High Idle and Surge

Hello everyone I've been reseaching this for a while and I still havent found anything to cure this issue. I hope someone can assist.

I have a 466 and it idles right at 1700rpm with a little surging. It has a Victor intake with a Hardcore series 1000cfm carb on top of a 1"spacer with a vacuum port. It had came with a 930cfm and was idling high 1500 with that too. I have the idle down far enough to where the linkage is no longer moving. I replaced gaskets between the carb and intake. I tried the spraying carb cleaner method. It has a hydraulic cam the person I bought it from says it has a Lunati voodoo cam. Timing is set to initial 12 degrees. A/F is adjusted to 1 1/2 turns out. When I hooked up a vacuum gauge to the port below the carb it was bouncing all over the place. The port goes to vacuum can and transmission. I had even put a cap on the intake port. I have been reframing from posting this on here until I reach my wits end. I can't think of anything else to check, any info would be appreciated. Thanks!

Big Vac Leak Somewhere.

Tell us more about the combo.

1968 block and 1968 heads 75cc, crane ignition, factory electronic distributor with vac adv blocked. This is all in Park.

try putting some timing to it also, with the vac stuff blocked your way retarded on the timing.

ok, I will try to do that tonight

well tried advancing and its still doing the same thing. I'll keep searching other avenues

reseal intake manifold to heads.inspect for cracks. carb spacer gaskets carb gaskt good luck...... :

Do you have a brake booster? If so, unplug it and see if the booster is bad.

intake may have a leak on the bottom.pull the oil cap and see if anythings comen out.

All of that and also check carb base plate and spacer for cracks.

retorqued the intake, going to pull the carb spacer tonight.

Seal the 2 outer valve cover bolts?

1.eliminate all possible external vacuum leaks
2. remove and plug pcv valve if you have one, plug all other crank case vents
3. remove oil cap while engine is idling place the palm of your hand over the oil fill hole making the inside of the engine air tight. The engine should create a slight pressure as it runs, if you feel a vacuum on the palm of your hand engine tear down is necessary if not engine is sealing fine.

Cam timing has caused werd things also, I have ran across a couple of engines that some did not or know how to line up timing marks and run fine but rev them up a bit and man what a surge, mostly timing belt stuff though. One was a 460 in an 89 f250 that hit a cow and the body shop went ahead and replace the timing chain, front cover, and water pump that was damaged in the accident and they lined it up a cog off, farmer ran the truck for years but it would not rev up passed 2500 without a bad surge. Finally showed up at my shop after thousands were threw at it trying to cure the issue and after investgating when it started I went for the timing chain and sure enough cured the issue. I have also had to jump cog on the chain to bring the cam into time. At this point it should be checked to eliminate it being an issue. Hope this helps

First off I want to thank you all for giving me ideas on this. I checked everything and it still idles at 1700 rpm in Park. I'm starting to believe that this is just the way it's going to be. When I put the car in gear it drops down to about 900, The car is running very well and the oil is clean so I'm thinking, it is what it is untill I build a new engine for it. Once again thanks for the help.

Seems most external options have been covered. How about increasing the main jet size by 5 numbers? Oh by the way, a can of starting fluid works great on those hard to find vacuum leaks.

Dave.

Propane works well also for finding that "elusive" vacuum leak

I decided to pull the engine apart for a cam swap and I found that the cam thrust plate had broken and the bolt was holding it in place. So I'm glad I pulled it apart. After research I think I'm going to look for a bronze thrust plate as recommended by many.

Call Lem,he prob. has them in stock

I just PM'd him about a cam recommendation too. I had already placed a cam order with summit for a comp cam but it's on back order so they are giving me the option to cancel. After further research I found it is highly recommended to have a custom grind so the plan is to get a cam from Lem too. I'm steady learning alot from the folks on this site.

Good move, most of the shelf stuff leaves alot on the table.

I know this is a little late but I bet the cam/rockers was adjusted to tight. This will cause just what your talking about. I set my hyd cams at 1/4 tight just as soon as the push rod play is taken up or you can't roll it with your fingers.

Ace