Mikuni RS tuning help...... Please

[DCRacing]

Got a set of Mikuni's for the race bike, yes i know a set of FCR would be the shit but i have not found a good/cheap set yet.
Anyway i haven't had time to stuff around with them before now.
What is a good base jetting for a 1100 oil cooled motor?
The engine has minor mods, dialled stock cams and a port matched head.
Thanks
James

[evilkarl]

Depends also on compression. I'm running a B12 engine with gixxer diaed cams but only stock pistons/compression, I'm running 155 main jets, however a mate with a high compression 13.5:1 gixxer 1100 runs 135's. I've suggest starting with 135-140's and go from there. If you are running better pistons with some compression this would be a good starting point.

[jmw76]

DC, what size carbs have you got.
I have 40's and they work fine with 140's as the mains for most states of tune (on pump fuel).

I am now running AvGas and a CR in the order of 13.5:1 and it is still a bit lean on 150's. I have also had to lift the needles with the AvGas.

Cams in my engine are standard (J cams).

You might find this link of interest
http://www.mikuni.com/pdf/rs_app_parts_lists.pdf

Cheers

[DCRacing]

Thanks Karl, Peter,
They are 38mm carbs, trying to run a smaller size carb so that i get a bit more torque out of the corners...... or that is my theory.
I will probably run AvGas/Tolulene mix at the moment, to try and help keep the motor a bit cooler.
Thanks James

[Dynomutt]

Start with a 135 mainjet,needle a 9CHY3, clip on 2nd groove,needle jet Y6, pilot jet 17.5, and the pilot mixture screw 1/4 to 1/2 a turn out from fully in. These are the stock settings that Mikuni reccomend for the RS38 when fitted to an oilcooled 1100.
Run them open or with short velocity stacks, fitting any form of filter will knock the performance down. I run all of mine open with short stacks and they run fine.
Initially set the accelerator pump to start activating as the slide passes 1/3 venturi height, and then shut off about 3/4 height, and fine tune from there. As long as your fuel is of 98RON you should not need any additives, and rather than trying to add toluene to control detonation three is a product available called "Power Pour" which is a specific anti detonant and works extremely well it was developed by the drag racing guys, and works well on high comp N/A motors as well as boosted ones.

[DCRacing]

Thanks Dyno, I will give it a shot and see where i end up, I have no real expierence tuning engines and rely on a couple of others who tune engines but not for racing as such, a lot of this stuff is falling by the wayside as it is all EFI, still tuning but a whole different world now.

[DCRacing]

Hmmm, Looks like the power pour is a UK product, I haven't found anywhere over here that supplies it.

Anyone know of a similar product? I am only using toluene based on another racer who runs a GSX1000 or 1100, he uses it in Avgas.
The ratio i am pretty sure is 15l Avgas, 3l Toluene, 2l PULP. The pump gas for the additives, the Toluene for the detonation and to help keep the air/oil cooled motor cool.
Also i can get Toluene for $85.00 for 20l

[Redmohawk]

There are a few in Aus Zoom magazine did a write up on most of the popular ones using a turboed beast that had pritty repeatable runs on boost.

Seems most are a ethanol/meth carrier with a few additives (some use toluene but not all) , and are of limited use with real octane boosting. Most will reduce pinging a little but if your looking for significant amounts and in "open fuel class" Making your own is prob the best bet. I would look at a meth/toluene/Xyleen mixed with some avgas (the 98 ron Pulp will only drag your ron down there is enough additives in avgas by its self and your adding what pulp has in it anyhow) . As I'm sure you know altering your fuel mix this significantly will alter the air fuel ratio.

As for a sorce for the Xyleen, I would chat with who ever is supplying you with Toluene as it also a paint thinner.

Here is some info I stole from somewhere a while back for your amusment/information. \/\/\/\/\/\/

Chemical: RON / AON / MON (RON for the Europeans, AON for the Americans, and MON for anyone else who knows that this number is more important for high specific output engines, when blending with fuel and not evaporating (for a number of reasons, but mainly because the test was on an engine under more load, with hotter coolant, and a controlled intake temperature))

Shell "91 Octane": 96 / 91 / 87
Iso-Octane: 100 / 100 / 100 (by definition!)
Toluene: 124 / 118 / 112
Ortho-Xylene: 122 / 112 / 102
Para-Xylene: 155 / 141 / 126
Meta-Xylene: 162 / 143 / 124 This one is great if you can get it !
Cyclopentene: 171 / 149 / 126
Benzene: 98 / 95 / 91
Cyclohexane: 110 / 104 / 97
Cyclopentane: 141 / 141 / 141
Butane: 113 / 114 / 114 (gasseous)
dicycloepentadiene: 229 / 198 / 167 (OMG shoes! )

Methanol: 133 / 119 / 105
Ethanol: 129 / 116 / 102 (beer! )
Iso-Propyl Alky: 118 / 108 / 98 (rubbing alcohol)

[DCRacing]

oh joy now i need to think about it.........
Thanks for the info it is what i am looking for, I just need to see what i can get and what ratios to mix it

[Redmohawk]

Old formula 1 mix was mostly (80%) toluene with some heptane But the motors did go bang fairly often (most would finish a race lol). I wouldnt go any more than about 15% Toluene 15% Xylene 5% meth 0.5% Acetone 64.5% Avgas, keep in mind this would be about the limit with off the shelf performance valves (you could cook an exhast valve if you push it to much further) the meth will help with vaporisation and with its ability to suck away some heat on an air cooled motor cant hurt.

