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Discussion Starter · #1 ·
Hi, New to the forum. I have a Fourtrax that has been running fine and then stopped starting. First I check for spark and it does have spark against the head when I pull the plug and hit the starter. Then I thought maybe carb was dirty so I pulled it and cleaned it then reinstalled but still will not start. Gas flows freely when I turn the bowl screw and has good flow when I pulled the filter hose and turned the petcock as well. Any ideas where to start next? Also I have a video of it trying to start but not sure how to upload it to the thread, or if that will help at all with diagnosis. Thanks for feedback.
 

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I'd check the compression with a known good tester next. Once cylinder pressure is verified to be within specs I'd check the timing chain and valve timing.

Let us know what you find,
 

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Retro is on time -- I would do a compression test , fresh it should be right at 200psi , when it gets down around 100 it is either dead or dying , I would eliminate a dirty carb by either spraying some starting fluid or gas into the carb and see if it hits , then I would check the slack on the timing chain by removing the slack adjuster and see if it will go flush against the block while it was loaded , if it does then the chain is stretched and the timing will be off -------- when you cleaned that carb did you soak it in a gallon can of carb cleaner then blow out every hole with compressed air , you think you have it clean ???
 

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Fish is a 100% right about a clean carb, it needs to be surgically clean, not even a microscopic bit of paper towel or cotton off a cloth.

Clean, clean and clean again ;-)
 

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Discussion Starter · #5 ·
Thanks for all replies

Thanks for all the replies so quickly. I will check the compression and timing chain next and get back with what I find. I did let the carb soak over night in carb cleaning bucket and blew all channels and jets with compressed air then checked against the sky for light in every jet hole. Everything that I checked looked very clear.
 

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So I checked the compression and it is only reading 30. The kick start can be pushed to the floor with my hand.
Was that compression reading with the throttle wide open? If it is 30psi that would explain why it won't start.
 

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Discussion Starter · #9 ·
Yes it was, should I start with checking/replacing valves or just pull the entire head and replace including timing chain if I go that far. Thanks for responses.
 

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being that you said it was running fine and just quiet and now has 30 lbs of compression and don't run , makes my first guess that it is timing chain , I have found that around 90 lbs of compression they run terrible it at all , so to get to 30 in one moment you would have had to drop a valve thru the top the piston or something bizarre which you should have noticed a noise or such , if it jumped timing then the piston could go up on the compression stroke and the valves be either opened or closed to long or too short a time to achieve higher compression , are you sure the compression tester is good , try another gauge and make sure the throttle is opened , just recently a friend tested 80 lbs of compression on a 300 and after I told him to open the throttle he got it up to 140 , which is still low but should have run , it was the timing chain on that one
 
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