"snatchy" throttle?

[mr72]

So I've been able to ride my GS quite a lot and it's been running great since all the work that went in to get it sorted. But there's now just one thing and I don't know if this is something I can/should fix or if it's just the way they are.

It's when going from throttle closed to throttle barely open, doesn't matter if it's off-idle or running down the road. But what it feels like is a slight delay when turning the throttle before the engine responds so it actually responds quickly like it has to "catch up". It's no big deal but really it's the only imperfection in how the bike runs now.

I am guessing it's because of the delay between when you open the throttle and when the diaphragms have enough vacuum to pull the slides up. I have read about others doing mods (to other bikes) to enlarge a hole in the slide to improve the rate at which the slide moves. Seems to be a bit of debate about whether this is a good thing or not, or whether it solves a problem. While one might think it's irreversible, I do have a spare set of carbs and I could drill those slides and try it.

Or would I be better off shimming the needles?

Is there some other remedy? Does it indicate a problem?

Or is this just the way it is and I should leave it alone?

[Watcher]

In my experience a carburetted engine is always a little "lazier" than EFI, but there shouldn't be that much of a delay from roll on to engine speed increase.

How's your jetting?  If you're lean it could be a cause.

I'd also double check float height.


I'd be inclined to play with the needles before drilling the slides, that sounds like a bad plan to me.

[mr72]

127.5 mains and 40 pilots with the equivalent of "slip-on" exhaust and stock airbox. I would guess it should be a touch rich if anything. No shims/washers on the needles. Plugs look like the mixture is perfect.

I have a spare set of carbs so I could drill those slides and put them in to test, always return to stock.

[Watcher]

Check your filter element as well.

[mr72]

Check your filter element as well.

It's new-ish (PO installed right before I bought the bike)... <1K but easy enough to check and cheap enough to replace.

I have the factory-manual-recommended 5mm of throttle free-play. I wonder if this might be part of the issue? Like maybe I wouldn't notice this as much if it weren't for the free play.

I really need to pull the tank anyway and reroute the throttle and choke cables (PO did it wrong putting the bike together). I've just been putting that off since the bike runs great and I'd rather ride. Need a string of rainy days while I have nothing to do.

[Watcher]

Can you get video?

[Joolstacho]

Worn or loose chain and / or worn sprockets can exacerbate this problem.
I'd adjust throttle free play down to 2mm.

[Endopotential]

If you ever get the gas tank off, maybe check that your throttle cable is actually pulling on the carb as it should be, no binding in the housing?

I know on my bicycles, if enough grime builds up inside the housing the cables never slide like I think they should.

[mr72]

I'm pretty sure the throttle cable is not binding.

I took most of the free play out of the cable but didn't get to ride again because it was just too cold over the weekend.

I suppose it could be a worn chain or sprockets. Bike's got almost 21K on it and these may be the original parts. It does feel like there's some "slack" between the crankshaft and the rear wheel that has to be taken up somewhere, but I figured that was largely the transmission.

[Watcher]

I didn't even think of the chain.


Aside from making the throttle response feel laggy or making rolling on and off the throttle more jerky, a loose chain will actually accelerate further chain stretching and overall driveline wear.

I would maintain my chains every 500 miles or so and it takes seconds to properly check the slack, so while I have a clean chain I'd get out a ruler and see where it's at.

If you want to make chain tensioning super easy look for a tool called a "Chain Monkey".  Works awesome, way more efficient than the whole guess and check method.