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.
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.
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
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.
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.
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.
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!
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.
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.
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.
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.
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?
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.
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.
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!
Spacer to head just a gasket.
Carb to spacer no gasket just the O ring, I suggest a new O ring.
The gasket and O ring will not seal if carb flange is bowed.
No jointing compound needed.
Does the slide move freely in the bore?
Mmm, Julian you say carb to spacer no gasket, but there is one there at present (see photo), and I ask myself why. I guess it might be there for a reason? Difficult to decide whether to keep (renew) it, or get rid of it.
I'll renew the O ring in the carb.
Forgot to check the carb flange for bowing, and have left it with the bloke who is making up the cable. Will check it when I get it back (actually he might well have checked it anyway.)
Bees, the slide didn't move completely freely round its circumference - when the slide was rotated it was loose in some places, tight in others - my local expert reckons it's been knocked at some stage. Anyway, apparently it's fixable.
Just checked the battery, which has been on charge since this morning: it's now full, so that's good. I can investigate my no-headlight-or-tail-light issue. (Stand by for more stupid questions!)
Phil.
PS shed not very inviting just now. A bit cold. Next time I move house there'll be a nice garage.
Here's the photo.
I see the drawing on the Draganfly website appears to show it as Julian says regarding spacer and gasket. I guess I'll try that: so, a gasket on the barrel side of the spacer but not on the carb side. And no jointing compound. A light smear of oil, I guess. Phil.
There is a lot of good information on the Concentric on the Amal site. It is worth reading.
http://amalcarb.co.uk/rebuilding-mark-1-concentric-carburetter
I have never used any jointing compound between any of these joints. It should not be necessary.
Just make sure the carburettor flange if flat -they do become distorted through overtightening. Check it with a straight edge and if necessary flatten it. I used a piece of thick glass with some valve grinding paste on it as an abrasive. Make sure you clean it of well!
When refitting, do not overtighten the carb nuts. Just nip them up so they are secure.
Took a few phone calls before I could find a heat spacer 1/4" thick. Most places only had thinner ones, but eventually I found one at Surrey Cycles - great service, arrived by post next day.
My local motorcycle repair shop made a new throttle cable up for me, and the twistgrip now snaps back fine. The old cable had on it a ferrule which appeared to be not right. The bloke who made up the new cable (hugely experienced) discarded that, didn't have the right ferrule, and said it would be fine without (see photo). As I say, the twistgrip appears to work absolutely fine. It begs the question: what does the top hat ferrule actually do? Any comments please?
Phil.
Most throttles need the ferrule to locate the cable and stop the end from disappearing into the body.
Your twist grip is a different pattern and does not need one.
I would not want my throttle to snap back when released.
Every time you want to hand signal, operate switches, adjust your goggles, scratch your nose etc, you would be slowing down
and holding up the traffic.
Mick
I've heard different opinions on this, and I expect it's been much discussed over the years without total agreement. I can see, of course, your points, Mick. What are the points in favour of snap-back? Is it a safety thing? Phil.
If the throttle does not snap back cleanly, the MOT man will not pass the bike. It's just one of the amusing things about making a right-hand turn when you haven't got indicators.
I don't know how many car drivers would understand the motorcyclist's right turn signal executed with the left hand.
A lot of the twistgrips have got a friction screw on them to adjust the "stiffness" of the twistgrip so it can be adjusted to stay open if not released so that right hand turn signals can be made.
It is OK to set the twistgrip accordingly but it is not good practice if the throttle wont snap back if the twistgrip is set loose. There is a chance the carb could stick open at high speed causing embarrassment to the rider and also a lot of grief for the engine!