Engine noise under load - is it normal?

[Al Gully]

So with all that said, what does the idle adjustment hand screw on the right hand side of the bike move when we adjust the idle, the starter valves or the butterfly valves.
It has been said at idle, the butterfly's are 100% closed and the moly applied to them create a 100% seal while the bike is idling.

 

[dduelin]

When I have had the airbox off my FI bikes during a synch, the SVs make quite a loud hissing sound, so while I agree they are small, they seem to flow a decent amount of air. My recollection is that they are something like 4mm diameter. The other thing to bear in mind is that the opening created around the 36mm throttle butterfly is not proportional to the degrees opened. So 10 degrees open is around 0.1% of the WOT opening, 20 degrees is just under 2% and so on. So until the throttle is opened the SVs make up quite proportion of the air.

I made a rough calculation assuming 4mm for the open SV, and the SV would make up 95% of airflow at 10 degrees throttle, 47% at 20 degrees open, 23 % at 30 degrees open and 14% at 40 degrees open.

You may be surprised how often you ride the bike with such small openings.

You can see the SV openings in the side of the intakes and they are nowhere near 4 mm in diameter. Someone will measure them soon. What we can’t see is the diameter of the passages within the throttle body. The pilot jets in their carburetor cousins that control mixtures from idle to 10 or 15% throttle have air passages so small we use guitar string to open clogged ones.

Another thing to remember is the demands that Euro 3 placed on control of emissions in first generation fuel injected motorcycles. Manufacturers could not give owners the ability to make meaningful changes to fuel air mixtures above idle. Many first gen FI bikes ST1300 included have that snatchy throttle take up off idle because the ECUs of the day are binary on/off in fuel injector commands during low throttle openings, holding injectors dry until butterflies crack open and the ECU can control of the mixtures.

 

[TerryS]

You can see the SV openings in the side of the intakes and they are nowhere near 4 mm in diameter. Someone will measure them soon. What we can’t see is the diameter of the passages within the throttle body. The pilot jets in their carburetor cousins that control mixtures from idle to 10 or 15% throttle have air passages so small we use guitar string to open clogged ones.

Another thing to remember is the demands that Euro 3 placed on control of emissions in first generation fuel injected motorcycles. Manufacturers could not give owners the ability to make meaningful changes to fuel air mixtures above idle. Many first gen FI bikes ST1300 included have that snatchy throttle take up off idle because the ECUs of the day are binary on/off in fuel injector commands during low throttle openings, holding injectors dry until butterflies crack open and the ECU can control of the mixtures.

This is a fun debate for a quiet afternoon!

I don't doubt that I might be off with my SV size guesswork! But it will be somewhere between 3 and 4 mm I think. And maybe there are two holes for each SV (see pic below)? I reckon the plunger in the SV is probably 5mm diameter (again a guess based on dim memory).

Pilot jets in carbs are for fuel only (that's why they gunk up and need guitar string) and I agree they are teeny-tiny. If you ever bench-synched the throttle butterflies on carbs, these are only a tiny fraction opened at idle (I recall using a sheet of paper as a rough guide) and as I worked out when I worked out the opening created by a butterfly, you have to turn the butterfly quite a ways before you get any meaningful increase in open cross-section.

 

[Chris09]

This is all very interesting I'm wondering how much of this I'm understanding correctly; 10 / 20 / 30 / 40 actual degrees of throttle rotation; [the twisty thing on the right, and not percentage of full travel] corresponds to 95 / 47 23 / 14 percent [based on a 4mm SV passageway calculation] total air supply through the starter valves.
At 10 / 20 / 30 / 40 degrees, 5 / 53 / 77 / 86 percent of total air would be supplied across the butterflies.
At 10 / 20 / 30 / 40 degrees again, butterfly rotation is 0.1% WOT / slightly under 2% WOT / unknown / unknown.
At rest [throttle position] the butterflies are fully closed provided there is no degradation of the molybdenum coatings, and that air flow is completely sealed off.
Would it be correct that WOT is equivalent to 90 degrees of butterfly rotation and therefore [for example] 2% of WOT would work out to 1.8 degrees of butterfly rotation?
If I have got it right so far, I'd be interested in knowing what method was used to determine the proportion of bypass air mentioned, and are those calculations based on initial cold engine / fully open starter valves.

