Can you flood a stopped engine by twisting the throttle?

[pop0tart]

I was sitting on a buddy's 80 something carbureted Honda and twisted the throttle. He warned me I could flood the engine by doing that. Two others echoed that their dirt bikes would flood if they did the same.

I never had a similar issue on my carbureted ninjette.

Any opinions on this?

They said this is just how they work, with no issues with leaky diaphragms or carb floats out of adjustment.

[Triple Jim]

Some motorcycle carbs have accelerator pumps like cars used to have. My Guzzi's carbs are like that, and will flood the engine if you twist the grip too many times. Carbs without accelerator pumps don't care how many times you twist the grip, since they don't pump fuel each time you do it. Our Ninjas don't have accelerator pumps, and although I could be wrong, I doubt if many dirt bike carbs have accelerator pumps either. You'd have to look up the specific carbs on your buddy's Honda to know if they have pumps, but it's possible. Generally they were used on engines that were jetted to run very lean to pass EPA regulations. Without the pumps, those engines would stumble when the throttle was opened.

On the other hand, I've seen guys twisting their grips as part of their starting procedure, when their carbs did not have pumps. It make me chuckle quietly.

Edit: I was curious, so I did a little searching and found out that some dirt bikes, probably mostly 4-strokes, do have accelerator pumps.

[pop0tart]

Good find. Thanks

[Motofool]

Originally Posted by pop0tart

.........
I never had a similar issue on my carbureted ninjette.

The carburetors of your Ninjette are activated by the vacuum that the suction of the engine induces.
Being the engine off (no vacuum), twisting the handles only opens and closes the two butterfly valves inside the throttle of the carburetors, which are there to regulate the amount of air+fuel mix that enters the cylinders (none when engine is not "breathing").

Link to original page on YouTube.

[JohnnyBravo]

I was gonna say that

[subxero]

What has already been said.

On dirt bikes there is no chance to flood the carb by twisting the throttle with out any engine movement unless there is something wrong with the carb, like the floats are set wrong or the needle jet is leaking ect...

With that being said if you hold the throttle and rock the bike or move the kicker then it can suck fuel into the cylinder.

I prime my 500 by holding the throttle open a bit and cycling the kicker. Do it too many times and it will flood.

[MrAtom]

Interesting. I've been told that holding the throttle open allows some of the evaporated fuel to go backwards into the carbs/airbox a bit, which in turn unfloods the bike a bit. The bike does seem to deflood quicker if the throttle is held open a bit, so maybe there's truth to it.

[jkv45]

Originally Posted by MrAtom

Interesting. I've been told that holding the throttle open allows some of the evaporated fuel to go backwards into the carbs/airbox a bit, which in turn unfloods the bike a bit. The bike does seem to deflood quicker if the throttle is held open a bit, so maybe there's truth to it.

If you think you may have a flooded engine, holding the throttle wide open while cranking (with the choke off) will help clear it.

Not sure how well it works with a CV carb though, but with a conventional non-CV carb (like on vintage and dirt bikes) it lets additional air in but the velocity is low enough that it doesn't draw fuel up from the floatbowl.

As noted - twisting the throttle does nothing unless the carb has an accelerator pump.

[Triple Jim]

Holding the throttle open and kicking/cranking does tend to un-flood a carbureted engine, mainly by moving a lot of air through it, sweeping excess fuel out the exhaust system. I'm sure there could be an occasional exception, but in general it works.

(posted in parallel with jkv45)