99 Yzf 400f

[Ajax]

Hi guys, new to the forum. I have purchased a 99 YZF 400F and I have really struggled to get this guy to stay idling long enough to really ride it. It seems very difficult and finisky to start. I am learning to do the compression lever routine and get it to kick over about 1 out of 3 times, but after a couple of seconds of idling, it justr quites.

I changed the spark plug and although the one I took out looked fouled, the new spark plug didn't change things.

Any suggestions would be greatly appreciated.

 

[BSWIFT]

The 400 is an awsome bike but you are realizing the frustration that many past owners have had. The problem can be cured. Try the search function and sit back and read. There are quite a few things to check but when you get thru it, you'll love the bike. As hard as it will be, be patient.
Start by checking the valves. See what jets are in the carb. Finding out what your compression is and doing a leak down test in conjuction with the jetting and valves will help get you the answers you are looking for. If you don't have a manual, you really need to get one.
My reply may seem uncaring but the information you are able to provide will get you quicker responses from some of the very knowledgeable people that frequent this forum. In other words, there is no quick answer without more information. Trust me, the members here can help you sort this out but do some reading, you'll enjoy it and you will know your bike thoroughly in the end.
Good luck and welcome to DRN.

 

[02yz426f]

I dont know much, but since nobody else is chiming in I'll have to say to atleast choke the bike. If it still turns off with choke, turn choke off and try it again. If all else fails, take it to a mechanic and spend $100 to get new jets or whatever

 

[Ajax]

The 400 is an awsome bike but you are realizing the frustration that many past owners have had. The problem can be cured. Try the search function and sit back and read. There are quite a few things to check but when you get thru it, you'll love the bike. As hard as it will be, be patient.
Start by checking the valves. See what jets are in the carb. Finding out what your compression is and doing a leak down test in conjuction with the jetting and valves will help get you the answers you are looking for. If you don't have a manual, you really need to get one.
My reply may seem uncaring but the information you are able to provide will get you quicker responses from some of the very knowledgeable people that frequent this forum. In other words, there is no quick answer without more information. Trust me, the members here can help you sort this out but do some reading, you'll enjoy it and you will know your bike thoroughly in the end.
Good luck and welcome to DRN.

No, your answer does not seem uncaring. It's what I need to hear...reality from somebody who knows what they are talking about. I'll take your advise and keep you posted.

And I'd rather spend the time than the $100.

 

[Ol'89r]

Ajax.

I had a '99 WR 400 and it was a great bike. The carbs on those years were a little tricky. BSWIFT made some good suggestions and after you check those, if the bike still won't idle, you probably have a clogged pilot jet or pilot air passage.

Remove the float bowl and remove the pilot jet and air screw. Look through the pilot jet and make sure you can see daylight through it. Blow compressed air through the air passages to make sure they are not clogged. Remove the little offset cap at the bottom of the float bowl and clean it. That is you accelerator pump and they sometimes get sediment and water in there and the bike won't take the throttle correctly. If there is sediment or water in the cap, check the little rubber boot on the accelerator pump rod for damage or misplacement.

Take part of that $100.00 and purchase a service manual if you don't already have one.

Good luck. :cool:

 

[Ajax]

Thanks for all the input here. I am impressed and appreciative of the quick and helpful posts.

 

[Ajax]

OK, here's where I am. I thought this progress report might save me some work. I did the search as suggested and came up with some more info on how to start this rather narrow minded bike ;). The information was helpful and it started fine and idled with the choke pulled out, but after 15 seconds or so, started to slow down and eventually died. I was able to start it again and it ran but then started backfiring as well.

This was without changing the gas like has been suggested, because I realized as I read the article that I had been doing a "no-no" previously. That being having my hand on the throttle and not quite getting the compression lever protocol right. So I wanted to see if just by doing the start up correctly if the results would be better. They were, but not confidence inspiring. So I will get some new gas in the tank tomorrow and try again, but what are your thoughts about the slowing idle speed and the back-firing?

Thanks again for the great help.

 

[Ol'89r]

what are your thoughts about the slowing idle speed and the back-firing?
QUOTE]

Ajax.

If you cleaned the carb and visually checked the pilot jet, then check the hot start button. Remove the hot start button from the side of the carb and inspect the rubber sealing area at the bottom of the plunger. Make sure it is sealing properly.

Also, make sure the little rubber boot on the hot start button is properly seated. If the rubber boot is not seated all the way down, it will hold the hot start button open a little bit and cause a back-firing condition.

If the carb is clean and everything is in its place, a final adjustment on the fuel/air screw and idle adjustment should take care of the idle problem.

 

[02yz426f]

My 426 will not idle at all with the choke off when cold. I have to keep the choke on and turn it off right when i take off. After about 1 minute of riding, it will idle no problem.

 

[02yz426f]

Hey no worries about the backfiring. If I even turn the throttle 1/4 way on my 426 before I start that bad boy up, it will backfire everytime. Have you tried to turn up the idle or just to stay on the throttle enough when choked to let it warm up. Here is my routine to start up the cold bike. Pull choke, then pull decompression lever and kick through 2 times. bring kickstarter all the way up and let go of decomp. lever. Next lighty press the kicker down until you feel the hard spot, then pull the decomp lever and move kick starter 4 inches down. Next let go of decomp lever and bring kick starter to top and yet again push it down lightly till you find the hard spot, then kick down hard. During this process and throttle movement will delay my starting 10-20 kicks and results in much backfiring.

 

[sp1tekiller]

My RM-Z backfires when I kick it over sometimes, but doesn't backfire when running. Only occasionally when cold and I rev it hard it might pop a couple of times.

 

[Ajax]

Another progress report. I took the screw out of the bottom of the carburater and sprayed carb cleaner in there, put new 91 octane gas and she fired right up. I rode it around the neighborhood for about 15 minutes before shutting it down. Then this morning, I took the bike to Carnegie Off Road park here in the Bay Area and had a great time with the bike. I did not have time to do the servicing that was suggested, but since the bike was running I thought I'd take her out. I noticed that unless I kept the idle speed up a little, the bike would die. It was also alternating between idling fast and then slowing down and dying, so I know that I have some service work to do, but I did have a blast with this bike today. It pulls strong going up hills with no sign of fading. It wheelies as you please, which I only did once as I was just exploring the bike's characteristics. I am new to dirt riding, have only street bikes in my garage currently.

Anyway, thanks again guys!

 

[SFO]

you can lead a horse to water...