High RPM at idle

I have twin Volvo Penta 220 HP

I have twin Volvo Penta 220 HP 5.0 GL PEFS engines with carburetors. Normal rpm at idle is 600-650 rpm. One engine throttle control sticks after you accelerate and return to idle. This engine then will idle at 800 to 1000 rpm. If you just touch the idle arm on the carburetor the rpm drops back to 600. The throttle cable is fine and free when the arm is at the throttle control stop. I have completely cleaned and lubed the throttle arms and linkage and nothing fixes it. By adding a throttle spring it works fine. The other engine works fine without a spring. I am looking for suggestions on what maybe causing the linkage on this carburetor from returning completely to the stop. I would rather fix it then add a spring if possible.
Jerry

I have temporarilly fixed the

I have temporarilly fixed the problem by adding a carb spring. Doesn't anyone have any ideas on this problem??? Jerry

"If you have exhausted your ef

"If you have exhausted your efforts with cable and linkage....., see if your Base Timing is jumping around while within this RPM range..... An in-consistant base spark lead can also cause sporatic low speed rpm.

Put a timing light on this and check. You should see no spark lead (other than BASE advance) until approx 900/1k rpm.

I'm not suggesting that this IS your problem, but it is one more item that you can check as part of your P of E (process of elimination). "

"Thanks, I will take a look at

"Thanks, I will take a look at it when I go up next week. Have to work this weekend so I can get up to the boat this next weekend. I will post what I find."