B4 Stalls Randomly...

[andrewsw]

It doesn't take much wear of the emulsion tubes to start causing problems. Shine a flashlight down there and look at the step all the way around. Pretty much any deviation from perfectly circular is a problem.


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A

[VW_NUT]

Update,

Took a close look at the emultion tubes and they look ok. 

Still stalled with the clip at position #2 and was very lean.  So I don't think the clip is the problem.  I checked the plug after hangin biposto rode it and it was darker than when I rode it.  I am guessing I am rich on the pilot.  I will try backing down the fuel screws again, or lowering the floats next.

I figured I was a little rich so why not try my "other" air box lid with holes in it to lean it out a little... Nope.... Way lean when I open the throttle.  I guess I'll be putting on the stock one back on when I get home.

Thanks for all the info guys...

[tomacGTi]

Tony, here's what I experienced yesterday when my modified airbox developed a leak and caused everything to go wicked-lean in the pilot circuit.

I experienced everything you had until I chased the problem down to a failing seal and reset it all after going to all extremes on the screws. Too lean and the bike would stall, too fat and the bike would bog till on the needle...

-The main and the needle are the least sensitive to these changes (especially if you've already dialled them in according to FP). You'll notice that 1/4 throttle is what is the most affected (ironically the most often used throttle position).

Once you decide what setup to use on the intake and exhaust side of things is when you'll want to dial in the pilots. FP is right when they say to set your idle to spec and make sure the screws can hold it. The other circuits will follow pretty seamlessly. Make sure the bike is at operating temp when doing this.

-Once your screws are set and you're done, resynch everything. This affects how well the carbs react to throttle, closed or open. Also, changes to your idle screw will affect synch as well (at least what I've experienced).

I spent a couple of hours messing with this yesterday and endt up back at the settings that I had originally started out with. I'm happy I didn't get crazy and started going after the main and the needle because after I marked the grip and controls with throttle positions, it really helped me dial it all in and find the trouble spots. Using the combination of both those websites is a big help.

[VW_NUT]

What does your modified airbox look like?  I have a bunch of holes in the back probably 8  7/8" holes I drilled with a uni-bit.  I kept the snorkel.

I was thinking it wouldn't matter much as on my duc when it was stock ish I cut the whole lid of and it felt great.  Not so on the bandit.  Stock one is going back on as it ran much better down low with it & hangin_bipsto is not concerned with ringing the last 2 hp out of the bandit.

[hangin_biposto]

hangin_bipsto is not concerned with ringing the last 2 hp out of the bandit.

not yet anyway...

[tomacGTi]

It's basically a 2" PVC pipe flared on both ends like the factory snorkel. I alter the lengths to tune the airbox. You can actually hear where the resonance starts and feel where it affects the powerband of the bike. Kinda neat experiment.

Difference is the size is the same as the hole that the factory snorkel sits in (roughly 10% larger cross section) and you can alter the length to change the resonant frequency in the airbox. The rub here is that the entire box must be solid: no duct tape over holes since it affects the resonant frequency and also no leaks as its "unmetered" air. I recommend plumber's putty for resealing as it's easy to work with and relatively cheap.

To make it quick change I was insulating the snorkel from the airbox with weatherstripping as a seal. Since I was using a very cut up airbox, sometimes the seal would fail and basically make the carbs run very lean due to the additional air. I've since zero'd in on what I want so I made it more permanent by puttying in the snorkel now. I still have an unmolested stock airbox with snorkel just in case I need a control or want to go back to stock.

If you want to try it, I suggest using the stock length first and then shortening as you go along. The shorter the snorkel, the more up the RPMs move in frequency. You can use it as a tool to help fill in a dead spot in jetting or beef up a weak part of the curve.

Making it is quite easy as well as all you need is a Dremel, some heat and obviously the tubing. To create the bellmouth, you need to sand down the inside of the pipe into a taper about 1/2" in and use heat to flare out the tube. Try to mimic the factory flare and you should be all set. I use a screw through the top of the lid into a part of the snorkel for support in the back . I ground down the end of the screw flat so it's flush with the tubing.

[VW_NUT]

Update again...  So I think I fixed it. 

It turns out that I was indeed too rich on the fuel screws.  2.5 turns is the happy spot for this bike.  Thanks for all the help guys!