!


How did the bigger slow-jets work for you?

thanks guys for the comments.
coalminer frank i would stake my jets on it, that something of this nature could be done to the earlier six's. an important lesson i learned this summer is its the balance between fuel and air that make it all work with this style carburetor.. i believe its like 14 parts air to one part fuel.. so if you introduce more air then you'll require very little unrestricted air flow in order to move up on the main jet.. i also wouldn't doubt if some old school racers don't already have some tried and tested method, i would search around abit and if you don't find anything, do what i did and just buy every jet size from jetsrus scaling from 130 to 140..

anyway i promised some carb photos and here goes..
ok so you have your carbs out and the first side you pull is the vacuum needle slides..
this is what you'll see, this is the top of the needle holder
Attachment 28660
now thats out of the carb body, take one of thee three screws that hold the cap down and screw it into this.
Attachment 28661
now pull it straight back, its ok to wiggle it.. and you'll end up with this..
Attachment 28662
now for the guys that have a jetkit this is what your needle looks like, on this picture its clipped on the second from the bottom and it actually needs to go up one more on the groove and the original washer still goes on last..
Attachment 28663
and for the guys who are building their own jet kit then these are what your washers should look like putting them on..
Attachment 28664
now when putting the needle back and sliding the holder back over you need to make sure that it goes in right and clicks, the way you'll be able to tell is from the holder side on weather or not its in there right and pushed all the way in or if something is keeping it from sinking right and still raised up a bit.. this picture illustrates its all the way in..
Attachment 28665
and the reason why im stressing this is through the years i've opened carbs and have found this..this picture shows it not seated right..
Attachment 28666
they say that needles can wear out in as little as 5000 miles, well this is the reason why..people cleaning their carbs but not assembling them right..
ok one last thing on the slide side and this is if you dont already have a jet kit installed and your slides havnt been drilled,
the guys who have jetkits installed already have this done!
with the needle out you'll have three holes in a row, drill out the two outside holes, with the drill size i mentioned above..
DO NOT DRILL OUT THE MIDDLE HOLE!! anyway heres a picture of a before and after.. this by the way helps the air pass through quicker in effect helping you to go quicker as well and dont forget to clip your springs..again ONLY if you dont already have a jet kit installed..
Attachment 28667

ok put it all back flip them over and take off the carb bowls being careful to line them up corresponding to the carb they came from..and it should look like this..
Attachment 28668
and heres a shot of replacing the main jet, its the top one.
Attachment 28669
and the is a picture of the air/fuel mixture screws.. as i mentioned above, lightly seat this and back it out four turns fro lightly seated and this way you'll have zero problem getting her started and adjusted back in later..
Attachment 28670
ok, i think that covers the carb setup and airbox next ill talk about finetuning. but thats will have to wait because i need to run some errands, but ill def have something posted up later today..

the bigger slow jets worked awesome..
just to clarify for anyone else reading this..
early in july i bought new slow jets ranging from 42 to 50.
and what i've read they actually play a significant roll throughout the entire range of throttle..
this is directly off of jetsrus's website..
3) Pilot jet (Slow jet): If unable to obtain a smooth idle with pilot screw, increase the pilot/slow jet until a smooth idle can be obtained. A larger pilot/slow jet will eliminate or reduce popping that occurs when letting off wide open throttle. The pilot/slow jet will also improve cold weather starts. Go up 1 pilot/slow jet at a time, don't skip sizes. After installing a larger pilot/slow jet, re-adjust the pilot screw. Now take it out and test ride at 1/4 throttle. If the pilot/slow jet is correct it will be easy to maintain a steady speed. Lean symptoms - if the bike surges, carb spits when throttle is opened, exhaust backfires or pops when throttle is closed, or the engine has trouble idling down, engine needs a larger pilot or slow jet to correct. If the engine idles rough, fouls plugs, or is hard to start, pilot is to big, or rich.
And this is a graph although it doesnt tell the whole story..
Attachment 28659
what this graph doesn't show is the pilot jet on our carbs go beyond the 1/8 to 1/4 throttle and actually gets added in with the needle jets until the main takes over and or something to that effect..

anyway it worked out really well..
i jetted a set of carbs for vinman, i ended up with 24 mains all across and 45 pilots..
since reinstalling the carbs after being jetted he has told me that he uses his choke alot less, which is good for the motor and it's running awesome..next he has to dyno it one more time to see if theres any real gains..
i also had the carbs on my bike up here in the north and pretty much had the same experience.. i believe it all comes back to air and fuel ratios.. so if you go up on the pilot the response on the throttle will be quicker, instead of the power coming in at 5000 rpm i started to feel it come in around 3500 to 4000 and thats legit..
instead if you go up on the mains you'll feel the power band come in at 5000 rpms as usual but the power band is so much stronger with bigger mains..
and thats my conclusion.. i hope you can make out what i mean..

wholly crap,
i needed to add this to the thread, i just got back from a riding my 97.
earlier today today i did the viking mod with a couple of differences and its dead on incredible. for starters i used JB weld to lock in permanently the spacers that raised the tank, worked awesome and i'm def doing it to my other blade..

second i went up one size on the pilots from 40 to 42 and instead of buying 4-40's from jetsrus i had about 15 or 16 118's in my collection and i decided to see if i could drill out 4 the brass mains myself.. well i didnt go from the top and i also didnt drill straight into them, what i did was put the drill in reverse and plowed the "BIT" in, that way there the drill bit wouldn't catch and carve its way into the wrong direction.. anyway it worked like a charm.. before i put everything back i double checked and balanced the carbs and good thing i did.
just took a ride and my god its the fastest rocket in the stable again..
i have to say i love this mod and would do it to every carbed bike i own in the future..

This is a great write up!!

Do you have pics on where you placed your tank spacers? I will def be soon this this winter when I have some down time to complete this

willie: i havnt forgotten about you.. i just havnt had the chance to pull the tank and snap some pictures.. ill def post some up this week.. its really simple though..
you need to find some longer metric bolts, like maybe from a local hardware store and if you can find them in stainless steel that would be even better..from that point you can build spacers a couple of different ways, either through thick aluminum stock or even stacking fender washers and tacking them together with a wielder or liquid steel or JB weld. then once its all in place especially the tank then i would mix up more JB weld or whatever and cement it all in permanently.. so you wont have to fumble with spacers every time the tank comes on and off..