Boggy running

[BonniePrinceHarley]

Hi, I'm a newby to the forum.
Just bought a 1991 KDX200, an absolute minter with less than 5000kms on the clock.

It runs a round slide Keihin and was on stock jets, 48 slow jet, N68K needle with the clip on the 4th groove down and 122 main jet.

Dealer has confirmed these are stock.

It runs boggy at low revs, but when it comes onto the main jet it is hard to keep the front wheel down. Lovely!

I tried tuning the air screw, and it made no difference at all to the running, which suggested to me that the slow jet was too big.

So I fitted a 42 slow jet, and it responds to tuning the air screw now, and is running 1 3/4 turns out.

Still running boggy in the mid-range, so I raised the clip to the top groove, which improved it a bit, but still boggy.

It seems to me that I need a leaner needle, but the stock needle's nomenclature of N68K cannot be translated to the more understandable needle sizes.



Can anyone advise me what the next leanest needle to an N68K would be?


Thanks in advance

[bossmans kid]

Kind of a caveman style exhaust valve in that 200. I would look at that and make sure it's working fine. Exhaust valve issues in a 2 stroke are a common factor in poor low end performance.

[Keystone]

Check your float height while tuning and re-jetting your carb. I'm no expert on carbs, but I was re-jetting my carb and found the float height was off. The manual says 16mm (out from the carb). Too far out or in will make the bike run more rich or more lean. I think, too far down into the float bowl makes in run leaner and vice versa.

[Julien D]

Welcome to KDXRIDER!

If it were me, I would start by sourcing and installing the stock carb. It should be a flat slide PWK35. You're going to play hell trying to jet that old round slide carb correctly. That is unless you actually have an 88 or earlier, they had some different carbs. This is a watercooled or aircooled bike?

[newbbewb]

^^ listen to this guy, he's right. Then check those exhaust valves, very common culprit, and can happen to even a mint KDX.

[BonniePrinceHarley]

Welcome to KDXRIDER!

If it were me, I would start by sourcing and installing the stock carb. It should be a flat slide PWK35. You're going to play hell trying to jet that old round slide carb correctly. That is unless you actually have an 88 or earlier, they had some different carbs. This is a watercooled or aircooled bike?

Interesting, Julian. Dealer says some bikes this model year had flat slide carbs and some round slide. The stock jetting data came from the dealer's micro-fiche, so I have to assume something is right. it's a watercooled bike.
Float height was checked and measured 16mm, BTW.
Haven't got as far as checking the exhaust as previous poster suggested.

[Julien D]

Is your bike a US model, or an SR? Either way it should be running a pwk, as far as I know. I'm not as clear on specs for the SR though, so.......

[6 Riders]

Sooooo, it's your anniversary!

Just thought I'd through that out there!