I have just gotten my small block back together after putting 200cc alluminum heads on it over the winter. This is the only change that I have made to the engine. I am hearing a poppong or banging type of noise that sounds like it is occuring inside the exhaust at about 2000rpm. I was having the same noise last summer with the old heads, but it dint happen as often and not unitl about 4000rpm. At the time, a friend of mine said that was caused by a lean condition. If so, how do I correct it? The carb is box stock and the only tuning I have ever done on a carb was adjusting the idle! Could it be a timing issue? I have it set at 12 degrees initial and 34 degrees in by 2500.

Any and all comments/ suggestions are welcome and appreciated!

p.s. Im also running a Holley Pro Strip Annihilator ignition. And my combo is listed in my signature.

my car does nothing but that when i run that LOW OCTANE ****....... i had to run that last week in it and it was pissin me off cause it was sounding like a POS......to bad the super pumps were out of order.RUN higher octane and if u are running high octane try a bottle of 104+ octane booster ;) :cool: then ull be on JET FUEL :eek:

I'm assuming the new heads are of a modern and more efficient design.We really need more information on the setup.Sounds like timing curve may be a little too quick.Try 10* initial,and 32* in at 3000.This should definitely help,but more info would be helpful. Steve

The heads are Pro Topline alluminum heads. 200cc intake ports and 64cc combustion chambers. The rockers are 1.6 Harland Sharps. The old heads were 66 or 67 327 heads with 64cc chambers and 1.94 intake valves. The problem existed back then, just not till a higher rpm.

The fuel I am running is 92 octane plus about 25% 110 octane Avgas so I should be good in that department.

Is the lean condition at all possible or is it way out in left field?

I would pull the front bowl and jet up 2 sizes and see if it gets better sounds lean to me.

Hey, this isn't the same motor as that leaking Holley in the other thread I talked with you about, is it?

Yes it is the same motor.

When would the popping occurr? <-- did I spell that right? :eek:

Is it ONLY:

a. When you accelerate
b. While cruising
c. When letting off the throttle while decelerating

If it is..

a. It's running lean, try bumping the nozzles, then maybe the secondary jets.
b. It's running lean, try bumping the primary jets.
c. The idle mixture screws are too tight. Back them off a 1/2 turn on each side and try again.

This is very general, I can't say it will solve your problems. First, I would try fixing that fuel leak.

Oh, and before I forget, read your plugs.

Reading plugs is just like reading coffee. A heavily creamed coffee color means lean. A black coffee color means rich.

Unfortunately I havent left the garage yet! The problem occurs when the engine has just started, from idle when revved over 2000rpm. I just got this thing running, so I dont think I have enough time on it to get an accurate plug reading.

Yes it probably would be a good idea to get the leak fixed before the whole works goes up in flames!

Thanks all for the info so far.

I'm with the idea of pulling the plugs and seeing what they look like. My cousin had a similar problem, whenver he would put it to the carpet the truck revved but popped, it also put out a not so natural exhaust visually. His truck was running too rich.

Just my .02cents.

-Matt

When I have had a "light" popping in the exhaust it has been a blown power valve in the carb causing it to run too rich.

I tried changing my timing curve to what was suggested above. It seemed to help some, but it didnt totally cure the problem. Any suggestions on how I might tweak the curve a little more?

I also bought some jets that are a couple steps up. This weekend I will try them out when I pull the carb to fix the leak.

Thanks to all who have commented so far!

I've been battling carb issues as well. I saw in Barry Grants website that it COULD be that your floats are set too high, causing rich condition. I think my problem is too much fuel pressure for my Demon.

Don't know if this makes sense, but what about a lifter/valve that is too tight?

Let's see how he is doing once he fixes the obvious problems first, then after that we can really get to work. No sense in fixing a loose bolt with a broken wrench.