If you want some real bang for your ml of fuel drop in a little Nitro to the mix just use Nitro mix from a hobbie store (you can buy it 50% nitro 50% methanol no oil) if you replace the 5% meth with the 50 50 mix you will gain a good push but not cause to much issue with tuning.

On the negitive side all of the first 4 will eat rubber and most seal types aside of silicon, and do tent to eat Aluminium to. Its also a little unstable and will seperate so mix your brew the night before a race then keep in a fuel can and shake the crap outa it before use (i used the ute bouncing to track to shake it lol)

Back in the old days of stone wheels n shit when I was racing, we would empty fuel tank after each meet drain fuel bowls then flush with avgas and a little castor oil ,running motor for 5 min with a little fuel bag made from blood bags hung from roll cage. (could do same from handel bars on a bike) Did see a fellow who didnt bother and his motor wasnt to happy at the end of his first year of racing.

Also keep in mind none of these are to good for your health, the toluene and xylene arnt directly carconogenic but can contain contaninants that definitly are. Burnt exhaust gases are not such a big issue as long as your not running a pipe from the exhaust to your helmet but the raw fuel fumes should be avoided !!!
And the fuel mix will smell very different to regular unleaded or avgas so people will know your runnning a Special Mix so I wouldnt bother if your in a fuel resticted class (very easy to smell a cheat)

[Redmohawk]

Also keep in mind this shit can be a little tricky to lite, so a tip top ignition is the key. Vaprisation of Toluene and Xylene isnt as good as the avgas but the meth/Acetone will help there a little.

[DCRacing]

Hmmm some serious stuff in there, but it sounds like fun!
I was thinking of running the 15% Toluene, and the Avgas, but i might try and run a bit of the Nitro mix. I have a Dyna2000 with Dyna coils so ignition should be alright..... i think.
This meeting is unlimited, but the others won't be. My plan is to run Avgas/Toluene mix as my main fuel source, and just hope they don't come round and do some fuel testing.
I think i am pretty safe as it is club racing, older bikes (1990/1994, they are old now) and only local at race meets. If i head down south then i might start chasing 'legal' fuels and tuning to suit.
Most of the race fuel on the shelf is bloody expensive and can be a pain in the arse to get here, some of it has been sitting for at least a couple of months, but they say it isn't a problem....

[Redmohawk]

If your planing on a "Standard Mix" then for the odd occasion a "little Nitro" to make it interesting be sure to keep the A/R ratio on the rich side when running the Nitro (it has free o'2 and when ignited needs a rich mix or you will have the same issues as running a motor had with a lean mix) If your running 12.5 to 1 A/R flat out "without Nitro" you want at least the equivalent on 12 to 1 A/R with 10% nitro in the mix (I'd start with something like 11.5 or even 11 to 1 first and lean for more power carefully while looking at plug earth strap etc).

Once you have your base fuel at a stage where your happy , and motor tuned to this. Try jetting/neadle setup with the same mix but with a combo that is at the richer setting then after you have the mix right (motor will be a little off but not much) then add the Nitro mix and test test test ! Don't be supprized if the nitro mix responds to some healthy timing advance to.

Top fuelers run mostly Nitro with some Meth to thin the mix and make it a little more handeling friendly (Nasty stuff at 100% nitro as it goes boom easy, hard to store at below constant 24 deg c needs container venting etc etc) They run around 1.7 to 1 A/F ratio hence the reason the motors hydrolic when one plug miss fires more then 2 times in a row lol Is a common reason for Blower's letting go.

Good luck and Dont Melt Shit lol

[DCRacing]

Thanks for all the info Red, it is going to give me a bit of fun. I have a bloke who is a bit more in the know, and has played with some of this stuff but i don't think to the extent that you have.
But that is what i love about this site and the people on it, Happy to help and give me a few pointers in the right direction............or heap shit on us :)

Thanks

[Redmohawk]

I know that when you fuck it up and don't know what your doing , you can turn a $4k rebuilt motor into slag. Start slow go smart and all will be fine.

[jmw76]

Hmmm.

Not sure why the interest in the witches brew.
Why don't you just stay with what you can buy.
AvGas or JFP105 should do it.
I am assuming this is for race purposes as you can not run AvGas on the road.

[DCRacing]

I am running a mix that a fellow competitor runs in his air/oil cooled GSX. He claims it helps keep the temp down, I was always going to run Avgas but he suggested mix a bit of toluene and that would make a big difference.
So i will give it a go and see how much betterthe final tune is over the current setup......