This just started happening lately and I'm not quite sure what the deal is. This went from happening a couple times a week to every other time I drive it. This is on a 71 Duster with a super six. 8* BTDC 750rpm in park.

I'll get in my car and drive it somewhere and the idle will be fine on start up and while I'm driving. When I come to a stop and put the transmission in park, instead of going to it's usual 750rpm mark it'll jump to 900rpm or so. Sometimes I can put it back in gear and then back in park and it'll drop the idle back to normal. Sometimes I can just rev the engine while in park and it'll drop down as well. Sometimes neither works. If I try and shut the car off with it idling fast, it'll diesel for a few seconds and then shut off.

Today I finally got around to checking it out while it was happening. I thought maybe the throttle would be pulled back a bit, causing the high idle. The curb idle screw was bottomed out on the carb so the throttle linkage wasn't causing the high idle. Choke was not engaged at all. It was idling around 950rpm or so this time so I backed the curb idle screw off to get it back down to around 750rpm. I drove it a couple miles and when I parked it, the idle dropped to normal and everything was fine. I drove it back home a couple hours later and the exact same thing happened where it was idling fine in gear and then as soon as I put it in park, the idle jumped way up to around 900rpm or so without anything visibly wrong. Any ideas? I'm stumped here.

Worn throttle shaft on the carb creating a vacuum leak? Cracked vacuum hose/blown choke pulloff diaphragm/sticky distributor mechanical advance mechanism/blown distributor vacuum advance pod?

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Casually looking for a Clifford hyperpak intake for cheap.

Yes, you have a vacuum leak somewhere. A vacuum pump is a big help in tracking these down.

Sam

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Thanks guys, I put the gauge on there and it was reading 18hg so I didn't think there would be a leak. Ended up spraying everything down with soapy water and shooting air up the pcv hose to check anyway. I get a little bubbling coming out of one of the carb studs. I removed the stud and put a good amount of blue loctite on there and it still leaks a little bit.

What else can I use to seal the stud? Napa is selling Permatex stuff which I'm sure would work, but it was like $25 a tube.

You can use the $3.00 a tube Permatex Ultra Black or the grey Motor Cycle Permatex. The motorcycles shops around here use the grey formula on heads, carbs, etc. I am finding it is very good on carb bases and thermostat housings. Much easier to clean up when I swap thermostats in the spring and in the fall. Never had a problem with sealing. I don't see how you can have a vacuum leak around the two carb studs, but give it a try. If for some reason you actually have the old style studs or bolts.......throw them away, clean the threads and install new studs and lock washers or star washers. Use the thick gasket and you should be good to go....

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Just throwing in another suggestion,it may be worth checking your timing as well,could be a prob in advance mechanism causing intermittent advance at idle??

I just had this happen on one of mine last week. Idle hunting all over, refused to return to a consistent setting despite my efforts at checking/changing return springs and throttle cable, etc. It finally had me fuddled for a few minutes until I checked the throttles and to my surprise, it was the sloppy secondary shaft on a vac secondary holley.

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1966 Coronet Deluxe