Coupla Rotax questions from a newbie

[Nick Weil]

quote

Quote:

1. I could not get my kart to idle but it ran fine. What way do I need to adjust the idler screw to get it idle? It just died as soon as I took my foot off the throttle in the pits

Matt,
I know you're gonna hate me for this, but read the owner's manual.

The idle screw should be screwed all the way in for the highest idle setting. Keep in mind though, this is a RACE motor; it's made to run and run well at one speed... WIDE OPEN. Especially after a set of really hot, fast laps most of the Rotax's I see won't idle on their own.

On the plug issue, you are looking for a real carmel brown color. Anything real black is rich, and white or lack of color is probably too lean. You can tell when the Rotax is too lean from the popping noise between 10,000 RPM and 13,000 RPM.

Good luck...

Nick

[ August 09, 2002: Message edited by: Nick Weil ]

[Matt Golden]

I did read the manual but I was not sure which way I needed to turn the screw to get it right.

Thanks!

One more question.

The jet needle seetings. Is the jet needle a finer tune than changing the jet itself?

For instance, it says in the manual that by moving the needle to position 4 it will make the mixture richer. Is this less of an increment than going up 1 size of jet?

[Charles Pou]

Matt, for idle adjustment I found the manual to be confusing too, reference page 67 adjustment screws 34 and 29.

Basically, as I understand it, adjustment screw 34 turned in moves the slide up a little. I turn screw 34 out so the slide is closed when I am off the gas.

Adjustment screw 29 turned in decreases the air supply a little at idle. So if the fuel supply is the same at idle and the air supply is decreased, the fuel/ air mixture becomes richer.

Anyway, I agree with Nick that idle is not important. I run mine as little as possible when not on the track at speed. Plus, if you idle when you come off the track, it will give you a false plug reading.

Search this forum for info on setting the needle and jets. There is a ton of good information on this topic out there. :-)

[Matt Cleaver]

quote:

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Originally posted by Matt Golden:
The jet needle seetings. Is the jet needle a finer tune than changing the jet itself?

For instance, it says in the manual that by moving the needle to position 4 it will make the mixture richer. Is this less of an increment than going up 1 size of jet?

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No, needles and main jets control seperate ends of the spectrum. The needle position has an effect on idle and when the throttle is partially opened. The main jet is used to fine tune the wide open (top end) air/fuel mixture.

[Matt Golden]

Just took my kart out to Willow Springs for it's maiden voyage yesterday.

I followed the breakin procedures per the manual to the letter and then I ran a gangload of laps.

1. I could not get my kart to idle but it ran fine. What way do I need to adjust the idler screw to get it idle? It just died as soon as I took my foot off the throttle in the pits.

2. What is a ballpark lap time for a Rotax on YGk's (400 lbs though) on the kart track? I was running it in reverse the same way it will be run this weekend by the RMC. Nobody else was out there so I could not ask anyone!

3. Is there a good website or FAQ to explain how to read plugs? I checked my plug a few times and nothing was obviously wrong with it but I am not sure I could spot the early warning signs of a bad condition.

Thanks!

Matt

[Richard Haight]

There are basically 4 things that control the mixture, and they go in this order:

(A) Slide cut-away (as this is something you can't change, it is a non-issue). This controls the mixture, at the smallest throttle openings, I.E., as you just begin to touch the pedal.
(B) slow speed jet = from 0 to 1/4 throttle opening.(approx).
(C) Slide needle, which controls the mid-range throttle position, and
(D) Main jet size, controls the mixture from approximately 1/2 to full throttle, IN CONJUNCTION with the needle, which drops down into the main jet.

Keep in mind that that these are throttle positions, not RPM ranges!

If you are going through a corner at 9000 RPM, and the throttle is closed all the way, the RPM is not what controls, it is how far open the throttle is.

For plug readings to mean anything, you must do a "Plug chop", which is shutting off the engine when it is pulling under a load, at near top RPM, and when it has been pulling at that speed for at least a couple of seconds. If you idle into the pits, there is no point in looking at the plug, as the reading means NOTHING....

The color you are looking for, is as light a brown as possible, but you must also look for other indications, such as overheating of the porcelin, or microscopic particles way down the insulator, or where the center electrode meets the porcelin insulator.

[Craig Nunn]

The International class (YGK - 355#) pole at Willow (reverse direction) last night was 44.3 sec. The times dropped off pretty significantly form there. I qualified 3rd at 44.79 sec. The Masters class (Vega Reds - 400#) pole was in the low 45's.

Craig
Rotax#20

[ August 11, 2002: Message edited by: Craig Nunn ]

[Matt Golden]

Thanks for the info. I have a lot of work to do!!! Shave 4 seconds off my lap time and I am right there man! I Don't expect to win but would like to avoid being picked out of somebody's radiator too!

[Jim Marks]

Craig;

That was a great race, last night. I especially liked your stealth piggy-back-fuel-saving "ride."

Exciting Race!

[Jaye Bass]

Matt,

You would be surprised how much time you will be losing as you gain experience and track time. My track is a 10-ish turn 1/2 mile road course and my first race times were in the low 42 to high 41's...a year later I'm running low 39's to high 38's and getting faster...enough so that high 37's seem possible. The very fastest international class guys (i run in the masters class) are running mid 37's to a very rare high 36. Some of these guys would grid mid-pack in the shifter races.

My rather long winded point is that you will probably see a drastic decrease in times over the course of a year.