Author Topic: Throttle twistgrip doesn't snap back  (Read 534 times)

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Phil C

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Throttle twistgrip doesn't snap back
« on: 06 January, 2019, 10:26:30 »
Hello everyone.  I've ordered a battery charger to try to sort out my "won't start" problem on my 1965 B40F. Whilst I'm waiting for that to arrive, I have got round to thinking about my throttle twistgrip. I think it needs a new cable and ferrule, but for some reason the twistgrip no longer snaps shut when I release it, even when the friction setting screw is set so that it turns very freely by hand.  Any ideas why? It turns freely by hand in both directions. Does it mean there's some issue with the spring in the carb?  When I operate the twistgrip by hand, I hear a faint click at the carb, which I guess is the slide closing?  Phil.

JulianS

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Re: Throttle twistgrip doesn't snap back
« Reply #1 on: 06 January, 2019, 12:19:07 »
Probably the cable or cable run. Try lubricating the cable with wd40. Avoid using any clips to hold the cable to the frame, make cable run as smooth as you can, is the cable trapped under the tank.

ianfoote

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Re: Throttle twistgrip doesn't snap back
« Reply #2 on: 06 January, 2019, 12:46:18 »
Hi,
Obvious but sometimes missed, do check out your rubber throttle grip. It can bind on the end against the handle bar or it may also bind against the throttle body where your thumb and index finger sit..... just saying like.
Ian

Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #3 on: 06 January, 2019, 14:22:04 »
Okay thanks Julian and Ian - I'll try those things.  But it really doesn't feel as though there is any obstruction. The twistgrip will turn pretty much effortlessly by hand, both ways. It just doesn't spring back shut when I let go - I have to turn it back, but I don't feel any resistance.  You can see why I was fearing it might be the spring in the carb?   Phil.

DaveH

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Re: Throttle twistgrip doesn't snap back
« Reply #4 on: 06 January, 2019, 15:00:09 »
Hi. Maybe the cable has broken or the nipple has come off one end of the cable inner? I suggest you remove the top of the carb complete with slide,spring etc to investigate. This may also be the answer to your no start problem. Good luck.

Dave.

Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #5 on: 07 January, 2019, 14:40:30 »
I've never taken the top of a carb before.  I was expecting the throttle slide to simply slide up and out, but it doesn't. Could someone enlighten me please (see photo)?  Phil.

AdrianS

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Re: Throttle twistgrip doesn't snap back
« Reply #6 on: 07 January, 2019, 16:29:27 »
The slide just lifts out when you pull the spring/cap/throttle cable.
The spring is there to return the slide to its closed position. There is nipple at the end of the throttle cable which fits into a recess in the slide and is retained by the spring pressure. The needle should also lift out with the slide assembly and is held in place with a small sliding spring clip which goes through the slide and through one of the notches in the needle itself.
It is this spring which should close your throttle and return the twistgrip when releasing it. If it doesn't, either the spring is not connected or there is something wrong with the routing of the cable or a fault with the twistgrip itself.If the carb end is OK, split the twistgrip by undoing the 2 big screws clamping it together and make sure the nipple is located properly in the cutout on the twistgrip. I have had one come adrift in the past!

Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #7 on: 07 January, 2019, 16:47:29 »
I got the slide out by giving it a squirt of WD40 and pulling slightly harder.
The spring seems to be okay.
So I'm still not sure yet what the no snap back problem is.
Think I'll get a new cable anyway, as the outer one is damaged where it was routed through a cable tie.
Anyway, with some of the carb in bits, and my throttle cable removed, please stand by for more questions in the next few days!
Thanks yet again for your help.   Phil.

Bees

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Re: Throttle twistgrip doesn't snap back
« Reply #8 on: 07 January, 2019, 18:52:40 »
I think you may have found the problem. The slide should come out quite easily.

Had a similar problem with my carb. On a cold day and cold engine if I opened up carb to full throttle the slide would stick in the carb body. Only happened really cold days. Fine on a normal day or when engine running.

I thoroughly polished both slide and carb body and been fine since.

There can only be 3 things to check. Its either the twist grip. Cable or slide sticking in the carb.

Let us know.

Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #9 on: 07 January, 2019, 20:17:13 »
What do you use to polish it?  When rubbing my fingers over the main part of the slide it feels smooth, even though there are some very fine visible score marks. There are however a couple of steps about 1/4" from the top, one which goes all the way round, another just above that which goes part way round. See photo attached. Does that top 1/4" matter in that way? I suspect that the main body of the slide is a bigger dia than the top bit so hopefully it doesn't matter?   Phil.

JulianS

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Re: Throttle twistgrip doesn't snap back
« Reply #10 on: 07 January, 2019, 20:34:10 »
The top step is as manufactured.

I use a spray carb cleaner or wd40.

Some times the carb body distorts when the retaining nuts are tightened which in turn tightens the slide in the body. Many bodies have been overtightened and distorted over the years. Check the mounting flange with a straight edge, if bowed you can usually rub it flat using a surface plate.

Bees

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Re: Throttle twistgrip doesn't snap back
« Reply #11 on: 07 January, 2019, 22:52:45 »
I used autosol. I don't think it really matters. It just a matter of seeing if the the bore if the carb and the slide are smooth  and run true. I think the slightest burr or bit of crud will cause a problem.

Is the carb on the bike?


Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #12 on: 07 January, 2019, 23:17:22 »
Yes, the carb is still on the bike. I guess I could have taken it off in order to have a good look at it (which would have been a useful learning experience for me), but I didn't bother at this stage, as I have a number of things to sort out (in addition to the no-snap-back issue, there is the no-start issue, the lights-won't-work issue, oh and an oil leak.)  Phil.

Bees

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Re: Throttle twistgrip doesn't snap back
« Reply #13 on: 08 January, 2019, 07:14:24 »
I'd be tempted to remove the carb.

Give the slide and bore a good polish whilst waiting for the new cable. When new cable arrives assemble it before you put the carb back on the check it works fine.

When thats all good put back on bike running cable in smoothest route. Loosely tighten the nuts that hold carb on and check again.

Then tighten nuts gradually checking it snaps back ok now and again to see if the carb is distorting as it tightens up.

Its good practice to use a new gasket between the carb and barrel.

I  would sort his before you try and get the bike running. You don't want the throttle to stick open when you get the bike running. That make the pulse race a bit!

Good luck. Keep us posted.


Phil C

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Re: Throttle twistgrip doesn't snap back
« Reply #14 on: 08 January, 2019, 18:23:37 »
I took the carb off and have got someone making up a new cable.
In between the carb and the barrel is a spacer, about 1/4" thick.  Not sure what it's made of. Tufnol maybe?
In between the carb and the spacer is a gasket, which I'll renew. Should I use any kind of jointing compound between the carb and the gasket, and/or the gasket and the spacer?
And what about between the spacer and the barrel? The spacer is held there at the moment by something - I guess some kind of compound. Should there be a gasket between the spacer and the barrel also? I guess so?

Thanks.  Phil.

PS Regarding no-start and no-lights, battery is now on charge - fingers crossed!