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2003 Suzuki ltz 400 compression problem/will not start


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Did you torque everything down to spec? Did you put the right size piston and rings in? When the new vavles were put in, did you get new guides or seals, did you get a valve grind? If any of these things is off, or wasn't done or done properly, you could be losing compression because of it. The problem could also be that your cam timing is off. If the valves are open when they should be closed, your motor won't build compression. Also, if you have a decompression mechanism and it wasn't put back together correctly, you could be losing compression because of that. Do you know if your quad has a decompression system? If it does, it is most likely built into one of the cams.

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What about the rest of the stuff I mentioned, did you put the valves in yourself? Did you get a vavle grind when you put the new valves in? If you didn't grind the valve seats, the new valves may not be properly seated. Did you torque everything down properly? Did you check the head to make sure the sealing surface is still flat? There are only so many ways you could be losing compression, you just need to take a really close look at everything to see where it is going. Good luck.

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Thanks for your input dirtdemon. Me and my buddy have been working on the quad for a few weeks now.. The top end on the wheeler has been torn down twice, and the head taken off about 4 times(not my quad not exactly sure how many) but anyways, the gaskets were never changed. Im thinking this could be leading to his compression problem but im not sure, any ideas?

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Very possible that the old gaskets are your problem, since the valve seats were not re-ground for the new valves, that could be adding to the problem as well. I would order a whole top end gasket set and double check everything when you tear it back down. New gaskets are pretty much necessary when doing a rebuild.

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Please watch the language JP, and good luck getting that thing fixed. If you are still looking for a place to get parts, Bike Bandit, Service Honda, and Babbits online are all good places to get O.E.M. parts. Rocky Mountaing ATV is a good place for aftermarket stuff. Ebay is also a good place to find good deals on parts.

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  • 3 weeks later...

I'm pretty sure I have tried to explain to you the idea of keeping your old thread going instead of starting a new one about the exact same thing. I'm not trying to be an as*, but I also don't like having to repeat myself. I moved your post into the old thread you started. PLEASE, don't start new threads unless you are jumping to a different subject. It cuts down on clutter in the forum and also gives people who might be trying to help a chance to read over the history of your issue and see what input others have offered, so it is to your benefit as well.

Now, it is really tough to know what you may have missed, diagnosing a problem with so many possible causes is quite difficult to do without having the machine there to look over in person, so any little bit of info that you may have to add will be of great help.

I think the most likely problem is that you may need to bore your cylinder and jump up to the next size larger piston. Some other things that come to my mind are; your vavles may be adjusted too tight, you may have some kind of damage to your cylinder wall, your cam timing is off. I know this has been a problem for you for quite some time, hopefully you can get that thing fixed. I know how disappointing it is to have a machine down. Good luck man.

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One easy test would be to use compressed air to find the leak. 30 psi is way too low. Drop the piston to BDC and use your compression tester fitting to pressurise the combustion chamber with an air hose. Look for the leak. The rings will blow buy but if it's a valve seat issue you will hear it thru the carb or exhaust. If the jug or head is cracked the cooling system will start to bubble out coolant. ( remove the oil filler cap and radiator cap before doing this) If it's air cooled, forget the radiator portion.

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well my wall is fine. and i set the timing a few times and i just got new valves. and sorry for putting up so many postes

Don't get me wrong, please feel free to post as much as you want, just don't start a whole new thread when you already have one going on the subject. If you have any questions, or want a suggestion on anything that relates to your problem here, post 100 times if you want. I don't want you to think there is such a thing as posting too much, if you have a question or something to say, feel free to post it.

When you say the wall is fine, do you mean that it appears fine? or did you have the cylinder measured with a micrometer to see if it is worn. You got new valves, but did you get a valve grind? New valves in an old head with worn valve seats may not seal too well. Did you check the valve adjustment? Replacing old valves with new will most likely change the valve clearance, if they are too tight, they won't close all the way and compression will leak by. Id say that the most likely cause is that the cylinder has become too large for a standard piston or your valves aren't closing because they aren't adjusted properly.

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