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Discussion Starter · #1 ·
Hi all, I've done a ton of reading about throttle body synch and I'm a little confused by it all. Can I just hook up my Motion Pro synch tool and dial them in or do I have to set the TPS etc? The bike (03 ST4s) runs good but has a "surging" vibration and TB synchronization is next on my list to try and eliminate the issue. Thanks in advance!
 

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You could try to sync without the TPS set as a quick fix, but I think i'd step back to the point where you close the bleeds. Just keep track of how much they turn to closed. You can go back to the same setting when done and see how it idles. Air bleeds are set for CO and idle speed, not balance. Also, they are out of the picture after a certain throttle angle, so honestly it may not matter much, I'd still close them first though. With luck, you'd be restoring the set up to where it was last time the full baseline adjustment was completed. If it doesn't idle well after, or feels off at cruise with the throttle just cracked, you'll need to go deeper.

When setting TB balance, remember that throttle angle under load for a given RPM is not going to be the same as the throttle angle with no load revving in your garage... You're syncing for throttle angle, not RPM. If you are having issues with vibration at say, 5K under load, you'll want to set balance to maybe 6 or 6.5K with no load. To see the RPM you want to get closest sync, ride the bike on level ground with the vibration. Note the RPM. Without letting off the throttle, pull in the clutch and let the engine rev. That no load RPM is where your throttle angle is going to be best synced when you get it in your garage.
 

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Discussion Starter · #3 ·
You could try to sync without the TPS set as a quick fix, but I think i'd step back to the point where you close the bleeds. Just keep track of how much they turn to closed. You can go back to the same setting when done and see how it idles. Air bleeds are set for CO and idle speed, not balance. Also, they are out of the picture after a certain throttle angle, so honestly it may not matter much, I'd still close them first though. With luck, you'd be restoring the set up to where it was last time the full baseline adjustment was completed. If it doesn't idle well after, or feels off at cruise with the throttle just cracked, you'll need to go deeper.

When setting TB balance, remember that throttle angle under load for a given RPM is not going to be the same as the throttle angle with no load revving in your garage... You're syncing for throttle angle, not RPM. If you are having issues with vibration at say, 5K under load, you'll want to set balance to maybe 6 or 6.5K with no load. To see the RPM you want to get closest sync, ride the bike on level ground with the vibration. Note the RPM. Without letting off the throttle, pull in the clutch and let the engine rev. That no load RPM is where your throttle angle is going to be best synced when you get it in your garage.
Thanks for the input. I may be in over my head on this, I'm great with carbs but I don't really understand motorcycle fuel injection. I'm not sure what closing the bleeds means or what that even does lol - time to dive in and learn.

Maybe I'm barking up the wrong tree here, I'll try to describe what's happening: I bought the bike in July 2019 with 4980 miles on it, the only service history was a note in the owners manual about an oil change done at 3000 miles back in 2006, and I had the dealer mount and balance two new Michelin tires as it still had the originals from 2003 on it. I rode the bike about an hour to get it home and it felt great. If it vibrated when I first got it I didn't feel it, but I may have just been too excited to notice! Sometime after changing the oil and filling the tank for the first time I noticed a vibration that seems to come and go and vary in intensity every few seconds when maintaining a steady speed between 50-60 mph in 3rd gear though I cannot replicate it in a different gear at the same RPM range which is approx 3k - 4k. That is why I suspected chassis at first and not engine, but it does seem to go away when pulling in the clutch.

So far I've changed the chain and sprockets thinking the original may have had some tight links from sitting (plus I wanted to lower the gearing), static balanced the tires to double check them (the front was perfect, the rear was close). Checked the rear engine mount (it's tight), changed front and rear wheel bearings (should have just left them alone). Oh and I changed the cam belts to be safe but the vibration was there before that. The bike now has about 6200 miles on it and the vibration doesn't seem like it changed over time but maybe seems like it does it less after I ride the bike hard so I try that as often as possible haha!

Is there anything else I should be looking at? I'm kind of thinking the synch needs to be done anyway just based on the age of the bike but I don't want to touch it if it doesn't need it.
 

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fuel filter, maybe valve clearance. if you can't do the idle mixture setting, then there's not a huge amount to be gained from just checking the sync imo, but i guess it's a start.
 

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Maybe some fuel system cleaner for a tank or two. Seafoam, or the like. If you're not sure when the fuel filter was last changed, it probably hasn't been... 2nd that thought. If you want to check CO / balance, PM me. I will need to get my old lap top up and running with the VDST software if fuel trim adjustment is needed, but I have a gas tester to at least see where you are right now.
 
