Engine "pauses" and idling is uneven

[tudorv]

Hi everyone! This is my first post here so bare with me. I tried finding some info on my problem but I could only find bits and pieces in other people's posts.

In short - I bought a 2004 gz250 in November and was only able to ride it for about 1000 miles before winter hit hard. I never took the bike to a mechanic - I figured I would do a full service in the spring.
However, I noticed that the engine doesn't run very smooth when idle. It's barely noticeable, but it goes up and down, up and down. And also from time to time it "pauses". It's hard to explain this. If the engine is cold, it dies when this happens. If it's hot.. it sort of resumes normal idling a second later. It ONLY does this when idling. Other than this, the engine runs fine. Pulls ok. No backfires.

A friend said that most likely the timing chain is loose. But the bike has only 10000 miles on it. Coult this be right? Or maybe dirty carburetor? Valve timig? Spark plug?

Where should I start to get to the bottom of this?

Thanks a lot!

Tudor

[bonehead]

Could be the carb needs cleaning, but mine was doing the exact same thing and I adjusted the valves and it went away. But I knew my carb was clean. Start with the simple stuff and progress up to the difficult.

[OldNTired]

Originally Posted by tudorv

Hi everyone! This is my first post here so bare with me. I tried finding some info on my problem but I could only find bits and pieces in other people's posts.

In short - I bought a 2004 gz250 in November and was only able to ride it for about 1000 miles before winter hit hard. I never took the bike to a mechanic - I figured I would do a full service in the spring.
However, I noticed that the engine doesn't run very smooth when idle. It's barely noticeable, but it goes up and down, up and down. And also from time to time it "pauses". It's hard to explain this. If the engine is cold, it dies when this happens. If it's hot.. it sort of resumes normal idling a second later. It ONLY does this when idling. Other than this, the engine runs fine. Pulls ok. No backfires.

A friend said that most likely the timing chain is loose. But the bike has only 10000 miles on it. Coult this be right? Or maybe dirty carburetor? Valve timig? Spark plug?

Where should I start to get to the bottom of this?

Thanks a lot!

Tudor

Sounds to me like an air leak by the carb. Check the clamps and air hoses.
You can also, when it is at a fast idle (preferably), spray the area around the carb with WD40 (or a carb cleaner but be careful to keep overspray off of the paint). If the RPMs go up there is a leak.

[PimpS]

Try the drain hose from air filter. Mine wasn't idling bad, it was when i gained throttled it stalled... The mess i made when removing the cap... But the bike went like new after...

[tudorv]

Thanks for your replies, guys!

I know it's not an air leak - i've experienced those before on other engines and i know what that does. It comes with loss of power and very high revving.. so most likely it's not that.
The air filter and carb will get cleaned in the spring along with the oil and filter change. But I am worried as to how complicated and costly would it be if the problem i'm having is coming from the cam chain.
Is changing it a difficult operation? I don't trust mechanics where I live (Romania) - would that be a thing I could do in my garage? And also is running the engine like this potentially damaging? I mean do you think that this kind of issue consists an emergency, or I could take my time fixing it?

Again, thanks!

T.

[Water Warrior 2]

Do the simple easy stuff first. Oil, filters and air box drain. Quite often it is simple and some maintenance is needed to get the bike running properly. I would suggest a new plug and an inline fuel filter also.
Before I forget. The air filter is a reverse flow arrangement so you have to remove it to inspect the inside where it gets dirty first. The air box drain must have the plug in the bottom too when the bike is running. It is actually a seal to keep the entire air intake system working as designed. Without the plug the engine will draw unfiltered dirty air.

[OldNTired]

Originally Posted by tudorv

Thanks for your replies, guys!

I know it's not an air leak - i've experienced those before on other engines and i know what that does. It comes with loss of power and very high revving.. so most likely it's not that.
The air filter and carb will get cleaned in the spring along with the oil and filter change. But I am worried as to how complicated and costly would it be if the problem i'm having is coming from the cam chain.
Is changing it a difficult operation? I don't trust mechanics where I live (Romania) - would that be a thing I could do in my garage? And also is running the engine like this potentially damaging? I mean do you think that this kind of issue consists an emergency, or I could take my time fixing it?

Again, thanks!

T.

I can't comment on the cost, I am sure prices are a lot different there from what thwey are here. AS far as dissiculty, it is not very difficuly at all. It will take a few hours if you are not experienced. There are a few of us on here that can walk you through it, and there is at least one very good write-up. Still, I wouldn't do it if it wasn't really needed.

[jonathan180iq]

Has the motor been harder to start in general, to coincide with the funny idle issue?
If so, it sounds to me like it's just time for a valve adjustment.

There is a guide here on the site:
viewtopic.php?f=8&t=5061

The other suggestions, like making sure your carb is clean and checking the condition of the carb boots, vacculine lines and maybe even installing a fuel filter for good measure anyway, are all sound. On this bike, a fairly consistent treatment of carb cleaner in the gas tank every few fill ups is a good idea. Better to have the peace of mind than to always be worrying about it. A simple fuel filter goes a long way in taking care of some of those issues as well.

I wouldn't immediately assume that your timing chain is wearing out... There is a tensioner in there designed to take up slack with age. If it was on the verge of failing, it wouldn't be running right at other speeds. If it's skipping a cog or something every now and then, you wouldn't have a well running engine. After a few skips your timing would be ridiculously off and you'd have knocking and all kinds of things. I don't think it's that.