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Discussion Starter · #1 ·
I wanted to share a simple and free "mod" I did to my 950 that has completely transformed the behavior of the bike, and has made it much more compliant and rideable. I have described it in another thread where I was dealing with my idle issues, but I figure not everyone had seen it, and this matter certainly deserves a dedicated thread.

There is a huge issue with the way the fuel injection system is setup on the 950 - when the throttle is closed and the clutch is squeezed in, the ECU almost completely cuts the fuel from the injectors, virtually cutting all the power from the engine. It is setup in such way for emissions and fuel economy purposes, but it makes for extremely jerky closed/open throttle transitions, almost like an on/off switch, which makes it very difficult to feather the throttle during low speed maneuvers.

Ivans tune certainly improves on this issue, but not enough to eliminate it completely. The jerky behavior remains, and it's not something that can be completely corrected with a tune. But I found a different solution. There is a throttle arm stop screw on the throttle body, and it can be adjusted to prevent the throttle body valves from closing completely. I've adjusted mine where the throttle body valves are a tad open, maybe 1-2%, and this prevents the ECU from abrupt fuel cuts, and the open closed throttle transitions are now smooth and predictable. It feels like a whole different bike, it's so much easier to maneuver, I wish I had known this sooner. I highly recommend this to anyone struggling with the same abrupt throttle behavior.

There is a small caveat however, the ECU is now tripping CEL code 37 - incorrect idle speed. It doesn't affect anything else, just illuminates the CEL light which can be annoying. I've set my throttle arm stop screw to where my idle speed stays between 1200-1400 rpm when the engine is warmed up, and the ECU expects 950-1050 to the best of my knowledge. I'll try messing with it to see if I can adjust it more finely to 1100-1200 RPMs, perhaps that won't trip the CEL.

 

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This is what makes this forum stand out from the others, members helping and giving each other information on new things they have found on the Star Line.
 

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Discussion Starter · #5 ·
I think on the service manual it says not to mess around with that screw.
Correct, but I saw a lot of people complain about extremely jerky open/closed throttle transitions, this really transforms the behavior.
 

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I've followed this thread with interest. I've owned and ridden bikes with similar issues. I've just always feathered the clutch and throttle never thinking twice about it. I've attended to "fix" things in the past and the "fix" created a whole set of new issues. I will continue to watch the thread as your issue must be far worst than I've ever experienced and a true "fix" would be nice to know.
 

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Discussion Starter · #7 ·
I've followed this thread with interest. I've owned and ridden bikes with similar issues. I've just always feathered the clutch and throttle never thinking twice about it. I've attended to "fix" things in the past and the "fix" created a whole set of new issues. I will continue to watch the thread as your issue must be far worst than I've ever experienced and a true "fix" would be nice to know.
I really don't think there is a true fix, its just the nature of these bikes, and from what I can tell it also applies to Yamahas ATVs and marine applications from that era. Yamaha started switching from carbs to EFI in the late 90ies/mid 00s, and they use a similar ISC system on many of their applications from that era - I saw photos of their ISC valves on marine engines, they look identical to the ISC valve on the 950, and probably the rest of their injected bikes. Early ISC/IAC systems were a common culprit in many automotive applications causing all sorts of rough idle issues. Yamaha's throttle body and the ISC valve are Mikuni parts, I wont be surprised if other Japanese manufacturers also use them for their application.

Either way, being an early design it is very poorly setup for open/closed throttle transitions, which makes the bike downright dangerous in traffic, especially on steep hills. I have seen many other people complain about the same behavior on the 950, as well as other Yamahas, particularly the Stratoliner, so its certainly not just me. I also own an older carbureted Suzuki and a much newer fuel injected KTM, and they do not have any such behavior, both have smooth and predictable throttle control. I've also ridden newer Yamaha MT-09, MT10 and R1 sport bikes, they also have very smooth throttle control. With my mod I have finally tamed the beast, and it now behaves as it should. There is no way I can ever go back to dealing with how it used to behave vs how it behaves now.

