Got the '71 455 in and running.('66 Lemans). Finally got crossmember mounts in and welded. Can finally drive her. The fool thing starts and runs great in park, EXCEPT when you put it in drive, it idles like a POS! Also, when in park, if you punch it to WOT, it'll either pop and stall, OR, it will catch and sound like a damned racecar! I've changed the bloody accelerator pump twice. Shooting a GOOD stream in there. Running a Carter 9635sa competition carb.(625 cfm, I know a little under sized, but PO had a 600 cfm on it and it run great). Rebuilt carb (twice). Running a Mallory Unilite ignition. New wires, etc... Plugs gapped at .045. Even going to half throttle, she burns rubber. Drive it normally, and it's fantastic. if you lift it just above idle, then stomp on it, clear the road-it's gone! Just that #^@>%&# crap idle in gear, and that stinking WOT bs that has me about ripping my hair out! Could it be that stankin' Chinese knock off of a Carter, or is it just me? ( I've had Carters on my '56 New Yorker, '63 Cadillac, etc... 17mpg & 24mpg respectively,and all the power at your disposal-NEVER had any problems like this). 30 over pistons. 4x heads. Edelbrock Performer Pontiac intake.New timing chain & gears. New upper gaskets, etc...rest is stock. Also, going up the road, I had light valve clatter under moderate load.(went away when I disconnected pcv & plugged it). I am about at the end of my rope with this thing. Any assistance rendered would be greatly appreciated. Thanks.
First off, re-connect the PCV, unless you want to blow all the gaskets and the rear main seal. Second, you need to do some basic tune-up stuff here. What's the vacuum at idle? Is it steady? Where's the timing at? What's the mixture set to? Vacuum leaks?That kind of thing. And gap the plugs at .035, while you're at it. A rattling PCV is a sign of a vacuum problem, such as a bad intake valve, vacuum leak, etc. It's a symptom, not a cause. If you're not a tune-up guy, take it to a shop to dial it in the rest of the way. It sounds like you're 95% there!!! Good luck.
Thanks for a response geeteeohguy. It's been a long time since I used vacuum gauges. I'll try it out. I actually did reconnect the pcv last night, and it seemed o.k. (haven't taken it back out on the road yet though). One thing I forgot to mention was the air jet (on drivers' side of carb)- when I screw it in slowly, it barely changes rpm- all the way in, doesn't really affect idle at all. (seemed to adjust on 326 o.k.) Isn't that the air jet? I Also thought electronic ignition plugs needed a wider gap? Also, with my carb. rebuild kit, they gave several base gaskets which fit. Used the thick one last year on the 326 (brush tacked it-just to make sure) so, couldn't re-use that one. Running a thin gasket now- seems to be sealing o.k.-or is too thin not good? Also, initially I set the timing @ 12 btdc- ran great, but started hard when hot, so bumped it back to around 8btdc- starts great. Idling around 800 rpm in park w/advance connected. I can knock it back to 600 (or less) runs beautiful-until you put it in gear. Brought it up to 1000- doesn't make much difference in gear. Thanks
It might be vacuum advance issue. Do you have the vacuum advance connected to manifold or ported vacuum? If it's currently seeing full manifold vacuum, I'd try it on a ported vacuum source and see if that helps. Also make sure the advance canister isn't leaking.
But it sounds like a vacuum leak to me.
Check vacuum at idle and coming off-idle. At idle, the gauge indicator should be steady as a rock, unless you have a cam with huge overlap.
I'd check everything thoroughly;intake manifold gaskets, all vacuum hoses and fittings, carb base gasket, power brake booster and lines, etc.
Also, if this is a TH400 trans, make sure your vacuum modulator is connected and there are no leaks in the lines or the modulator itself.
One last thing I failed to mention was the way the vacuum setup is configured. On the rear of the carburetor, there are two blocks attached back to back. First one has power brake line attached. Second block has a nipple for vacuum advance AND has the vacuum modulator line connected there. This seemed kind of odd, and I'm not sure if this is correct or not. Thanks for mentioning the modulator. This seemed ok when I drove it, but I thought there was a spot where it malfunction briefly. There's no fluid in the line, but these can leak vacuum internally if they're bad, yes? Thanks again.
That the idle mixture screws don't have much effect is a clue. A common cause of this is if it's got a rowdier than stock cam, you've got to set the idle speed screw "up" so much to keep it running that the throttle plates are open far enough to expose the transfer slots in the carb --- it's already beginning to run on the main or "off idle" circuits in the carb thus taking the idle circuits out of the picture, so to speak. Having a carb that's "too small" for the engine can contribute to this as well - i.e. a carb that ran fine on a 326 can't pass enough air to keep a 455 alive on just the idle circuits alone.
I see you've got 4x cast iron heads. Even on a zero-decked .060 over 455 with flat-tops, it would still be at 9.3:1 compression with 98 cc 4x's (unless they've been milled a ton), so I'm thinking that detonation due to too much compression is unlikely. Take that with the other symptoms and my suspicion is that the carb is way too lean and that's what caused it to rattle. If that same carb came off a 326 and hasn't been touched, in fact I'll guarantee it's too lean and you're taking a big risk until that get's corrected. I'd address that first, then make sure the total ignition timing was right (I'd start out at 33-34 degrees and work from there). I'm not that familiar with those carbs so I don't know for sure if the sizing on the main metering circuit also affects the idle circuit. I know it does on QJets, and if it also does on those then that too could be contributing to your idle problem. Sounds to me like your engine is starving for fuel "all over the place" and that will definitely make it idle rough.
You may be on to something there. To me, it's got that distinctive "lean smell"-(my brother-in-law says it's running rich. True, the smell is quite acrid, like it's rich. And the plugs are dark, like it is running rich). BUT- if it was running lean, then wouldn't the plugs indicate a white stripped look to the electrodes? The PO did have an Edelbrock 600cfm on it. Could that have been built to accommodate the 455? Or is that totally not possible? Also, what would be a good candidate for a carb, that won't break the bank? Thousands have been spent bringing this car back from the grave- almost tapped out, and still haven't put 200 miles on it yet! All I want to do is go out for a good cruise. If I stick a couple of hundred dollar carb on it and it does the same crap, i'm going to wring my hands of the whole affair and call it quits. (I've got hundreds of photos over the past 14 months, documenting what I've done, but now am starting to get fatigued and discouraged). Any suggestions on a carb? TNX.
Yes bear- I believe you're correct that it is running above the idle settings. The fuel jet makes a difference when I adjust it. Not the air jet,though. Messed with all settings today, timing,etc... when I brought idle down to 550-600 in gear, then tried to set it back up, it kind of surged.(advance plugged, 10btdc)-once it hit 650- the rpm's wouldn't go any higher when I set the actual throttle plate idle screw. Pretty odd. I'm almost convinced that the carburetor is at fault. Cam is (according to PO) stock. But who really knows? She likes 10btdc& 800rpm.
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