morpheus
01.05.2021 23:06:21
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If the bike runs strong then I wouldn't worry about it. here
I know jetting can have an effect on the way a bike sounds at idle but this is way beyond jetting. My bike is jetted properly and has a pro-circuit pipe on it. The silencer has recently been repacked (sounds the same either way). Any ideas on what variables might effect this sound. or lack thereof?
That's not a bad thing seriously. We owned a 86 that was slightly worked on, head milled ported mildly. No ping but one of the fastest CR250's I have ever ridden. It sounded STRONG very burly as you mention and all stock exhaust.
My bike has the Eric Gorr mo-bettah porting along with a 265 cc overbore but the sound didn't change after these mods. The bike does run strong although it has zero top end power, it is pure low and mid. The power valves function properly but it almost feels like half throttle and full throttle produce nearly the same results. The clutches aren't slipping and the engine revs out cleanly. just nothing happens power wise. This could be due to my basis for comparison though as my other bike is an '09 CRF 450x.
What I am referring to is the ping-ping-ping of the exhaust, not detonation. I have an 86 CR250 and it sounds good but it just doesn't have that crackling pinging sound at idle. My bike has a much deeper sound. In fact, no 86 CR250 that I have ever heard has that pingy sound. They are always more of a glug-glug glug-glug-glug sound. I have heard 89 CR250s that have the pingy sound. The best that I can figure, the sound is only present on the CRs with low boy pipes.
NOTE: Over advanced ignition timing can also cause the same thing. The engine computer controls ignition timing. As a result, ignition timing is not adjustable on today’s engines. The only way to change the timing advance would be to flash reprogram the (PCM). more
Vacuum leaks in any of these components may cause knocking or pinging. Check vacuum hoses in these systems for damage and loose connections. here
High back pressure is a common exhaust system problem. This may happen because, of a clogged exhaust pipe; catalytic converter or muffler. As a result, a clogged converter is the most common cause of exhaust back pressure buildup. It will restrict engine airflow causing the engine to run hotter and lose power. Consequently, leading to pinging or knocking. Most of the time, a catalytic converter will clog because, of old age overheating or fuel contamination. [links]
Engine spark knock happens when, the fuel mixture is subjected to either too much compression heat or both. So, if your engine is making that annoying knocking, pinging or rattling sound; then you’re probably experiencing engine spark knock.
Pinging is two flame fronts colliding and is caused by hot spots in the combustion chamber. A seperate flame front starts elsewhere in the combustion chamber and collides with the flame front from the spark plug making a high pitched "ping" noise. Your dirt bike is so loud, you'd likely have a hard time hearing any pinging. Detonation is the explosive ignition of fuel/air under very high pressures/temperatures. Detonation's sound is best described as shaking a can full of rocks and is definately audible over the bike if it becomes severe. Pinging can lead to detonation because the 2nd flame front can cause a sharp rise in cylinder pressure similar to running too much spark advance. But, the two are not the same. None of these have anything to do with fuel burning in the pipe. [links]
You don't ride an RM, do you?
What the original poster is describing sounds like a mechanical issue of some sort not a combustion issue.
Deceleration knock is the same as detonation it's can accur under deceleration and acceleration. Knock occurs because the pressure and temperature in the cylinder are high enough when combustion is occurring that the unburned fuel/air mixture spontaneously ignites. Some things that can cause this are combustin temps, ignition timing, fuel grade, engine load , compression etc. If the bikes runs great everywhere else it could be just some jetting issues that would need to be addressed. Could start by going one size richer on the pilot jet or maybe the needle, but we don't what your current jetting spec are. here
I think the actual bang is caused by unburned fuel/air burning in the pipe. The cylinder doesn't fire when you shut the throttle, therefore, some fuel/air gets pushed into the pipe. Periodically, the cylinder will light and that will ignite the fuel/air in the pipe.
So there's no clicking sound.
I have never heard of a street-going 2-stroke motor that turned 17,000 RPM like a Yamaha R6, and Honda built 500cc 4-stroke GP motors that turned 20,000 RPM.
There's also no whirring sound like a cam chain makes, because there's no camshaft or chain.