Author Topic: hesitation pulling away  (Read 53 times)

Offline tobyd

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hesitation pulling away
« on: October 12, 2019, 04:34:04 PM »
I'm a little stumped by this one.

When riding off from a standstill, just normal clutch out / throttle on my GS hesitates. It starts to move but the revs don't really rise for a second or two then it gets it together and away it goes. If I bring the revs up then let the clutch out the problem doesn't occur but isn't particularly smooth. If I coast to nearly a standstill, clutch in but then then carry on the problem doesn't occur - moving away with a bit of momentum prevents the problem happening. Behaves perfectly the rest of the time but it makes moving off from the lights a pain.

I'm at clip position 4 (1 richer than middle), about 2.25 turns out (this is the best position for my bike, 3 turns bogs down, 2 turns and below hangs the idle). Plugs are relatively new, air filter is fairly new float position is at the bowl join point, carbs are synced. 125 mains (tried 120s, 125s are a little better) and 40 pilots. charging system works ok, battery is past its best but will still start the bike. The bike starts very easily, like on the button easy, barely needs any cranking. hestitates both on choke and off choke. idle is somewhere between 1100 and 1500 but the needle bounces so its hard to be precise.

Any ideas? I can only think the ignition is slightly advanced (I snapped the rotor pin on the crank and jb welded it back together so the rotor could be slightly out - the rotor itself is a replacement but looks about the same) - last time I checked the timing marks on the cams and the rotor were about perfect though.
« Last Edit: October 12, 2019, 04:55:18 PM by tobyd »

Offline herennow

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Re: hesitation pulling away
« Reply #1 on: October 14, 2019, 06:13:47 AM »
Hi, is this new behaviour? Has anything changed recently? You probably know this but , The GS is not very powerful and needs revs to get going.

Offline tobyd

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Re: hesitation pulling away
« Reply #2 on: October 14, 2019, 06:57:00 PM »
its been around longer than I've had an SV which doesn't do it. My XJ600 didn't do it either.

The marks on the plugs is about right with the discolouration starting around the mid-point of the ground. The plugs are even a fair tan colour. I suppose I should compression test it really, it seems alright otherwise.

or maybe you are right and I just need to give it more beans off the line.

Offline Bluesmudge

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Re: hesitation pulling away
« Reply #3 on: October 14, 2019, 10:35:35 PM »
Have you tried adjusting the clutch cable? Almost sounds like you are not matching your throttle position at takeoff with your clutch disengagement. Could be caused by too much free play at the clutch lever. I.e. your clutch is fully disengaged but because you haven't fully released the lever you haven't started giving much throttle yet.

But yeah, GS needs to be revved pretty good to get going. I tried going +2 on the rear sprocket just because of how much I dont like the GS500's lack of torque off the line. SV650 probably has double the torque of the GS at low rpms.
« Last Edit: October 14, 2019, 10:38:27 PM by Bluesmudge »

Offline mr72

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Re: hesitation pulling away
« Reply #4 on: October 15, 2019, 02:30:33 PM »
I'm going to go the other way and suggest it's a position-dependent vacuum leak, like at the intake boot o-rings. Tiny air leak there will result in the slide not lifting as it should and that's what this sounds like.

Also, I had similar odd behaviors when my carbs had what I suspect are dynojet needles, which were completely and utterly fixed when I went back to the stock aluminum needles. No, I didn't put those DJ needles in the carbs, but I happened to have a spare set of carbs to rob OEM needles from. For me, the problem was an undiagnosable stumble under certain rpm/speed/throttle conditions and a hesitation similar to what you describe. Turned out it was just too rich at tip-in. Also I got way better mpg (like >10mpg better) with the alu stock needles.

Offline tobyd

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Re: hesitation pulling away
« Reply #5 on: October 15, 2019, 06:57:03 PM »
I think the bike should be able to get moving without revving it up first - I hadn't really considered a tiny air leak, the boots are new with oring but maybe I screwed up fitting them or trap the oring or something - their replacement might just about coincide with this starting and we attributing it to otherstuff I was doing at the time? Good idea man! will investigate, does make sense that the slides are slow to rise under those conditions and its got nothing to go on until the vacuum vacuums (or whatever it does). Certainly the bike runs badly with the needles at mid-point, its much happier at 4/5 (euro-5-clip-needles) rather than shimmed.

Offline mr72

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Re: hesitation pulling away
« Reply #6 on: October 15, 2019, 07:34:29 PM »
You know, it might be the opposite: it might be rich under these conditions. Maybe the answer is return the needle to middle and jet up a notch.