Topic: 75 550 carbs or 77 550 carbs?

[Loki]

so id like to know what you guys think. i have both set of carbs and im leaning towards the 75 set because i love the choke right on the side of it, as apposed to havinng to have a cable with the 77 set.aside form that what differances in performance or anything else would be better for the 77 set?

[edbikerii]

Personally, I prefer the 77-78 carbs, but they are what I know best.

For a ton of information on the 77-78 carbs, see the thread links in my signature.

[TwoTired]

 Critical mission information is lacking in the query.  Like, where they are intended to be used; stock or modified.
Either type can be made to function correctly, as they both use exactly the same fuel delivery method.  The 77-78 PD carbs have a finer control over the idle mixture.  Therefore, the earlier carbs can be said to be sloppier and less critical when tuning for exhaust and inlet changes.  The earlier carbs are incapable of lean mixtures at idle and still get descent off idle engine pick up response. (I think this is due to the different venturi shape, the emulsion tube well volume, and the fuel distance between float reservoir fuel surface and carb delivery port.  But, that's just an educated guess.)

[Loki]

ok well id be running them on a bike with a drag exhaust and a 650 cam,so not entirly stock.

[TwoTired]

Then go with the earlier sloppy carbs.  You'll will still have to readjust the slide needles and find bigger main jets (seems unlikely you'd use the stock air filter).  The earlier carbs main jets are a bit harder to find in non-stock sizes, though.  These guys list them.  Don't know if they stock them, though.
http://www.motorcyclecarbs.com/Keihin_Push_In_Secondary_Main__C838.cfm

Be careful not to break the spring clips that hold in the main jets.

[Loki]

ok but whne it comes down to power and performance which would be the better carbs?

[TwoTired]

They both have the same 22m venturi size.  There is no power advantage from either carb style, when jetted correctly.

"Performance" is one of those words that means different things to different people.
 Fuel economy is a performance factor.
Peak power at red line is a performance factor.
Engine longevity is a performance factor.
Throttle response at mid-range RPM around town is a performance factor.

To some, performance is an amalgam or compromise of all of the above.
To others, only one item is paramount.  Again, it depends on the primary mission of the machine.

[Loki]

thanks alot TwoTired  youv been a awesome help! iv always liked the choke on the side of the carbs so im probly going that path.cheers