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Discussion Starter · #6 ·
Thanks guys! I did try some Toyota EFI cleaner that I've used before with good luck through two tankfuls, honestly I didn't notice the vibration until after the first tankful now that I think about it. I have been thinking about the fuel filter, I'll change it tonight and see how tomorrow morning's commute goes.
 

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Did you clean the throttle body throats ? Strangely enough, the little dirt ring that forms where the butterflies close can affect smoothness. A Q-tip and carb cleaner works well. If it was mine, I’d at least check the synch, just with a gap gage or small Allen wrench. That will tell you if it needs synchronization. If you can’t tell, it’s close enough. If you feel competent enough, do the tps sensors, it couldn’t hurt. Also , a spark plug change wouldn’t hurt. A “ tune up” can only make it run smoother. Mine run better on non ethanol, especially at low speed. Try changing your brand of fuel.
 
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There is a great explanation of the EFI system in the Service Manuals. See the Sticky.

Have a good one.
 

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Discussion Starter · #9 ·
Did you clean the throttle body throats ? Strangely enough, the little dirt ring that forms where the butterflies close can affect smoothness. A Q-tip and carb cleaner works well. If it was mine, I’d at least check the synch, just with a gap gage or small Allen wrench. That will tell you if it needs synchronization. If you can’t tell, it’s close enough. If you feel competent enough, do the tps sensors, it couldn’t hurt. Also , a spark plug change wouldn’t hurt. A “ tune up” can only make it run smoother. Mine run better on non ethanol, especially at low speed. Try changing your brand of fuel.
Thanks, I will check that tonight as well!
 

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Maybe some fuel system cleaner for a tank or two. Seafoam, or the like. If you're not sure when the fuel filter was last changed, it probably hasn't been... 2nd that thought. If you want to check CO / balance, PM me. I will need to get my old lap top up and running with the VDST software if fuel trim adjustment is needed, but I have a gas tester to at least see where you are right now.
If you don't get the abacus up and running, I have the ScanMX tool on my android tablet and all the cables to hook it up. :wink2:
 

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If you don't get the abacus up and running...
LOL. If you saw this laptop, you'd realize how kind you're being! It was cheap and it has a real live serial port for my old VDST cables. I had an old garage desk top that was about the same vintage, it died a well deserved death.
 

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Looks like tosow will need to have a complete tune...including belts and valve clearance check...I wonder if he brews his own beer too?
 

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Looks like tosow will need to have a complete tune...including belts and valve clearance check...I wonder if he brews his own beer too?
Hmm... Don't know if he brews, but I bet he has saddle bags on that bike:wink2: I don't know that we've settled on a day and time yet, but you're certainly welcome to join the fun! Likely be at my place because I have the lift and I'm too old to lay on the floor these days.
 

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Discussion Starter · #15 ·
Hmm... Don't know if he brews, but I bet he has saddle bags on that bike:wink2: I don't know that we've settled on a day and time yet, but you're certainly welcome to join the fun! Likely be at my place because I have the lift and I'm too old to lay on the floor these days.
The more the merrier! I don't brew but I do indeed have saddlebags, I know they'll swallow a full face helmet with a little room left over but I have not tried a case of beer yet!
 

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Discussion Starter · #18 ·
Thanks for the link, I should have added it at the beginning for others reading this in the future! That's the very article that has caused my confusion though lol

Well, I can add the fuel filter to the list of things that didn't change the issue but it did need to be replaced anyway.

I drained the tank (which I had just filled the day before!), lifted the tank, removed the 3 brass nuts, gave a gentle but firm pull and the sending unit slid out, but only a little, like an inch and a half or so... Cool I thought, the filter is right there... but try as I might I couldn't get the assembly out far enough to get to the inlet clamp. Hmmm, I thought it would pull right out, I didn't realize there's hoses in the tank that don't come out so I kept finagling until I could just barely get the clamp loosened and the old filter removed.

I grabbed the new filter, installed the outlet first, then said hey, where's the inlet hose? It slid back into the tank but no big deal, I was able to fish it out after a few tries with one finger, while holding the new filter with my other fingers and the sending unit with my other hand. I thought this was going to be a simple two minute job! Looking back now, I probably should have just removed the two hoses that stay in the tank that were keeping me from pulling the entire sending unit out of the tank, but I was rushing (why does that always cost MORE time?!).
 

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You were quick enough before the o ring swelled up on you anyway.
 
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