Idle screw having no effect

[Essexwriter]

My Toledo has been running a bit rough, and she started her stalling at junctions trick again.

I guessed that maybe the mixture was too lean. I adjusted the jet adjusting nut on the carb to richen her up, but little difference. I tried doing the 12 flats and then tweaking from there, but now she's idling fast and the idle adjust screw is having no effect. Nothing happens when I push the piston lifting spring either.

Are the carbs gunked up do you think? Or the needle stuck? She still drives, but rough and fast. The fast bit is quite nice, but the rough bit isn't - it judders the steering quite badly.

Apologies for this elementary stuff. Any advice would be appreciated.

Cheers,

Ben

[Tims Triumph]

Twin SU's?

[Essexwriter]

Twin SU's?

No, single SU.

[Jon Tilson]

Let me refer you to this....
https://www.dollywiki.co.uk/wiki/SU_Carburetor_Tuning

Although written mostly with twin SU's in mind the bits about the fast idle screw are what you need I suspect.
I also reckon the piston lifting pin isn't actually lifting the piston. Take off teh air filter plumbing so you can see the carb piston and do it with a screwdriver.
That will help you get the idle mixture close, and hopefully help identify the problem.

Your worst case scenario is a worn throttle spindle letting in air, which will mean your idle screw doesnt really work at low rpm as air gets in round the spindle.
You can test for this by spraying wd40/easistart/carb cleanrer aerosol of choice on the throttle spindle....if revs pick up its sucking it in and burning it, so you need rebushing.

Jonners

[Essexwriter]

Let me refer you to this....
https://www.dollywiki.co.uk/wiki/SU_Carburetor_Tuning

Although written mostly with twin SU's in mind the bits about the fast idle screw are what you need I suspect.
I also reckon the piston lifting pin isn't actually lifting the piston. Take off teh air filter plumbing so you can see the carb piston and do it with a screwdriver.
That will help you get the idle mixture close, and hopefully help identify the problem.

Your worst case scenario is a worn throttle spindle letting in air, which will mean your idle screw doesnt really work at low rpm as air gets in round the spindle.
You can test for this by spraying wd40/easistart/carb cleanrer aerosol of choice on the throttle spindle....if revs pick up its sucking it in and burning it, so you need rebushing.

Jonners

Thanks Jonners.

It's a bit dark, but I just sprayed WD 40 round the spindle and - truth be told - quite a bit of the rest of the carb. The revs didn't pick up, but I did pull the choke cable in and out, moved the jet assembly up and down a couple of times, and then magically the idle screw started working. Then I realised I'd left the choke out about a centimetre, so put it back in and tested again. Idle screw still working. The mixture was I think on the lean side - quite a splashy beat coming out of the exhaust - so I enrichened it and it's now a bit too rich and lumpy. But it'll do me fine till the morning when I can fine tune in daylight.

One thing - the rhythm of the engine seems to rise and fall very slightly - almost imperceptibly - though at this stage I think it could be my mind playing tricks on me.

Thanks for advice. No idea what that WD 40 shifted or did, but it has certainly done something good.

Cheers,

Ben

[Essexwriter]

The carb wasn't the problem after all.

Tried starting her up yesterday morning. Took an age - as she had the previous morning (I had put that down to the cold).

Then I found I couldn't get her to run except at half choke. Anything less and she'd die.

So I got some Wynn's Carburettor Cleaner and shot a load of that through the carb this afternoon. I followed that with a half bottle of Redex direct into the carb and stuck the air filter back on.

Same problem. Wouldn't stay running at anything less than half choke.

So I unscrewed the fuel pump and pulled out the filter. It was about 2/3 blocked with what looked like metal shavings - assuming they were bits of rust from fuel tank. Perhaps dislodged by the experimental addition of Redex the previous fill (I know lots of you say it doesn't work - but I wanted to try it for myself).

So I cleaned the filter out by firing Wynn's through it, replaced it, and hey presto - the engine began to run like a maniac.

I gave the carb and idle screw (now working beautifully) a few adjustments by ear, and I've now got an engine that's running more smoothly that I remember.

Let's just hope it starts up again in the morning... Think I'll be investing in an inline fuel filter too. I found some of those shavings in the oil when I gave her an oil change a couple of weeks ago.