 

[dduelin]

This is a fun debate for a quiet afternoon!

I don't doubt that I might be off with my SV size guesswork! But it will be somewhere between 3 and 4 mm I think. And maybe there are two holes for each SV (see pic below)? I reckon the plunger in the SV is probably 5mm diameter (again a guess based on dim memory).

Pilot jets in carbs are for fuel only (that's why they gunk up and need guitar string) and I agree they are teeny-tiny. If you ever bench-synched the throttle butterflies on carbs, these are only a tiny fraction opened at idle (I recall using a sheet of paper as a rough guide) and as I worked out when I worked out the opening created by a butterfly, you have to turn the butterfly quite a ways before you get any meaningful increase in open cross-section.

I was referring to the idle air passage opening in the side of the intake below the butterfly.

 

[TerryS]

This is all very interesting I'm wondering how much of this I'm understanding correctly; 10 / 20 / 30 / 40 actual degrees of throttle rotation; [the twisty thing on the right, and not percentage of full travel] corresponds to 95 / 47 23 / 14 percent [based on a 4mm SV passageway calculation] total air supply through the starter valves.
At 10 / 20 / 30 / 40 degrees, 5 / 53 / 77 / 86 percent of total air would be supplied across the butterflies.
At 10 / 20 / 30 / 40 degrees again, butterfly rotation is 0.1% WOT / slightly under 2% WOT / unknown / unknown.
At rest [throttle position] the butterflies are fully closed provided there is no degradation of the molybdenum coatings, and that air flow is completely sealed off.
Would it be correct that WOT is equivalent to 90 degrees of butterfly rotation and therefore [for example] 2% of WOT would work out to 1.8 degrees of butterfly rotation?
If I have got it right so far, I'd be interested in knowing what method was used to determine the proportion of bypass air mentioned, and are those calculations based on initial cold engine / fully open starter valves.

Ha ha lots of approximations and guesses were made. I looked up reference flow rates through a 1 1/2" butterfly valve from an engineering website, and guessed at the SV bore size. The degrees that I referred to was the opening of the butterfly so 0 was closed and 90 is full open. The % of total air supplied by the SV was based purely on the relative cross-section areas of the openings (% = SV area / (SV area + butterfly open area)).

I was just curious to see whether the airflow through the SVs was significant other than at idle. At small throttle openings, starter valves do make up a meaningful proprortion of the total airflow entering the engine, and if they are not correctly synchronised they might make for a rougher running engine. Anything that affects the uniformity of revolution of the crank can induce vibrations or rattles in other rotating components.

 

[Chris09]

Well, I think you've elucidated some interesting stuff here; I've looked at motorcycle throttle cable linkages and stuff for forty years without really getting it; or thinking much about it, butterfly valves are basically ____ from a control standpoint with the possible exception of multiple opposed blade types in mixing applications; yet one particular manufacturer of equipment that I work on uses them on gas fired equipment exceeding 1,300,000 up to at least 5,600,000 btuh, and these are burners with 15:1 turn down.
Controllable / repeatable [predictable] air flow across a butterfly valve occurs across a narrow portion of the full gradiant; but to plot those values [that you've given so far] on a graph, would approximate the characteristics of an equal percentage valve.
How you arrive at the cross-sectional area of the resultant crescent at each butterfly position is interesting as well, in any event, the bypass [4mm or whatever it is] cross sectional area does not work in a similar orifice plate way that the throttle plate does; and cannot be imagined solely on the basis of relative cross sectional area to provide proportionate flow, It has length that translates into resistance that is [roughly] proportional to the square of velocity, so there's all of that,