Snap throttle Big Bang Theories

[charismaticmegafauna]

I didn't hear no noisey pops when I did my sync but I can't hear real good.

Your technique is wrong. While the engine is idling along nicely, grab the throttle and instantly snap it fully open. Not only will you hear the bang and feel the frame shudder, you may notice the motorcycle to rock back and forth too.

People have found other engine and drive line design faults too. For instance, with the motorcycle on the center stand and in gear, if you turn the throttle all the way up and suddenly turn loose of the clutch all at once you can hear the drive shaft and rear diff go bang and the see frame shake before the rear wheel starts to turn. I have no idea how Yamaha could release production machines with problems like these.

Sometimes, some unbelievable R&D gets done in 'the crucible of the consumer'. There was once a customer who brought his m/c back to the repair shop complaining that it still misses (even after having been in the shop for service). So, finally, with the serv.mgr. and other techs in attendance, he's asked if he can make the bike 'do it'? He says, yep...starts it in neutral, and holds the throttle wide-open untill it starts missing -- valve float or rev limiter (whichever comes first?) -- this particular event happened BRL (before rev limiters) but, the effect would be the same.

Another had a 'knock' in his engine that no-one could seem to hear/find. The m/c engine in question (brand & model) had an excellent reputation for long-life and reliability. Eventually, after many 'knocking' complaints, the engine was dis-assembled and nothing out-of-the-ordinary was found. After assembly and testing and payment the bike was delivered to the customer -- only to have continued 'knocking' complaints. When asked, "Can you make it 'do it'?" He says, yep...and rides away and is in top gear (5th or 6th) while still within a block from the shop -- accelerating hard with the engine 'knocking away'.

I'm sure there are many more... :blink:

 

[boomerang]

Rainy here in Ohio today, so I used the time to do a throttle body sync. While making all the small adjustments, where you have to blip the throttle about a hundred times, I started to notice a terrible sound. It may have been there all along, but because I do not tend to blip the throttle while waiting for the light to change, I had never noticed it before.
What happens is this... with the engine idling smoothly, if I snap the throttle open, there is a very slight hesitation followed by a loud bang just as the revs start to rise. It is as if the first combustion chamber to take the increased fuel mixture combusts violently. It sounds like a hammer hitting the top of the piston. If I roll on the throttle at a normal drive-away speed, there is no bang. It only happens when I snap the throttle open...and is quite scary!

Here are some more facts that may or may not be significant: This is a 2008 FJR1300A. The TBS is perfect, thanks to my Carbtune II. I run premium gas (93 octane) to avoid having any alcohol in the tank. Temperature was normal with 6 or 7 bars showing on the temp gauge.

What the heck is making this sound? Could it be caused by the Throttle Position Sensor which I have never touched? Maybe the premium gas is retarding ignition somewhat?

Any and all opinions welcome.

I think that sound is just simply the sound of combustion, I mean you are dumping a ton of fuel into an engine that is at idle,it has to go some where quick. My 06 fjr does the same thing. The only other bike I ever owned that made that sound,that hard single hammer sound, when you dump the throutle was my old yamaha xs1100. I'm Guessing it's probaley not good to make it do that on purpus.

 

[GypsyCaravan]

My '06AE has done it since I bought it. I try not to blip it cold, but sometimes forget and rev it, then remember why I tell myself not to...

My 06 Kawi Z750S was fuel-injected and also did it, when blipping the throttle, usually while the bike was still in the garage and hadn't been ridden yet / not fully warmed up. It wasn't as loud, but that motor was also half the size.

I'm sure it's all something to do with idle speed, instant fuel flow to an engine / exhaust not completely warmed up, not under load, etc.

I wouldn't sweat it.

 

[ohiofjr]

If you want to hear another bike my '04 is only a few minutes away. But I think what you are hearing is normal.

 

[road runner]

and my two cents.
When you blip the trottle, you reduce the amount of vacuum in the intake tract. This has the effect of leaning out the mixture for the first revolution because the fuel injection has already injected the gas into the intake tract based on the last known readings of closed throttle, low revs etc.... When you snap open the throttle, you get a little back flow from the intake valve opening while the piston is still in the exhaust stroke whcih wouldn't happen at lower throttle openings, and then that gets sucked into the cylinder. It's lean and probably detonates. It's why carburetors have accelorator pumps.

That's not my immaginings, that's a generalization I took from my "how to tune weber carbs".

I tried using the accelorator pump feature for my pc3 but I can't get it to work.

+1

A lot of closed loop EFI engines will do this, some worse than others.

Mine does it when I blip it, so I don't blip it.

I think it's normal and would not worry about it.

My .02 worth A.C.

 

[Hawk1]

My ´06 did the same thing. The throttle response is not

better than this. Lean on the mixture.

PCIII fixed mine and is now way better to ride after installing.