sublimemike
Well-known user
Oh , JR - it's a 70 year sorry,
Carb idle circuit issues
- Thread starter sublimemike
- Start date
sublimemike
Well-known user
Not at the moment. Here's what I know; The original owner had a Bill King racing in Michigan build the motor. Bill was going to put in his proprietary grind in with mushroom lifters that went in from the bottom. The owner told him not to has he would have to take the crank out to change the lifters so instead he put a crane roller in with the same power curve. Power comes in from around 3500rpm. I'm still in touch with owner, ex vietnam vet who now has mobility problems. He has a storage container with stack of stuff relating to the car , engine build receipts , green sheets, dealer receipts etc. He has the cam number in there. He's promised me if I come to Michigan I can have the lot as he appreciates my enthusisam for the old girl. I've missed the dream cruise at Woodward as its in August but I'm sorely tempted next year as he lives only 6 miles from there.
Here is a dyno pull from a bit before I got the car
Here is a dyno pull from a bit before I got the car
sublimemike
Well-known user
Thanks Tim. I'll get back on it next week. The timing light is close. I can't remember the numbers for these motors. Mopars are about 19 then 34 all in on a tuned 440. I know it's all about feel but I don't want to go silly and have her kicking back on start. Bowl me some numbers If you would be so kind. The dizzy is stock Delco remy, I'm guessing the springs and weights are too but I'll maybe shoot the guy an email see if he remembers. They won't have changed since the dyno. All I know the guy that rebuilt the carb and set it up in a rush he backed the advance off.
Oneball
CCCUK Member
36 all in is the ballpark figure. They do like a lot of initial with a big cam but you’re somewhat limited by the dissy so I’d set it for 36 and see how you get on. mines got 26 initial and doesn’t kick back on start.
If you’ve got a standard vac advance dissy disconnect the vac for setting the full advance and also make sure it’s connected to manifold vacuum
Wind the idles fully in then out one turn as an initial set up.
You can use a vac gauge attached to manifold vac, the ports below the throttle butterfly. Turn the screw out 1/8 and see if the vac increases. If it doesn’t turn in. Turn the other 1 the same amount. I just do it by ear to be honest. You’ll need to re adjust idle speed each time. You’re looking for max vac
If you’ve got a standard vac advance dissy disconnect the vac for setting the full advance and also make sure it’s connected to manifold vacuum
Wind the idles fully in then out one turn as an initial set up.
You can use a vac gauge attached to manifold vac, the ports below the throttle butterfly. Turn the screw out 1/8 and see if the vac increases. If it doesn’t turn in. Turn the other 1 the same amount. I just do it by ear to be honest. You’ll need to re adjust idle speed each time. You’re looking for max vac
sublimemike
Well-known user
Great as you say , do it by ear. So that's 36 at 3500 yeah?
sublimemike
Well-known user
ok, will let you know how I get on
Roscobbc
Moderator
Don't you love the sound of an engine being revved out on a dyno - shame you never hear that sound in the car. IF the dissy is still has a stock advance curve you should be able to source an advance curve kit from someone like Real Steel (see below). They normally come with three sets of springs and three sets of bob weights. the lightest springs and heaviest bob weights obviously get the advance comming-in and maximising at a lower rpm. TBH I be surprised if previous owner didn't sort something out here.
teamzr1
Supporting vendor
Well if engine was stock, Idle specs depending on auto, manual tranny and 350 or 454 CI engine
If Stock - GM Timing
Really need to know what custom grind of CAM is as
esp the LSA (Lobe separation) as if too narrow like 114 or less than vacuum is killed off from startup to like 2,000 RPMs
and would require more timing at bottom end (over what stock was) to maintain a closed loop idle
sublimemike
Well-known user
Good point , I will try and find out but not hopeful. I will check the timing at the weekend.
sublimemike
Well-known user
Bit of an update....no timing gun as yet and no word on cam spec. Had the carb off and opened secondary throttle stop 1 turn. It was already open a smidge. Having done that and got it back together did some static adjustments. The idle screws seem to be responding. Got her properly warmed up, went for a drive and she was running away with herself at times ...1500 rpm without touching pedal. Gassed her around and idle would be all over the place. I think too much fuel going through the secondaries on idle so maybe turn back a smidge. Good news is she never cut out on me. Can tweaking those throttle secondaries overcome the idle circuit or do I need to delve into the timing for a bit more advance?
Roscobbc
Moderator
Not so sure that secondaries on a vacuum secondary carb would have an idle circuit - or even have enough vacuum with the respective throttle plate barely cranked open a knats cock to activate secondary main jets?
sublimemike
Well-known user
Will check carb gasket etc carb surface etc. There is slight leak on wiper door vacuum - that wouldn't effect it would it?
Oneball
CCCUK Member
Can’t be helping, depends how small but look at how little the area is that’s open in the carb at idle and then compare it with your leak. Even a little intermittent leak can give you enough air to change the rpm by a few hundred. Same with carb gasket, are all the vac tubes on the Holley in use or plugged with no cracks, there’s usually 3.
sublimemike
Well-known user
The wiper door just opens and closes on start up. Been chasing it for a while, but you get fed up upside down under the dash not achieving anything. My friends got a smoke machine but we did do the rear mains crankshaft oil seal in the spring which was a priority so maybe cure the door leak over winter. Thought the door vac button thing under the grill I changed would sort it but will have to chase elsewhere. I did find one aperture not plugged that was a while ago and sorted that. I'm with you Tim on a vac leak throwing the idle out. I was going to get the feeler gauges out to let you know how much the blades are open but then remembered its cylindrical chambers so no hope. On the positive side I've got no dieseling on shut down that was an intermittent problem. I've got a barely used gasket so will swop that as that could be a possible leak as it's been on and off a few times for various things while I've had it. I'm going to wind the sec throttle stop in half a turn while I got the carb off again. I got a few I guys local I know if I run into a brick wall but it's always more satisfying fixing it yourself and learning the process.