Bonneville America Forums Forums Technical Forums Performance Mods TBS Needles in...first run not what I expected

First off I'm running a FREAK, 160/42 jets and long Scepters on an '03 Speedmaster. I read on some post about there being 4 screws to hold the tank on, well there's only one and it's a bolt just under the front of the seat. The tank has slots that fit against rubber bushions on the upper underside of the frame. Just undo the bolt and pull the tank rearward and it will come loose. Obviously, take the gauge console off first. BIG NOTE TO ALL...the screws in the tops of the carbs are CRAP! I only managed to strip one...the back right one on the left carb as you're looking at it from the side. Luckily, I could get my small needle-nosed vise grip on it and got it to turn enough to get it out. Note to self...replace screws next trip to the hardware store! I put one shim on the needles and trimmed what I estimated to be one link off the springs then went out for a ride.

Holy $&8*#! It ran like doo-doo. My guess from the sound is it was way too rich...when I gave it throttle it sounded OK, but at an even throttle and constant speed anywhere over 30mph it sputtered horribly and backfired out the carbs occasionally. Back to the house I went totally bummed out! Off with the tank and carb tops. I removed the shims, then replaced everything and tried it again...MUCH BETTER! Throttle response was noticibly different with the springs trimmed and I could feel a definite push at the rear wheel when I shifted that wasn't there before. I almost lost traction turning left after a red light as I shifted from first to second. I also get much less back sputter out the pipes. I didn't really have any backfire before, but had that minor popping on decel everyone complains about. It's almost non-existant now. I'll probably make some minor carb adjustments after I put a few miles on it, but both screws are somewhere around 1.5 to 2 turns out. Sorry, but I adjust by ear, so I stop turning when it sounds right. One thing I didn't do is drill the slides although I don't know if that would have had any impact on the first run. If anyone knows, please clue me in.

Lesson learned here is every bike is different. I duplicated what others had done successfully with the same bike and set up. Didn't work for me...it's all trial and error. Hope this info helps anyone else out looking to do the same.

Hold on now, if you're backfiring through the carbs, your probably running lean and not rich. Now if you were backfiring through the exhaust (and probably with black smoke coming out) then you'd be running rich. But yeah, every carb is different; my CRS carbs have a full turn of difference between the two carb air screws, and only with that is the idle mixture roughly equal across the two. Good luck with your continued tuning, you'll feel proud as hell when She's running right!

I called it backfiring through the carbs, but it was more like spitting, not a pop...kind of a wet squishy sound that would happen when I gave it a lot of throttle. Only happened one or twice, but it was running so bad I only rode about 5 miles before heading back home. Correct me if I'm wrong, but shimming a needle allows more fuel because there's less needle metering the fuel, right? So if it was running bad with a shim, then better without one, it was too rich...or do I have it backwards?

I think you have it right. The TBS needle has a more agressive taper, so a shim will have a more dramatic effect than it would on the stock needle. I think you would have been running rich for sure. I'm surprised you didn't end up even backing off the main jet a little. Glad to hear it's running good. I've drilled the slide (very noticeable), but I haven't cut the spring yet.

Also, order the carb hex screw kit from Brent. It's cheap! Or, you could just grab the two different sized screws from the carb and run down to the hardware store and find them.

I didn't have any jets other than the stock ones to swap out with, but as I duplicated some identicle setups others had, I didn't expect such crappy effect on the initial run. I understand drilling the slide allows more vacuum. Does it actually do anything to affect the fuel mixture or just help with throttle response? Thanks for the advise about the hex screws...I wanted to do bad things when that screw stripped out.

It only helps throttle response. It allows the slide to move faster. I may end up cutting the springs to see if it helps it even more, but I want to get used to the way it rides now. I've changed so many things I probably wouldn't notice it if I did it now.

How is it just of idle right now? If you are rolling along in first gear just a little over idle and then crack it, does it jump? I had to go to a 45 pilot to get the "just off idle" snap. But if you do that, I'll bet your 160 main is too rich. It's delicate balance.

Actually, I played a little on the ride to base this morning and the throttle is crisp and responsive throughout. I may drop down a main jet size just for curiosity, but if I didn't, I'd have no complaints with it now. I only cut one loop off my springs and the change can really be felt. When shifting, especially through third, I never had the feeling that the front wheel would come up like I do now.