TB Synch question

[SANTA]

i was just synching the TB's yesterday, I started by bottoming out the BBS left and right and turned them out 1 full turn, after synch'ing the right one is now 1-1/2 turns out.

 

i counted the turns to full close initially, and there was a difference of about 1/2 turn.

 

from the TB Synch for dummies i got the impression that this much difference is not good...???

 

with only 20,000km and since i have never touched the butterfly stops, nor had the TB's of the bike, what could this be?

 

plugged passage way?,

or leak on the other side?

 

suggestions?

[T__]

i was just synching the TB's yesterday, I started by bottoming out the BBS left and right and turned them out 1 full turn, after synch'ing the right one is now 1-1/2 turns out.

 

i counted the turns to full close initially, and there was a difference of about 1/2 turn.

 

from the TB Synch for dummies i got the impression that this much difference is not good...???

 

with only 20,000km and since i have never touched the butterfly stops, nor had the TB's of the bike, what could this be?

 

plugged passage way?,

or leak on the other side?

 

suggestions?

 

 

Claus, doesn’t sound that far out to me.. Especially if you haven’t cleaned the Brass screw tips & cleaned the carbon from the brass screw seats (that can alter the air flow a bit) .. Doesn’t take much to leave the brass screws slightly different from each other, such as __ Slight valve adjustment variation,, carbon (coke) build up in the TBI throttle bores or brass screw seats,, a little throttle shaft or shaft bushing wear,, a slightly tight throttle cable,, a slight vacuum leak on the throttle body boots (check the boot clamps)..

 

Twisty

[smiller]

I agree, nothing I'd worry about, mine are different by that much at least. There are expected minor variances between cylinders based on a number of variables... that's what the adjustment screws are for!

[Stan Walker]

In 160,000 miles of doing TBS's on my 2 different RT's I've yet to measure how far out the BBS screws are on either bike.

 

Nor have I ever cleaned them, I just hook up the gauge and tweek the adjustments starting from where it is currently set.

 

Stan

[twilmotte]

Not meant to be a hijack, but another question on TB sync ... is it possible that adjusting the TB too lean would cause an engine to run noticeably hotter? Just curious ... might be a reason my '04 RT is running hotter since my last valve adjustment and TB sync.

[T__]

Not meant to be a hijack, but another question on TB sync ... is it possible that adjusting the TB too lean would cause an engine to run noticeably hotter? Just curious ... might be a reason my '04 RT is running hotter since my last valve adjustment and TB sync.

 

 

Tom, you are sure thinking outside the box here..

 

I n theory possibly enough hotter to measure with some very sophisticated instrumentation.. In reality I doubt you could ever tell the difference while riding or idling along..

 

On the 1100/1150 Alpha-N systems it would be possible to add a little more air at idle that the computer wouldn’t know about.. As long as the TPS voltage is at base idle (under .4 volts 1100,, & under learned base on the 1150) the computer would supply a finite amount of fuel based on RPM, engine & air temperature sensors, atmospheric sensor, etc.. On a warm engine the lambda (02) sensor would adjust the fuel injector pulse width to keep the engine idling at close to 14.7:1.. So on a warm engine adjusting the brass air screws would just add or subtract air & the computer would look at the exhaust & keep the idle mixture close to optimum.. On a failed 02 system you could probably effect the idle fuel/air ratio slightly.. But as you add more Brass Screw air flow the RPM’s would come up so the computer would just add a little more fuel.. Probably in reality they run so rich at non 02 controlled idle that adding any extra air will just increase the idle speed.. You couldn’t run it under load at idle without opening the throttle more to keep it running so about all you see is no-load engine idle anyhow..

 

OK, the above pretty well covers the idle (closed throttle) end of it.. Now to the off idle or mid range end of it.. The brass screw air ports in the TBI’s are located in such a manner that they soon drop out of the low pressure area inside the TBI so as the throttle plates are opened the brass screw air flow is pretty low at that point.. As the throttle plates are opened any air leakage or brass screw air flow becomes a small percentage of the total air flow anyhow.. Once the throttle position has stabilized the 02 sensor would take back over fuel control anyhow so the fuel/air mixture would go right back to that 14.7:1.. Once the throttle plates are opened far enough, or the engine RPM increases enough, the 02 sensor drops out of control (outside the emission compliance area) & then the system is strictly Alpha-n.. Here is the area that theoretically adding a little air leakage could lean you out some.. There are a couple of reasons why that doesn’t happen.. First,, as you add more air the RPM increases so the computer adds more fuel (unless under a fixed heavy load) Under a heavy load the RPM might not increase with more air added but due to the throttle position vs. engine RPM the computer would add plenty of fuel there anyhow (they run plenty rich at open loop high load) .. The other thing is, as the engine load increases the throttle plates are opened farther to compensate for the added load so manifold vacuum drops (the lower the manifold vacuum the less air volume flows in through the Brass By-Pass screw area).. If you don’t open the throttle more to compensate for engine load the engine load decreases as you will not maintain vehicle speed..

 

At wide open throttle there is very little engine manifold vacuum so any small air leakage points like vacuum leaks or the brass screws will allow very little air to enter & even if it did it would be such a small percentage of the total air flow that it would make no appreciable difference..

 

I really don’t know how the 1200 handles the above as it has stepper motor idle air control so could conceivably add more fuel as it adds idle air increase..

 

Keep in mind the above is based on my years of working with Alpha-N automotive computer controlled systems but I have no reason to believe the motorcycle derivative of the basic Alpha-N system operates any differently..

 

Twisty