coming down from RPM's

Problem: when I give it throttle it takes a while to come down from the higher rpms. It will take almost 5 seconds to come down from 3500 rpm back to idle.

I'm a pretty typical case:'79 SR 650, with the same mods as everyone else, 4-1, pods, 110 mains, 17.5 pilots, 5th slot (no ignition mods)

The compression is good, timing is good, just synched the carbs this weekend, runs pretty darn good otherwise.

My throttle linkage is all really smooth, easily goes to both ends of travel

I sprayed WD40 on the carb holders and didn't notice a change in RPM. My carb holders are old, but don't seem to be leaking.

Anybody got an idea of the root cause? I did mess around with my air screws, they are currently out 2.5 turns, would this have an affect?

Thanks for reading this. It's good to finally get this thing running, but it's still not 100%

sounds like you have pretty well coverd everything but it sounds like the air screws are out way to far to me.never had to open them more than 1.5 turns.

Might be ignition's automatic advancer assembly sticking the advanced position. These should be periodically cleaned and lubed.

Easy to check operation of advancer unit with a strobe-type timing light, and watch it move back and forth as the rpm's are blipped up amd down.

But am still suspicious of an air leak. Are the clamps snug around the carb holders? Sometimes propane gas gives better coverage than WD40 when spraying around the carb holders at idle rpm and trying to detect any difference in performance.

Would also check for snug fitting vacuum caps. If vacuum petcock, also check integrity of vacuum hose from carb nipple to petcock, with snug fitment on both ends, and no cracks in the hose.

Good Luck!

bison wrote:

...5th slot...did mess around with my air screws, they are currently out 2.5 turns, would this have an affect?...

Remotely possible that choke plunger pads might be leaking so as to allow air intrusion via the separate independent enrichener circuit (without being detected by the usual spray-around-the-carb-holders method). Or that choke is not going into the fully closed position (would double-check choke linkage).

If "5th slot" means either the top or bottom clip slot in the jet needle, this seems an unusually drastic setting (thinking middle slot is the norm under most operating conditions, even with pods and freer breathing exhaust).

What do the spark plugs look like?

Are the pilot adjustment screws on the side (pilot air screw, turn in to enrich, out to lean) or on the bottom (turn out to enrich, in to lean)? If side located, 2.5 turns seems way too lean because too much air is being allowed into the pilot circuit fuel mixture. And might be so loose as to be allowing outside air intrusion past the adjuster screw). If bottom located, 2.5 turns seems way too rich. In any event, would defer to settings prescribed in the factory service manual.

Would also check for o-rings on pilot adjustment screws being in good condition. And inspect pointed adjustment screw tips to assure the tips are undamaged (damaged tips disallow precise pilot screw adjustment).

Good Luck!