Blip the throttle and she keeps on revving

[Colonial-Clive (yindi)]

Hi all, it's me again D the bike is now firing on all four new plug, points, carbs stripped and rebuilt and bench set as p r forum and all gone over twice to eliminate possable cockups! So here we go on cold start there is a phisst back throug #4 carb this gets less as bike warms but the main concern is that when I blip the throttle the bike keeps high revving (around 3k) until I press down on the 4 large brass cover caps. I have lubricated all external moving parts, but this has not helped. Ideas please before I go for an expensive option like a refurb set.

[K2-K6]

Disconnect both throttle cables from the carbs to eliminate half the system from your enquiries and just turn the carbs by hand.

What have you set the idle air screws at? 

[Colonial-Clive (yindi)]

Cables are free air idle screws I haven't touched!

[K2-K6]

You need to have some slack,  about 10degree at twistgrip to make sure the cable can't conflict with one another.

If you turn the idle air screws in one a time and count the turns they are set to, for example 1 1/4 turns and then bring them back to where you started to find out what you've got there. They may have been set with another error on the bike, so may now be wrong. We need to know that for each carb to help understand what you've got there.
Also make sure your igniting is not set advanced and the advance / retard mechanism is working properly.

[deltarider]

What model bike?

[Colonial-Clive (yindi)]

It a bitsa believe the engine is 550 f just rebuilt with 600 Bore,skim head, new shells and chains.
Car be pulled apart cleaned with new vettol replacements new points,plugs the advance movement turns freely back and fro set slides all at same height. It ideals well but blip it and it stays reving till you push down on carbs??.

[K2-K6]

Something puzzling about it, sounds like it could be running idle on the main throttle slides, for example the tickover set screw is holding the slides up to keep it going. It may need this if the idle circuits are not working properly so main throttle is required to stop it stalling,  when you push on the linkage you are effectively pushing the slides down past the tickover screw setting that you've got.
If it's running in this way,  it's not accurate enough to give a reliable repeat idle speed.
 I still feel you need to verify the idle jets are actually working. For this you should get a response from each one of them by turning them individually with the engine running on tickover. If you get no response, you'd expect that one you are working on to have an impaired idle circuit.

[Colonial-Clive (yindi)]

K2-k6 see where your going, when the throttle stop screw is not in contact with the plate it still does it so will try the idle screws tomorrow and see if that helps solve the problem will also recheck the advance unit just to be sure.

[petermigreen]

sounds like sticking carb slides to me.

[Colonial-Clive (yindi)]

Petermigreen sticky slides that sounds like a spray of lubricant job and the easiest place to start would spray carb cleaner work or would it need something like wd40 or similar?

[petermigreen]

I guess a squirt of carb cleaner would certainly not hurt, but in my experience tends to be a dry substance if that makes sense. Similar to brake cleaner it drys and leaves the surface dry or put another way, non-lubricating.
I'm not sure if any lubricant that you could get onto the slides would last long due to the environment of the carbs.

I'd be more concerned with why the slides are sticking (if they indeed are). I'm not familiar with any other carbs than the 400s but imagine a return spring is involved. If it were me, I think I would ensure that operation is correct with no foreign bodies in the carb slides/bodies etc and all working as it should.

My experience of over revving ranges from stuck/sticking throttle cable splitters (my RD200) to poorly set up throttle linkage (CB400F) but I'm aware that non returning slides will do it. Whether it be the slides themselves stuck/sticking or linkages in the hole throttle chain.

Hope you get it sorted.
Peter.

[deltarider]

Sure there are no airleaks? Like the O-rings between the head and the intake manifold or the rubber boots between carbs and the head? Easy to check by spraying some brakecleaner or WD-40.

[Colonial-Clive (yindi)]

Deltarider All new rubbers and clamps but will mist them to be sure.

[matthewmosse]

One of my k3s had the return spring? in the centre of the carbs fracture. I cannot recall what issues it gave but it was a pest to spot as the spring in question was right in the middle of the controll rod sat between 2 and 3, wrapped around the rod. Break only visable with carbs off the bike and throttle held open. Only a thin spring, but enough to stop it working.

[Ashdowner]

Are you sure the valve clearances are ok and they.e not too tight? Compression test? Have you tried vacuum gauges to see what the difference is between the pots?