Big Bore Bandit done, some fueling issues

So built my 97 B12 this Spring, but didn't have much chance to ride it but been slowly breaking it in. Took advantage of 50 degree temps in Wisco today and took it out and finally gave it the berries, found an issue. When at more than 1/2 throttle, it revs very very slowly for about 2 seconds, then takes off. So issue is with the main, yes? I'm thinking it's too fat. Here's the motor specs:

1216cc 10.8:1 JE pistons
GSXR intake cam
Stock carbs, Dale Walker Holeshot needles in recommended notch (can't recall exactly which one)
Can't recall offhand what mains, but it was whatever the Holeshot kit recommended initially. Obviously I'll be going back into them.
K&N Oval air filters (1 filter for 2 carbs)
Stock timing advancer, have a 5 deg advance unit but never installed it.
4:2:1 Hindle header
I'm at 600 feet above sea level.

The bike and motor is for all intents and purposes, brand new. Full rebuild and a ton of custom chassis shit done last winter. Fuel is 2 weeks old. It starts, ides, and revs beautifully. However, anything over 1/2 throttle under load is shittsville, and feels really down on power.

Just looking for some tips in the right direction as I have basically 4 days to test/tune before the snow flies.

 

If it's at exactly 1/2 throttle, I would look at raising or lowering the needle one clip, as the mains don't come into play until above 3/4 throttle (effectively). At 1/2 throttle the needles are still in the needle jet/emulsion tube, so it's either too lean or too rich at half throttle. I would drop them one notch (raise the clip) making it a tad leaner, and see what happens. If it gets worse (or no significant change at 1/2), then raise the needle (drop the clip) two notches so you are richer than at first. This should give you a range of conditions.

Lean on the main jet would be surging or faltering at WOT, and too rich would be stuttering at WOT, and anything above 3/4. It doesn't sound like the main is a factor, not at 1/2 throttle.

 

It’s the main for sure. I said 1/2 throttle as there is some poor performance there as well. If I just crack the throttle the response is fantastic. I agree the needles do probably need some fiddling.

If I wack it open full throttle, literally nothing happens for like a second. The bike barely picks up revs. It doesn’t stutter or cough or break up, just nothing happens. Then after another second, it goes like hell.

 

Maybe you've got the wrong color powerband in it.

 

No, I checked. Rainbow.

 

Then I got nothing. I seem to remember that CV carbs don't like pod filters, but beyond that I would start swapping mains if that's what it needs. You should find out pretty quick which way to go. But needles should be easier (and less smelly) for a quick check, I would think.

 

Actually needles are a pain, I have to pull the tank. I can get to all the mains without removing anything but the bowls. I’m digging into it as soon as I finish this god damn yard work.

 

What do the plugs look like? I didn't see it mentioned. Were the throttle slide-lift holes drilled? Any main air jet "correcters" installed?

 

Nope, none of that shit. Emulsion tunes looked good and not oval-ed out also. Haven’t pulled the plugs yet.

 

Right. A Suzuki "feature." I remember this from my GS750. The pods are likely contributing, so if you have the Dale Walker setup, I can't go much beyond that, except for the "fettle until it's right." Sorry and good luck.

 

I’m not having the typical pod issues. Idle doesn’t hunt, it doesn’t surge, etc. it’s wierd, it’s absolutely perfect until it gets on the main. I think the fact that it’s two ovals and not individual pods helps, gives it some volume like an air box.

I’ve been down the pods on CV route before, this isn’t like that.

It’s just SO pronounced, and it’s so good elsewhere, has me wondering if it’s a timing issue or some other nonsense.

 

Okay, well this might be simple. Plugs are rich as shit.

Unless it’s jetted right and the ignition is having an issue.

 

do the carbs have a mixture screw?

 

Yes. They’re 3.5 turns out. Thinking about going in a half turn.

 

Okay I know this isn't the recommended method, but based on how nasty those brand new plugs were I made wholesale changes. Went from 150 to 147.5 on the mains, went from the 3rd notch to the 2nd on the needles (lowering the needle) and turned the fuel screws in 1/2 turn. We'll see. I gotta work tomorrow and Monday is probably gonna be the last day above freezing here for a while.

 

The rule of thumb on mixture screws is out anymore than 3 turns doesn't do much more, go up a size on the pilot. So you might have to go in another half to see much change.

 

I’m hoping to make a test run this aft. Last chance before the weather turns.

 

Bandit 1200 is a really underrated bike, IMHO. Back when "Bullrun" was still airing, I was considering trying to modify one and enter it with my brother. I never saw a bike on the show, but I thought it could have been a fun gimmick for the show to have a lone motorcycle. Obviously some of the challenges would have been extremely difficult, if not impossible on a bike, but I thought it would have been fun (and probably miserable) to give it a try.

 

Well, it didn’t like that lol. It was definitely much faster everywhere, but now it’s popping on decel and breaking up like crazy anywhere above 1/8 throttle.

I’m gonna throw some .040 shims under the needles and give that a whirl.

 

Okay, I'm an idiot. Fuel line was pinched, AND the vacuum line for the petcock was barely hanging on. Fixed that, went back out and it's much better than before, but now it's a touch lean. It's popping pretty bad on decel. I'm gonna add the .040 shim under the needles and see how that treats me. Sadly, I'm probably not gonna get another run in because the weather is closing in. Guess I'll find out in the spring!