Technical Tips > Engines - Carbies - Exhausts - Dissys

pinging suspect new manifold

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MADLT1:
if it was running OK before I would tip your out a tooth on the distributer when you wacked it back in. I know you say its bang on but I have never trusted timing marks (been brung undone with sliped or poorly remaufactured ballancers. make soure you are at actual TDC not jsut the ballancer and check were your at, then go form there.

MADLT1:
I doubt the manifold would be the course of the problem, one thing to try though would be to check the mixture on the carby if he's positive the ignition timing is correct, one of the idle circuits may not be working.

may also be an air leak, has the engine got a high (ish) idle?

easy way to check if an engine is lean it to squirt a bit of good quality carby cleaner (I use the Nulon one) into the intake, if the revs increase then the engine is on the lean side

another trap it to use a non ported vacuum source for the vac advance, by this I mean it doesn't bleed off, just holds vacuum. try disconnecting it to see if this is a problem.

MADLT1:
I was also thinking the vacuum is connect to manifold vacuum rather than spark ported vacuum. Manifold vacuum will advance on startup and retard under acceleration (rather than the other way around) causing massive pinging. Other than that I would think the dissy (the only other thing you changed) would be the problem, either wrong advance curve or not enough spark.    Manifold vac will advance a few degress at idle, but during acceleration both port and manifold vac behave the same. The curve is similar if not exactly the same.

If the vac is suspected in this case, well block it off and try it. If no better, then retard the dizzy a bit and give that a go. Only a couple of things it can be...1..to adavanced...2...running to lean under load ( power valve or main jets to small ). I suspect with the old manifold that the vac was not plumbed in correctly. Now it is, the timing needs adjusting.
_________________
See ya on the road or at a run somewhere.

Gray-man:
Hi again,to answer your questions,Holley dual plane no part No. on top I think it was underneath,Carb is standard Rochester rebuilt by carb specialist,Timed with T/light 8deg then with vacuum guage then at 36deg with adv springs removed but you can advance or retard it all you want it still pings from 2grand on.fuel shell optimax with flash lube,Its the orriginal 350 standard carb rams horns bouble hump heads mild cam, it was fitted with a offenhauser 360 manifold when I got it lot of corrosion at water neck and carb mount had been milled down to fit under bonnet but to far as carb barley covered the hole but it ran fine. I pulled radiator support out to fix usual rust and decided to replace manifold that when it started to ping, had a mechanic look at it to day drove it pulled a plug out and said running way lean and that I have a vacuum leak probably let a gasket slip a little when fitting so I'm gonna take it back off and try again thank for your input Ill let you know how I get on

MADLT1:
OK keep us posted:b2

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