starting bike 1998 yz400f

17 replies to this topic
  • honda0071

Posted January 03, 2008 - 08:57 PM


to bviously everyone here knows this topic if they have ever owned a yz400f or 426 they are a bitch to start... im only a 17 year old kid thats a whole 140 lbs and i finally got the startin sequence down... i finally got it down.;... and then i broke the kick starter.... ok heres the question. i would start the bike after i ot sequence down and it would run with choke on great and idel for about 30-50 seconds then i would go to put the choke down and it either die or die eight when i gave it gas??? wat is it.... i already changed gas with new gas even drained carb... and put new plug in... then okay heres big situation i was pull startin it with a quad and it was workin i just woudl put it in third pull compression brake then let go and jump on it.;. and it would start but take long time to warm... i messed with the idle on the carb... it was better then i had to let it idle for about 3-5mins while being pulled behind quad.... i dont know y its doin this just is... is everyones else take this long to warm? and does it back fire? i do have to fmf titanium pipe on it and it is ****in loud and it does back fire but once warm stops basically... can ne one help.. o and does ne one know how to make the starts a little easier..????? wat can i buy to make it easier? cuz its a bitch on the trails lil me tryin to start it... and does a spark enhancer help i've seen them and they say they do but do they really? and does ne one or ne thing make an electric start for this bike... ne help greatly appreciated

  • smokin529

Posted January 03, 2008 - 09:07 PM


Have the valves adjusted.

  • sac36555

Posted January 03, 2008 - 09:15 PM


hey, your in luck. i have a '02 YZ426F and had the same problem. It was impossible to idle, it was either too high or too low. and when you crack the throttle back, it dies. also, it backfires when you let off the gas...i hope this is exactly what is happening to you because i have the solution!!!!! RE-JET/RE-BUILD the carb!!!! if you cant re-jet it yourself, bring it to a shop. I did it a while ago, and its like night and day better. also helped with starting. ITS STILL A BITC... TO START, BUT LESS OF ONE. the electric start is going to add weight which the bike is already heavy. try the carb first and see how that goes.

  • honda0071

Posted January 03, 2008 - 09:50 PM


will it really help?

  • sac36555

Posted January 03, 2008 - 10:42 PM


re-jetting/re-building the carb, while taking it apart and cleaning everything is the first thing to start with. you can find carb re-jet/re-build kits at your OEM dealer, or online. here is a good sight to look at, and there are several others that you can find online.


  • Birdy426

Posted January 04, 2008 - 12:13 AM


Most likely your pilot jet is plugged up. Take the carb off, take it apart, and clean everything. Remove the jets and blow them out with compressed air. If they are gummed up, soak 'em in carb cleaner. Be careful not to lose the o-ring, washer and spring on the fuel screw when you take it out as well. Before you spend the time and money to get a jet kit (although the James Dean JD jet kits do rock!), make sure what you have is working right.

If you don't think you can do the carb, have a reputable shop do it for you. It's really not that hard to do with basic hand tools and a manual. Where in Cali are you?

Once the carb is cleaned out, you should also check the valves as previously mentioned. Tight valves will cause hard starting. Again, checking the valves isn't hard with basic tools and a manual.

Once you're sure the valves are right and the carb is right, it should start. For what it's worth, my big bore 426 takes about a minute or minute and a half to warm up enough that I can take the choke off without it quiting.

A PowerNOW or other intake wing (search the ThumperFAQ site for JamesNOW to see how to make your own) also helps starting, but really doesn't help low end power like the folks from ScaryFast say it does...

Good luck and get those wrenches turning...also, check eBay for a kick can usually find one cheap there.

Oh, and just cuz you're 17 and a buck forty shouldn't make the 400 harder to start. The kick through really isn't that big a deal.

Finally, I don't mean this as a flame or anything, but how about taking a little bit more time to punctuate, check spelling, capitalization, would make your posts much easier to understand and really help those of us trying to help you.

