Bonneville America Forums Forums Technical Forums Performance Mods Blipping troubles

Anybody know why my engine dies if I very quickly blip the throttle ?. Opening the throttle slightly slower, then all is well. Bike runs fine otherwise, just that annoying habit of dying if I am too quick on the throttle. Running with a unifilter, snorkel removed, air-injection removed, 135 mains, standard pilots, TBS needles, off-road pipes.
Any ideas ?

It's our carbs and the nature of the beast

Might be interesting to set the mix screws to stock turns, then blip it and see how it is. then go 1/4 or 1/2 turn more and try again, then keep checking at each 1/4 or 1/2 turn interval and see if it get's any better at a certain setting. Could be a good way to reveal what amount of turns is best, who knows.

Might be the TBS needles. Too much fuel too soon. MY bike has never stalled when "blipping" the throttle.

145 mains, 45 pilots, 1 shim on stock needles, K&N filters, Triumph short offroad pipes. Bike tuned using dynamometer.

Are you sure the idle speed is fast enough? Should be 900 - 1100.

Not sure about the idle speed, haven´t got a tach. Might be an idea to speed it up a tad though.

Bottom line here is that your engine is slightly lean. Enrichening it should cure the problem, as others have said above, as should revving up your idle speed, too.

And for you curious folk, Bollebygd, Sweden, is just outide Gothenburg.

40 km´s to be precise !

Enrichening, would that be turning the air/fuel screws outwards even more ?, They are already at 3.5 turns out.

Actually, it could be too lean or too rich. When it is too lean, the increased vacuum when the engine speeds up and the throttle snaps shut will make a low pressure lean mixture that won't burn and the engine stumbles or dies.
Same thing with a rich mixture except the increased vacuum pulls more fuel through the idle jet. The increased amount of fuel and the decreased amount of oxygen (high vacuum = low air pressure = less air) also produces a mixture that won't burn.
Another thing to consider, electronic ignition systems don't do well at low engine speeds because the crank position sensor output gets fuzzy. If the idle speed is a little low, the overshoot when the throttle is snapped shut can drop the engine speed below what the ignition system can tollerate.

I seem to have a similar problem when i down shift through the gears,usualy into 2nd or 1st at low speeds it will sometimes give a cough back through the carbs when i blip the throttle, but the engine doesn't die.I have tried every mixture screw setting there could possibly be to remove it with no luck,even changed to 45 pilots and it's still there,
Also ever since i cut the bottom of the airbox out I sometimes get a single backfire when backing off the throttle from speed and letting the compresion slow me like when entering an intersection, that was never there before the mod.

Been there , done that, too rich, wind in the idle mixture screws until it stops, cheers, Tadpole

Camphor & increase hole size in carb slide for WAY better throttle reaction!
How To Link:
http://www.nightrider.com/biketech/hd_cv_mods.htm#vacuum_port

Member,
G@ry J@mes

-----Notes: This TBA MOD formula = F-in WHIPLASH! -----
*Pingel petcock (more fuel...$90.00
*Carb slide MOD (more response)...FREE
*"Hole in bottom of air box airbox mod" (more air)...FREE
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*UNI Air filter (more air) $30.00
*Ballanced & Sync carbs (WOW) FREE (if U have a carb tuner)
*Air Injection Removal Kit = no restriction, no blown reed valve, less "POP", no blue pipes & less exhaust heat. $20.00
*18 T sprocket (-less motor torque +highway 5th cruze gear w/lower RPM's) good trade off! $30.00
*Iridium Spark Plugs (not much noticed here) $10.00 pair
*dielectric grease on spark plug boots & coil boots(as well as all lights & fuses)eliminates corrosion! (O-Yea...just pull out a fuse & look @ the "white corrosin" $5.00
Notes:Clean all contacts w/small file & replace!
*Replace carb manifold clamps w/wider/tighter "marine grade SS" clamps. (no air leaking) $6.00 pair
*NAPA gold oil filter $7.00
*Valvoline wet clutch motorcycle oil (NAPA) $16.00 4quarts

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