Unprovoked throttle acceleration in first gear

2874 Views 11 Replies 7 Participants Last post by On2Wheels, 9 mo ago

On2Wheels

I've had this issue ever since I got it, and I've learned to live with it. It's a nuisance nonetheless, and I can't reproduce it to show to a mechanic. I'm wondering if anyone else had this issue.
After starting the motorcycle and going into first gear, the throttle kept at exactly the same point (no more or less input from me) will cause the motorcycle to suddenly accelerate (as if I added more throttle). This only occurs in the very first first gear after firing the machine up. It disappears after the very first upshift, and any subsequent downshifts to 1st gear.

On a slightly related note, lately I've been getting sick of the very sharp on/off throttle. I have it on B mode, but anytime I reduce the throttle while slowing down (gently, obviously), fuel delivery abruptly shuts off leading to engine brake. From my understanding this an emissions control thing. Still very annoying. I wonder if there's a part that can smooth out fuel delivery when closing the throttle?

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Motorpsychology

· #2 · 10 mo ago

I'm not sure if this is what you are referring to, but there is a fast idle feature actuated by the clutch lever. In first gear with the clutch fully disengaged, hold the rear brake on, with your hand off of the twist grip and let the clutch out ~1cm (5/16") without engaging it. The engine will rise about 200 rpm. It's sort of a newbie feature to help prevent stalling while accelerating from a stop.

As I understand it, I believe that US-spec bikes have a slow throttle close mapping that eases the engine deceleration during sudden off-throttle events. This is to lessen the potential for unburned fuel to suddenly be dumped in the exhaust system, which could shorten the life of the catalytic converter.

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On2Wheels

Discussion Starter · #3 · 10 mo ago

What you're referring to is called RPM Assist, and it's another annoying feature that I can't turn off. But that's not what I'm referring to here.
The engine acts as if the throttle has been flicked wide-opened, when in fact there's no change in input.

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PeteW

· #4 · 10 mo ago

It's a safety issue. Get a video of it, take it to your dealer and tell them to fix it. If that doesn't work, Suzuki.

I can understand the hard to repro. thing but leaving it with the dealer overnight should be enough with evidence it happens.

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On2Wheels

Discussion Starter · #5 · 10 mo ago

I haven't been able to reproduce since I've posted about it!!
Maybe it's related to some factor?

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Mak0

· #6 · 10 mo ago

I have had the same on my last few Hondas, nothing to worry about actually. From cold start, the bike computer wants to keep the revs a bit higher than its normal operating temps rev count (about +200 as another commenter said). It might also try to prevent you to reach too high rpm (not tested).

It also dictates how much fuel to inject in the engine. As you ride, the temperature goes up and the computer adapts its injection. What you feel is the not so continuous mapping they did based on the evolving condition of the temperature.

It is not limited to first gear, it does the exact same thing in all gears. At least on mine it does on 3 first gears for the first 30-60 seconds.

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NateHarris

· #7 · 10 mo ago

Yeah, sounds like an ecu rich startup thing. As for the ride mode, I stay in B because A is too harsh. If I ever tracked the bike I'd be in A. But who tracks Vstroms?

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V-Tom

· #8 · 10 mo ago

@On2Wheels

Longshot here: Do you have a throttle rocker on the bike?

I recall when I first got them that I would accidentally work the throttle when pulling in the brake lever.

..Tom

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MeefZah

· #9 · 10 mo ago

Mine does this, too, and there's at least one other recent thread on it, though he describes it differently but the end result is the same.

If I start and take right off there is some low end hesitation which, when it clears up very shortly after starting, manifests itself as unintended acceleration as you maintain constant throttle.

The easiest solution is to let the machine warm up more completely before riding regardless of engine temp or ambient temp. Give it 60 seconds and a few good blips of the throttle before going into first gear and it'll be fine.

I'm sure you could throw money and time at it if this is not satisfactory.

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On2Wheels

Discussion Starter · #10 · 10 mo ago

When it starts up it maintains higher revs to warm up. I always wait until the revs come down, about a minute or so, and usually by then the first coolant temperature bar is on. Then I start moving.

@V-Tom: No I don't

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On2Wheels

Discussion Starter · #11 · 10 mo ago

Update: I haven't experienced this issue in a significant way since I've reported it! I guess complaining works? Perhaps I was doing something unconsciously, and now I'm more aware of it and don't do it? I don't know

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On2Wheels

Discussion Starter · #12 · 9 mo ago

Update 2: I finally figured it out. For some reason, even on a hot day and after warming up the engine, it's still running very rich and choked. Keeping the throttle at the same angle when I start rolling leads to the choking clearing up and the engine suddenly gaining power. I don't know why this happens, there's no hesitation when revving from idle. I just give it a couple twists before moving to help clear it, and that helps.

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