Big Block Idle Timing
Thread Starter
Intermediate
Joined: Apr 2005
Posts: 28
Likes: 0
From: Royal Oak MI
Big Block Idle Timing
I just torn my 68 427 down and went through the whole thing. Had all the beat up components replaced, and new cam and mechanical lifters. I for the most part am still running the stock setup. Stock intake, quadrajet, stock bore size, stock heads. The main difference is the new cam. Its not really radiacal, its just a bump up from the original with the rounded off lobes.
Where should I set the timing at idle? The thing runs great, but the idle is way too high. It won't idle and stay running until you hit about 1500 rpm. The manual I have does not list any initial settings.
Where should I set the timing at idle? The thing runs great, but the idle is way too high. It won't idle and stay running until you hit about 1500 rpm. The manual I have does not list any initial settings.
Melting Slicks
Joined: Apr 1999
Posts: 2,675
Likes: 13
From: Sudbury MA
According to motor manual I am looking at, idle speeds for 68 427s are as follows;
the 385 & 390 horsepower = 700 rpm with manual trans in Neutral or automatic transmission in "Drive" (emergency brake applied)
400 & 435 horsepower = 750 rpm
add 50 rpm to all of the above numbers if equipped with Air Conditioning; (except the 435 horsepower)
the 385 & 390 horsepower = 700 rpm with manual trans in Neutral or automatic transmission in "Drive" (emergency brake applied)
400 & 435 horsepower = 750 rpm
add 50 rpm to all of the above numbers if equipped with Air Conditioning; (except the 435 horsepower)
Thread Starter
Intermediate
Joined: Apr 2005
Posts: 28
Likes: 0
From: Royal Oak MI
It is a 390 HP car originally. Like I said, it is mostly stock except for the cam and lifters. I am seriously considering scrapping the quadrajunk...I know there are arguments both ways, but there have been a lot of issues with this damn carb. Maybe I need a rebuild by someone other than myself. Anyone know of a good person to rebuild quadrajunks? I am in MI, but if there was a guy that could do it mail order like, that would work too, if the turn around was reasonable.
Senior Member since 1492
Joined: Aug 2000
Posts: 87,929
Likes: 156
From: Just because I'm paranoid doesn't mean people aren't out to get me...
St. Jude Donor '09
Are you sure you don't have your timing "retarded?" (ATDC)
I've got a real rumpty-rump solid XE-282 and can get her to idle around 700 once warmed up.
I've got a real rumpty-rump solid XE-282 and can get her to idle around 700 once warmed up.
Melting Slicks
Joined: Apr 1999
Posts: 2,675
Likes: 13
From: Sudbury MA
The guy you want to rebuild your carb is Lars Grimsrud. He is a member of this forum and he rebuilt my Rochester via mail order. Turnaround was very quick and price was very reasonable. My L79 has never run better. I think everyone on this forum will tell you that Lars is your best choice for a carb rebuild.
Melting Slicks
Joined: May 2001
Posts: 2,131
Likes: 4
From: May help you? You can sure as hell try!
Try advancing your timing slightly. The more overlap your cam has the more advance at idle it's gonna like. The problem is you'll want to limit your total timing (full mechanical advance) by limiting the advance mechanism. There are bushings available to do this or the advance plate can be welded up at the end of the slot and filed down to give you the advance you want. If you decide to change the q-jet, determine if it is the original 7028209. If it is, you'll want to hang on to it as it's worth a lot of money even if you consider it "junk" and replace it. Also make sure that you don't have a vacuum leak somewhere that's wrecking your idle.
Melting Slicks
Joined: Apr 1999
Posts: 2,675
Likes: 13
From: Sudbury MA
I agree with LeMans Blue about saving the Rochester carb. Back in the seventies I got rid of mine and replaced it with a Holley dual feed, double pumper. Then when I began restoring my 68 8 years ago and realized i need a Rochester to make it factory original, I searched until I found the correct model number and date code and paid $1,000.00 for a used carb, $250.00 to have it restored and then another $100.00 or so to have it correctly set up and calibrated for my car. Boy did I kick myself for throwing away the Rochester I previously had. You may think it is junk, but somebody else will need it so don't throw it away.
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