Stock COLD weather jetting

After one kick she does start

But all is not well

As the throttle is slowly opened

She sputters like hell

Once opened past a quarter

The engine revs to the sky

But if timid on the throttle

She continues to die

Ah... cold weather is settling in. I have had enough winters to last a lifetime, but I'm stuck here until further notice.

I am new to TT, and I have to say that there is plenty of information on this site to keep me busy for a long time ! Very nicely done !! I have read MANY MANY posts, and all of the FAQS/TIPS/HOWTOS... all full of useful info. However, I have a question I havn't found a direct answer to... Stock jetting, and the frigid North Air.

I have a virgin TTR125. No mods of any form have been done. Also, it has less than 10 miles on it ( if I continue to let my wife ride it, it will be a "collector" before it hits a 100 miles ). :cry:

The first ride on the bike was ( ME ) at home, and the temp was around 70degF. I had no trouble whatever. It started well, and rode fine. Last weekend, however, we went to the North Woods to teach the wife how to ride... ( She's much better at cooking, but I'll give her time ). She kept killing it. The temp was about 35degF.

At first I thought it was her inexperience. Killing the engine a hundred times is par for the course, right ? Maybe so, but as I listened to the engine it seemed to be more than her letting out the clutch too quickly on an empty throttle. So I jumped on the bike myself and tested it. Sure enough, if the throttle is SLOWLY opened, it will die immediately. If I gave it a little punch, it would open up ,but with a slight hesitation. I figure from all of my reading that the "RPM death" has to do with being lean( thanks of course to TT and it's posters ! )

Here is the question ( finally )... Prelim: ALT 700ft. Gas: 92 Octane and fresh.....Do the STOCK jets on an unmodified TTR125 (VM20SS) have the flexibility/latitude to be adjusted for moderately Cold Air ( above 32degF but less than 45degF ) ??? Will I have to "rejet" with air temps in this range.

BONUS QUESTION: As I try to dial out the "death" using the stock jets and the (yamaha) Pilot Air screw, how far should I be expecting to turn it before it drops out of the carb :cry:????????

Cooler air is much more dense than warmer air. IE, it has more oxygen in it so it leans out the mixture.

I would start with the jets that I installed for a baseline to get it running. I would think the 17.5 pilot/110 main would work fine for you up there, but don't do the airbox mod or exhaust mod unless you go bigger on the jets.

the 17.5/110 combo should get you running correctly again, then you can adjust it from there as you get an idea of how it is runing.

As for the fuel screw, I wouldn't feel safe going out more than around 3 1/2 turns on it.

Thanks for the reply, ovrrdrive.

I have read in the forum/FAQS/Tips/etc that some believe that the stock jets are absolutely too small stright from the factory (except for high altitude ridiers). I will order and replace the jets next week sometime. Until then, I will see if I can adjust the Pilot to overcome the "RPM death" :cry:

I had to adjust our pilot screw out of the box to get ours to run, but jet wise it would have been ok I think. It was mildly lean, but ran great.

I wanted to get a little more pep out of it so I did the simple mods and went up in the jets to compensate for it. It really does make a difference when you open up the intake and exhaust and rejet. When you guys get it running right and get used to it, then start the mods.

You'll be glad you did. :cry:

Btw, when you start changing jets, keep us posted as to help out the next guy that comes here reading and looking for the same answer. :cry:

ovrrdrive, thanks again for the response.

I went out this weekend. The air was quite a bit warmer, and not nearly as humid. I still had some off-idle troubles, so I opened the pilot about a quarter turn from the factory setting. Seemed to help as the bike ran pretty well.

The fact that it was 20deg warmer may have solved most of my problems. I'm not sure if turning the pilot 1/4 turn would normally make any difference :cry: You could advise on that issue...

I will update if I get a chance to get out this weekend.

No problem. :cry: Just keep it in mind that I'm just speculating on my advice. None of it is written in stone.

It does sound like the cooler air was just leaning you out. If and when it cools off again, you'll probably start having problems with the stock jets again.

Look at the bright side though, when you get some bigger jets in there and the air cools off more think of the extra power it will have! Nothing like an engine that normally runs a tad rich leaning out in the cool crisp air.

Btw, I usually try to have mine run just a tad rich most of the time. Too rich and it will run bad and foul plugs, but just a little rich keeps it running cooler and is easier on the engine. It's a fine line though, I try to keep it really close to perfect. At least when the cold air leans it out, the air around you helps keep the engine cool.

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