Topic: Weird Idling issue...help please

[PastorIke]

Hey...I have a 75 cb750 with 2-1 pipes...I have recently cleaned the carbs throughly...synced them...set the idle exactly where it needed to be at (about 1200-1300 rpm since I have the aftermarket pipes).  This past week I installed some baffles into the 2-1's because they had been straight open REALLY LOUD pipes.  I had this issue before installing the baffles and now it seems a little more noticeable...my issue is that when I start the bike it idles really low(under 1000 rpm to the point it will chug and die if I dont cheat it with the throttle), but after it warms up (like driving it around for about 30 minutes) it wants to idle high (like over 2500 rpm).  I cant seem to find a happy medium.  It has been really warm here (100 +) and humidity has been at 25% or less so I dont think any of that should affect it.  Anybody got any ideas on what I need to do or check?

[scunny]

have you adjusted your "on the choke idle" and the normal idle screw ?
 

[PastorIke]

If you're talking about the large screw that affects all 4 carbs...then yes.  And I set all my individual air screws 1 full turn out (give or take to keep it from popping while running).  Carb work is sorta new to me on motorcycles so maybe I am setting something wrong...bike runs strong with no popping and the exhaust doesn't smell like unburnt gasoline so I assume I'm not to rich and it doesn't bog when I pull back on the throttle.

[Duke McDukiedook]

Do you have the stock airbox on? Any changes from stock usually means jetting up or raising your needle settings.

If you are using the moto gauge as your tach, it is inaccurate. 1300 rpm is probably actually more like 900 rpm if you hook up an outboard tach.

If your plugs read right after a chop or just looking at them to see color then you will want to set your idle to around 1000 rpm when the bike is fully warmed up. You'll just have to goose the throttle until it warms up. You want a good tan color on the end of your spark plugs without black carbon or oil/gas on them.

[fasturd]

Depending on the type of carb rack your bike is running there is a fast idle ramp that can be adjusted to pick up idle when choked, that way you do not have to adjust the main idle screw to keep it running cold which would make it run fast when warm. Make sure you have no air leaks around the manifolds.

[PastorIke]

I have the stock airbox and I aint real sure what the carbs are...Im pretty sure they are stock, but I am not 100% sure about it...i think from dissassembling the carbs for cleaning that I had a 40 idle jet and a 120 throttle jet (I think :-P...its been a few weeks since I had them apart).  That would make sense if my manifolds are leaking when it first starts running and then maybe the heat from the engine seals off the leak...am I right in that thinking?  (sorry, I am still new at this motorcycle stuff)