Curvy won't idle without choke, won't do mid throttle, will rev

[northwind]

Oh yeah, hello Org- it's that annual post I do where I remember I own a bike. How are we all?

Actually decided to do some work on it this winter though, and first things first, it starts but it won't idle even when warm without choke, and as soon as you add throttle it stalls. But if you just blast it open it'll run happily, it's only low revs and idle that it's trouble. Filter in or out makes no difference.

So I am thinking, fuel or vacuum basically, some of the hoses look pretty dubious but fuel has to be the number one suspect since it's probably full of varnish. Anything else I should think about before I get into the carbs themselves? I may do the vac and fuel hoses on general principles.

Oh yeah, these Yuasa YTZ12S batteries are flippin amazing- it's been dead for years, stuck it on the optimate for a day, and it's as strong as ever.

Also, I was taking it to bits tonight and thinking "I remember nothing" but my hands totally remember how to get the carbs off. Now i just need to figure out what all this apparently random extra wiring I added is for.

[Biker Biggles]

Your bike is registering its displeasure at having been left in a dark corner, unloved and ignored for yonks. As a penance you are required to strip down the carbs and remove carp from very small spaces.

[R1ffR4ff]

Buy a bottle of RedX fuel treatment.Stick half a bottle into half a tank of fuel and give the bike a good run.See if that clears it out

[Bibio]

i'll say blocked primary jets in the crabs. once the choke is off then the primary jet takes over as far as i can remember.

give this a try first. using a can of compressed air or brake cleaner with the straw attached blast some down the two jets you can see at the top of the carbs making sure that the straw is making a seal between jet. only use small bursts till it clears.

start bike and warm up then turn tickover up a little then shut choke off and do the same as above.

redx wont shift gum in blocked emulsion tubes or jets. it requires a strip and blast with compressed air.

[northwind]

Originally Posted by Bibio

i'll say blocked primary jets in the crabs.

Blocked crabs, got it.

[SV650rules]

Originally Posted by R1ffR4ff

Buy a bottle of RedX fuel treatment.Stick half a bottle into half a tank of fuel and give the bike a good run.See if that clears it out

I will second that, worked like a charm for me with bikes that had stood for a while, then I took to adding it to fuel before laying them up, that prevented it happening at all, also worked on motor mowers, start second pull after 6 month winter layup and idle well straight away.

For me it is a no brainer not to try a good dose (in a case like yours tip 500 mil in - don't mess about with reading dosage on bottle) you would be amazed the effect it has.

At £5 or so it is cheapest option.

[johnnyrod]

WINDY! How are you, you old stick? Frankly Redex is mindless optimism, but who says it won't work, it'd be easier than spannering. Sounds like a blocked pilot jet or two, it's a faff but after this long the crabs could do with a bit of attention.

[SV650rules]

Originally Posted by johnnyrod

Frankly Redex is mindless optimism, but who says it won't work, it'd be easier than spannering.

I have seen the effect sploshing a bit of redex around in a dirty lacquered up carb has, the gunge disappears like snow during an 'H' bomb explosion. It is mainly kerosene but has other stuff in as well.

[mikerj]

Originally Posted by Bibio

i'll say blocked primary jets in the crabs. once the choke is off then the primary jet takes over as far as i can remember.

Agreed. My dad has a rarely used curvy and it suffers from this problem almost every time it's dragged out. An old trick that can sometimes provide a quick fix is to remove the airbox, start it up and rev the engine and then stick your hand (or some other flat object) over the end of the carb for a few seconds. The sudden high vacuum helps to drag any blockages out of the jets, though it will splutter a bit as it will run very rich whilst you are blocking the carb.

Obviously repeat this on both carbs in the case of the SV. Don't try this using your hand on large capacity engines either...

[SV650rules]

I have successfully treated a number of carbed bikes (and lawnmowers and generators) displaying exactly the symptoms you describe, when carbs are left unused the Dinosaur Juice evaporates and leaves gum and lacquer from long dead trees and plants behind to glue things together and block jets, this is easily removed with a good glug of good ol redex (without using any tools other than the key to the fuel cap). After it has sorted this problem I would put some in before you leave it unattended in a lonely dark garage or shed again. £5 to try it WTF! are you delaying for ?