Beginner YZ400f


6 replies to this topic
  • Jeff22

Posted December 06, 2012 - 09:51 PM

#1

Hey guys, I'm new to dirtbiking and I have picked up a 1999 yz400f, I have only been out on it for a couple of hours and so far I've noticed a couple things:
lots of backfiring on decel, and hesitation when cracking the throttle either in gear or in neutral. My friend, who has been dirtbiking all his life and does his own repairs, figures the pilot jet is clogged and we plan on taking it apart and cleaning it out. Is he right? I ride at around 1300 feet/400 metres and just wondering if the stock size 45 pilot jet is good for this elevation. The previous owner said that he had adjusted the needle jet a couple of notches to richen it.

So far I have done nothing to this bike, just wanted to get some opinions on the things I should do to it in the spring before riding. I plan to do a fresh oil/filter change and air filter clean for sure. My friend suggests we do the wheel bearings and possibly linkage bearings. I also want to gear the bike down to maybe 14/52. I plan to do mostly trail riding and the stock gearing (14/49 I believe) is way too tall.

I am somewhat capable of doing repairs/maintainence and what I can't do myself, my friend could help me. I am open to all opinions and suggestions, keeping in mind that I do have a tight budget, being 16 and only working a couple times a week. I am only looking for a trail ripper that is easy on the wallet, and not a done out motocross bike. So please do share what you think I should/shouldn't do to my bike.

One more question about oil, I know the manual says to run the yamaha factory oil, but this stuff is expensive. Is it really necessary? Would I be okay as long as I run the proper weight oil?

Thanks.

Edited by jdwxyz, December 06, 2012 - 09:58 PM.


  • grayracer513

Posted December 07, 2012 - 07:35 AM

#2

lots of backfiring on decel, and hesitation when cracking the throttle either in gear or in neutral. My friend, who has been dirtbiking all his life and does his own repairs, figures the pilot jet is clogged and we plan on taking it apart and cleaning it out. Is he right? I ride at around 1300 feet/400 metres and just wondering if the stock size 45 pilot jet is good for this elevation. The previous owner said that he had adjusted the needle jet a couple of notches to richen it.


Read:
http://www.thumperta...599#post3710599
...then if you proceed with the carb:
http://www.thumperta...726#post8021726

You might want to restore the needle to its stock position.

... please do share what you think I should/shouldn't do to my bike.

Maintain it. Keep the oil, filters, chain, linkages, etc. clean and lubed and in good condition. Don't get caught up in spending for trick stuff on such an old bike. It's a good machine, and nearly as reliable as a manhole cover, but it's old tech (mostly in the suspension department) and when you could get an '06 or '07 for $2000-2500, why spend $900 on fixing up a '99 that already works? Ride it and enjoy it.

It's a purpose-built MX bike, so it has a close ratio gearbox. That means low gear is tall, and fifth gear, not so much. Lowering the ratio with a bigger rear cog will help with trail riding a little, but it will do more to cut the top speed, which may or may or may not be a problem for you and how you ride.

One more question about oil, I know the manual says to run the yamaha factory oil, but this stuff is expensive. Is it really necessary? Would I be okay as long as I run the proper weight oil?

Everyone wants you to use their branded products, and oddly enough, it's not the best stuff you can get for the purpose. Oil is, to an extent, oil, and if you use something reasonably good and change it all the time, you can get away with it. The thing is that your engine oil lubes the transmission as well as the engine, and that introduces another element to the equation.

Read:
http://www.thumperta...s/#entry2132297

  • Jeff22

Posted December 07, 2012 - 06:03 PM

#3

Thanks!

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  • vic2340

Posted December 08, 2012 - 10:07 PM

#4

Listen set the carbto stock jetting specs. Your elevation allows for it no problem. Make sure to check your accelerator pump, leak jet, and everything else to make sure nothing is clogged. If it is clogged soak the parts in parts cleaner, dont try to stick stuff in the jet holes for this can scratch them/ bend them and increase your jet size without you even knowing you did so. If the carb is cleaned well and accelerator pump has a good diaphram and is set to stock and the problem continues its either your valves, or an exhaust leak. check your valve clearances, I would do that even if the bike runs well (its easy and doesnt hurt) and make sure you are running at least 93 octane gas. If you do all this and it still runs like shit I can tell you some more things it could be but they are more involving and rare.

  • Jeff22

Posted December 10, 2012 - 07:52 PM

#5

Thank you, I will be looking into this in the spring, as my bike is currently put away for winter.

Edited by Jeff22, December 15, 2012 - 10:30 AM.


  • beercan

Posted December 11, 2012 - 07:04 PM

#6

Hey its nice to see im not the only one still riding a 400. The 14/49 gears i found not to work in tight trails your idea of going to 14/52 is what im using and i find it works really well u can do this cheap im using primary drive brand sprokets and there dirt cheap and last for a long time. Im not really into spending a lot of money for a old bike. As far as your carb i went one size bigger for my fuel jets it seams to work and most of the popping is gone checking your acc diaphram is good again a couple of jets and a diaphram dont coast a whole lot. Now one thing iv figured out is the gasket between your header and muffler is a wear part i go threw 1 a year but i ride year round there about 18 bucks still not expensive. as far as your linkage and bearings i just pull mine apart and grease them a couple of times a year as needed for the bearing if they dont wable i wouldnt change them. thats about all i really changed with mine other than that do your regular maintance and mine has been a really reliable bike i hope yours is to.

  • Jeff22

Posted February 13, 2013 - 05:59 PM

#7

Thanks, beercan!





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