Ok you edelbrock carb guys.... I have a Edelbrock 1406 on my 330hp Chevy 350. I am experiencing some slight engine knocking at slight excelleration from 2,000 rpm up with the engine running at 175 degrees. When I apply power the engine rattles and then the temperature starts climbing to around 200 degrees. I notice this when climbing a hill. I have checked and double checked my distributor curve setup and timing and even had the distributor set up on a Sun machine. The engine idles great, seems to run clean (plugs are tan collored), doesn't hesitate, stumble, or seem sluggish. My main jetting is at .098 and the metering rods are 070x037. Any suggestions of where to start? Any suggestuions to replace it with something else? Thanks....
What is your initial timing, and idle speed? Did you set it with a timing light, with the vacuum advance disconnected and plugged, and the transmission in drive, if it is an automatic? Are you running the vacuum advance to ported, or manifold vacuum. There is likely nothing wrong, but the state of tune. It sounds like your timing is off.
This is all purely conjecture since I don't have enough info, but start here: If that motor makes a lot of vacuum then change to orange (guess) or pink (guess) spring under each metering rod holder. Sounds like lean out under load. My hypothesis is that rod stays down instead of raising to the smaller (power/more fuel since less restriction section of the rod) so it leans and gets hot. The earth friendly blended fuels also mess up what would be normal calibration. If you have access to a 4 gas analyzer then check out what it does at around 2400. Even though its not loaded you should still see what hydrocarbon, O2 and CO . Compare it to your idle numbers and the results should be noticible. Did you leave the secondary at 95? Do you have proper fuel flow? Sounds crazy but a small air leak upstream of the fuel pump will areate the fuel making it do weird stuff under load but appear normal at idle. Check that old crusty piece of fuel line coming from the tank that most people dont change since its too hard to get to, or look for a faulty fitting. Sometimes leaks like that are not apparent since they are not under pressure. Of course these are just scientific wild ass guesses so check it out and give us some more info.
The symptoms your engine exhibit sound like too much timing to me. Back it off a tad and see if it quits pinging. You may have to go to heavier advance springs. What kind of distributor?
It will have a lot to do with manifold vacuum, get a gage on it to see if the 'step-up' springs are in range. If you have the book that came with the carb they have a very good chart for tuning, spend a little time to read it (i'm not being a smartass here), you'll find they give some very good information on how to tune the carb. I've read tons of stuff on carbs from holley manuals to college text books and that is the best i have read.
If you don't have an adjustable vacuum advance here is what I would do. Using a mytivac and a dial-back timing light determine which advance you have now. Write it down. Retard your initial timing 4 degrees and see if that cures the part throttle ping, if not go 2 more at a time. Once you figure out where you need to be pick a vacuum advance from the table below, remember it is in distributor degrees. Another alternative is to use a small bad clamp to limit the vacuum advance movement and experiment about an 1/8 of an inch at a time. Also if your current vacuum advance comes in early you could pick a higher vacuum unit.
set the timing right and i bet the knockin goes away. from what you are saying it does sound like timing isnt right on the money.atleast thats a good place to start.
His knock is part throttle, not full throttle. If it doesn't knock full throttle it's more likely too much vacuum advance for that load condition. jm2c
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