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I don't have a 950, do they have an idle set? Carbs normally have a set screw.. wondering if your idle is just plain set low.. sorry, trying to learn this stuff..
 

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I’m wondering if a throttle body synchronization might help, if you want to “cheat“ I believe there might be a throttle blade screw on the the throttle body that I have circled in red. Just trying to throw out some ideas that may help. (Edited) I just added a troubleshooting pic on idle speed: Flooded throttle body & improper throttle cable adjustment was cut off in the pic…………..


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2015 V Star 950, 2013 Suzuki S40, 1967 Yamaha YSC1, 2022 KTM 690 SMC-R
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Discussion Starter · #24 ·
Thank you torinogt, I was actually considering doing the throttle body sync, but I spoke to Ivan earlier this afternoon, and he wants me to send my ECU back to him. He says there might be a value stuck on my ECU that still reads the temperature of the O2 sensor, which may be causing the issue, as the bike seems to only do this when fully warm.

Earlier today I had a very bad episode on the highway. Someone cut into my lane, so I squeezed the clutch, released the throttle and slammed on the brakes - and by the time I was back on the throttle the engine shut down from the RPM drop that I was describing. First time after the filter clean/spark plug replacement that the engine actually shut down, and in the worst possible moment too.

I'll be sending the unit to Ivan, and hopefully the issue gets resolved. If not, I'll cheat with the throttle plates.
 

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Be careful out there, lots of idiots on the road, keep us posted when you get your ECU back.
 

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There may be some gunk in or on that throttle body you are not seeing.
I would get a can of cleaner and squirt it down good inside and out.
Also run some Seafoam in your gas.
It can't hurt anything
 

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Discussion Starter · #27 ·
There may be some gunk in or on that throttle body you are not seeing.
I would get a can of cleaner and squirt it down good inside and out.
Also run some Seafoam in your gas.
It can't hurt anything
I ran a bottle of Liqui Moly fuel system cleaner, also checked the throttle plates, they are super clean.

The ECU is going to Ivan today, we'll see what happens.
 

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Discussion Starter · #28 ·
Ok, so at this point im 99% confident I know what this is, and I kind of feel like an idiot, but I'll post it in case anyone else runs into a similar issue. It probably applies to most any injected motorcycle out there.

I started playing with it this afternoon. There are two ISC (idle speed control valves) under the left side cover. Unplugging these valves while the bike is running causes the RPMs to drop down immediately, and check engine light turns on. Plugging them in causes the RPMs to climb back on, very similar to the way RPMs climb back up after dropping off throttle when im riding, when the bike doesn't shut off. This tells me that a) the valves are operating properly, and b) they are compensating for low air, but in certain situations they are either not compensating quickly enough, or just not compensating enough in general. Thus I conclude the bike is not getting enough air.

I took apart the intake, and the throttle plates are very clean, no build up, they are operating freely. The K&N filter on the other hand is pretty clogged up. And as luck would have it, I am completely out of any brake/carb cleaner.

I just ordered a K&N cleaner/oil kit. I'm am 99% sure it is as simple as clogged air filter and ISC valves not compensating quickly enough in certain scenarios. I will update it in the next few days.
These we actually ignition coils, lol. Unplugging one ignition coil causes a quick RPM drop, which the ECU adjusts for and RPMs climb back up. Whats interesting, the engine sounds just the same running on one vs on two cylinders.

The actual ISC is on the back of the throttle body.
 

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Discussion Starter · #29 ·
So here is an update for anyone that might ever run into this same issue. First, I sent my ECU to Ivan, and I am very thankful to him for spending a lot of time working with me and analyzing the settings. The ECU seems to be working properly, and there is nothing in stock or Ivan's modified settings that could cause this. There is something else going on, but either way, Ivan modified ignition timing in the ECU to advance whenever RPMs drop below 800rpms - that should help somewhat to push RPMs back up quicker, and prevent from dropping lower causing the engine to stall.

Meanwhile, since this only happens when closing the throttle, and otherwise the bikes runs and idles flawlessly, I suspect that it must be the idle speed control valve. It is connected to the back of the throttle body, and it is not sold separately from the throttle body assembly. I figure it functions, but sometimes gets stuck and opens slowly when closing the throttle. A new throttle body assembly is $450, and I really don't want to dspend so much money unless I was 100% sure of the culprit.

Besides the whole RPM drop and engine stalling, I never liked the nature of this bike when releasing the throttle - even when running as intended there is such a sudden jolt, it's like an on/off switch, which makes it impossible to finesse the throttle and makes it difficult to maneuver at slow speeds. So I instead I decided to cheat and set the throttle body plates to always stay slightly open, even when the throttle is released. There is a throttle stop screw on the throttle body that is set from the factory and is not meant to be adjusted. Effectively what is does is set the closed position of the throttle plates. So I turned this screw up to keep the throttle plate slightly open, maybe 1-2%, this way the engine is getting air through the opening in the throttle plates and not relying on the ISC valve.

