ToolsnTrack
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Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Apr 21, 2012 20:23:07 GMT
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So I got her running. Now what??  To bring those not clued up on my Camaro up to speed, here is the story: Took a 305 lump, suspected ex injection but running a rochester since I got it, and dis some things. Ditched the horrific headers for some nice flowing tubulars with a dual system. Also fired in a 284 duration Crane Cam in, cos I'm special. Have done my first start and got the 2.5k bed-in running sorted. Will be changing the oil once I'm back from this job. What I have found since running the engine again is that it will now not idle. Probably not that big a shock since changing the cam AND the carb not having any working choke, but when I warm the engine up then slowly let off the throttle, it seems to bog down as the revs drop and stall. Opening throttle again usually saves it. What's going to be the best way to go about getting this lump to idle, or just not stall unless revving to 2k? |
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Apr 22, 2012 13:10:04 GMT
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have you checked for an air leak, timing would be the next thing id check
should sound nice and lumpy with that cam in it when its running sweet
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Apr 22, 2012 13:11:54 GMT
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I'd be checking for air leaks, vacuum leaks and so forth. The 284 will have a lopey idle so expect it to be "choppy" at tick over and you'll need to turn the idle speed up a bit
One thing does make me nervous is that cam is often recommended for stroker 350s like 383 etc. and talk of 10.5:1 compression minimum...
what heads, intake and carb are you running? Again recommends as far as I see for this cam are aftermarket heads, single plane intake and a 750cfm carb (based on a 355)
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Apr 22, 2012 14:12:50 GMT
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Alistair, its stock heads and a edelbrock performer dual plane manifold, and stock Rochester 4bbl. It does fire up and run pretty nicely, just seems to be the idle. I threw some run in vids up on the build thread (in my sig). So the next step will be the timing. It may have been covered before but what should I be looking for as far as advance goes?
Also, where can I turn the idle speed adjustment up on the Rochester? Does it have the provision for this?
I'm not wanting to address the heads until there is no other viable option. Will have a good scout for vac leaks once i'm back. I do have a 750cfm holley double pumper, but its a drag carb with no choke either...
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30psi
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Posts: 1,024
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Apr 22, 2012 23:00:54 GMT
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After the above, I'd go old school. Get a vacuum gauge on it and set the mixture and idle to get max vacuum. Then see what the vacuum is. Probably will be low (like 10 inches).
What was the static theoretical compression of the engine?
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1962 Ford Thunderbird 6.4L
1981 Datsun Bluebird SSS CA18DET
1981 Datsun Bluebird SSS SR20DE
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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What was the static theoretical compression of the engine? The what now?? |
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This engine is like about 8.5:1 in stock form usually.
Once you start with big cams what is more important is the cranking pressure. That is how much squeeze there is in the chamber as a long duration cam like that will hold the valves open on the compression stroke a while. This is fine if you have static compression like 12:1 (and its how some of those high compression motors get away with it) because its pushing charge either out the exhaust or as reversion back into the inlet.
Big nasty long cams like that do idle bad, just by nature of them, and the smaller the displacement of the motor the more pronounced the bad idle is.
I had the same duration cam (Comp NX284) in a 350 in my old Victor. I used Rhodes lifters to try tame it but it still idled like the thing had a HT lead off and about shook the car to bits idling in gear.
You'll never have the thing tick over like a Cadillac with a lumpy cam.
Search youtube for some examples of cars idling with hot cams like that
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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This guy has same cam I think and a 406" SBC. the longer stroke and greater displacement masks some of the cam's lope.
