Snap throttle Big Bang Theories

[Mackeroni]

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.

 

[Silent]

Probably the fuel injection having a hard time keeping up with your rapid throttle change. If it doesn't do it under normal riding conditions, I wouldn't worry about it. Just don't whack it so hard doing the TBS. Regular 87 is cheaper and all this portly girl needs B) YMMV on the gas.

 

[El Toro]

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!

Hmmmmm..... Is it an after fire in the exhaust, a back fire through the throttle bodies, or is it the dreaded pre-ignition/knock? If you'd just said that there is a loud bang, I would have suggested that it was an afterfire with a large slug of fuel igniting in the exhaust. Fuel and timing maps often not only look at TPS, but also look at the derivitive of TPS. You are creating a huge derivative for your TPS, and if the engine control module is reading it and using it, it is probably dumping a slug of fuel, just like an accelerator pump on a carburetor. If there is a lot of enrichment, it is not surprising if some of the excess charge makes it into the exhaust and bangs there.

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.

Alcohol is an octane booster, and if they're putting it in your regular grade gas, they're probably putting it in your premium grade too. Sadly this is just a fact of modern life. The government has dictated to the oil companies that they WILL SELL more ethanol. The only way to really meet the mandate is to blend in 10% and sell gasohol instead of straight run gasoline.

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.

Premium gas isn't going to retard your ignition timing. If your problem is knock, its because your timing is advanced. Since bikes generally don't have knock sensors, premium gas isn't going to advance your timing either.

If you can be more certain of the location of the bang, it will be easier to figure out with certainty.

Meanwhile, if you don't blip the throttle in normal operation, why spend time trying to figure out how to keep the bike from doing something when the throttle is blipped. You're happy with your TBS, so head on out and enjoy the bike.

 

[Mackeroni]

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!

Hmmmmm..... Is it an after fire in the exhaust, a back fire through the throttle bodies, or is it the dreaded pre-ignition/knock? If you'd just said that there is a loud bang, I would have suggested that it was an afterfire with a large slug of fuel igniting in the exhaust. Fuel and timing maps often not only look at TPS, but also look at the derivitive of TPS. You are creating a huge derivative for your TPS, and if the engine control module is reading it and using it, it is probably dumping a slug of fuel, just like an accelerator pump on a carburetor. If there is a lot of enrichment, it is not surprising if some of the excess charge makes it into the exhaust and bangs there.

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.

Alcohol is an octane booster, and if they're putting it in your regular grade gas, they're probably putting it in your premium grade too. Sadly this is just a fact of modern life. The government has dictated to the oil companies that they WILL SELL more ethanol. The only way to really meet the mandate is to blend in 10% and sell gasohol instead of straight run gasoline.

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.

Opinions are like a**holes. Everyone's got one.

Premium gas isn't going to retard your ignition timing. If your problem is knock, its because your timing is advanced. Since bikes generally don't have knock sensors, premium gas isn't going to advance your timing either.

If you can be more certain of the location of the bang, it will be easier to figure out with certainty.

Meanwhile, if you don't blip the throttle in normal operation, why spend time trying to figure out how to keep the bike from doing something when the throttle is blipped. You're happy with your TBS, so head on out and enjoy the bike.

The sound comes from the engine bay... from right where normal combustion occurs...or possibly back through the throttle bodies. It is a sudden and loud bang... and the whole bike gives a shake on the center stand. Maybe it is knock... but it is louder than any knock I've ever heard.

I plan to drive normally, without blipping the throttle, so this should not be a daily operation problem. However, it is a bit troubling and knowing the reason would certainly put me at ease.

I was under the impression that premium gas contains no ethanol, but if this is not the case, I will switch to regular. Maybe that will make a difference.

 

[jekirby]

By all means take what I say with a grain of salt, but after reading the endless discussions on the forum about high octane gas, I think the cheapest adjustment would be to use regular. Just as above, I would think a combination of the high octane and throttle blips in an engine that was designed for regular would cause a problem. This usually manifests itself as a backfire, but I don't really recall hearing a backfire with a fuel injected engine, so it may sound closer up the header toward the engine.

For those more familiar with the inner workings of this engine, could it be the cam chain tensioner or slap in the chain, caused by the tensioner from the rapid blip?

 

[ionbeam]

When you do the blippy thingie your engine is unloaded, when driving your engine is 'loaded'. When you blip the throttle with an unloaded engine it is able to rev significantly faster than when loaded. Also, there is nothing to make the spinning, meshing, reciprocating parts take up what ever slack there may be. I expect what you are hearing is normal for an unloaded engine. I also suspect that it is really hard on your engine. IMO.

 

[Ramblin Man]

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.

 

[Mackeroni]

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.

Well, that's the best explanation I've heard so far. This is really hard to explain. It's not a really loud sound, like a backfire. It's more like a hammer striking a piston dome really hard... and as I said, the bike gives one big shake when it happens.

Do I worry about this? What can I do to eliminate it?

 

[Mackeroni]

When you do the blippy thingie your engine is unloaded, when driving your engine is 'loaded'. When you blip the throttle with an unloaded engine it is able to rev significantly faster than when loaded. Also, there is nothing to make the spinning, meshing, reciprocating parts take up what ever slack there may be. I expect what you are hearing is normal for an unloaded engine. I also suspect that it is really hard on your engine. IMO.

If this is 'normal', it must be happening to everyone else... and yes, it sounds like it would be really hard on close tolerance moving metal parts.

Would a PCIII fix it?

 

[odot]

don't blip the throttle.

 

[El Toro]

don't blip the throttle.

+1

Careful, ODOT. You're treading on thin ice with useful advice. :drinks:

Not gonna go into the difference between Weber carbs and EFI...

 

[odot]

Can't wait till S&S comes out with an aftermarket carb for the fudger. That's gonna be fun to tune....."start out by completely closing the mixture screw all the way, then back out one and a half turns...........".............

 

[Mackeroni]

don't blip the throttle.

Oh jeeze. I hadn't thought of that. Thanks Mr. ODOT.

What should I do about the uncomfortable seat? Not sit on it?

 

[odot]

Now yer catching on. You want my theory on whiners, too?

 

[James]

Now yer catching on. You want my theory on whiners, too?

Teach what you know...

 

[big ears]

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

 

[ionbeam]

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.

 

[fjr55]

Hey Mack, I have the same noise you are talking about. When I had it in for 600 mile service, they said everything is fine. I did mention it when I brought it in. It does though seem to go away once it is warmed up. I have not synced the injectors yet, I am waiting to buy the tool. So I am just going to keep riding it. Hopefully it wont blow up LOL but thats why I have a warranty.

 

[Sherman]

There is an old Jackie Vernon joke that goes something like this:

"I was talking to my doctor one day...

I said, 'Hey, Doc, it hurts when I do this.' (Jackie pokes himself in the eye.)

So my doctor says, 'Then stop doing that'