An even better fix is probably to get rid of the ISC completely, adjust the throttle body with the stop screw, and reprogram the ECU to ignore it, and program TPS values to correspond with fuel maps - but I don't have the knowledge or the equipment to do so.

As far as any potential long term issues, I am a bit concerned what can happen from constant driving with the CEL, and if the ECU is constantly trying to send power to the ISC trying to open/close it, but I don't think it does, I can't feel any vibration from the its motor once the valve is closed. I will call Ivan to see if he has any input, and ask him if he can modify the normal idle range in the ECU.

One way or another, I will report back after I put some miles on the bike whether or not I experience any other issues as a result of my mod.
 

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I've experienced this in my 1300. It definitely occurs on the bigger motor as well. I am not a fan, it makes me feel like a bad rider because I can't feather the throttle from 0% to engaged without it being jerky. I've ridden numerous bikes and dirtbikes and these v stars are the only ones i've experienced this on.

Edit: I thought the reflash was supposed to take care of this issue though?
 

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Discussion Starter · #9 · (Edited)
I've experienced this in my 1300. It definitely occurs on the bigger motor as well. I am not a fan, it makes me feel like a bad rider because I can't feather the throttle from 0% to engaged without it being jerky. I've ridden numerous bikes and dirtbikes and these v stars are the only ones i've experienced this on.

Edit: I thought the reflash was supposed to take care of this issue though?
I think the bigger the motor, the worse it gets. If you google up Stratoliner stalling, there are tons of threads on various forums. That big 1900cc is going to be very prone to stalling when its staving for air. It is basically a design flaw with Mikuni throttle bodies, there is no effective base idle air bypass, it is relying on the ISC valve which can be sluggish to respond, and open/closed throttle transitions are just awful.

Ivans flash does wonders to disable fuel cut on closed thorttle, so if let go of the throttle with the clutch still engaged, there is no fuel cut and no popping/jerky behavior when you get back on the throttle. But the flash can not control the physical speed of the ISC valve, or how fast the computer is able to communicate with it to adjust it accordingly, and so open/closed throttle transitions with clutch disengaged are jerky, and you feel like a bad rider when you can't handle the bike in situations requiring precise throttle control. And inherently small clutch friction zone on Yamaha Stars only makes things worse.

There is one member on a different Stratoliner forum who went as far as getting rid of the ISC valve completely, and set his idle by limiting how much the butterfly valves close with the throttle stop screw.
 

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Let's get some input from Strat owners to see if they are having the same issue or if clutch throttle modulation works for them. So I'll call out @Yamaha Pat and @Jspree. Different ends of the continent, different altitude, one is mainly a one up rider, the other two up a lot. Different riding styles will amplifier certain issues.
 
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I don't have any modifications on my only FI motorcycle. The only problem I ever had is engine braking , it shuts the fuel off to the point if I engine brake too long it will die. So I just don't engine brake on that bike. We don't have enough hills in Florida to make that big a difference for me. If it was an area with more hills I would have Ivan do a flash to correct it.
 

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I've got a Warrior and the removal of fuel cut with Ivan's flash is one of the biggest draws for the Warrior community, so I was going to say something about that, but it looks like you've already covered it with your comments about the specifics of when you've got jerky throttle. I don't know that I've run across that with my bike yet, but now I want to get out and do some testing to see if I can confirm it's on the Warrior too with Ivan's.

A thought crossed my mind about how to have some "air bypass" for the closed valves but I have no idea if it would work. Please, someone say this is dumb... drill a small hole in the butterfly plate. It'll provide some air bypass while allowing the valve to close. So long as your injector is still spraying some fuel, you should be good.... right?? Like I said, no idea if it'll work and is probably a dumb idea to begin with but maybe something to experiment with using an extra plate. And of course, just in case it needs to be said, DON'T DRILL ON BIKE. REMOVE PLATE, DRILL, CLEAN, REMOUNT. ;)
 

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Discussion Starter · #13 ·
I've got a Warrior and the removal of fuel cut with Ivan's flash is one of the biggest draws for the Warrior community, so I was going to say something about that, but it looks like you've already covered it with your comments about the specifics of when you've got jerky throttle. I don't know that I've run across that with my bike yet, but now I want to get out and do some testing to see if I can confirm it's on the Warrior too with Ivan's.

