Rising revs on tickover

That's normal behaviour. If the revs are too high when it's properly warmed up just back off the throttle stops.

The A/R unit in the dissy may be sticking or have tired springs.

If the motor was tight it may have run in .

No airslides. Could it be that air is getting in where it shouldn't? Just a thought.

I've had a persistent problem like this with a pair of Concentrics. They are very easy to distort. These are new but were left fitted over a period of years and I believe had been overtightened. I had sincefitted gaskets between all the manifold components (heat proof spacer and distance pieces) to try and stop leaks but was told that the gaskets themselves can distort the manifold flange, so have fitted without and with a smear of Wellseal. That seems far better but I think that as the bike stands running, the heat causes the tickover speed to increase and become uneven? I have a feeling that it's the carb bodies acting on the throttle slides? Only an inexpert theory, and subject to comment by those much more knowledgeable than me, but you aren't alone with the problem!

I don't think any were supplied new without airslides. Racers routinely removed them. Something less to clutter up the handlebars. Because the carbs were designed to be used with airslides, I always fit them even if they are pretty much redundant, in summer anyway. A lot to be said for reverting to a single carb - one of the better things I have done to my bike. Take a good look at the A/R springs on the distributor. It does sound as though you may be getting stuck on full advance. Gordon.

Have you checked that the throttle slides are able to bottom. Even with ignition timing stuck, it should be possible to stop the motor with the throttle stops backed out and fully closing the throttles. Is there a little slack in the cables when the throttles are shut? As far as A/R springs are concerned, they are not going to suddenly get tired but they can break. Are you running twin cables from the twist grip? I had the junction box stick once on the 1 into 2 setup. BTW I never use air slides but then I live in the sunny south not up in the Arctic like Gordon.

Are the throttle slide springs strong enough? It might just be that they are not closing the slides sufficiently, especially if the cables are old/sticky. As an aside, I once had the throttle jam fully open due to carb icing just at the point where the well-lit dual carriageway ended and the twisty unlit snow-covered single carriageway began. And the magneto kill switch wouldn't work. Oh how I laughed.

Martin,

When you say new carbs were they new or "used but good" your problem sounds to me like worn throttle slides/bodies but if they were new carbs and you have only covered 600 miles it is unlikely that wear in the carbs is the problem.

It does sound like too much air, you say you sprayed WD40 but without success, as you have a twin carb set up you may not have got to the offending leak, how about running the engine, let it speed up and drop off a plug lead and see what happens, you might be able to isolate it to one cylinder, you may want to plug the balance pipe to make sure that the cylinders are isolated, if that does not work try wrapping Denso tape (really greasy tape used by plummers) around all the carb to manifold and head joints basically wrap it around anywhere that you think air may leak into the carbs.

Two years ago I had the same problem as you on my single carb 99, I tried eveything but to no avail, in the end I fitted a brand new carb, since then I have had the sweetest running Domy, problem was a worn carb body.

Good Luck

Tony

Previously wrote:

BTW Alan I'm in the sunny south too - well south east anyway,

Remind me, where?

The only reason I can think of for carbs changing themselves is sticky cables.

Sounds like your cable + splitter etc has shifted and is now pulling the slides. I'm sure there are other views on this but I lash the splitter to something stiff (probably the head restraint).

It's worth using a spanner to tighten the cable adjuster nuts on the carbs to stop them from vibrating away from optimum. But my money would be the cables.

If you open and close the throttles, you should hear the clicks as the slides bottom. (Engine off, obviously.) If the slides stick before bottoming they don't click. The odd part of this development is that it happened relatively suddenly. Did you do disturb anything?

Just wondered if you were in range for a ride out. You're a bit far for this time of year. I haven't been your way since the Weeley Festival in 1971!

Previously wrote:

Justa quick update and a heads-up to all who have tried to steer me in the right direction with this. I thought I'd give the old girl a shine whilst I contemplated my next move, and lo and behold found that the left hand sparkplug was suspiciously loose - a little more than finger tight. Took both plugs out to compare, left hand one definitely burning leaner than the right. Back in and tightened properly, the revs were significantly reduced. Turned throttle stops back by about five degrees, and engine settled into a nice tickover. Also appears a bit more responsive on the road. I don't know if I should be embarrassed about this or not, as it's clearly my fault for not tightening them up properly in the first place. In my defence I will call it age-related absent-mindedness. Personally I've not heard of a loose plug causing this problem before, there were no discernibly odd combustion noises, so it hadn't even crossed my mind - apologies to all who assumed they were helping someone with intelligence!

Thanks again all. Dont be embarrassed about making a simle mistake just be glad its sorted,i could fill this site up with the mistakes i have made? and someone reading this post may remember it if they have the same symtons on their own bike and find the fault instantly regards nick

"Turned throttle stops back"!