Topic: Do you have to use the Choke to start your bike?

[mattd]

always in the morning then off immediatly then have to hold it at a fast idle for a couple of mins then it'll idle on its own. then for the rest of the day just a brush of the button and its up. it will not idle on the choke at all which ive been told is normal? the bike (stock 550f2) is an excellant starter hot and cold (a hot daybn where i live is 19 degrees!!)

[bjatwood]

I'll try the full choke then immediately off after starting it tomorrow morning. I have never done that before. But that seems to be the consensus on how owners use there chokes on this thread, and that was what promompted me to start it. Thanks for all the responses =)

[DedHed]

Stock K4 750 - 3/4 choke and a tweak of the throttle, and she fires up every time cold, once warmed up, a tiny touch of the starter or one kick (When I want to show off) gets her running again.

[BobbyR]

no wonder you get lousy fuel mileage.  It's running too rich, possibly to compensate for owner "improvements"?

Mid 40's is "BAD".... I thought HONDA said that 42.23 MPG is what a early 750 should get milage wise? Did I read that wrong?    And my plugs are a nice light brown color, not Black at all. Maybe I would get better milage if I didn't drive 70 MPH... and I KNOW I need a carb sync, my Buddy has a sync kit that he has promised to come over and do, but he's been too busy with his business to come over and do it.

No, mid 40's average is not "bad".  I don't know your 42.23 MPG reference.  Some have reported 50MPG or better with a CB 750.

At what throttle setting do you start up?
Are you aware that throttle position makes a big difference with the fuel mixture that's delivered?
You could have tan plugs with a lean Main, normal midrange, and too rich idle throttle positions.  Your plugs would show an average of all the throttle positions you used.  And show different deposit patterns if you changed your usage of throttle.

There are a lot of variables here.  But, if you are starting without choke, then whatever throttle position you are using during start is too rich and will remain so whenever that throttle position is selected thereafter.  You can burn off black deposits and turn them tan by running the engine lean at some other throttle position.

If your carbs do not have accelerator pumps, they must run rich to yield decent throttle response.  However, you should not be able to pin the throttle at low speed and have the engine pick up smoothly without engine wheeze.  If you can, then the low speed mixture is too rich.  It should accept up to 1/2 of total throttle travel and deliver smooth pickup (if not quick) in any gear from low RPM.

Until the air speed in the carbs increases to the point where the venturi provides the pressure drop needed to dominate fuel draw from the metering jets, the carb throat pressure is what makes the fuel flow.  That pressure differential is lost when the throttle is snapped open, and fuel flow is either curtailed or severely reduced, (just when the rider is demanding more).  It is common to run the carbs slightly rich at idle position in order to compromise engine needs with rider demands.  If the mixture was over rich at idle position,the throttle will not make the mixture over lean and cause wheeze.  Other other hand, if you make the idle way too rich it will begin to soot plugs during idle and be burned off when operated at other throttle positions.  It may even be set so rich as to not require choke when cold started.  The effect on MPG will depend on throttle position dominance during use, mitigated with the fact the idle position is still the most stingy fuel metering position even if set too rich.  However, it can still be said that the MPG would be better, if the pilot circuit was set more lean than way too rich.  If set correctly, you WILL need choke to start the bike when cold.  And the colder it gets, the more choke will be required.

Maybe an older post will help? : Understanding duct physics.
http://forums.sohc4.net/index.php?topic=83904.msg945765#msg945765

Cheers,

After reading this and other posts I understand why Honda put a fast idle cam and accelerator pump on these bikes. They probably leaned them out in the later years as some nod to the EPA. I would doubt I get any where near 50 mpg due to the types of roads I ride on and my riding style.