A thought crossed my mind about how to have some "air bypass" for the closed valves but I have no idea if it would work. Please, someone say this is dumb... drill a small hole in the butterfly plate. It'll provide some air bypass while allowing the valve to close. So long as your injector is still spraying some fuel, you should be good.... right?? Like I said, no idea if it'll work and is probably a dumb idea to begin with but maybe something to experiment with using an extra plate. And of course, just in case it needs to be said, DON'T DRILL ON BIKE. REMOVE PLATE, DRILL, CLEAN, REMOUNT. ;)
Ivan's flash addresses the fuel cut issue, but it cant address the behavior of the ISC valve that causes air starvation at the worst possible time. To your idea of drilling holes in the butterfly valves, there are certainly cars and bikes that have holes in the butterfly valve(s) from the factory, I imagine for the purpose of setting base idle air. I dont know If I am comfortable with this idea, it is a permanent mod vs adjusting the stop screw that can always be set back to factory default. If anything, I would rather enlarge the size of the ISC ports with the next side drill bit.
 

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it is a permanent mod
That's why I suggested experimenting with an extra plate. I'm 100% on board with not doing this to your stock plates. If it messes anything up, that would be a horrible mess to have to live with. But if it works using replacement plates... I mean... maybe, just maybe it would address both issues (air starvation and CEL).
 

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Discussion Starter · #15 ·
That's why I suggested experimenting with an extra plate. I'm 100% on board with not doing this to your stock plates. If it messes anything up, that would be a horrible mess to have to live with. But if it works using replacement plates... I mean... maybe, just maybe it would address both issues (air starvation and CEL).
You would have to be very precise with the drilling, making sure to start with a very small drill bit and gradually increase. Also try to make the holes precisely in the same location on both plates for proper balance, and then resync the throttle body. Best done if done in a shop on a drill press, to maintain required level of precision. Plenty of factory throttle plates are setup exactly like that if you do a google search for throttle bodies.

I'm yet to call Ivan to see if he has any thoughts, and if there is a way to reprogram the behavior of how the ECU controls the ISC valve, and to raise idle RPMs to around 1100.
 

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Discussion Starter · #17 ·
Yeah, sounds like you know what would need to be done. I have absolutely no experience with any of it but I think if you got some extra plates, you'd be well on your way to a worthwhile experiment.
I actually have an entire extra throttle body, and I own a metal fabricating shop. If it ever gets to that, I may experiment with drilling holes in the butterfly valves.
 

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Years ago I raced Yamaha 2 cycle, they had reed induction, we figured out if you split the reeds it had faster throttle response. Little things can make a big difference.
 

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Discussion Starter · #20 ·
So I've been riding this whole week, and so far I am very happy. The CEL is most certainly dynamic, it triggers when it detects idle above ~1100 rpm, and shuts off once the ilde stays at ~1100 or under for a couple of seconds.

Whats interesting, when I start it cold in the morning after a few seconds the idle sets at right about 1100, and if the CEL from the day before was on it shuts off. And then during my ride the CEL doesn't trigger for at least 20-30 minutes, until the engine is fully warmed, and only after I come to a full stop. So generally on my ride to work, it takes me about 20 min to get to the highway, and then about 20 min highway ride, and I don't get the CEL until I get off the highway and stop at a red light.

When the engine is fully warmed, which takes a while now that the temperatures in NYC are in the mid/high 30ies, idle can surge to about 1400 at a stop, but then the ISC does it's just and it flunctuates between 1100-1300.
 
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