Cold Starting Problems

I have a '01 YZ426. I absolutely love the power but there is something very bad about this bike. I'm about to trade it in on a 2-stroke. I had no problems in warm weather at all. Now that it's cold, the bike will only start on a new plug. And you guys know what a pain it is to change plugs. It will run all day and you can re-start it as long as the bike stays warm but as soon as it cools off ya gotta change the plug. Then it'll start on the first kick. I have a WB E-series exhaust, BK mod. I've tried both the stock jetting and a 148 pilot with a 165 main. Any help would be greatly appreciated. I love every other aspect of this bike. But it caused me to miss a moto at my last race. If I can't get it fixed I WILL be mixing gas again.

I am assuming you are using the drill properly to start w/o constant blipping of the throttle like you would do on a two-smoke. If not, do a search on the "drill".

If you are then note that you MUST adjust the fuel screw when the weather turns colder. Are you experiencing any popping on deceleration? An idle that "hangs" a little high after the throttle is chopped? If so, your idle circuit (and starting) is too lean. A cold bike needs RICH to start. A hot bike needs lean.

Try adjusting the fuel screw OUT (to richen) in 1/2 turn increments before you trade it in for a two smoke. If you get more than about 2.75 turns out you need a bigger pilot jet. Be sure and note your original position. I usually adjust to get a very very slight popping on decel with no hanging idle.

You may also benefit by giving one or two blips of the throttle prior to starting to richen it up. No more than that though!

If that doesn't do it repost for more advice!

I adjust my fuel screw almost every time I ride. Sometimes two or three times. Depends on how big the temperature difference throughout the day.

Steve T

[ February 11, 2002: Message edited by: skthom2320 ]

I had the same exact trouble as you with my '01, except it was happening in warm weather too. Ran like a top and started great all day. Then after sitting over night the next day it needed a new plug to start. The solution for me was to change brands of gasoline. Fixed the problem 100% with no other changes. I'm not swearing that this is your problem, but it's worth a shot before you trade it in. I've ridden in temps from the high 90's to the high 60's without touching the carb and haven't had any plug problems, though it does run a little lean in the cooler weather with the stock setup. Good luck!

Ok, up untill last week I hadn't even touched my carb. It was doing this with the stock jetting. After reading quite a bit on this site I took the carb off, and did the BK mod. I also went from a 42 up to a 48 pilot. I went from a 162 up to a 165 main. I rode the bike for about an hour, it ran great, probably better than ever. The next day it wouldn't start. Yeah I do the correct drill. I will try a different fuel but I doubt that is it because I never ran just one brand and it's been doing this since like Oct. Maybe I should try the 45 pilot? With the 42 it definately had a lean pop on bottom end. By the way my air screw is at about 2.5 turns out.

It can't hurt to try a 45. Maybe you are excessively rich on the pilot. I would think you would feel it when riding though??

I have seen quite a few posts talking about weird starting and plug fouling issues. Some of them were solved by careful cleaning of the carb particularly the pilot circuit. Other's were solved by swapping CDI's, and yet others were solved by switching to race fuel.

A search using the term "plug fouling" turned up all of these posts. Too many to link to for you though. You'll have to do it yourself (search function is at upper right of page).


Steve T

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