palandor Posted May 14, 2010 Report Share Posted May 14, 2010 So far I've heard the same answer to my question, but I don't agree with the answer and I don't understand the mechanical -why- of it, so I either have a misconception or am missing some vital piece of info about how carbs work. I have been told to fully twist the throttle and let it return to resting position before I push the e-start button on a hard-to-start bike. Others have told me not to twist the throttle if I'm "playing" on their bike while it is off because it would give the bike too much fuel and make it harder to start. This doesn't make sense to me based on what I understand of carbs and throttle interaction. I know there are different types of carbs and fuel feeds (gravity feed where fuel flows unless the fuel petcock is turned to "off" and suction feed where fuel flows only when there is a suction force making the fuel move into the carb). My understanding of carbs is that when you twist the throttle, it moves the carb plunger (for sliding carbs) up, which changes the venturi so that fuel is sucked from the float bowl from differently sized holes (aka thru the main jet, pilot jet, or needle jet). Given that, it shouldn't matter if I twist the throttle with a suction feed setup since no fuel should flow due to lack of suction. It also shouldn't matter if I twist the throttle on a gravity feed since fuel will always be going to the float bowl and the limiting factor of floats & the fuel inlet valve needle (the thing that changes level based on the float position) shouldn't let more fuel in than will fit in the bowl, plus there is still no venturi to suck fuel up from the float bowl.So where am I misunderstanding how carbs work? Or, what am I missing that explains why twisting the throttle of a bike that is off will cause fuel to go into the engine section and flood the engine?Thanks,-b Quote Link to comment Share on other sites More sharing options...
wfrpalm Posted May 14, 2010 Report Share Posted May 14, 2010 The only time that would be true is if the carb had an accelerator pump imo. If there is no vacuum sucking fuel into the motor I can't see that twisting the throttle would do anything. Quote Link to comment Share on other sites More sharing options...
conn-e-rot Posted May 14, 2010 Report Share Posted May 14, 2010 If your making vroom vroom noises at the same time then it can lead to problems Quote Link to comment Share on other sites More sharing options...
yotaman88210 Posted May 14, 2010 Report Share Posted May 14, 2010 If your making vroom vroom noises at the same time then it can lead to problems^ for truth! Quote Link to comment Share on other sites More sharing options...
garysol1 Posted May 14, 2010 Report Share Posted May 14, 2010 The only time that would be true is if the carb had an accelerator pump imo. If there is no vacuum sucking fuel into the motor I can't see that twisting the throttle would do anything.What he said..... Quote Link to comment Share on other sites More sharing options...
Steve Butters Posted May 14, 2010 Report Share Posted May 14, 2010 yep...just be careful on things with accelerator pumps...was trying to get my stang started and had someone under the hood working the throttle (cable was broke)...they hit it too many times and when the car fired, it actually backfired and lit my carb on fire Quote Link to comment Share on other sites More sharing options...
RSVDon Posted May 14, 2010 Report Share Posted May 14, 2010 My old CBR was carb'd with an accelerator pump. I hated it when idiot friends would jump on and start twisting the throttle which always inevitably led to it being flooded. Quote Link to comment Share on other sites More sharing options...
jporter12 Posted May 14, 2010 Report Share Posted May 14, 2010 The only time that would be true is if the carb had an accelerator pump imo. If there is no vacuum sucking fuel into the motor I can't see that twisting the throttle would do anything.I don't know of many bikes that have accelerator pumps to have to worry about it. Most carbed bikes that I've dealt with don't like the throttle to be touched when starting it. On my 250, I have to start it and as it starts I put some choke on. Quote Link to comment Share on other sites More sharing options...
palandor Posted May 14, 2010 Author Report Share Posted May 14, 2010 (edited) My old CBR was carb'd with an accelerator pump. I hated it when idiot friends would jump on and start twisting the throttle which always inevitably led to it being flooded.I had an acquaintance (he was too creepy-scary to be called a friend) who was P.O'd due to me twisting the throttle on his Honda XR650L. At the time, I didn't know any better about bikes and he wasn't a patient person so no explanation was offered of why.Thanks Y'all. I've now learned about accelerator pumps. When starting my dual sport (xt225) I've never noticed that it helped if I twisted the throttle before starting it and never thought it should matter either.-b Edited May 14, 2010 by palandor Quote Link to comment Share on other sites More sharing options...
magley64 Posted May 14, 2010 Report Share Posted May 14, 2010 Accelerator pump is the answer I was gonna give. It's how I prime the dune bug, and my old tempest. Quote Link to comment Share on other sites More sharing options...
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