How do I get rid of "spark knock"
 

I finally got my truck running a 7 out of 10. After a fresh carb rebuild, new HEI dist, new spark plugs. I run premium gas all the time. When I get on the gas it sounds like the the motor is going to fall apart. Just in conversation people tell me "that's a timing issue". How do I fix this? can I just advance the dist or retard?

Re: How do I get rid of "spark knock"
 

You need to check the timing with a light to make sure it's on spec. With vacuum advanced disconnected first for initial setting. Then check with vacuum advance connected. I'm assuming you have a vacuum advance on it. Don't know what your engine is to give much more info.

Re: How do I get rid of "spark knock"
 

Spark Knock or "preignition" or if you can if you can remember the early 80's the term "labor knock" was also thrown about. those conditions all all from timing that is to high, retard the timing a little bit and it should all clear right up. Do you have the timing set with a light, or did you just set it by ear? Or static time when building [or working on] the motor just to get it going and then it was so close you wanted to try it. If you put a light on it did you set it at an idle or an all in type thing at a certain rpm? Jim
?

Re: How do I get rid of "spark knock"
 

Its a '72 307 with a 2bbl carb. I am very new to doing this on my own. I havnt checked it with a light yet. I know the difference between advance and retard but that's about it. Ill check it this sat and try to retard it a little and see if it goes away. I put new plugs in it and didn't gap them. It was having the knock before the new plugs as well.

Re: How do I get rid of "spark knock"
 

If I stomp on the gas it wont do it....its only under load at light-mid throttle.

Re: How do I get rid of "spark knock"
 

Pull timing out and also better fuel, colder plugs all will help get spark knock out

Re: How do I get rid of "spark knock"
 

its really bad for a motor, better gas. and check engine temp.

Re: How do I get rid of "spark knock"
 

Check the timing with a light or you can also use a vacuum gauge. With the idle turned up to about 1000 rpm, advance or retard the timing until you get the highest vacuum reading. Then retard the timing until the vacuum gauge drops 1 inch of vacuum. Then turn the idle back down. If it still pings it also could be a lean air fuel condition. What did you do to the carb?

Re: How do I get rid of "spark knock"
 

Like others have posted, retard the timing and check the fuel/air mixture needles on the carb...also verify the timing with a timing light.

Re: How do I get rid of "spark knock"
 

Go back and start from the beginning ,

pull the plugs and gap them
set the timing with a light
a fresh carb rebuild does not mean it is correct just close ,many guys can tune a carb by "ear" I would imagine these steps should easily fix your issue .

Re: How do I get rid of "spark knock"
 

This sounds to me like a vacuum advance issue. Unhook the advance, and then go for a drive. A lot of distributors have lots of vacuum advance (like 24 degrees) to make up for a really weak timing curve. If you set the initial timing for more advance than stock, the vacuum can may push it too far during light throttle, high vacuum, driving. If this is the case, you simply need to limit the vacuum advance. About 10 degrees is a good number for a performace type of timing curve.

Re: How do I get rid of "spark knock"
 

Agreed, if the knock occurs just at low speed/part throttle, it's more than likely a vacuum advance issue. BTW...if it's a stock 307 with 2BBL you only need to run regular gas. You are just wasting your cash with premium. It will do NOTHING to improve economy or performance.

You might find this interesting...
http://www.consumer.ftc.gov/articles...ctane-gasoline

Re: How do I get rid of "spark knock"
 

Retard the timing.