tickover to high

[mrshells]

Can anyone help
My 1952 A7 Star Twin(single carb) idle speed is to high
if i wind the idle screw almost all of the way out it has no effect on idle speed
if i the screw air screw all the way in it drops but is still to high
as far as i can tell tha 276 Amal has all the correct parts
And otherwise it runs very well
maybe a little rich
 

[a10gf]

Hi, regarding running generally rich or not, check the sparkplug immediately after some normal riding. Here are some scanned pages about the 276, gives a very clear explanation of the carb, this may help in evaluating the possible cause for a high tickover: http://www.audioworld.net/BSA/276.htm

[mrshells]

Thanks for that
I have allready done all that and as i said it runs fine just idles too fast ??
i thinks there could be some wear in the Carb
also I will have to check Ignition timing again

[mrshells]

Tickover not really a problem now 
went for a ride today
stopped for a cuppa agter about 40 miles bike started ok then went on to 1 cylinder
swopped the pick ups and leads round and the problem moved to other cylinder
so rode it home on 1 cylinder
changed the pick ups and leads now it wont run at all !!!!!
Its not drawing any fuel through !!
spark is good
checked all the usual things
think i will have to take the head off for a better look
compression is ok
but not a lot of suction through the carb
valve clearances are good
 

[groily]

Something not stacking up here. If you swapped leads and the non-firing cylinder swapped with it, then that says there was a spark problem - with one pick-up or HT lead or plug cap. If it ran home on 1 cylinder, then fuel was getting through.  Now you've changed the pick-ups and HT leads you say it won't work at all, that there are sparks - but no petrol. Strange to say the least if swapping the leads round/ replacing them has stopped the fuel getting through. Worth just checking fuel flow by disconnecting a fuel pipe and seeing how wet the floor gets. And checking over the float needle, filter above it etc, if the carb won't flood when you tickle it plenty.

But, as a first move, suggest you clean the slip ring on the mag with a bit of clean cloth (a bit of electrical contact cleaner spray wouldn't hurt too) through a pick-up hole, check the state of the brushes and springs on whichever pick-ups you choose before putting them back (plus HT leads and plug caps), then check the gap on the contact breaker for size and sameness on both cylinders. I'd do that before thinking of taking the head off. If it ran fine till you had a cuppa, and then ran on one cylinder all the way home, I don't think, from far away, that there is a fuel problem. Nor, on the face of it, a cylinder head problem. My bet is that you have an ignition problem. Could be that the magneto is starting to protest when hot - not uncommon if the windings or condenser are on the way out - but more likely something less serious and a lot cheaper. Am assuming the plugs are correct and not too knackered, as they seem to have worked OK, depending on which side had the good lead on it when it did agree to run!

[mrshells]

turns out to be the magneto which was rebuilt 6 weeks ago !!! 
thats under warranty so going back for another repair
Ive tried a freinds mag and it ran ok but a little lumpy
so i bit the bullet and whipped the head off
possibly need a new valve guide and head gasket has been blowing
so a few weeks before she rides again !! 
it will give me chance to sort some oil leaks out !!

[groily]

shame - and not what you'd expect. But there are Rebuilds and 'Rebuilds' . . . sounds as if you have a warranty, so good luck with getting it fixed. I have to say I am quite lazy with valve guides - there has to be good few thou wear before I do anything much about them and often the wear is as much on the valve stem as the guide. I'd check that, see whether a new valve fills the hole a bit better as valves are easy, then come back to the guide if you really have to! But a head gasket, no choice there . . .

[mrshells]

According to the guy who rebuilt my mag
the after market pickups that i have been using are to hard
and have caused pitting on the slip ring
hence the erratic misfiring
so i have sent him the pickups for new brushes  well see what happens
in the mean time Ive had the head off just for the hell of it
I knew it would cost me !!!!!! 
but fortunatley only gaskets and 4 new valve guides !!!
otherwise shes in really good shape !
he says breathing large sigh of relief !!!!!
are the majority of the bolts used British standard cycle thread ??

[groily]

Hmmm! It's possible that the brushes were 'too hard' I suppose, but as all new pick-ups one buys today are probably'after-market' (and I doubt there are all that many suppliers) I do wonder a bit. Might be worth your going back to whomever supplied to ask more questions.
However, if you can get your slip ring cleaned up and the 'right' pick-ups you'll be up and away.
Shame about the guides though - that's a pain, relatively.
Re threads, no, they aren't all cycle. BSF and Whitworth too, depending on what bits we're looking at. But same spanners for all of them. Then BA for the lekky bits.

[mrshells]

got the mag back with a new slip ring and the tickover problem has returned 
but its not the mag as i have tried 2 other known good mags and it still ticks over to high
might bite the bullet and by a new carb body and jet block

[dpaddock]

High idle - throttle cable core is too short; throttle slide and/or slide bore are worn.
Screw threads - mostly 26 tpi CEI; Whitworth (coarse) in aluminum; BSF for cylinder head bolts.

[mrshells]

its not the throttle cable that was the first thing i checked
but used good left hand 276 carbs are not the easiest things to find
i think i will have to get a new one

[trevinoz]

As David said, worn slide / bore. Have a good look at the slide to body clearance. If it is sloppy you will get air going around it. I had problems with my Norton with setting idle speed and also back firing with the throttle closed. Resleeving the carbys fixed it.
                Trev.

[Brian]

One thing to watch out for is you really need to check the slide in the body with the jet block removed. Because the slide goes over the upper part of the jet block putting your fingers on the back and front of the slide and seeing how much it moves is not always a good indication of the wear. Thats always a problem when looking at carby's at swaps.

If your carby is worn excessively which it would appear it is then you have a couple of options. You can bore the carby and sleeve the original slide or bore the carby and fit an oversize slide. Oversize 276 slides are readily available on e-bay and probably other suppliers.

The other option if you are prepared to spend the money is to buy a complete new carby.

[IanH]

Before u do anything expensive chec that there are no air leaks:

a, you ve got a good seal beteen the carb and the manifold (use grease on the thin gaskets or use the thicker hallite gaskets without grease.

b Check the flatness of the carb flange with a small steel rule and make sure the nuts are not too tight, in fact I just nip these up with a spring washer underneath.