Thread: Spark knock/pinging theories.
07-20-2009, 04:47 PM #1
Spark knock/pinging theories.
I have had this annoying pinging in my engine since I put it together. Much like low octane gas when high octane is required. It seems to occur at aorund 5,000-6000 RPMs under light throttle. It goes away if I hit the throttle while it is doing it.
I have the Pro-Tec recreational head that makes 175 PSI compression. I use 93 octane gasoline.
Here are my two theories:
1. Somehow the spark plug cables are cross firing, and causing one of the cylinders to fire early. I only think this because the manual says that at 1,500 RPM BOTH cylinders are at 15 degrees BTDC. However, at 5,500 RPM The front is 20 deg BTDC, and the rear is 18 deg BTDC. This is why I have a feeling the plug wires are cross firing. Remember I said it starts pinging at 5,000 or so RPM.
BUT... I also heard that both of the plugs fire at the same time. So does the difference in timing come from crank flex?
2. Too much heat in one cylinder. I don't know how this can happen, but it has been suggested.
This pinging annoys the crap out of me. I swear it is some form of spark knock. I also don't want to melt my engine down.
The only way I can rule it out is by emptying the gas tank (or close to empty) and running 5 gallons, or so of some Sunoco 110. If the ping goes away, then I have to start digging.
Has anyone run into this problem with a twin before?
07-21-2009, 06:07 PM #2
Okay, so after talking to a couple of people. This engine is somewhat famous for the set screws coming loose that holds the CDI pickup, and falling down to full advance. Now I just need to figure out where it should be set.
07-21-2009, 06:50 PM #3
Look at my tripple...they say that's why I lost 3 although #1 and #2 have more timing and compression.
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