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What does detonation sound like?

  • Thread starter Thread starter 79-GS550-L
  • Start date Start date
7

79-GS550-L

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I finally got my hanging idle problem fixed - it turned out to be a torn carb top gasket (covering the throttle linkage). So I took my bike for a ride and decided to test the upper range of the throttle...

It doesn't have much power at all above 1/2 throttle, nearly dies at 3/4 throttle, coughs/pops and slowly picks up a little at full throttle. But the thing that bothers me is if I hold the throttle constant at around 1/2 throttle, just before the point where it's power drops off, I hear what sounds like bits of sand hitting the exhaust pipes. Now, it's possible that what I'm hearing IS sand hitting the exhaust :-D. But I don't know what detonation sounds like while on the bike doing 45mph with a helmet on, etc. I don't want to damage anything but I'd love to get a bit of riding in while I'm working on the other problems.

So, would detonation be subtle? Or would I definitely know when it was happening?
 
its bits of piston hitting the pipes, not sand. lol

detonation, also known as pinging is a pinging sound that starts as a light rattling sound like small metal shot in a can and can grow to severe detonation that sounds like marbles are loose in the engine.
 
focus frenzy said:
its bits of piston hitting the pipes, not sand. lol

detonation, also known as pinging is a pinging sound that starts as a light rattling sound like small metal shot in a can and can grow to severe detonation that sounds like marbles are loose in the engine.
Click to expand...

LOL: I was just going to write "like marbles are bouncing around in the engine" :-D
 
going lean will cause heat which causes pre ignition. Pre ignition is where two flame fronts slam one another in the chamber and can cause just as much damage as detonation. Detonation is where the gas burns too quickly in the chamber causing one flame front to slam the top of the piston.

Fatten your ride up.
 
I tried to do a plug chop by running on one cylinder in neutral, and was not able to get it all the way to full throttle, only about halfway. The plug (which started out very black and sooty) ended up with a greyish white haze on the ground strap. So I am thinking this bike is running too rich at low throttle and too lean at higher throttle. I've gone through everything I can think of on the intake side (short of rejetting, but carbs have been completely disassembled and dipped, and are spotless). Could the exhaust have anything to do with that? I believe it's the stock exhaust, but there are some nasty patch jobs in it. Where the pipes (headers?) come from the engine and join into the 2-1 sections, there is a lot of red silicone exhaust sealer gobbed on there, and it has gotten oily and so now it's black and peeling away.

Anybody figure this as the problem? I'm not sure how to fix it properly... are there supposed to be any gaskets at that spot? It's right where the exhaust reaches the clamps that hold it together.
 
I have one doing this - 90% sure its coming from horribly leaking air boots.
 
Air intake boots are perfect, I just did those. I pulled off as much of the nasty red silicone gunk as I could from the exhaust, and now it seems to pull a LITTLE stronger at around 1/2 throttle, but makes louder noises (predetonation?) as I give it more. Of course I could be imagining whether there is any difference, as it is doing the same thing as before, just seems like more so. One thing that I'm NOT imagining though is that my hanging idle is back. Would leaky exhaust cause hanging idle?

I picked up some muffler tape at ace, which I will try to put on tonight. It won't be pretty, but I don't care, I just want to ride! Maybe later on I'll upgrade the exhaust. We'll see what this does.
 
Okay you dipped the carbs and they are squeaky clean, what jets did you find in the carbs? Are they the correct mains and pilots for this bike or did the PO screw around with jetting and then sell the probem he created? Hope you get it sorted out soon
 
Did you adjust the valves? If it still happens after that fatten up the main jet. It could also be the needle jet adjustment. I'd ask Keith Krause. He knows the VM carbs.
 
This might be a stretch, but did this bike sit for a long time unused? There might possible be an exhaust blockage (like a mouse nest) in the exhaust? Does the flow feel the same out of both pipes?
 
Let's see... airbox is in good shape, I added some weather stripping, valve clearances have been done. Unfortunately when I had the carbs dismantled I didn't think to check the jet sizes. If this exhaust thing doesn't help I'll take them apart again.

How can I check for exhaust restriction? I guess I'd have to take the mufflers off and blow some compressed air into there? How much restriction *should* it have, with the stock baffles in it?
 
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