This is about how mine idled, that was at like 900 rpm (again, this is a larger capacity motor, slightly different grind on the same duration, I think the .484 is a lower lift cam than the EX284)
I think this is your cam, Ford version, similar displacement, so this is about the idle quality I would expect you to be able to achieve
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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30psi
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Apr 23, 2012 11:52:25 GMT
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What was the static theoretical compression of the engine? The what now?? As Alastair explains, a wild cam reduces the compression of the engine. Because the inlet cam closes at the beginng of the compression stroke, the first part of the pistons movement doesn't compress anything. This 'valve lag' reduces the compression. Similarly the 'valve overlap' is when the exhaust closes after the inlet valve opens, this reduces the ability to draw fresh mixture in the combustion chamber. Hence the reduced vacuum. |
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1962 Ford Thunderbird 6.4L
1981 Datsun Bluebird SSS CA18DET
1981 Datsun Bluebird SSS SR20DE
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Apr 23, 2012 15:09:48 GMT
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I don't mind a lumpy rough idle, if its still an idle. i don't have that just now though...
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ToolsnTrack
Posted a lot
Homebrew Raconteur
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Club RR Member Number: 134
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Apr 23, 2012 15:18:45 GMT
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Also, i have put in variable hydraulic lifters...
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Apr 23, 2012 16:02:41 GMT
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I'm putting my money on some kind of leak then.
Did the cam not come with a spec for intial (ie static) timing?
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1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Apr 23, 2012 17:14:09 GMT
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Not that i could find....
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Apr 23, 2012 19:57:48 GMT
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id get a timing light on it and set it to around 10degrees as a starting point . make sure the carb has no leaks and try that then slowly bring the idle down . the cam you have in that with that capacity motor your not going to get much of an idle below about 1000-1100rpm . the Rochester carb your running is it just an old carb that came with the car ?was it running on the before hand ? reason i ask is if it just came as an unknown it will probably need calibrating great carbs when they work but notoriously trick when they want to be .
exhaust sounds good , flowmasters? will be great once you have it idling
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Apr 24, 2012 10:37:57 GMT
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They are thrush welds. No the quad came on the car and ran fine, although I think there may have been an issue with it as it bogged down on what, but always idled fine.
Fairly sure it's a vac leak somewhere now. Will try those settings and see what I get.
So can anyone point me in the direction of the idle mixture screw on the quadrajet? Or any online guide for setting up a quad?
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SA Autobooks do a great book on the Qjet. Amazon has it.If you don't want to buy the book, then theres info for free too: You'll find a bunch of info on this pageLars Grimsrud's guides are very good - a couple of them relevent to you are linked off this page |
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Last Edit: Apr 26, 2012 7:55:33 GMT by akku
1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1994 Ford Fiesta
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ToolsnTrack
Posted a lot
Homebrew Raconteur
Posts: 4,132
Club RR Member Number: 134
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Magic Alistair, thanks for that!
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I think that mustang sounds fantastic at idle!
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Remember the days when sex was safe and motorsport was dangerous. Vintage bling always attracts pussy.  |
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stinkwheel
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Doctor Of Gonzo Journalism - One of gods own proptypes, never even considered for mass production.
Posts: 2,280
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I'm having a little idle problem at the moment too, although mine seems to be timing (wrong vacuum advance cannister) but have this pic............  Is yours the same rochester as mine? Where the throttle cables/kickdown etc are on the r/h side as you stand in front of the car, below the levers for all those is a simple idle stop screw, I'm assuming you've tried this? If not how about the old you keep the car running at an even RPM whilst someone sprays WD40 or similar round the base of carb/inlet etc to see if the engine speed changes, my favourite way of finding an air leak. |
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1973 Citroen Dyane 6 1980 Citroen Acadiane
1992 Citroen AX 1990 Citroen BX
1997 Citroen XM 1993 Citroen BX
1997 Citroen Xantia 1977 Citroen Ami 8
1996 Ford Escort 1989 Citroen BX
1997 Suzuki RF900 1988 Yamaha TDR250
1979 Honda CB400.
'I need less vehicles'
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Apr 28, 2012 12:29:09 GMT
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i should think the idle screw needs winding right up and larger idle jets fitted.
you will have poor vacuum, charge robbing and reversion all happening at once in the inlet until the engine is singing , hence the lumpy idle (when you do get it to idle).
probably need loads of advance at the bottom end of the rev range to get any performance and thats if it works at all. big cams don't work with low compression.
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