Another stupid spark plug question.

12 replies to this topic
  • Craig E

Posted March 08, 2006 - 10:03 AM


I know some of this has been covered before, but here goes. I have the cold start for my 2000 YZ down. When it gets hot however it is a different story. I am only about 5,9 so not the ideal height for starting this type of bike. It is mainly a problem when in the middle of a salt lake or on a sand dune where I can not get some extra height. At the momment I am running 1 plug colder than standard. Would running 1 hotter make it easier to hot start? Have tow started it hot and no real problems, so no loss of spark etc. Clean fuel in tank too. Would running higher octane fuel eg 98 make hot starts easier?

  • grayracer513

Posted March 08, 2006 - 10:22 AM


Running the plug the bike calls for is the best choice. Running hotter will lead to the plug overheating, shorten its life, and possibly make it a hot spot that causes preignition. Colder plugs don't stay hot enough to keep themselves clear of fouling deposits. Neither will very much influence the temperature of the engine, or compensate for jetting problems.

The octane number of the fuel won't change it much either. It may have some effect, depending on what specific chemical means of raising or lowering the octane was used, but for the most part, it will do nothing for you. As long as you have 95 research octane (88 motor, or 91 R+M/2), you're OK.

Your problem is more likely in one of two areas: poor spark performance, or an incorrect idle mixture. For the first, start with a new plug the right heat range for the bike. Then, set the idle mixture according to the manual (an extended fuel screw helps this a lot, especially since you're going to have to do it more than once). Once you get the jetting right, and you stick to the routine that the bike likes, a 426 starts pretty reliably.

  • Fizz

Posted March 08, 2006 - 01:19 PM


i´ve found that it helps me (i´m short too, 179cm, cant put both sole´s to the ground at the same time) to sit pretty far back on the seat and kick ...
(when the bike is hot though, when its cold i need something to lean on)

  • odlaw19

Posted March 09, 2006 - 01:15 AM


I'm 5'7 and dont seem to have too many problems (now).
I dont mean to state the obvious, but make sure you are using the hot start!
I ride in temps from 10-40+ deg C and i just use an NGK Iridium plug.
As said above, its probably more to do with fuel rather than spark.


  • Yamaguy4Life

Posted March 09, 2006 - 09:07 AM


I'm 6' 2" and still have a problem. If I put the bike on the stand, it will start on the first kick. Out on the track, it's hit or miss. I can't tell you how many times I had to push it back to the truck to get it to go. It's really frustrating. I'm sure that it's me, but I can't seem to make it for a full ride without having to push it back to the pits at least once to restart it. Other than that, it runs great.

At times in frustration I have found a little hill or something so that I can get my left leg up and get in a full down kick. Sometimes it works sometimes it doesn't. The thing has a mind of its own.

  • 2fastwhitey

Posted March 10, 2006 - 10:42 PM


I have the same bike but not the same problem cause I am 6'8"(nice huh).

I had the same problems, with mine starting. When I unloaded from the truck it was usually a one kick start. When I was out riding around I could kick 3 times or more times to get it to fire. And when I was on an uneven surface I rolled the bike so that the kick was on the down hill side. (Trust me being that much taller is that great either = higher center of gravity, and my legs aren't that long my upper body is!)

How I solved this problem was to:
Run a CR8EIK from NGK, it is an iridium plug, and it made my 00' 426 start easier than it had prior. Now, I usually only have to kick it once wherever or whenever I am out riding.

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  • tmckeown

Posted March 10, 2006 - 11:01 PM



First of all it really doesn't sound like a spark plug problem.
But what comes to sparkplugs use Iridium plugs, they'll last a year.

It sound like too small pilot jet to me. My little brothers bike had similar starting problems and when I re-jet it no more probs

One thing what causes starting problems after you have transported your bike to somewhere is that when the bike is on a trailer or on a bed of truck or how ever you transport it. Bike shakes up and down and this makes that carburator to shake and empties the carburator.

Timo Mc

  • grayracer513

Posted March 11, 2006 - 01:02 AM


One thing what causes starting problems after you have transported your bike to somewhere is that when the bike is on a trailer or on a bed of truck or how ever you transport it. Bike shakes up and down and this makes that carburator to shake and empties the carburator.

If you leave the gas on in transit, it may end up causing the float to bounce some and overfill the carb, which could lead to a flooded engine. That may be what you meant.

But as far as empying the carb? The carb fills by gravity as soon as the gas is turned on.

  • tmckeown

Posted March 11, 2006 - 01:57 AM


Just like I said, it sounds like a too small pilot jet or fuel screw is too tight

To float 4-stroke, you really need to have all conditions perfect for it.

Timo Mc

  • Matt96xr6

Posted March 11, 2006 - 08:36 AM


Heck ricky is like 5'5" and he can start a 450 without issue.

I am like 5-9 on a good day. Never had a problem starting the 426. You have to jet the bike properly though. They are not jetted very well at all.

Do a search for the BK mod, then I installed the JD kit and extended fuel screw. Ran like a top, started first kick.

  • Fastest1

Posted March 11, 2006 - 09:00 AM


If it starts great when cold but not when hot I would suspect too large of a pilot not too small. Are you having to choke it when cold? If you dont have to, the pilot is too big already and giving you a rich mixture besides making it hard to start when warm it is killing your plugs. PS always turn off your fuel and let it run for a minute prior killing the engine, it will eliminate any possibility of flooding. I do this every time I kill the engine, every time.

  • grayracer513

Posted March 11, 2006 - 03:09 PM


If it starts great when cold but not when hot I would suspect too large of a pilot not too small.


  • smokinu454

Posted June 07, 2006 - 07:40 PM


Matt96xr6, I am having some jettin issues,and was just wondering what elevation you are at and what jets you are running in the 426. I got my bike (01 yz426) a few months ago, pulled the carb off and it had the stock main jet but instead of the stock 42 pilot it had a 40. i ordered a 42 , 45 , and 48. and was just wondering which one you would recomend for sea level riding. By the way i am tryin to make it easier to start. I have already done the BK mod and the hot cam AD cam.


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