Spec bike carb issues. (UPDATED with fix)

I need some help sorting out the jetting.

I know that I'm running lean, I'm just not sure the best place to start.

Here are the symptoms:

1) My header is blue and purlple now, the plug is white.
2) Full throttle, idle, and acceleration all feel good.
3) Steady throttle at any position other than wide open stumbles while cruising around my nieghborhood.
4) Also notice stumbling while tring to hold steady throttle in between turns 1 and 2 at the track.

I tried raising the needle, as this is usually the problem at 1/4 to 3/4 throttle problems. It did not help. Also, since most time at the track is wide open, and I'm still showing signs of running lean, I think I should go up on the main jet, but I'd also like to check the fuel/air screw.

So, I'm open to any general advise, but I'd really like to hear from people that own the Spec Bike and have sorted this out.

Also, where the hell is the air/fuel screw on this carb, I can't find it anywhere?

it sounds like you should get a bigger main but first you may want to make sure you don't have another issue like a vacuum leak, we've never needed to change any carb setting on these bikes, that's also why I don't know where the air /fuel screw is; it should run ok as it comes from factory.
to give you an idea I won the nationals riding a bike I've never touched the carb on , I don't even know what jets are in there.
closely check that black insulator plate betwen the carb and the intake tube.

That's a good point about the spacer, it didn't look like it was perfectly aligned. I also did a lot of reading over at the SEMRA website. Others have had this problem and fixed it with the fuel/air screw. I'll play with it tonight.

Thanks.

Problem Solved!

I did some digging around the internet and everything kept pointing to the fuel/air screw. This is what eventually fixed it. I figured I'd write what I did and why I did it so that if anyone runs into this problem again, it might help.

The big help was that I read on SEMRA forum http://semra.org/forum/viewtopic.php?t=1548 that some people were experiencing exactly what was happening to me. Now, here's the problem. The proper way to adjust the fuel/air screw is to idle the engine at about 10-20% higher than where you actually want it to idle, then start turning the screw 1/4 turn at a time and try to find where the RPM's are highest. Then turn the idle back down and do it again. Only problem is that it is near impossible to reach the fuel/air screw while the carb is on the bike. So it can be a tedious process, I had to make a tool.

The screw faces down in the very front of the carb, directly under the inlet tube to the head. The means you have about an inch between the screw tube and the head...and you can't see it without a mirror. Not the best design.

I was only able to turn the screw very little, I wasn't really getting anywhere. So I decided to take the carb off and see where the screw was to see if I was even in the ballpark. The usable amount of turns on just about any carb is 3 out from fully seated. So the first thing to do is turn it all the way in (being carefull not torque it, you can easily damage the seat) until it just touches bottom. Count the number of turns as you do it. I read in some carb manuals that the right amount of turns is usually right in the middle somewhere. So if there are 3 usable turns, the 1-1/2 turns out is a good start. I also read on the SEMRA link above one guy asked where a good place to start was, his was at 1-1/2 and he was still feeling the stumble. The guy that answered said his was at 1-3/4. Mine was at about 1/4 turn out!!!!! Way too lean.

So I turned it to 1-1/2 to start with. I put the carb back on and took it for a ride. It was not fixed, but felt a lot better. I took the carb back off, and turned it 1/4 more to 1-3/4. Put it back on and took it for a ride....problem fixed! Took off the plug and it is already starting to change to a more normal color. Power seems much better too.

Something else I forgot to mention. Once the fuel/air mixture was right, the idle was way too high. I had to adjust it back down. The idle screw is on the right side of the carb (opposite side of the filter). Also, I don't need to use the choke to start it anymore, even when it's bone cold.

wow!!! I must be lucky, I have had at least 6 thumpstars and never needed to touch that screw.
Anyway thanks for the info.

Actually I was just UNlucky I think. My bike has sort of strange history. When I ordered mine, they didn't have any available, so Ras put one together for me from stock parts he had. Most of my bike came from one that was in a show display if I remember right. I've had a couple of issues, the last being that spacer and shorter spring in one fork leg that I told you about. I also didn't get the standard plastics and graphics, if you remember, I had blue plastics with the Toxic graphics my first time down there. Also many of the bolts were not torqued at all.

In all fairness, Ras has been absolutely great about everything. Any issue i had was quickly fixed or replaced by Ras. He sent me new plastics and graphics so I could meet the spec bike requirements, new clutch cable (original wasn't long enough), new fork spring and a couple other things, it was missing the rear brake pedal return spring too. So I wasn't really surprised to find the fuel screw so far off.

I don't really mind because I'm pretty mechanically inclined, and these are all things I was going to check over anyway, and like I said, Ras has been excellent and very helpful. Never gave me even the slightest hard time about shipping me parts that weren't right. He was also very appologetic. Even though the bike wasn't perfect, I'd gladly deal with Ras again anytime. Things happen with any bike, it's how it's handled once things go wrong that counts.

I think you still lucky you was able to get your new spec bike, they've been in back order for a couple of months and I don't think too many companies would take the time to put a bike together form parts (which also makes it way more expensive that a crated complete bike) just to satisfy a costumer.
Since your bike did not come from an assembly line, all those little misshaps are understandable.