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By Mike. - 8 Years Ago
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Hi guys, just a quickie. I built my 312 last year and shes done about 500 miles. I built it stock and fitted an Isky E4 cam with an adjustable timing set. When installing the cam I dialled it in but I can't remember what figures it came out at. Anyway she runs fine but needs a lot of juice at idle just to run smooth, i had to wind the mixture screws well out to get it to idle at all. I suspected a vacuum leak, i found one and fixed it. I swapped out the Holley carb for a new Edelbrock performer (500cfm) but still have the same issue, needs a lot of mixture to idle. I've just decided to check the cam timing. Checking the cam card it states inlet opens at 22degrees at 17 thou lift, mines reading 26. At 50 thou lift it should be zero, at this lift I'm reading 2to 3 degrees on the crankshaft. Im not sure if this would cause my weak idle situation, or should I be looking at some other issue? I did a smoke test on the inlet and found no leaks. Thanks.
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By charliemccraney - 8 Years Ago
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What is your initial ignition timing?
The cam card figures are usually lobe lift, not valve lift. Make sure you are getting the right lift measurement.
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By miker - 8 Years Ago
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Just a random thought. If you're running a PCV valve, try blocking it off and set the idle. There's been some talk that some valve/engine combinations need to be restricted.
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By Mike. - 8 Years Ago
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Running ignition timing at 10 degrees initial, it's ok up to 12 but tends to ping at any more than that. The car runs great at speed and acceleration is good, just have this rough...Ish stumbly idle that can only be bettered by richening the mixture to the point where the exhaust stings your eyes. Spark plugs show it's running weak. It all points to as vacuum leak but I have not been able to find one.
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By Mike. - 8 Years Ago
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I'm not running a pcv valve on this engine. Perhaps I'm trying to make it idle too low with this cam. I'll do a vacvuum gauge reading once its running again, the radiator is currently removed because it sprang a leak....again!!!
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By charliemccraney - 8 Years Ago
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Does this problem get better at 12 degrees?
What is your idle speed?
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By Mike. - 8 Years Ago
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It does improve it slightly but only by the fact it speeds it up, I then slow it down with idle screw but it still runs lean . I don't have a tachometer on it at the moment, I'm guessing it doesn't like any less than 800rpm or it stumbles when I select drive. It would idle quite low and smooth before I rebuilt the engine with idle mixture screws out about 1.5 turns, I almost have to screw them nearly all the way out now to get it to idle at at all.
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By charliemccraney - 8 Years Ago
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And that timing is with the vacuum advance disconnected and the hose plugged, correct?
In order to trouble shoot effectively, you need to have all of the info possible, including RPM. Otherwise, it is more of a guessing game.
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By Sandbird - 8 Years Ago
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I put an E-4 in my 312 along time ago in a standard shift car and the cam profile produces a rough idle. While 260 deg. is not an extremely radical cam the extra lift and duration along with a tighter lobe separation angle creates more overlap that results in lower vacuum and a rougher idle. If your degree wheel readings are accurate it looks like your cam might be a few degrees advanced, which I wouldn't call a gross error. When installing my cam there were three of us there checking each other on accuracy and it is right on and it idles rough, so I don't think you would gain the idle your looking for by retarding the cam a couple deg. even though that is a step in the right direction. The engine likes 10 deg advance on ignition and it pings if I don't use higher octane gas than what is sold at the pump. The engine idles at 750 rpm and surprises people how hard the engine pulls at high rpm in high gear. If a smooth idle and take off coupled to a Fordomatic is what you like you might be happier with a stock '57 245 hp cam.
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By Mike. - 8 Years Ago
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Thanks guys. Yeah it's difficult to get any data as it's not running at the moment. I guess the question i was asking is would retarding the cam give me a better idle? The E4 was the only cam I could get hold of easily here in the UK.
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By chris70 - 8 Years Ago
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Hi Mike,i 've the same cam in my truck,forget a smooth idle!I have the same problem with idle mixture screws,things got better by plugging vacuum advance to a manifold source and opening the secondaries a bit on my Holley at idle,i don't know if you can do that with an Edelbrock.With this set up i'm having 16-17 HG of vacuum at 800 RPM.
