Bobbyz

iTrader: (1)

been running the speed demon 650 vacuum secondary carb on my zz4 for a couple of years now and besides it never running perfect. i ran into a new problem.

i took the carb off to adjust the transfer slots and afterwards the carb ran fine and the idle was perfect air/fuel screws 3/4 turns out. i then took it for a drive and everything was good. took it for another drive that night and still ran good till i came to a stop and the idle started to rise to 900 then up to 1500 rpms and couldn't get it down.

i then changed the carb gasket thinking vaccum leak and made sure transfer slots were ok bolted it back on ran spot on for a couple of days then again high idle again i even backed out the idle screw all the way and nada. no signs of vacuum leak. and nothing else was touched.

any ideas?

built91Z28

I have a Mighty Demon. Every now and then when letting off the gas the motor will keep a high idle. I just give it a quick small rev and the idle goes back to normal. Not sure if it has anything to do with the carb or not though.

EvilCartman

iTrader: (1)

Put it on ebay now and put that money towards a Holley. Or if you are going to just throw it away, box it up and send it to me.

89redliningRS

My throttle hangs up alittle high sometimes also. I just snap the throttle and it goes back to normal. If your outside the car try pushing down on the throttle to close it more. Mine usually will move about an 1/8th of an inch and slows the motor down.

EvilCartman

iTrader: (1)

Are you guys using a dual return spring? I'm still using the stock ones and have never had a problem through all 4 carbs that have been on my car. Another high idle problem on some engines is actually caused by the distributor weights flinging out and advancing the timing which raises the idle. So if it's on the boarder line of when the timing starts coming in, you'll have problems.

Bobbyz

iTrader: (1)

well after going through the carb and even bringing it to a local carb guy who was also stumped for a while turns out. the idle screw was turning by itself i didnt know that was possible but after i adjusted the idle i took a note and the position of the screw took it for a ride and after the idle raised again i looked and the screw was in a different position.

so i changed the idle spring screw and all is well for now.

89redliningRS

That seems pretty odd. My screw won't turn without a decent size screw driver. Seems like the spring should keep tension on the screw.