Jetting & tire question

Dai Feng · Posted: Mon Sep 23, 2002 9:40 pm Post subject: Jetting & tire question

Hi,

More novice questions. According to the RM manual, using lean jet could cause engine sizure. I assume this is becaue a lean jet causes the engine to run hot, thereby damaging engine. So if I watch my engine temperature carefully, even with lean jet, I should be able to spot the problem before damage is done, right?

I understand the spec tire for RM is Bridgestone YGK. Is there a longer lasting tire for practice? I plan to run lots of practice laps until I can get real consistant lap times before playing around with setups. Any pointers on the kind of tires and where to get them for a good price is most apprciated.

Dai

erik nystuen · Joined: 06 Mar 2002 Posts: 319

Dai,
Being new to Karting and Rotax this year myself. I spent the year practicing and have finally decided on trying BS tires for the first time.
I tried Dunlop, Ok the ones I had were great for lots of laps of practice, but I didn't see much improvement in my lap times with them. The harder I pushed there was just very little gain. (this could be set up, and a learning curve too. So don't judge by that alone) Tires were good for 300+ laps on 3/8ths mile sprint track.
Tried Vega XR's and chopped off a full sec on my lap times, Rear tires were great, but had a real problem with the front. Seems that the rubber on the front is not as thick as in the back and went through a set in just over 100 laps on the same track. (set up and time of year "summer" could have some to do with the wear)
BS YKC's, Have almost 100 laps on them and chopped almost another full second on my lap times. Little to no wear and I am very pleased with the handling.

Granted this all could be my learning curve here, but I am amazed at how well the BS YHC's perform and the wear I am getting from them. They have brought confidence in my driving to the point where I plan on racing for the first time this w/e. Finally I'm only 1/2 sec off the normal lap times of the front runners in the class, So maybe I will not get lapped in my first race

Sorry can't help you with the lean stick question, as I haven't stuck my engine yet. Then again I haven't touched the Carb either. All I have done is clean the filter, exhaust valve, change gear oil, Plugs and replace muffler packing. My engine might be a little on the rich side, but fowled plugs are cheap insurance IMHO.
Cheers and best of luck.
Isn't it a blast!

Nick Weil · Posted: Tue Sep 24, 2002 6:42 am Post subject: Jetting & tire question

Dai,

You're going to get in trouble if you keep reading that owner's manual. Just kidding, I wish I had more customers like you actually...

Unfortunately your assessment of how to 'see' a lean condition before it happens will not work.

A lean situation can occur at any engine temperature, and can seize the motor within a few seconds if the conditions are right.

Your primary defense against this is going to be to ALWAYS start out running a rich jet and rich clip setting and gradually adjust towards the leaner end of things.

The best way to determine if you are where you need to be is through the plug reading.
Hope this helps...

Nick Weil
SpeedQuest Website

[ September 24, 2002: Message edited by: Nick Weil ]

[ September 24, 2002: Message edited by: Roger Roatch ]

Jim Emerson · Posted: Tue Sep 24, 2002 8:02 am Post subject: Jetting & tire question

Dai,

The BS YGK are pretty hard and have lasted pretty well and seem very consistant from our racing this past year. They won't beat a SL4 Dunlop or YHC BS in lap times but they also don't fall off after being worn down some. Not a bad training tire in my mind!

-Jim

I saw some good prices with Acceleration Karting for a set, unless Nick can match the price when you buy jets from him!!!

Dai Feng · Posted: Tue Sep 24, 2002 7:31 pm Post subject: Jetting & tire question

Erik, Nick, Jim,

Thanks for your insights. It looks like I will stick with YGK and see how long it would last.

I had seen in the owner's manual about repacking the muffler, but can't quit understand why. Perhapse the sound damping material is all gummed up with unburned oil? But the muffler is closed with rivets, which does not seem to be intended for openning. How do you repack the muffler and what material to pack with?

I did not see any mention of cleaning exhust valve in the manual, however. When I detached the pipe from the exhuast port, I didn't see any thing obvoius that need cleaned near the openning. What is there that I should clean

Dai

erik nystuen · Joined: 06 Mar 2002 Posts: 319

Dai,
Go to the Rotax web site Rotax and select the "More Details" on the Formula Engines FR 125 MAX.
From there select the "Repair Manual" link.
Page 29-31 has the Exhaust valve info. Page 42 has the exhaust packing info. SSC has the packing and it is realy easy to replace. Drill out the rivets and remove, replace packing and reasemble.

Cheers