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By Mike. - 8 Years Ago
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I tried all sorts with the Holley Chris, gave up and bought a new Edelbrock. In retrospect I should have persevered with Holley as I don't like this Edelbrock one bit. I'm guessing I'll have to live with it now, I'm sick of messing about trying g to get it to idle nice.
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By Ted - 8 Years Ago
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I have the Isky E4 in a 272 engine with the stock compression ratio and have had a variety of carbs on it over the last 145,000 miles since it was rebuilt. The Carter/Edelbrock carbs were the most troublesome in getting them dialed in right. Holley carbs ran well but fuel mileage was always a bit less than desired when getting the drivability just right. Put a lot of miles on the engine with a Road Demon Jr. 525 carb that ran quite well with fuel mileage in the 17-19 range but when it needed a kit after 13 years of driving, I simply installed a new Summit 500 cfm carb which I have not had to tinker with at all.
The vacuum advance is hooked up to the ported vacuum port at the carb while the intial timing is set at 12-14° with the vacuum advance unhooked. At idle, there is no vacuum advance signal at the distributor and idle and the timing does not change when the vacuum advance hose is hooked up. That simply means the throttle blades are in the correct position at idle. Haven’t done a legitimate fuel mileage check with this particular Summit carb but it’s good. While the E4 camshaft does have some rumble to it, the idle is smooth at 800 rpms and the idle mixture screws are totally adjustable.
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By 57RancheroJim - 8 Years Ago
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Looks like everyone's engine experiences different results. My 292 with the E4 idles nicely at 625 RPM, this is a standard trans car, just a slight rumble, you can hardly tell its got a cam which is what I wanted. I'm using a small rejetted 390cfm Holley. 12 degrees initial timing with a 34 degree mechanical advance distributor. Best I can get is 14 HG at idle..
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By Mike. - 8 Years Ago
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Thanks chaps, seems it's a characteristic of this cam. I'll get it back running and see what i can do with the carb. Annoying when it ran sweet before i rebuilt it even though i had 2 blown head gaskets, one cracked head and a cracked block 80 thou overbored. I wish I'd dumped it now and put another motor in it.
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By miker - 8 Years Ago
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Mike, I had the same sort of frustrations more than once. Just some more thoughts, as I think you've got either a vacuum leak or a bad carb. Funny to have two of them bad.
What manifold are you using. There's been some conversations about some manifold/carb combinations not sealing well from the base plate to the manifold. I've not run any stock manifolds in years and I don't remember the particulars, maybe someone will chime in.
Also, did you deck the block and/or mill the heads? If so, did you dry fit the intake and check the head manifold surfaces were parallel? In some cases you have to mill the manifold also. I think Ted's site has something that addresses that.
Years ago I ran an RPM300 Isky, which I think was a little more cam. It liked 900 or so rpm at idle, maybe a bit more when it had the fordo in it. But it was definitely a street cam.
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By Mike. - 8 Years Ago
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Thanks , I know that the heads and the block were milled, problem is I don't know by how much. I'm guessing this might be my problem. I did a smoke test on the engine but couldn't see any leaks, however i did have an intake leak on first start up after the rebuild and had to replace the gasket. I think this needs further investigation. If I take the manifold off I think i would be able to see where it's sitting by the indents left on the gasket. It's an original Ford 4 barrel intake.
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By charliemccraney - 8 Years Ago
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When composition head gaskets are used, which are included in most gasket sets, rather than original style shim gaskets, you have to remove about .030" from the heads and / or block just to get things back where they were. More or less than that and you do need to pay attention to the alignment.
I'm sure you'll find the problem. Even if you had swapped to another engine, no other engine is immune to these types of problems and you could still be fighting the exact same thing.
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By Mike. - 8 Years Ago
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Thanks. I'll have a look at the alignment this weekend, for now the car is outdoors and its raining....as ever in this wet country 😀
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By Talkwrench - 8 Years Ago
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This sounds similar to a problem Rick [Rick55] was having with needing some juice or it wasn't running right off idle, pretty sure he has the same cam with a 465 carb. He finally sorted the problem all it was for him was upping the jet sizes considerably and now all runs sweet so he said. Maybe Rick will see this an confirm.
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