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Discussion Starter · #1 ·
So I just rebuilt my 400ex top end and I put it all back together and it won't start. I have read and read and read online trying to figure out what might be wrong.
Here's a little background on the problem I am having. After I put the quad back together I turned it over a few times and I heard something that I hadn't heard before. I seemed as though there was air got back into the carb and coming out the air filter. I figured the timing was off and took the valve cover back off and re did the camshaft and timing. After attempting to start again I gave up and here I am.
I have a few thoughts on what could be wrong. 1) Timing is still of and I just fail at that or 2) the cam spring and plunger have fallen out causing the quad not to start. I suspect that it is most likely 2 but i have no idea what these things do. If you guys could give me some detail on what these things do that'd be great and if you guys have any pictures on what I should look at to check to see if it's there or not.
Thanks everyone
 

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First I'll guess the cam timing was wrong and you bent the valves

Second, I'll guess you didn't retract the cam chain tensioner when you installed it possibly damaging the tensioner.

Do a cylinder leak down test to find out where the air is going.
 

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Lock the crankshaft at TDC of the compression stroke, install an adapter into the spark plug and using comperssed air, slowly put air in the cylinder increasing the pressure up to 150 psi. If the valves are bent, you will detect air exiting the combustion chamber through the intake, exhaust or both before you get more than 30psi into the cylinder.
 

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Discussion Starter · #5 ·
well i didnt do that but i instead took the whole head off and poured some liquid to see if any of the valves were leaking and it turns out one of the intake valves leaks. The thing is I cant get the valve out bcz its bent. How should I get it out??
 

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Discussion Starter · #7 ·
When I took the engine apart the first time I brought it to school and took all the springs off with a spring compressor and took the valves out and cleaned them. When I did this the valve that is leaking now wouldn't come out then either. So is it possible that I have had a bent valve the whole time and have been running my four wheeler like that? Also, how hard should I hit my valve. I attempted to take it out with a hammer and pin but was scared on hitting it too hard and decided to just leave it in.
 

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trx400 big bore problems

I have a 2004 trx400 ex and i put a 440 big bore kit. I couldnt get my quad to star i had my timming right and i ll only crank but nt start . After a while i figure out that if i loosen out the valves ill start . Now what can be done to fix the noking of the lossen valves
 

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trx400 big bore problems

I have a 2004 trx400 ex and i put a 440 big bore kit. I couldnt get my quad to star i had my timming right and i ll only crank but nt start . After a while i figure out that if i loosen out the valves ill start . Now what can be done to fix the noking of the lossen valves
Hi I'm having this same issue, have you figured out the issue?
 

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Hi I'm having this same issue, have you figured out the issue?
jrodtrx has not visited the forum since Jun 6, 2013 - you would have better response just starting a new thread, describe the problem IN DETAIL and wait for an active member to respond. Now while jrodtrx has not been active, if he hasn't changed his email address or died of COVID, he will get a notification and might get back with you.
 

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So I just rebuilt my 400ex top end and I put it all back together and it won't start. I have read and read and read online trying to figure out what might be wrong.
Here's a little background on the problem I am having. After I put the quad back together I turned it over a few times and I heard something that I hadn't heard before. I seemed as though there was air got back into the carb and coming out the air filter. I figured the timing was off and took the valve cover back off and re did the camshaft and timing. After attempting to start again I gave up and here I am.
I have a few thoughts on what could be wrong. 1) Timing is still of and I just fail at that or 2) the cam spring and plunger have fallen out causing the quad not to start. I suspect that it is most likely 2 but i have no idea what these things do. If you guys could give me some detail on what these things do that'd be great and if you guys have any pictures on what I should look at to check to see if it's there or not.
Thanks everyone
Have you checked the valves and make sure there adjusted correctly I had same problem and valves needed adjusted hope this helps
 
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