Question about 2004 Yamaha YZ 450 F

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Machine will not start ...having cheked the timing time and time again i am 100% sure it is spot on.... but the machine will not fire up. I have stripped it down to replace the big end bearings and it will not fire up ...any suggestions ?

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I am also having this problem with my 03 yz 450f, took it apart to replace crank and now it wont start. how much do i need to ****** the timing, also i am checking for a fouled plug, but i'm pretty sure its not getting gas or its out of time, thanks for any info that can get me in the right direction.

Posted on Sep 30, 2009

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Check for spark. Check for gas. timing must not be dead nuts on TDC it must be retarded a little. Do you have the manuel?

Posted on Sep 28, 2009


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1 Answer

Timing correct firing off

what engine Shawn. ? how can we guess that?
besides following the FSM steps, we could:
ive rebuilt many engines (done many from scratch) +machine work.

1: I check compression 1st. on all cylinders. (i put oil in the cyl, 1 teaspoon) (some pros run oil gallery primers pumps first in pro rebuild shops) i just crank the zero fuel engine until i see max oil pressure.)

oops. ? no oil pressure, oops, compression bad. on 1 jug.
(all that good, so)
2: i then crank it over , with no spark or fuel and check for top end oiling. Valve covers off. (so those V.C go on last)
ive watched many an noob burn up a new engine, not doing the steps in the rebuilders books. it only takes me 30min. to do this. why skip it.?

3: ok , I got top end oil, got 150psi on all jugs. (hard work pay back)

4: i check for spark all cyl. it's strong, & out comes the timing light.
oops, timing is off, or spark wires routed wrong, (dizzy engines)
i check all cylinders for hot spark and #1 timed right. and routed right.
the strobe light never ever lies to me....

5: wow ,car runs on test fuel (spray can, CRC engine start with top end lube feature) (fuel pump is shut off on purpose , in all steps to here)
i repeat this say 3 times, listening carefully for noises, that are not good. (why start the engine and watch it blow up. )
It is so good, to hear it run for 3 seconds,, wow.
im 100% sure you can get here..... if you do the steps.
Now comes, light the fires and kick the tires. not FIRST.

6: now comes fuel
how to get fueling to work.
that takes understanding the ASD and how to use a $1 NOID lamp.

I check injectors then add fuel pressure.
are the injectors firing?
injectors ,click cranking ?(stethoscope tool $5)
if not, use the NOID, is the PCM firing the NOID? y/n?

why do this , with pump dead.
Answer to not wreck your new rings, all washed free of all oil buy
injected, unburned raw fuel .. that is why.
i get all my injectors firing then , turn the fuel pump on.
its your hard labor, 50 hours? to build and engine?
wana waste all that? nah.
I last , plug my fuel pump back in,
does the PCM start enging for 2 seconds, and then cuts fuel?

ive never burned up a new engine, yet,
im not lucky, or smart, just had good teachers.

jeep ways!
I kill my pump by pulling the pump feed wire.
i do that because some newer jeeps , kill everything (ASD) including spark,
if you pull the fuel pump relay. (jeeps with new pump monitor features)
so i cut the feed AFT of the relay, on all cars. (conn. pulled)
the FSM shows this spot.

hope that helps.

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Will not stay in time

Are you sure it is coming out of time? What are the machine simptoms?
There are many spots that a machine can come out if time, there are also more that one timing aspects of a sewing machine.
It is important to find out where it came out of time (what joint came out if time) and reset it there.
Usaly if it comes out of time again and again it is a loose timing belt(not sure if it is that because some brothers have timinig belts and some dont).
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if the car ran fine before you did the timing belt, than most likely you dont have it in time or the distributor is not in the right spot.

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If it has fuel, air and spark, it only needs one more thing to fire,...compression. If it has those four things, in the correct ratio, it MUST fire. If you are 100% sure on the fuel, air and spark issue, start looking at the timing. I would also have the codes read off the ECU. Could you have " thrown " the timing belt?

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Will not kick over have cheked and replaced carby and still no fire there is not a great deal of spark but it is a new spark plug and coil so do u have any ideas ???

If this is a 2 stroke, it's probably time for new rings. Do a compression check. If it's under 85 psi, it'll never start.

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Hi just read your posting.Are you 100% sure the black marks are grease or oil?If you are then the only place the oil comes from is the gearbox.This means that to repair this fault you need a new gearbox.Unfortunately the repair is not cheap so I would recommend getting a service tech out to confirm.Every time I went to a customers house and I saw this problem then I would tell them the same thing.Once again sorry for the bad news and please reply if you need any more help or advice.Good luck.

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