CG Fuel/air mix isn't right

[Ingah]

Having finally got a reliable bike on the road for the first time in 3 years (my good old CG125 which had been laid up for that whole time whilst i repeatedly repaired my CB500 "and it'll be fine after this"), i've decided it's a good little bike.

However, that said, it's surging, for want of a better term, at any speed above 20mph or so. Power inconsistent, and definitely a good chunk slower top speed than it was before i laid it up. It also pops and backfires a little when under engine braking (decellerating with the throttle closed).

I'm going to be checking the plug, which whilst it was put in a year ago, hasn't been used, and was cleaned a few days ago with paraffin (because of my having issues starting the bike due to my jet needle having fallen down into the body of the carburettor, causing the plug to have black sooty deposits covering it). Have full intentions of changing the plug anyway, but don't want to ruin a shiny new iridium plug until i've sorted everything out.

Obviously there's a fair amount of potential causes with it being laid up so long, but things like the oil and air filter have been changed/cleaned.

Am going to be checking the Haynes when i can, but looking for ideas (partly because i'd like to sort it ASAP, partly because i want to use this bike more, so it'd be really nice to have it running right). The fuel/air mix is clearly not right, and as i have been playing with the mixture screw (when i was trying to sort the needle having dropped, before i knew it was the needle for sure) i'd probably best try resetting that as a first order of business. Then look at that spark plug. Would a plug chop be significantly more useful than just looking at it when i'm home?

[Fozzie]

Set it back to how it was is deffo the best course of action to pursue here!

If youve recently modded it, think of everything you did to do with fuelling and set it back and check it.

[Ingah]

One thing i can think of is that i was unsure of which groove i should place the washer in on the top of the jet needle (there's 6 grooves, i believe this is kindof a "setting"). I placed it in groove 3 or 4.

Will be putting mixture screw back to manufacturer's setting, assuming it's in the Haynes manual. Wasn't try to "mod" it when i was messing around with it, merely get it running again

[eastanglianbiker]

for the mixture screw turn it right in then open it up to between 1 1/2 and 1 3/4 turns for basic settings and yes plug chop while hot and on a run is good for teling whats going on

[Lumor_uk]

if it fell right through has the degraded rubber not got stuck in the needles, have you give the carb a proper clean out?

[Ingah]

if it fell right through has the degraded rubber not got stuck in the needles, have you give the carb a proper clean out?

Rubber?

Needle fell through because the washer had been slightly malformed when i was messing with it and so didn't hold the needle tightly enough.

Carbs were *properly* cleaned out a while back. And then petrol hasn't been left sitting in them for long since (definitely not long enough to varnish up).

Brand new iridium spark plug hasn't solved it, so i guess mixture screw is next

[Ingah]

So mixture screw was 1 turn out. After changing to 2 turns it seemed better, but not fixed. But at 2.5 turns it WAS ok for a couple of miles, and THEN stopped working! only way to complete my journey from that point was on FULL choke (running just as badly as it had with 1 turn out) otherwise it wouldn't run at all, which seemingly defeats my theory that it was running too lean as letting the screw out was richening the mixture to my knowledge. Really quite confused so might take the carb off again. But am working against the clock as its dark soon and i've work again in the morning lol.ng the screw out was richening the mixture to my knowledge. Really quite confused so might take the carb off again. But am working against the clock as its dark soon and i've work again in the morning lol.

[Ingah]

As an update i found it would run if i put the mixture setting to 1 and 3 quarter turns (the manufacturer's setting). But very badly, kangeroo'ing, juddery, bogging down on 1/4 - 3/4 throttle. But still, got me to work and back a good handful of times.. before giving up the ghost again:

http://www.themotorbikeforum.co.uk/view ... 8&p=694105