[GreenRE]

Hello

I have a 2008 RE classic. There is nothing wrong with it. Crap, I jinxed it now. Anywho...If I am riding say at 1/3 throttle and snap it wide open, it kinda resists, and wants to die. However, if I gently open the throttle, it accelerates just fine. not that I have a need to snap the throttle open, nor is it going to take me from 50 mph to a 100 mph...just curious why that happens.

Thanks.

[ace.cafe]

It is a relatively normal occurrence with a throttle slide carb, which is the type carb we have.
With a throttle slide carb, you can open the slide more than the engine is prepared to accept, by whacking it open like that.
The result is that manifold vacuum is reduced by the rapid opening  of the slide, and the available air is increased, and the engine stumbles until it can recover.

If you gently increase the throttle, engine can keep up with the movement of the slide, and so it works fine like that.

In some carburetors, an accelerator pump is used to overcome this behavior. In CV  carbs the behavior doesn't present itself because there is a butterfly valve that you move with the throttle, and  the slide is on a spring which  prevents it from opening more than the engine can take.

[kauai1800]

Ace you just explained that really well!

[GreenMachine]

I didn't know that about the CV carb..Thanks

[Superchuck]

I'm convinced ACE is a Jedi.

[single]

More like Guru,probly.I prefer Expert.Something I understand.I can open my 34mm really pretty quickly and have not experienced a stumble.Kinda weird.I thought I would have to really be careful.

[Desi Bike]

If it was a multicyclinder automotive engine I'd be looking at the spark advance weights in the distributor or a vacuum leak

[Arizoni]

The air velocity traveling past the main jet must be at a fairly high velocity for it to suck up the fuel.
When someone rapidly opens a throttle slide carb rapidly that velocity drops down so low that the fuel to air ratio becomes very lean so the engine hesitates.

As Ace mentioned, the CV (constant velocity) carbs have a secondary slide controlled by the vacuum in the manifold to keep the air going past the main jet moving fast enough to  pick up the correct amount of fuel even when the main throttle plate is wide open.
As the engine speed increases this secondary slide moves up to a wide open position to match the main throttles position.

[single]

Just remembered that my Trident had a just barely noticeable hesitation when the throttle was snapped open.Was considered normal.What happened after that was more memorable.Still miss it.

[GreenMachine]

What happened after that was more memorable

kinda like the two additional barrels of a 4 barrel carb kicking in on a lead sled...U felt your body sinking as if u were taking off in a saturn 5 rocket in the those fine sofa style seats of the 60 + 70's...I swear u could watch the fuel gauge move while driving..

[tooseevee]

What happened after that was more memorable

kinda like the two additional barrels of a 4 barrel carb kicking in on a lead sled...U felt your body sinking as if u were taking off in a saturn 5 rocket in the those fine sofa style seats of the 60 + 70's...I swear u could watch the fuel gauge move while driving..

         ...and the sound of those secondary barrels (or barrel) opening when you tromped it will never leave my memory banks. Almost orgasmic. As Jackson Browne said in The Loadout .. "that's a sound they'll never hear". A lot of people now have never heard that sound or felt that feeling. Of course, JB was talking about the sound of slamming doors & folding chairs, not a V-8 with two 4-bbls. Or my old Alfa with the two 2 bbl Webers.   

[GreenMachine]

funny what u remember..friend  had a grand torino like the Clint eastwood movie...same feeling when he mash the pedal on the Atlantic city expressway...I had a 73 lincoln with a 460 and was painted dark navy blue high gloss paint...look like a mafia staff car..wife could barley see over the steering wheel....we use to call it the tuna boat.....good fun

[ROVERMAN]

I must be one of the lucky iron barrel owners,snap mine open and she just goes. I have the Gold Star Deer killer exhaust and jets to match (too senile to remember the sizes). All i get is some slight softness in response when starting out from a stop,which i can live with until i graduate to a richer slide.We are not much above sea level in the sunny S.E. Michigan swamplands and 70+ mpg is nothing to sneeze at!
Regards, Robert & REnfield.

[ace.cafe]

If you get your jetting just right, or maybe a tad rich, then I have found it doesn't hiccup when you whack open the throttle.

With the Fireball and the TM32 carb, we can slam that baby wide open  from a very low throttle position and it just wails, with no hesitation effects.
We have seen no need for a pumper carb with the Fireball and the jetting we use on the TM32.

[500KsGerry]

Hello

I have a 2008 RE classic. There is nothing wrong with it. Crap, I jinxed it now. Anywho...If I am riding say at 1/3 throttle and snap it wide open, it kinda resists, and wants to die. However, if I gently open the throttle, it accelerates just fine. not that I have a need to snap the throttle open, nor is it going to take me from 50 mph to a 100 mph...just curious why that happens.

Thanks.

Get a richer slide

[Ice]

There is some variation from blueprint in the cams of our Iron Barrels, sometimes a lot.

 Combine that with different jetting and atmospheric conditions and some Bullets will hesitate while other will just roll.

________________________________________________________________________

 On the other subject of four barrel carbs,,,,,,went for a ride in a Hemi 'Cuda once.

 The sound of two four barrels doing what they do best still reverberates in my mind.
It was quite a ride even though it was only a quarter of a mile.  

Modified to correct spelling.
slaps self on forehead

[Chasfield]

On my single carb Triumph twin, I could wind it fully open in top from 30 mph and off it went without a hiccup.

On my old Honda 250 single, any hint of enthusiasm with the throttle at low rpm would leave the engine behind - even though it had an accelerator pump. That ultra lean set up ruined the rideability of a good bike.

My Bullet is between the two extremes. If I set 75 percent throttle at 30mph in top it pulls cleanly. If I whack it fully open from low rpm it bogs down.