(The problem is at idle with throttle closed. I talked to someone about a different pilot and he said the fuel screw covered the range of several pilot jets so if the screw is not getting me any benefit this is not the problem.)

That statement came from someone with NO jetting experience. So you are going to replace the top end without knowing you have the right jets! Just send me your credit card info and I can fix it!

P.S. If the exhaust is plugged up it will feel lethargic.

Edited September 24, 201411 yr by lineaway

I dont think the stroke of the motor has ever changed. The manufacturer of the piston may have changed but the size should be the same. In a bike that old fitting a new piston without re coating the cylinder is a bit pointless as the new piston will wear to the shape of the worn cylinder in no time.

Does the engine rattle at low rpm with the clutch in ?

(The problem is at idle with throttle closed. I talked to someone about a different pilot and he said the fuel screw covered the range of several pilot jets so if the screw is not getting me any benefit this is not the problem.)That statement came from someone with NO jetting experience. So you are going to replace the top end without knowing you have the right jets! Just send me your credit card info and I can fix it!P.S. If the exhaust is plugged up it will feel lethargic.

Ok, thanks for the input as always. My only issue is with the throttle closed and the bike idling. I thought that meant there is only one jet at play, idle/ pilot jet. There is also the fuel screw of course. Not sure if changing the main or the position if the needle would affect how cleanly the bike idles. So I can go up or down on pilot. Should I buy a jet two sizes larger, and another two sizes smaller and tune from there? I could stick my beta techno carb on there if it would even fit to see how she runs? Plug is a nice color brown. This is a dellorto VHST carb.

Bike does not rattle when clutch is pulled in.

Can you post a video of it idling?

Need to know what jets are currently in it and at what elevation you ride to decide which way might benefit the jetting of your bike.

Pilot is an S36 which is stock and was also recommended on the trialspartsusa site. Main is a 107, recommended is 110. Southern California weather, so 80 degrees and within 1000 feet of sea level.

Here is a video of the bike from today. If the bike sounded as quiet as it does in this video I would be chuffed; you have to take my word for it it's really bloody loud! It's also fluffy off the bottom and when you crack the throttle blue smoke comes out the pipe AFTER the throttle is released.

Sounds sweet!

If it's a bit too loud for you, just repack the exhaust.

Are you sure that is not the 200. ( It also looks like a 2003?) Hard to tell by the vid. You can tell by the vin number. Most people ran a 38 pilot on the 280. At sea level the 107 would be way lean.

Edited September 25, 201411 yr by lineaway

I used the vin decoder and it says she is an '04 280. The cylinder has '28' on the side also. New jets ordered today, thanks! I'm going to clean out the mid pipe also with brake fluid... Because the guy at trialspartsusa recommended that and I have a bunch. I'm hoping this will preserve whatever packing is left in it rather than burning it out.

Hate to sound too basic here, but have you tried a new plug? Not a recently cleaned one but new from the box.

Plugged baffles in the mid box could make for loud popping because the pressure wave is forced through rather that expanding through the baffles. Should not create the surging problem you reference.

Did the previous owner lighten the flywheel?

Does the surging only happen in corners? What about straight line at idle?

Thanks for the replies.

I put my beta techno carb on the bike and she pulls like an ape on crack. Much less popping and surging at idle too.

The bike is an '04 year she has the VHST from an '03. I will try some new jets. Thanks again, I'll post if I get her working!

By the way those carbs came from the factory with a 107 main. It has a 110 in there now. Plug is nice an brown, hopefully a larger pilot will so the trick, she has the factory s36 in there now.

IS the small washer behind the spring of the airfuelscrew still there? Also on the idle plug?

Edited September 26, 201411 yr by crazybond700

Yes it's there. But the fuel screw makes no real difference an the idle screw is almost all if the way in meaning the pilot is not even within range?

The iddle screw only adjustes the hight of the slide. So has nothing to do with the mixture.

Still the fuel screw makes it richer/leaner (should be around 2.5/3.5 out>bigger pilot jet)

Edited September 26, 201411 yr by crazybond700