1999 YZ400F NO START??

B

BrettC95

I got this bike on a trade a little while ago, and it was running. A little rough, but running. When I brought it home, I put some fresh gas in it, since it sat for a little while, and I rode it around the back yard to get a feel for it. It lasted all of 3 minutes before stalling and never started again. I'm fairly confident this isn't user error (as far as starting procedure goes) considering I started the bike 2 times before taking it home and then again, twice, when I got it home. The carburetor was rebuilt by one of our local shops in August, but sat since then. Naturally, I assumed it to be a carburetor problem so I pushed it into the shop and began tearing the carburetor apart. Everything was spotless, as if it had just came out of the shop the day before. I took care probably everything back together and then went on a hunt for the spark plug (what a pain that is). Spark plug fouled out. So I went and bought a new one. Put it in. Adjusted the fuel screw down from 2.5 turns out to 1.5, started it, it ran for about 15 seconds and died while I was playing with the idle. I tried to start it again. Nothing. 30 minutes of kicking, yelling, and breaking my foot, and nothing. So I pulled the new spark plug out and whaddayaknow?? It's fouled. Black. Still running rich? At only 1.5 turns out? Surely it shouldn't go in any further?

Anyways, I put another new plug in, and now.... I'm getting nothing. Still has good compression, still has spark, still getting fuel (as far as I know), but it doesn't even seem like it's trying to start anymore. Is it flooded?

For the record, I can turn a few wrenches but I am in no way a mechanic nor do I claim to be. But I would like to learn.

P.S. I know this type of thing has been covered many times before, but I'm at a loss right now and having trouble piecing together information from numerous threads and forums.
 
PALMER84ONE

PALMER84ONE

WOT and kick the piss out of it at TDC in compresssion stroke. I would say flooded maybe, if plug is wet, if the carb is clean, and it's getting a good blue ark of a spark and fuel. How are the valves? If not, check resistance on coil, and stator, make sure electrical is hot, and ground is solid. Would not hurt to pull all the connectors and give them an electrical cleaning, and dialectric grease.

Good luck, keep us posted.
YZDOC out
 
Last edited:
timoyz

timoyz

PALMER84ONE:
WOT and kick the piss out of it at TDC in compresssion stroke. I would say flooded maybe, if plug is wet, if the carb is clean, and it's getting a good blue ark of a spark and fuel. How are the valves? If not, check resistance on coil, and stator, make sure electrical is hot, and ground is solid. Would not hurt to pull all the connectors and give them an electrical cleaning, and dialectric grease.

Good luck, keep us posted.
YZDOC out
Click to expand...
:smirk:

BrettC95:
I got this bike on a trade a little while ago, and it was running. A little rough, but running. When I brought it home, I put some fresh gas in it, since it sat for a little while, and I rode it around the back yard to get a feel for it. It lasted all of 3 minutes before stalling and never started again. I'm fairly confident this isn't user error (as far as starting procedure goes) considering I started the bike 2 times before taking it home and then again, twice, when I got it home. The carburetor was rebuilt by one of our local shops in August, but sat since then. Naturally, I assumed it to be a carburetor problem so I pushed it into the shop and began tearing the carburetor apart. Everything was spotless, as if it had just came out of the shop the day before. I took care probably everything back together and then went on a hunt for the spark plug (what a pain that is). Spark plug fouled out. So I went and bought a new one. Put it in. Adjusted the fuel screw down from 2.5 turns out to 1.5, started it, it ran for about 15 seconds and died while I was playing with the idle. I tried to start it again. Nothing. 30 minutes of kicking, yelling, and breaking my foot, and nothing. So I pulled the new spark plug out and whaddayaknow?? It's fouled. Black. Still running rich? At only 1.5 turns out? Surely it shouldn't go in any further?

Anyways, I put another new plug in, and now.... I'm getting nothing. Still has good compression, still has spark, still getting fuel (as far as I know), but it doesn't even seem like it's trying to start anymore. Is it flooded?

For the record, I can turn a few wrenches but I am in no way a mechanic nor do I claim to be. But I would like to learn.

P.S. I know this type of thing has been covered many times before, but I'm at a loss right now and having trouble piecing together information from numerous threads and forums.
Click to expand...

Followed by a carb cleaning.
 
B

BrettC95

I'm going to check valve clearance tomorrow, if it's out of spec, how do I go about correcting it? Never done it before :noidea:
It's definitely getting good spark, carburetor is spotless, all Jets are clear, but she won't even fire with a shot of starting fluid
 
PALMER84ONE

PALMER84ONE

BrettC95:
I'm going to check valve clearance tomorrow, if it's out of spec, how do I go about correcting it? Never done it before :noidea:
It's definitely getting good spark, carburetor is spotless, all Jets are clear, but she won't even fire with a shot of starting fluid
Click to expand...

It's electrical, or timing is off.
 
Trfsrfr

Trfsrfr

I love no-starts.
If it were mine, here is what I would do;
1 - remove valve cover, put piston at TDC, line up the timing marks on the cams and crank, ensure tensioner & guides are installed and working properly
2 - hand spin the engine over a bunch and make sure timing marks come back to TDC correctly, every time
3 - check valve clearances while you're here, if out, they're a PITA stupid design IMO. Caution, measure shims with a micrometer, not a caliper. NOTE- 99 WR400 valve specs are .15-.20mm int, .25-.30mm exh, measured cold, yours should be similar if not the same
4 - get a baseline compression reading
5 - do whatever is necessary to ensure fuel is good, clean, and available. make sure cap breather tube is clear
6 - Ensure the carb float-valve is functioning properly and float height is correct. Ensure correct jets installed for elevation/temp, write it all down. check, double-check, triple-check. Check TPS and enrichener/choke.
7 - ensure clamped surfaces like airbox and filter, and carb boot are air-tight
8 - ensure adequate spark - check stator, CDI, coil, neutral switch, etc
9 - take lots of pictures of it all

Provided you have good compression and all of the above checks out, it should fire.
 
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B

BrettC95

I believe I've found the culprit.
Valve clearance is within spec on intake. Exhaust, not so much. .23mm and .18mm. along with clearance being out of spec, the bike jumped time. Cause most likely being a loose chain which brings me to the cam chain tensioner. Went back to look at it, and it's somehow cracked?? Not sure how or why but it needs to be replaced. Thinking of just having the whole top end done as well as throwing in some hotcams.
 
2Wheels

2Wheels

Perhaps the valve seals are letting in oil as well. Parts might be hard to find for this model have you done any research on that yet? Might be a deal breaker.
 
PALMER84ONE

PALMER84ONE

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