Mechanically it is no different than never fully releasing the throttle grip, and always keeping it open 1-2%. The screw setting keeps the plates open, and the TPS is also turned accordingly, so the ECU is getting the correct signal from the TPS. The throttle cable is not affected, I still have proper amount of slack in the cable. The only negative is slightly higher idle speed. I got rid of the cheap digital tach, and without a tach I can't say exactly, but by ear and feel I'd say I'm idling at about 1400 rpm. I have a Baron tach that I am planning to install, this way I'll know exactly.

I rode the bike for a few hours yesterday, and it runs gloriously. No more RPM drop since the throttle is never fully closed, and as an added benefit no more sudden jolt when releasing the throttle. This is like riding a whole new bike, I can now finesse the throttle and it is just so pleasant and compliant at slow maneuvers, no more jerky, abrupt behavior. There is some sort of setting that Yamaha programs in the ECU for emissions/efficiency purposes, and it causes for jerky open/closed throttle transitions. Ivan's tune improves on it quite a bit, but my cheat takes it a step further.

Now, while I was fiddling with the adjustment screw, at first I set it out far too much, bringing the idle speed to probably 2000rpms. I adjusted it back and forth a few times until I found the sweet spot. In the process, I tripped CEL code 37 (high idle speed), which I was able to reset. I have no idea why it even triggered, as far as the ECU is concerned it should be getting the proper signal from the TPS, so it should be thinking the throttle is simply open, but I guess it has some sort of logic to detect it, perhaps prolonged high RPMs at idle? Either way, I reset the code after I adjusted the screw to its current setting and it went away.

I'll keep riding and monitoring the bike. I'll be installing the tach, perhaps over the upcoming long weekend, and I am also planning to remove and inspect the ISC valve. It is not meant to be removed, but it's only held to the throttle body with 3 screws, I'm sure it will be fine.

Picture below shows the throttle adjustment screw.


 

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Och really nice thread and good info for 950 owners.

You said"
Mechanically it is no different than never fully releasing the throttle grip, and always keeping it open 1-2%. The screw setting keeps the plates open, and the TPS is also turned accordingly,
Can you explain a little more in detail.
Is this an ajust you made manually?
Do you have a pic?
 

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Discussion Starter · #32 ·
Och really nice thread and good info for 950 owners.

You said"

Can you explain a little more in detail.
Is this an ajust you made manually?
Do you have a pic?
Yes, manually, its right in the picture in the post - I circled the screw. It basically adjusts the throttle body arm stop point, it is preset from the factory and isn't meant to be adjusted, but it's a good workaround for the problem that I was experiencing, and an awesome improvement for the terribly jerky open/closed throttle transitions these bikes suffer from.

Even if I did not experience the RPM drop, I would still do this adjustment just to improve the behavior or the throttle transitions.
 

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Discussion Starter · #36 ·
Got quite a bit of riding yesterday and the bike is tripping code 37 - incorrect idle speed. It is running great and behaves much better than before, I'm willing to deal with the CEL for the vastly improved rideability, but I wonder how it even detects the incorrect idle speed - as far as the ECU is concerned, based on the TPS input I could be just holding the throttle slightly open at all times.
 

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Discussion Starter · #37 ·
I have been doing more research, and it seems to be a an extremely common problem on the Stratoliner, so much so that Yamaha even released a TSB M2009-025 to alleviate the issue, but it doesn't seem to resolve it, many riders still experience stalling even after the TSB is performed. Here is a screenshot from the TSB - in short it instructs to back out the throttle sync screws at least 2 turns to allow the ISC valve to let more air through.



But this TSB does not really resolve the issue, it seems to be an inherent issue with the design of the ECU and ISC/throttle body operation. There is even a member who removed his ISC valve completely, capped off its ports, and set his idle essentially the same way I did - with the throttle body arm stop screw.

There is gentleman who goes by the nickname FXStein who had a solution on his website, unfortunately his website is shut down. I found a cashed text version of his instructions, without any photos. His explanation seems to make a lot of sense, but his adjustment procedure is a lot more involved than mine - he reprograms the ECU after adjusting the screw.

How to fix the Yamaha Roadliner/Stratoliner engine stall
admin | 21 April, 2007 17:20

The Yamaha Roadliner/Stratoliner is one of the most desireable VTwin cruisers on the market. It comes with little supirse that review after review ranks it as the top cruiser in the >1800cc category. The aricooled VTwin runs smooth, produces gobs of torque and makes some serious power. Riding the Roadliner is fun. You can cruise in 5th gear all day long or yank the bike through the twisties for some sporty feeling. Its no sportbike but the handling has currently no match in the cruiser world.

With all the raveing about the bike there is one issue that bugs a growing group of Liner Owners: More and more people report of stalling bikes. In particular riding the bike in stop and go trafic at extremly low speeds or down slight downhill stretches can cause the engine to stall when approaching a stop or pulling in the clutch.
This article describes a very simple procedure how to adjust some of the idle characteristics of the bike to prevent the engine from stalling.

