can anyone help me out with this prob?
I have just built a new 378'' clevo and am having problems turning it off, it has modified 2V closed chambers opened up to get a static comp ratio of 10.6:1 ,which is the minimum recomended for the camshaft (250-260deg @ .050''). The old girl idles at just over 1000rpm otherwise it gets a bit lopey & wants to die, but even at 1000 I cant find why it just keeps going when turned off. I did hear somewhere that when using premium unleaded fuel, the jet size can be reduced by up to 4-5 sizes due to the denseness of it, has anyone else heard that?
also the carb is a 3310-2 750 vac holley with all standard jetting & valves as a guide to fine tune it.
This morning I have changed the coil voltage to 12V but have'nt had a chance to see the results,
any help would be appreciated: kenny

Sounds like too rich ??? at idle....
Have got colder plugs fitted ??
I'd guess two munbers colder than std...
Double check timing etc...

kenny,

Unfortunately, thats the problems you will face with a holley, and idling at 1000rpm. There is no way you can do the idle mixtures at 1000rpm because you will find the butterfly's in the carby are open that much that your running on the transition circuit.

Also double check your ignition system, make sure coil voltage drops off completely when the key is turned off, sometimes if your running an MSD or the ignition off a relay it will run on due to the alternator.

What you need to do, is play with your distributor, limit the amount of centrifugal advance to 16 or 19 degres if you can (real easy to do on msd dizzy's) and then set your base timing to around 16 degrees (you need to aim for around 34 degrees total timing)

Next, back off your idle screw all the way and then wind it in until the butterflys are only just open, and have someone start the engine while you are at the carby trying to help it idle.

Get it idling at around 700 or so rpm, even if its lopey, but keep track of how far you need to screw the idle stop screw in. If its more than a couple of turns you may need to drill your butterflys (start with a 1/8 hole)

Once its idling on its own, then do your idle mixtures, basically 2 ways you can do it, one is with a vacuum gauge, or the other is by ear. There is heaps on info on the net and on the holley site on how to do this.

Start off with them all the way in, and out 1.5 turns, and work from there. Remeber to adjust them evenly.

You'll find the increased static timing will fix the idle lope and you can leave it idle between 700-900 rpm.

timing is at 12deg btdc with 28deg total advance reached @ 3200rpm
plugs are NGK bp5fs as used in the XD-E 351 ,when using bp6fs(colder) the plugs foul in a matter of 200km street driving, but I do see where you are going (less heat in the cylinder , less chance of firing)

I have actually used the secondaries as a part of the idle circuit as I have experienced idle probs b4 with my last engine, so the primary idle transfer slots are only exposed by.050''
The cam is a bit extreme for an idle much less than 1000 as it has a duration of 250-260 deg @ .050'' with lifts of .596'' & .622''
I do have 2 sets of butterflies pre drilled from my last build one 1/8 & 1 at 1/4'' but I was hoping to not need to use em'
also vacuum is nearly non existant!
Have you got the same book as me, HOLLEY Rebuilding & modifiying ,an SA publication? great read if you don't

Try give it more initial timing, about 5-6 degrees more, you should be fine if your total is around 34 degrees, this will help idle vacuum.
If your running premium, it still shouldnt ping until you get upto around 36 degrees total.

Plugs most likely are fouling due to the minimal vacuum, the power valve is probably staying open in light cruise conditions - do you know what power valves you have in the holley?

just finished rooting round with it, and have found a real sweet spot at 14deg initial, total can be taken all the way to 45deg total!! providing the springs regulate advance as well as they did, as for the power valve is just a 6.5 with the spring being chopped a little at a time until I got off idle stumble, so now I will have to get a valve with slightly more tension. The power valve circuit has been reduced in size until a surge appeared then opened up a little, now the secondaries are being pulled open too early due to the extra vacuum, so a medium spring will have to be employed!
thanks for the help, I'll let ya know how it goes, but from early indications 320hp at the treads is looking quite easy to achive