  • honda0071

Posted January 04, 2008 - 10:55 AM


ya i will take the carb apart its pretty easy I've done it before just never messed with the jets before... and is the valve adjustment hard to do... no special tools needed? i've never done on a bike before i've looked and messed with heads on cars just not bikes and this is my first big thumper i've had smaller others and to strokes just never big thumper so ya thanks for help greatly appreciated.

and i am located in northern California.. i am an hour north of Santa Rosa in Lakecounty by Lakeport or Clearlake... theres some bomb trail riding up here u should come check it out or if this helps Cobb, CA 95426 thats where i live or Lakeport's area code is 95453.

  • stnkbg1

Posted January 04, 2008 - 01:41 PM


Forget the bike, you need to study more. That was so painful to read I just gave up.

  • yamaha racing 230

Posted January 04, 2008 - 06:07 PM


i agreew ith birdy426 im 16 and 140 pounds and my yz400f isnt hard to start once u know the drill

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 1rkcooper

Posted January 04, 2008 - 07:03 PM


If you don't have a manual, get one BEFORE you start. Do a good job of cleaning the carb. Adjust the valves, be careful not to drop the retainer clip into the motor when you remove the cam caps. You best have an extendable magnet for getting it out, I think most of us have probably dropped a clip. Read the manual and follow it and you will have no trouble. After you have it running correct then you can do the auto decompression mod to make the bike start almost as easy as atwo stroke, yes it does make that much difference.

Read this thread it is about the decompression mod

  • dave_k_714

Posted January 04, 2008 - 09:09 PM


I have a 2002 426 and i agree with the carb cleaning.
I as well put a low compression cam in my bike and i don't have a compression lever anymore. Ever envy someone with a newer 450 and how easy it is to start?
Get the cam. I almost sold my bike to get something that would start easier until a guy at work told me about the cam. I can start my bike in flipflops!!!
$150 for the cam and they can drop it in when you get a valve job.
I LOVE my bike

  • Birdy426

Posted January 04, 2008 - 09:10 PM


Checking and adjusting the valves is not difficult, but you need a manual (See the sticky on FAQs on this forum to download in multiple languages in PDF format, and also to find a thread on checking valves), patience, a quarrier inch drive torque wrench that reads in in-lbs, and you may have to order or buy new shims. Also, get a set of motion pro valve feeler gages (http://www.motionpro..._feeler_gauges/) ...they make getting to that center intake valve a lot easier.

If you were in SoCal, I was going to offer to give you a hand, but NorCal is a bit of a haul...

  • moto416

Posted January 05, 2008 - 09:22 PM


if you were pull starting it alot could have stretched timing chain

  • grayracer513

Posted January 06, 2008 - 12:43 AM


if you were pull starting it alot could have stretched timing chain

Please explain that one.


Posted January 06, 2008 - 10:55 PM


I have a 98 YZ400F and I adjusted the valves,rebuilt/rejetted/tuned the carb,new plug,91 or 104oct fuel and it starts on the 1st kick after prime and idles for about 3mins with the choke on and runs like a raped ape.:banghead: Hot starts no problem.......I wish my Husky 610 started like that:banghead:

  • BergArabia

Posted January 07, 2008 - 08:24 AM


I agree that the drill thing is very important as is having a good clean carb.

I did the cleaning thing on my 450 and also noticed a great improvement

  • moto416

Posted January 07, 2008 - 06:56 PM


I was told at my local dealership to NEVER roll start a 4 stroke mx bike because it would stretch the timing chain i have no explanation but thats what i was told

  • grayracer513

Posted January 07, 2008 - 07:58 PM


I was told at my local dealership to NEVER roll start a 4 stroke mx bike because it would stretch the timing chain i have no explanation but thats what i was told

You can categorize that tale correctly as Bovine Scatology, or as the techs in the field like to say, BS. The timing chain is aware of nothing that goes on other than whether the crank is turning or not, and if it does, it drives the cams. Driving the cams is no harder regardless of whether your foot, the rear wheel, or the piston is driving the crank.

How the hell some of this crap gets started....:banghead:

I'll bet one of the guys in Sales told you that.

Related Content


Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies

Chubby dad, looking at bikes , First trip to the orange/black forum ! by Slow_ride

Dirt Bike   Make / Model Specific   KTM   250-530 EXC/MXC/SXC/XC-W/XCR-W (4-Strokes)
  • Hot  28 replies

Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • * * * * *
  • 1 review
  • Last review by Tommyk_55
  • On January 15, 2017
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.