Question about 2002 Yamaha YZ 426 F

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Yamaha YZ426 not starting after head gasket repair. bike was starting easy before repair New timing chain new spark plug, everything done by the manual.triple checked before assembling and still get nothing. what could be the problem

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This could be a compression problem, Try Removing spark plug and use a compression gauge

You may not have sealed the head proper and bike is lacking in compression..

Posted on Jul 06, 2010

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Well, the first thing to check is compression.
If the valves are miss-timed that will affect compression.
If the gasket is not seated correctly, that will affect compression.

So compression can tell you a lot.

My first suspicion would be valve timing.
You could possibly have damaged the spark plug wire

Try a little starting fluid. If it starts easily with starting fluid, then the problem is probably associated with the carburetor. (If it has a vacuum-opened fuel petcock, there could be a small hole in that vacuum line, for instance.)

Posted on Jul 06, 2010


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Hi, Brian you need "FIVE" things in order for a cylinder to run properly:
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Bike will only run on center 2 cylinders,it was woking fine and then it started to run ruff and now it only will run on 2 cylinders,the other 2 have spark.could it be a timing chain?or fuel? when i removed...

The timing chain runs the cams for all no it shouldnt be the chain
with 4 cylnder bikes the two outside cylnders run off the same coil, but if you say it has spark the next step is fuel.
Make sure the battery is good and the bike is charging, and put some new plugs in after the carb clean.

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On your yz426 you have 1 spark plug.Its located in the center of the head. Look for the spark plug wire. unplug it from the plug you may not be able to see the plug its down in the center of the head. Hope this helps

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Hi everyone I got problem with yamaha yz426f Well head gasket was leaking. the bike was staring good before repair. How I had head gasket replaced and head machined I assembled bike by the manual...

get a leak down test it answers all questions gasket leaks or valve leaks piston leak down its the only way to tell answers with out tearing it down again you can do your self or your local shop can do it
My guess would be leaky intake valve giving blow by under compression and I have seen plenty come back from machinest still leaking when you assemble them back together
Leak down test is the answer then you will know where to start

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