Kick starter locked after valve adjustment '98 YZ400F

[ezekielvictor]

So I did the valves on a '98 YZ400F. Both exhaust valves needed 1 size down (180 to 175), and two intake valves needed 3 sizes down (they had 180 shims and no clearance so they're now at 165 and the clearance is in spec). However, the bike still does not start (it didn't before the valve adjustment either) but also the kick starter is consistently stuck about 3/4 of the way down, which was not the case before. I can pull in the comp release which allows me to kick it through, but no matter what the kick starter will not go all the way through.

I want to fix this problem before continuing on trying to figure out why the bike won't start... I looked it up and saw issues regarding the crank or kick starter gears, but considering that the only thing I did was adjust the valves in the time that this problem happened, I'm horribly in the dark as to the cause of this problem.

Thanks for any help.

-Zeke

[grayracer513]

Can you kick the engine through with the compression release held in? If so, what you're experiencing may simply be the resistance of normal healthy compression.

If not, first, separate the kick starter from the condition by removing the spark plug and turning the engine through using a socket on the crank through the access plug on the left side cover. If this works, and the kick starter does not, the problem is with the starter.

If the engine does not turn through freely by rotating the crank directly (don

t force it), you may have the cams timed incorrectly since setting the clearance.

Watch these two videos regarding the starting procedure:

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_a.mpg

http://www.yamaha-motor.com/sport/4stroke_vid/4_stroke_vid_b.mpg

[ezekielvictor]

Here's the rundown:

1. Engine cranks over smoothly through the access plug.

2. Kick through is easy and without resistance with the comp lever pulled in.

I guess there's probably no issue here then given your notes.

At this point, I have to deal with a leaky float bowl (swollen float gasket, a la this thread), so unfortunately I can't go out and attempt that starting procedure right away. But I think (and hope) you're probably correct that it's just healthy compression. ?

This is the first racing 4 stroke I've owned and attempted to kick over, so I'm probably not use to that huge compression resistance anyway. I had a street legal KLX300 that at times was extremely difficult to kick through, and that one didn't have a comp release. I guess the resistance is probably to be expected for this YZ.

Thanks for your help! I'll let you know what happens.

-Zeke

[bluethumper98]

You can not kick that bike through the compression stroke. I know because I have a 98 yz400. You have to cycle the engine to the compression stroke, pull the decompression lever and allow the kickstarter to move 1 to 2 inches. Bring the kickstarter all the way up and then kick. There is a video on YouTube on how to start this beast. If you do not follow this ritual it will NEVER start. But once the bike is right it will almost always start on one kick. I bought mine for 700 bucks because NO ONE could figure it out.

[ezekielvictor]

OK, so I fixed some impending issues (namely a leak around the float bowl lip), and I attempted to fire her up given the method shown in the video. I actually got it running for a fraction of a second using the hot start before it died out after having kicked it over 5 or 6 times by the method.

If my idle screw were way off, could that prevent it from starting, even if only for a few seconds? I ask because when I got the bike from the PO, the idle screw was turned literally all the way in. I backed it way out, but I really don't have any guide or judgment as to where it should be. Any tips on this would be much appreciated... I have a feeling this issue isn't helping my situation any.

Thanks,

Zeke

PS: I've already checked/changed/adjusted a lot of things, namely:

1. Oil

2. Air filter/air box

3. Carb cleaning/gaskets

4. Acc. pump/float valve rebuild

5. Sealed exhaust

6. New plug

7. Valve adjustment

8. Unplugged kill switch, which was testing bad

[grayracer513]

If by "idle screw" you mean the mixture screw in the bottom of the carb, yes, screwing that all the way in will mess with your starting. Gently bottom it out, then unscrew it 1 3/4 turns as a base setting.

If you mean the black idle speed knob on the side of the carb, that needs to hold the throttle slide slightly open in order for the engine to idle or start properly.

[ezekielvictor]

If by "idle screw" you mean the mixture screw in the bottom of the carb, yes, screwing that all the way in will mess with your starting. Gently bottom it out, then unscrew it 1 3/4 turns as a base setting.

If you mean the black idle speed knob on the side of the carb, that needs to hold the throttle slide slightly open in order for the engine to idle or start properly.

I meant the idle speed knob... There's not really a spec for it.

The pilot screw I've already adjusted to the spec in the manual, which was 1-3/8 turns. Should I disregard that spec and back it out to 1-3/4, or will that tiny difference not matter as much to keep the bike from starting?

On a side note, I tested the spark wire and it is sending a spark, and the plug is new. That should be good.

I backed the idle speed knob way out and turned the hot start on and could really hear it attempting to run for a few kicks. Those could be very revealing conditions, but then again I'm not experienced at bringing a bike back to life. -_O

Thanks,

Zeke

[grayracer513]

When you backed the idle speed all the way out, you closed the throttle completely, and it won't start that way. The hot start helps it because it adds in some of the air that should be coming past the slide.

Hold the throttle grip closed with a very slight pressure while you turn the speed screw back in so that you can feel when it starts to actually lift the slide. Either that, or remove the linkage cover and take a look.

The bike is set up to start and run at idle speed. If the idle speed is set to zero, that's all you'll get. You can hold the slide very slightly open manually, but this is difficult for most people to get the hang of at first.

[ezekielvictor]

grayracer, you're a madman and a genius. (!!!) I know it may not seem like a big deal, but it is to me... Thanks! ;D

I have most of the external stuff off right now for ease of diagnosing/testing, so I was able to look at the slide wheel and watch as I turned the screw in. I turned the screw in until the slide pulled just a fraction of a millimeter as you described, pulled the choke, and fired the bike up first kick!

