Throttle cables - push/pull?

Craig321 · 5 Nov 2016 at 18:18

I installed my Hornet's bar end mirrors today which mean taking the throttle tube/assembly and throttle cables off.

The throttle cable is fine and the throttle snaps shut when I let go, so all is fine.

I noticed when taking it all apart, there was another cable attached to the throttle tube. Apparently this is a 'return' cable?

Well, it was snapped and probably has been for a while.

What is it actually for? The throttle is still closing absolutely fine.

It's item 2 on here: https://www.fowlersparts.co.uk/parts/4773246/cb600f4-2004-e/handle-leverswitch-cable-cb600f3456

Thanks.

Edit: oh right. Looks like it's basically just a safety mechanism and some people remove them anyway? It means if my throttle tube get sticky then the throttle is going to be sticky whereas the push cable will ensure the throttle snaps shut, always.

ShakenNstirred · 5 Nov 2016 at 18:29

Its to help you close the throttle should it get stuck open.
I'm all my years of bikes I have never needed it.
my ZR7 now has a quick action throttle so I took the return cable off

It all goes back to some stupid yank not doing something right and suing when they fall off.
same way the side stands now have a cut-out to stop you riding off with it down
again some yank sued a manufacturer saying it was there fault it was down not his stupidity

Craig321 · 5 Nov 2016 at 19:49

Thanks

I'll leave it then. Might take the entire cable off actually, unless it leaves a big open hole somewhere.

ttaskmaster · 7 Nov 2016 at 13:28

Under the right conditions some engines can create enough vacuum to make a carb slide stick, causing a run-away.
A single cable doesn't push, so you have the second cable to pull the throttle shut.

I'd have to check, but I *think* it's a legal requirement to have both...
Also, if your primary snaps, you can jury-rig the Close cable as a spare to get you home.

ShakenNstirred · 8 Nov 2016 at 07:54

ttaskmaster said:
Under the right conditions some engines can create enough vacuum to make a carb slide stick, causing a run-away.
A single cable doesn't push, so you have the second cable to pull the throttle shut.

I'd have to check, but I *think* it's a legal requirement to have both...
Also, if your primary snaps, you can jury-rig the Close cable as a spare to get you home.

Mine passes its MOT every year without it.
The return spring is more than enough to close the throttle, all the ones I have seen the close cable is totally different to the opening one

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Terminal_Boy · 8 Nov 2016 at 08:01

ttaskmaster said:
Under the right conditions some engines can create enough vacuum to make a carb slide stick, causing a run-away.
A single cable doesn't push, so you have the second cable to pull the throttle shut.

I'd have to check, but I *think* it's a legal requirement to have both...
Also, if your primary snaps, you can jury-rig the Close cable as a spare to get you home.

Flat slide, non CV carbs were prone to sticking back in the day. Never seen a push/pull setup with CVs.

ttaskmaster · 8 Nov 2016 at 12:47

ShakenNstirred said:
Mine passes its MOT every year without it.

Technically it could be failed:
"f. a malfunction of the throttle control or linkage that does not allow the throttle to operate as intended"
If your throttle came with two cables, that is how it's intended to work. Technically...

ShakenNstirred said:
The return spring is more than enough to close the throttle, all the ones I have seen the close cable is totally different to the opening one

All the ones I have seen, the close cable is just a slightly different length, which is why you can rig it to serve as the open cable, although not ideal.
The return spring may be fine under ideal conditions, but springs snap, dirt gets inside the throttle tube, cables lose lube, the system can get fouled at any number of points... all reasons for why you have the close cable. Increased vacuum on larger engines is another, which has actually happened to me once. It's usually very slight to look at, but you can often see the valve fluttering and it's still enough to make a very audible difference and cause problems.

Terminal_Boy said:
Flat slide, non CV carbs were prone to sticking back in the day. Never seen a push/pull setup with CVs.

Even CVs generate vacuum which can hold the butterfly open, or the system can become fouled somewhere along the route, or a mis-adjusted idle speed can increase as the engine warms, resulting in the carb hanging or not returning to idle.
Plenty of CV Carb bikes have dual cables, from scooters to Harleys.