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Top end engine noise when revving hard

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Hello all!

I'm new to this forum so please be nice! :p

I recently bought a 2000 drz 400k (unknown hours) and it has been running pretty well. I went out riding with a few friends (one of which also has a drz 400 (2011 model though) ) and he said I wasn't revving it anywhere near as hard as it could go. I started revving it out a little harder and in a particular rev range it rattles quite vigorously and looses power. It kinda sounds like a tea spoon landing on a kitchen table, but obviously really fast. Maybe a valve adjustment? It definatly sounds like its coming from the top end, and it's worryingly loud so I don't rev it that high anymore. I thought it was valve bouncing until I read they have a rev limiter.

I was told the engine has had a top end rebuild although he had no receipt for it. It does seen to produce a pretty decent thump so it sounds like its had a rebuild.

I was going to take it into the local mechanic to have a look but due to a lack of funds I am unable to. I can more than likely do the work myself if its not overly difficult.

It has also been backfiring a little lately. Some very small when rolling on the throttle from decelerating but other can be extremely loud and only occur when decelerating (in gear with no throttle or breaks applied). Could this possibly be related or is it common for a drz?

Sorry if this question has been asked on here before but I couldn't find anything that matches the description of my bike's issue.

Thanks in advance for any help :D

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Stop riding it until it has been inspected by a good mechanic. It could save you a lot of money in the long run. Most likely the person who rebuilt it was incompetent and hasn't done it properly. Better to get it checked out before your cylinder head gets a hole blown out of it. And I'm not sure what your friend means by telling you to rev it a lot harder... Like to the limiter? If so it's completely un-necessary. Bikes don't make their maximum hp/torque at the rev limiter so it's pointless revving that high apart from it sounding kinda cool.

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This is what happens when you ignore engine rattles... ImageUploadedByThumper Talk1377081536.326263.jpg

I bought it off a guy knowing it was blown up and spent $1000 completely rebuilding it. I got the bike cheap so it didn't bother me about fixing it.

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Thanks for the fast reply! Looks like ill have to take it to the mechanic to have them check it out (the only place for 250kms is Honda but they should be able to suss it out). The weird thing is the engine sounds perfectly fine until that high rev range!

I completely agree about not revving it to hard as I've read that they make their power down low so there is no need to rev them too hard.

Any ideas on the backfiring issue?

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Thanks for the fast reply! Looks like ill have to take it to the mechanic to have them check it out (the only place for 250kms is Honda but they should be able to suss it out). The weird thing is the engine sounds perfectly fine until that high rev range!

I completely agree about not revving it to hard as I've read that they make their power down low so there is no need to rev them too hard.

Any ideas on the backfiring issue?

The problem may only be as you said the valve clearance. Hopefully that's all it is because that's easily fixed.

It may be backfiring because the fuel mixture is to lean. The Carburettor probably needs adjusting. It's not a drz thing. All bikes should run without backfiring if tuned properly. If you tell the mechanics about what it does they should be able to fix it if they know what they're doing ;)

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Good luck with it. Let us know what the go was with it when it's fixed.

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If you're wondering about the mechanical sound that sounds like valves, it's valves; and not usually a big deal. Wouldn't hurt to adjust/inspect your valves (mine sound like that at perfect adjustment); however my cylinder ignition sounds quite a bit different, but it could just be your exhaust/camera audio that makes it sound bad.

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Update:

I did an oil change and the bike seems much happier. The rattle still occours every now and then but now not as often.

The oil was extreamly black so it was pretty screwed lol.

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Thanks for the fast reply! Looks like ill have to take it to the mechanic to have them check it out (the only place for 250kms is Honda but they should be able to suss it out). The weird thing is the engine sounds perfectly fine until that high rev range!

I completely agree about not revving it to hard as I've read that they make their power down low so there is no need to rev them too hard.

Any ideas on the backfiring issue?

what does "suss" mean? Is it like sort? or figure? 

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Hello again!

-just keeping you all updated.

I was riding down a dirt track and the bike just stopped. There was a small metallic sound then no compression. It sounded like with every stroke it was backfiring (like a bent valve or a broken timing chain).

Got it home and without looking at it (don't have time to as I'm flat out with work) I took it into the local motorbike mechanic.

Apparently it spat out the spark plug! So they replaced it an tested it with no other issues found. That rattle in the top end must have been the spark plug coming loose! (as it's the only component I haven't checked since I bought it ( didn't have the tool :p)

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