First off, lets have a quick look how the Roadliner & Stratoliner (basically identical bikes with bags and windshield for the Strato) manage idle rpm. With this model Yamaha engineers introduced an Idle Control Unit that adjust idle to a preset rpm. Unlike prior Star Motrocycles that leveraged an idle screw, the Liners idle is controlled by the ECU and is kept within 850-950 rpm. The advantage of this system is that there is virtually no need for idle adjustments even though outside conditions might change over time.

However the smarts of the ICU are also its downfall. The ICU works within a range to be able to raise and lower idle rpms. Instead of adjusting the butterflies of the throttle bodies, the ICU bypasses the TBs by allowing a controlled amount of air to reach the intakes. The further the ICU opens the more air bypasses the buterflies and the higher the idle rpm - and vice versa.

When the idle rpm is a touch too high or too low, the ICU will open or close more and therfore correct the idle rpm. This happens within seconds while running the engine at or around idle.

The problem is that if you intentionally ride the bike very slow e.g. in 2nd gear at around 1000 rpm (like in stop and go traffic), the ICU might interpret this as the idle being too high and correcting it by closing the air bypass. As long as you ride at that speed the rider wont realize the chang in behaviour and will feed in more and more throttle to keep the slow speed.

Once the clutch gets pulled in or the throttle gets closed all the way, the engine will drop in rpms below the point in can sustain a stable idle. The ICU is not fast enough to correct the situation and the engine will die. Very dangerous, especially in heavy traffic.

There are rumors that raising the idle rpm will fix the issue. In fcat you can raise the idle rpm on the bike unless you are willing to run at 1100+ rpms, which is to fast for ongoing operation.

Lets look at the ICUs behaviour to understand the solution to this problem: The ICU has a range to let more or less air bypass the TBs for the automatic idle adjustment. In this particular case the down adjustement capability is simply to great and is he reason why the engine might stall in certain situations. This is where this procedure comes into play: adjust the amount of ICU flex to lower the rpms.

So how do we do that? The top picture is a closeup of the idle range adjustement screw. The screw does not really adjust the idle itself but the range the ICU can leverage to raise or lower the idle rpm. Make sure that you loosen the lock nut before atempting and adjsutements.

Before you start with this procedure, make sure that the engine is fully warmed up. Ride the bike for at least 10 min before attempting the following steps:
It is best to use a laptop connected to your PCIII (Power Commander) or WBC (Wideband Commander) to get a precise measurement of the engines rpm. The bike should idle around 900 rpm (somtimes a little lower) before you go to the next step.
Screw in the adjustemnt screw very slowly (turn to the right). The engine rpm should increase for a moment but should return to the previous setting after a few seconds. Continue this process until the ICU is no longer capable of lowering the rpms. You will know you have reached this point when the idle rpms are at or slightly above 960 rpm. Make sure you DO NOT turn off the engine during this procedure. Once you have arrived at 960ish rpms you have identified the bottom end of the ICUs ability to lower idle rpms.
Now stop the engine and turn off the ignition. You must turn the bike all the way off or the next step will not work as described.

After a few seconds (or minutes - no rush) turn the bike back on and let it idle for at least 5 min. Ignore the fact that the bike idles too fast. The next step will resolve this issue. The reason why the bike needs to idle for a few minutes is because the ECU must have cycled through its warmup program before you can make reliable adjustements.
After having run for 5min the idle rpm should be at around 1100-1200 rpms. Too fast for proper operation. At that rpm the ICU will not attempt to lower the bikes idle. In order to get hte ICU to do its job, you will have to slowly turn the set screw to the left (out). Do it very carefully and whatch the rpms drop. Once you get to about 1000 rpms or slightly below that, the ICU will take control and will lower the idle rpms to about 900 rpms (+-50). This is where you want to be.

To validate the settings tunr of the engine and ignition and restart the bike after a few minutes. After the initial warm up procedure the bike should settle in at around 900 rpms. If this is the case, lock down the lock nut. You are basically done. The engine should show little to now tendency to stall in any conditions. If you run into situations where the idle wont settle down to about 900 rpm, you might have to adjust the set screw a touch more (turn to the left)

By the time you are done, your PCIII or WBC should read 1-2% of throttle at idle. You will need to go into either software and adjust the idle throttle position to compensate for the difference. This is important or you map will be off.


What did just happen? Rather than adjusting the idle rpm we have moved the mid point of the ICU and have taken away the ability to lower the idle rpms too much. Riding at very low speeds or on slight down hills will not get the ICU to lower the idle settings so much that the engine can stall the next time the throttle is closed or the clutch is pulled in.
 

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Excellent information @och, thanks for sharing your findings & valuable info 👍
 

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Discussion Starter · #39 ·
I've been playing with resetting the CEL, and after the reset it doesn't come back while riding, only when I come to a complete stop. I can coast in neutral or with the clutch squeezed in and closed throttle, no CEL. This tells me the logic of the ECU is setup to expect idle when stopped, so technically a CEL can be triggered by holding the throttle open with RPMs reaching about 1200. Anyone willing to experiment to see if their 950 does that?
 
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