It idled pretty low with the choke on and would die with the choke off, so I'm assuming that I can probably can get it going fine by turning the idle speed screw in as needed. Unfortunately, I had to run to work and tonight I'm going out of town, so I won't be able to test this until tomorrow morning.

That said, it's definitely running now, and I'm super excited... Maybe if I can tune it right and there's no other issues, I can take it for a spin this weekend. ? Thanks again!!!

-Zeke

[ezekielvictor]

So I turned the idle speed up a decent amount and it idles great but only with the choke on. As soon as I push the choke back in, it just dies immediately. On another note, it got real hot, smoked a little, and smelled like burning slightly when I first fired it up. Coolant and oil levels are good (and it's fresh coolant/oil).

[grayracer513]

So I turned the idle speed up a decent amount and it idles great but only with the choke on. As soon as I push the choke back in, it just dies immediately.

Sounds like a blocked pilot jet. It might not look blocked, but the orifice is so small (<.020" quite often) that just a dried film of fuel varnish will reduce its size by as much as half.

https://www.thumpertalk.com/forum/showthread.php?p=8021726#post8021726

[ezekielvictor]

Is it worth trying to clean that kind of super tiny gunk out (as opposed to just getting a new one), and how should I do that? I've already blown out all the jets and passages with carb spray and compressed air. That was one of the first things I did actually...

Should I just soak it in carb spray for 15 minutes or something?

[grayracer513]

I posted a link to cleaning techniques. Did you read it?

It can often be a simple matter of dislodging the film. Air and canned carb cleaners won't usually do it. If that fails or if you damage the jet in the process, then a new one is in order.

The biggest problem with the YZ400 carb is the YZ400 carb. It's the old FCR design, and they can get to the point where there isn't a point any more. In this case, buying a good used '05 or later YZ450 carb is great drop on mod. Really fixes the situation.

[ezekielvictor]

I read it; I just don't know with that measure of success/error how I can be sure the problem is with the pilot or not. I guess I'll just try cleaning it using those techniques... But if the problem persists, I can't really be certain I actually cleaned it fully and without damaging it unless I replace the pilot, right? (This is the computer programmer in me.)

But if it's easy enough to dislodge the film, then I guess I shouldn't be concerned about the above.

[grayracer513]

... But if the problem persists, I can't really be certain I actually cleaned it fully and without damaging it unless I replace the pilot, right?

No, you can't.

[ezekielvictor]

All right, I made sure to clean it out real meticulously (but carefully) with a brass bristle, followed by carb cleaner + air. Went all over the carb once again cleaning and putting everything to spec (namely float height, pilot screw) while I had it off.

Still the same problem. ? I took this opportunity to catch the problem on video, though, which might help you help me.

[grayracer513]

Did you also check the pilot air jet in the mouth of the carb?

[BlindLOKI]

If you try everything gray says and it still doesnt work, you should sell the bike lol That guy is a genious and knows yammies like the back of his hand? hes helped me on more than one occassion.

edit: double check your hot start isnt leaking... that would make it die with choke off and run with choke on, kind of lol

I think it could be that your pilot jet is too small though... I had to back my screw out to almost 2 1/2 turns before it ran right, meaning I need the next size up in pilot jet. There is a good write up in the intake section of this forum on how to decide which jet you need. Its pretty easy to tell, if you get it running like you did, leave the choke on, and start backing the mixture screw out. if the idle rises, turn your idle screw (black knob) to bring it back down and continue the process untill you can get it to run w/out the choke... then do the same thing untill you get to a point where backing it out actually slows the idle down and makes it seem to bog out, then go a half turn in and set the idle... that should be about where it needs to be. From that point turn your bike off and turn the mixture screw in counting how many turns out you are. If you are over 2 you need next size pilot, under 1 next size down, between 1 and 2 you are ok.

also, bit of a side note, this is a mx bike w/ no fan, so youll need to blow air into the radiator and watch for it to overheat during this process. If it starts spitting coolant shut it off and give it a break leaving the fan on. It may take a bit to get right but will pay off in the end, I promise.

as far as the bike idling down after start up could simply be that it pulls extra fuel for a second when you kick it, not so much of a problem as long as it doesnt constantly fluctuate.

hope this helps! ?

[grayracer513]

...double check your hot start isnt leaking... that would make it die with choke off and run with choke on, ...

That's a good point. I thought we had touched on that, but apparently that was in another thread.

The hot start on the 400 is mounted to the frame near the air boot, and runs a hose to the intake port on the head. If the valve does not fully close, or if the hose is leaking (or actually missing), this would cause your problem. If in doubt about the valve, just plug off the port with a vacuum cap or a piece of hose blocked off with a golf tee or a ball bearing.

[ezekielvictor]

Thanks for your continued help.

Did you also check the pilot air jet in the mouth of the carb?

Yes, fully cleaned, no obstructions, look good -- both air jets in there.

I think it could be that your pilot jet is too small though

Do you have any suggestions as to how to adjust it while the carb is on/bike is running? I actually wanted to put an MSR extended screw in when I first took the carb off, but the threaded part won't fit through the hole in the float bowl.

double check your hot start isnt leaking

I'm going to run and get some vacuum caps to plug it off, so I'll get back on the results of that.

Meanwhile, here's some jetting specs for this bike:

main standard: #175 (#178 on BikeBandit)

my main: #175

pilot standard: #45

my pilot: #45

starter jet standard: #65 (#72 on BikeBandit)

my starter jet: #65

Of note is that the starter/pilot jet numbering is switched around on the '98 diagram...