rotax carb

[jeremy shaw]

I have an older rotax carb. The 8.5 venturi with 30, 60 jets and 5.2 gram floats. I wont be running rotax series. Is there any added benefit to keeping this set up or should i go to the new jet/float combination? Also with the 8.5 do most people run the 3.6 floats or the 5.2?

[Russell Stevens]

Stick with the 8.5
http://www.ekartingnews.com/viewtopic.php?t=103418&sid=2dbc8a148ab432afdc996cebeeb1c1a2

Use the search function for info on the floats, but I would say stick with what you have for now.

Main jets - I don't know personally (I use the adjust a jet I keep telling open Rotax folks to get) but there is a chart, and a lot of good posts on jetting. From what I understand you will want a range of mains based on location and current weather.

My Rotax is an '06 with the 8.5 venturi and whatever floats it happened to come with. It has no problem getting me to the next corner at "Oh my God this is too fast" speed.

Side note (I know the question is coming) I run my powervalve within 3 clicks of 12 clicks out from fully tight. Start in that ballpark and check your tach and your but dyno. Adjust the P/V so that you get a hit at ~7500RPM.

[jeremy shaw]

haha do u wanna just tell me everything you know russell? Im looking into that main jet adjuster like you said, seems like it would make life alot easier. I've done some homework with the jetting and float height information but i was curious bout the 30, 60 jets.....i planned on using those just was wondering if the change to new current standards was more beneficial. Thanks again for the reply.

[Peter Zambos]

If you really want to spend the cash on the adjustable jet, I'm not going to get on a soap box, but really, it's a waste. I had, prior to using the FR125, had never used a fixed jet carb. We purchased Jet Tech software and did our homework and hit the track without a skipped beat.

Fyi: everybody's RAVE will be set differently. The age of your bellows, spring, and the depth of the stud in the blade will all effect the number of turns your valve is set at.

[Russell Stevens]

Peter,
So you got a laptop, a series of jets, a weather station, and the JetTech software for less then the $125 it costs for the adjust a jet? That's some deal!
Your way:
1) Boot laptop and check weather station
2) Plug numbers into the laptop and select the suggested jet
3) Drain carb, loosen boot and twist carb to get at the main jet (or remove the fuel pump)
4) Remove the plug and change the jet
5) Put everything back together, refill the float bowl, race

Not bad, that doesn't seem too hard

My way:
1) Turn main jet adjuster out 2 turns
2) Start kart on the stand
3) Close main adjuster till the engine revs free
4) Race - and I have the ability to tweek my adjustment as needed while I'm driving...

You decide which is easier and less expensive.

As far as the power valve setting, yes everone is different. I read on this very forum, however, that 10-12 clicks is a good starting point (have to start somewhere, right?) and was passing that info on to a new Rotax user. Could you imigine the frustration of a new user starting from fully closed or open, run a lap, click it a couple of times, run a lap, click it a couple of times, run a lap... If you have a better place for this new user to use as a starting point on his P/V please feel free to share. If not then stop being a negative nancy.

[Russell Stevens]

Jeremy,
You may want to note that you are running local only unsealed or open Rotax when posting. I'm making this assumption as you are doing your own rebuild. You may find that the Rotax Max gang is slightly less helpful, however, the answers you get will tend to have less of the RMax rule book mentality. Folks forget that there is a secondary market for these engines that isn't really interested in sealed national racing. Honestly if I had known what the Rotax was I wouldn't have bought mine. It's a great engine, and the RMax program does a pretty good job as it was intended. For a local guy just looking to drive fast around the track there are less expensive alternatives. In fact we just switched our RMax to a standard TAG airbox. The stock airbox is cracked, and we refuse to pay double the price for the RMax replacement. The radiator is bent and we will be replacing it with an inexpensive aluminum unit mounted like every other TAG has it mounted. Saving $200 here means that we can spend it on another set of tires and have more fun. We are running Vega Blues instead of Mojo's. The list goes on. If you have no plan to take the kart traveling, and racing at regional or national events, there is a lot that can be done to make living with a Rotax less expensive and more enjoyable. Just be aware that these changes make the hardcore Rotax guy's head spin. You have a 6+ year old engine, so I wouldn't worry about needing to get it sealed for resale value. Once you get it up and running nice, it will make a nice starter kart for someone else to buy from you if you decide to upgrade to a newer rig.

If I am wrong, and you do intend to run it in a sealed RMax class, you cost yourself money the second you cut the seal. Put the whole thing in a box and get it to an authorized service center immediately. It's going to cost you as they have to check that everything inside that engine is still to spec before they can fix it up and reseal it for you.

Oh and about the carb, most of the changes (float weight etc.) are going to get you +/- a couple of tenths depending on the track. It should run fine with whatever combo you have in there. Hardcore racers will find a way to gain any advantage they can "within the rules". Most of us schlubs wouldn't notice the change.

[Cory Ross]

If you are running any of the Rmax races I believe the 12.5 carb is no longer legal.

[Russell Stevens]

Thanks, I haven't been paying much attention to that rulebook. Guess they closed that loophole.

[Peter Zambos]

Hey, Russell, I was merely sharing what my experience was. Frankly, if you take offense at reading other peoples' opinions that might actually be different from yours, then why do you come on to a forum? Sheesh.

To be fair, we already had a laptop we could use, so I didn't really consider that. The software and the adjustable main jet are about the same price, and since a jet change only takes me about a minute or two, I really don't see the big deal. On top of that, if you're considering actually running a Rotax sanctioned race, you can't run the thing anyhow. So, since it really didn't seem like there was much benefit to us, we've avoided it.

[Russell Stevens]

Hey Peter,
Touchy much? I didn't even call you names. I simply used fact to counter that validity of your opinion. My first sentence wasn't any more snarky than your entire post.
If you had initially said that the Jet-Tech software was the best solution for those running in the Rmax series I would have had no argument. It would have also alowed the reader to make an educated choise as to whether the information applied to them or not.
As far as the jet change only taking a minute or two, I said that it wasn't that hard to do. It is easier to start the kart and turn a knob no matter how you want to slice it.
As far as running the RMax series, it take sabout 5 minutes to pull the adjuster out, put a legal jet in, and move the fuel pump back to the stock location. So like you keep saying, not that hard to do. Now, swapping back to Mojo tires for one series race (ouch) is a bit of a PIA and would certainly be a factor in me personally never running a Rotax sanctioned event. The local track I run at is all Vega Blue and MG Yellow. I have a choice of a less expensive tire, and a stickier tire that costs the same. Why would I ever run Mojo here?
In conclusion I'd like to thank you for your last post. You disclosed all of the information, and stated your opinion and why the solution worked for you. Now Jeremy and anyone else reading this post can take the information provided and make a decision for themselves.

Rusty

PS From other posts he has made, and PM's I've had with the OP I happen to know that the RMax rules do not apply to his particular situation. I've asked him to clarify this when asking questions, to help him get more applicable answers from the rest of the community.

[jeremy shaw]

sorry bout this i will be sure to include i will not be running in rotax sanctioned events in future questions.