Weird Sound at Startup

[Gabbox231]

Hi everyone,
I've just bought a mint 02 GS500 with just 10K Km and it's been perfect so far. Nice power, nice handling, smooth (compared to my previous XT600 at least  )
The motorcycle has some pretty big resonances at around 5K RPMs and the tank gets a little squeaky at times, but not much to worry about.
However at startup there is this weird sound that's bothering me.
It happens only when idleing with the engine cold.
https://drive.google.com/file/d/1PzLwgNmOGFo4Eivq1VA-G7vbNUnUfscx/view?usp=sharing
It feels like the engine "stumbles", it gains a little bit of speed, and then suddenly a big clack and the RPMs drop.
Is this normal? Does it happen to everyone?
The sound goes away once warm.
Thanks in advance for your responses.

[Bluesmudge]

Probably a vacuum leak, or possibly just needs a valve adjustment and a carb synchronization. The fact that it only happens when cold means that it is probably very minor.

If the carbs haven't been touched since '02 all those rubber bits are getting old and hard. Best to refresh all the air/fuel related rubber. Carb O-rings, fuel lines, vacuum lines, intake boot o-rings, and check that the intake boots are still uncracked and pliable.

[moe_tunes]

Since the GS is new to you you might not be familiar with how much it does need the choke on startup. I give it full choke, start the bike and wait a couple of seconds then back the choke off so the revs are just under 3000 then put my helmet on, back the choke off again to keep the revs under 3000, sit on the bike and back the choke off again, put my gloves on and back the choke off so the revs are about 2000, roll backward out the garage and back the choke off again to keep the revs around 2000 then head off on my way. After a couple of corners I back the choke off all the way and enjoy the smiles for miles.
Even after work on a hot day I give the bike half choke to start just because it never idles well when first started.

Hope that helps.

[SK Racing]

That sounds like normal cold idling - even the occasional hesitancy and "clack". Like the others said, use some choke till it's warmed up a bit.

[HPP8140]

Sounds like a lean misfire, my 02 does it when cold as well.

[HPP8140]

Also, confirm the bike has the correct air filter...the 2002 uses a different filter with restrictor ring than the earlier models.

Air filter 13780-01D10

[Gabbox231]

Thanks everyone for the responses.
Yes, I do use the choke when starting from cold, and even then, with the engine at 3K RPMs you can still hear a faint "thump" once in a while that goes away once warm.
Rubbers seem fine, as the motorcycle was kept in storage and run once in a while. Hoses and rubber mounts are still squishy and soft, not hard yet.
The air filter is probably the one it came with from factory, I'm planning to swap it soon. Right now, I'm waiting on some tools and parts to give it its first valve adjustment and carb sync.
What is the restrictor ring you're talking about? Do I have to worry only with aftermarket performance filters? (i.e. K&N)

[HPP8140]

Take a look at the attached picture. The restrictor ring is the black part inside starting at the top of filter to the red line I have drawn. The 01-02 GS has a specific filter to restrict the airflow...otherwise it runs lean and will misfire when cold. Yes, you do need to worry about an aftermarket filter with a stock jetted 02 GS500, which allows even more air making the problem worse.

The pre 2002 E GS500 filter does not have that ring and is more forgiving of different air filters. Believe me, I have had a few GS500s, when I got my 02 I thought something was seriously wrong with the engine, until I learned about the difference in air filters and the previous owner had the wrong one....it was a sigh of relief....I purchased the bike with 14K, now the bike has 89K miles. When cold, sometimes the bike still misfires a little bit and looks like that's how it is....not as crazy as when you have the wrong filter.

[HPP8140]

Here's past information:
http://gstwins.com/gsboard/index.php?topic=68999.msg830342#msg830342
http://gstwins.com/gsboard/index.php?topic=51677.msg585003#msg585003
http://gstwins.com/gsboard/index.php?topic=46920.msg815085#msg815085

[Gabbox231]

Quick update.
I eventually got to change the air filter. The parts list showed two options for my 2002 GS500:
- 1378001D00000 35€
- 1378001D51000 40€

I went for the second one 1378001D51000 and I believe I got it right, it's the same as the old one which probably came from factory.
I attached some pictures if anyone needs them. It's more of a restrictor barrel that runs down inside the filter instead of a "ring". (maybe it's just that english isnt my mother tongue, idk)

Where do you get valve shims? They are of a weird size and they seem very hard to find online. OEM go for 14€ a piece...