New to Karting, Vortex Rok TT questions

[Charles Gallant]

OKay, very new to karting and trying to feel my way through things without finding out the hard way (been there, done that with motorcycle racing).

Have a couple questions on some rather basic setup/maintenance items with a Rok TT.

1. Pre-Mix ratio - Seeing a wide range of numbers and trying to get a more definitive answer on what to run. Some people are saying run 16:1 (8 oz) while others go as high as 25:1. I know with motorcycles I would run a lower ratio to provide a safer setup in my engine (more oil hopefully equals longer life). Of course that also means less actual fuel which meant higher jets to get the power. What are people actually running for pre-mix on a Rok TT engine?

2. Jetting - The (very limited) documentation I can find on the Rok TT is saying High Speed with 1 turn out and Low Speed with 2 turns out. What are people finding works best with what pre-mix ratio?

3. Exhaust Length - Okay, I know mine is REALLY Short! Previous owner had the flexi pipe cut short with the length of the exhaust flange/Cylinder head to the first weld on the pipe at about 295mm. I am finding it should be at about 395mm (and I am assuming measurement should basically run down the center of the top of the exhaust header/pipe). So I need to cut me a longer section of flex pipe. What length are people cutting their flexi pipe at to get the desired length in the exhaust? And again, what are the high and low jetting at and the pre-mix ratio for everything together?

4. Vortex Starter/Kill button plate - Okay, trying to figure out how this is supposed to attach to the steering wheel using the backing plate and screws? Just can't put the puzzle together and have it make sense (oh and actually work on my steering wheel). If anyone has any pictures how it attaches to the steering wheel, that would be good to see. I have a CRG steering wheel (three spoke with the top spoke used to mount my MyChron4). previous owner had the plate zip tied, which worked, but didn't look clean.

5. Arrow AirBox Mounting - The arrow airbox comes setup with the intake tubes mounted on the side of the airbox. There looks to be options where it can be mounted on the front, or on an angled face. With the pre-mounted tubes on the side, where should those be pointing? Up, to the side of the outside towards the pod or inside towards the drivers leg (thinking up or the outside)?

6. Operating Water Temps - What is a good operating water temp for this engine? Some people mentioned 150 F, which seems a little high. That and I couldn't get mine above 130 F this weekend, even with tape on the radiator.

Okay, so that was more then a couple questions... Thanks in Advance for any help.

Charles

[Jim McMahon]

The Vortex likes to rev so I would stay with 16:1 with a racing oil, ideally castor based. Theres some debate that extra oil makes more power with a two stroke, but im not sure if its as much of an advantage with a watercooled motor. Anyway, most people run 16:1, for the sake of simplicity stick with that.

With jetting you are entirely at the mercy of air density and to a lesser extent, where your pop off is set at. The settings that are documented are a starting point and should not be considered optimal. Sounds like you are already aware that exhaust length will affect jetting too but air density will be the high order bit. There are a lot of guides on the web for tuning two jet pumper carbs, read everything you can find by a guy called EC Birt
. You can use guides you find about leopard motor and tilotson carbs. The process/technique is the same.

Water temp ideally should be 125-135. It can go higher than that without damage but you will start to leave power on the table. Sounds like it was spot on the last day you drove it.
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[Charles Gallant]

Thanks Jim... Should have clarified for all the settings I am looking for base lines and will adjust according to conditions. But want to start at base line first rather then stumble around from random settings. Right now I think it's pretty far off and not running optimal.

The two jet pumper carbs are new to me, but should be anymore difficult then two carbs on a Honda rs250 with different setting for each cylinder

Thanks, will look p the reference material you mentioned.