Hi there from a newbie

I'm inches away from finishing rebuilding my '02 GS500 and have got to the point where I'm pottering around trying to get it running right under load. We've managed to get it running pretty well (we think), but I was having a bit of difficulty with it cutting out when I was trying to pull away from standstill. Being as I'm pretty much brand new to bikes, and I gather they require a bit of a different technique to cars, it may just be that I'm pants at pulling away on a bike.

I've been working on it with a mate of mine who does know about bikes and has been riding for years, and he thought it wasn't just me so we faffed about with the mixture screw a little and managed to get it better but not perfect (in his opinion).

So, is it a bit of a known thing that GS500s need a bit more slipping of the clutch/revs than your average bike to pull away from a standstill, is there something that might be causing bogging at take-off rpm but ok for the rest of the rev-range, or is it entirely psychosomatic?

Potentially confounding variables:

Bought the bike for £50 as a non-runner. Sat on it for 2 years before getting IoM tickets for next year, so thought I should probably learn to ride. It was running pretty poorly, backfiring and snorting back through the intake. We cleaned the carbs with an ultrasonic cleaner (marvelous things) and rebuilt them, checked the valve clearances which were all pretty tight so reshimmed. I've also fitted a K&N filter and made my own silencer, rejetting accordingly (20/65/145 jets as recommended for a K&N lunchbox and a higher flowing exhaust). Spark plugs changed, but other than that nothing on the ignition side.

There's still the occasional popping even though the valves are all within spec. Haven't checked to see where it's coming out of yet, but if it's exhaust then I'll probably need a new head as one of the exhaust valves needed a 200 shim to get it right.

Can't take it out on the road yet to check what it's like at speed as I haven't got my license yet, and can't tell what the rpm is exactly because the tacho doesn't work (I'm hoping that's the tacho cable itself as I've got two separate tachos neither of which work on the bike, but the old one definitely works when you stick a drill into it).

Lastly, pictures! Mainly because it's so damn pretty

Before:


After:


A little video of my mate riding it when we were adjusting fuelling:
https://www.youtube.com/watch?v=1wsV9DyJOFM

I've got some more pics of the modifications and stuff like the home-made exhaust (collector-back) if people are interested.

Even knowing bikes well, gauging the rpms for a bike new to you is difficult, even more so new to bikes in general. It would be most helpful to have a working tach.

But yes, in general GSs need a little more revs to get going than many other bikes. Rev range under 3k won't get you anywhere fast.

I'd say figure out whether it's truly an issue that it's stumbling or flat on the low end or if it's the typical GS under 3k you are using to take off.

Redline is 11k, so you've got quite a useable range above 3k. Powerband is a little after 6k.

- Bboy


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That's exactly what I wanted to hear a combination of 'I'm not very good at pulling away' and 'the GS isn't exactly known for being able to pull away from idle'.

We'll still keep tweaking the fuel slightly to see if we can get it better, but just knowing that it's not necessarily a red flag for something is useful

Truth be told my bike did this until I upped the main jet, in my case I think I probably went further than necessary (it's a 127.5, but mine's a '92, different carbs) but adjusting the pilot mixture is not going to get you there. Remember that pilot jet is only really active when the throttle is basically closed. When taking off you are going to be pulling fuel from the mid jet.

If it's running right, it's no harder to get rolling than any other bike I've ridden. However it's not a 1000cc pushrod V-twin with gobs of torque at 1000 rpm so you can't just dump the clutch at idle and roll on the throttle like you can with an American cruiser. You will have to learn to really use the "friction zone" to get it rolling, you know hold the revs around 2-3K and adjust the clutch/throttle to keep them there until you are underway.

When set up right the bike should pull away fine in any gear from 3K or so rpm. Not talking about winning a drag race but if it's jetted right it shouldn't bog or stall at 3K. Even moreso with your bike with 3-circuit carbs, better midrange tuneability. If you're stalling it taking off at under 2K rpm then it's your technique, you need to rev it a bit higher. But you shouldn't have to slip the clutch at 5-6K to get it rolling, if so you have a tuning issue.

