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Discussion Starter #1
I'm totally stumped as to why my quad won't start. It was running fine, until I replaced the head gasket and valve cover gasket. Once the engine was together, it made a clicking sound, so I replaced the starter and the solenoid, just to be safe. Now it just cranks, and won't even try to fire. The quad has air, good fuel, and spark. It also has compression. (I checked) Any help would be awesome, this issue is getting the best of me.
 

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I'm assuming you removed the carb and tank when you replaced the gaskets.

Double check the fuel line connections, the pet cock valve, and check your idle screw on the carb.

Why did you remove the head gasket?

Do you have a compression gauge?
 

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My bet is timed wrong. Did you put the cam lobes facing down with piston at TDC? Also did you make sure when you removed the head that the spring and plunger for the auto decomp mechanism didint fall out? Last though would be a sheered flywheel key but that would make it not spark or atleast spark very inconsistant. To rule out a fuel issue spray some starting fluid in the intake tube and see if it fires on that at all?
 
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Discussion Starter #4
Ok, I'm going to double check the timing like you said. That would make sense as to why it is not firing. I'm 100% sure it has fuel, air, and spark, and I checked compression with a gauge.
 

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Ok, I'm going to double check the timing like you said. That would make sense as to why it is not firing. I'm 100% sure it has fuel, air, and spark, and I checked compression with a gauge.
Good deal keep us posted. Also double check the sping and plunger while you have the valve cover off.
 
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Alright I BELIEVE that the timing is 100% now... it still won't start. The cam lobes were facing down, the timing marks on the sprocket where level with the head, and the piston was at TDC. (I looked into the little hole until I saw the "T" mark.) Totally lost at this point. What did you mean when you said to check the spring and plunger?
 

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On the cam just inside of the timing chain sprocket there is an auto decompression mechanism. What it does is hold open a valve to help it turn over easier. It is entirely not needed on the 400ex. It was a carry over from the xr400 dirtbike that our quads get there power plant from. The dirtbike was kickstart so it was designed to keep guys from snapping there legs in two. Under that in a small hole in the casting of the head there is a metal plunger with a spring in it. That is what catches the mechanism to stop it from holding the valve open. If that is not there it will hold a valve open at a very specific time every revolution and will not start. It is very easy to have set the head valve spring side facing down on something and those 2 pieces to fall out. Happens all the time. The good news is it can be removed from the cam and tossed in the trash. You do have to plug up the oiling hole for it though in the side of the cam under it or the rest if the cam will starve for oil.
 

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Discussion Starter #11
Ok so I bought a Hotcam stage 1 for the 400ex.
I just want to clarify so that I don't screw anything up... with the spring and plunger removed and the timing set correctly, the quad should run, right? There is nothing else that has to be done?
 

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With the aftermarket cam there will be no auto decompression mechanism on it. So with the plunger and spring gone it will be perfectly fine. So yes you are correct in your thinking.

I take it the plunger and spring fell out? If they were there when you checked this last time then there would be some other reason it wasnt starting. If they were missing then yes more than likely that is your problem.
 

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Discussion Starter #13
Ok so I bought a Hotcam stage 1 for the 400ex.
I just want to clarify so that I don't screw anything up... with the spring and plunger removed and the timing set correctly, the quad should run, right? There is nothing else that has to be done?
 
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