Brill thanks that's helpful here's hoping that the tacho does just need a new cable so I can actually tell what rpm I'm at. With the louder exhaust it's a lot trickier to gauge by ear, so it may well be that I'm only at 2k or something like that.

I'd be surprised if the main jet is under what it needs to be, unless I've somehow managed to luck into making a better flowing exhaust than the aftermarket ones you get. I don't really know what the quality of construction for aftermarket performance GS exhausts is, or their specs. If they're anything like the Motad system that was on it I can definitely see the jets being too small as that was awfully designed.

Popping out of the exhaust when you let off the throttle is a symptom of the carb being too lean at low throttle openings. I was used to my Yamaha SR500, bored and stroked, which had lots of low-end torque. I had to get used to slipping the clutch a little more and giving more throttle after I got my GS500f. Just make sure your carb is not too lean.

Actually popping through the exhaust is a symptom of your bike having a carburetor. It'll happen even if it's quite rich. It'll happen more if it's more lean. It's because the exhaust is hot enough to ignite unburnt fuel on decel.

BTW it's usually the main jet that may be lean causing the exhaust to be hot enough for lots of decel crackle, so trying to "adjust" it by turning the pilot jet screw won't help, but will probably actually make it worse since you'll be providing more unburnt fuel into the hot exhaust with the throttle closed. So you might jet up and have less crackle, but it may be too rich.

My bike has 127.5 main jet, which is too big by at least one notch (runs awesome in winter, is too rich now in summer), and even in summertime it will crackle on decel. Plug check shows it's rich, smell test says it's rich. I am just too lazy to take it apart and put the 125 jets in, I'd rather wait for it to get cold again.

I actually really like the crackle. Reminds me of my 240Z.

Quote from: mr72 on August 04, 2017, 09:33:03 AM
Actually popping through the exhaust is a symptom of your bike having a carburetor.

EFI machines aren't immune.

mr72 almost always has good, cogent ideas and recommendations. However, I disagree with him on the popping through the exhaust upon deceleration. My GS500f, as well as the carburated bikes I have owned in the past, have not popped through the exhaust. I just make sure that they are rich enough and that the exhaust, where it meets the head, does not leak. I'd like others to weigh in on this issue--I am often wrong.

Pops and crackles on decel are pretty normal on any bike with stock fueling (slightly lean). You usually don't hear it as much with stock mufflers though. Put a slip-on or cut can on the end though and you'll hear it.

Quote from: Watcher on August 04, 2017, 10:06:28 AM

Quote from: mr72 on August 04, 2017, 09:33:03 AM
Actually popping through the exhaust is a symptom of your bike having a carburetor.

EFI machines aren't immune.

Oh, for sure. If they don't do a COMPLETE fuel cut when the throttle is closed, they will also be able to crackle or pop on decel.

Thanks guys it's not so much pops and crackles on the over-run (which I agree sounds pretty damn cool, even if it is usually symptomatic of running rich and/or an exhaust leak). It was popping while you were revving, which was a little more concerning.

We've actually had a bit of a better go at tuning the carbs. Rather than moving it in quarters roughly around 3 turns out we've decided to lean it off in quarters as far as we can go before it starts to run rough and then back it off a little (slightly less concerned about running it lean as it's started a rather ominous knocking noise from the crank-case which wasn't there before so we might be due an engine swap/lower end rebuild).

Turns out we had it set really quite rich. Ran out of time at roughly 2 turns out and it was running so much nicer. Genuine night and day difference when it comes to pulling away. It also hangs less when you come off the throttle, presumably because we can dial the idle screw back when it's running leaner and still have a decent idle speed.

No luck on the speedo cable though. New one in and it's still not working properly. It now actually moves which is an improvement, but it's dead slow and doesn't really move as much as it should :S