another carb query

[phayeser]

Greetings. Be kind to me I’m new to carbs! Got my shiny red ‘85 sj413 1298cc, original carb, 3 weeks ago. It was running a little high when I drove it home so I turned the idle speed screw and it was sweet for 2 weeks. Hit a speed bump hard last week and then started cutting out when off the gas, decelerating, etc. I played around majorly with the screw (and have no idea how far off ideal setting it is now).

Its auto choke with a cable installed converting it to manual. Pulling the cable opens the choke (or closes the butterfly valve – took me a while to work out that creative use of the words open and close!) and I’m guessing that the valve stays open as long as the cable remains pushed back in. It tilts slightly open with the throttle as I think it should do. Holds idle okay but goes a little all over the place when I adjust the screw – not simply up when turned clockwise and down with anti-clockwise turn. When it sounds about right I will drive and it tends to go high again. So I gotta figure out why it dies after driving and then stopping. No idea how to get the screw back to a good position to set the idle appropriately with tach and turning the mixture screw – I’ve shyed away from turning this so far and don’t have the tool (do I need a tool?).

I drove it to the mechanic with a racing idle – drives fine like this and less likely to die at lights - pulling the choke cable then stops it over-revving when I stop. But if I drive away like this it hesitates (guessing this is normal as not much air getting in), so pushing the cable sees me right again, probably with a super rich mixture though?

The mechanic has no clue (rarely sees carbs I guess and is confused with the bits missing due to conversion) - so I’m gonna take the truck on Monday and hope to get it set in time to drive home for Xmas as I got this for the misses while I’m in between cars. Hope I’m not dreaming.

Anyway, looking at the carb, it seems the fast idle lever moves freely in any direction given that the cam is removed and there is no spring (whether by design or accident) – so I wonder if this could be anything related to the source of the issue??? I don’t understand what the throttle valve should be doing at any rate.

Another confusing aspect for me is it takes a while to warm up – but the fan runs permanently from starting and I’m wondering if this is another PO fix or is it usual?

Shit sorry such a long post! What I plan to do is hit the carb with plenty cleaner (can I do this in the car?) and throw some additive in the petrol while I’m at it in case dirt has gotten down there somewhere (after the bump?!). Then fiddle with the fast idle lever – maybe it needs a spring – try to get the idle screw right, and then follow up with a few things that came up in searches which as yet I don’t really understand fully:

Pull out the butterfly valve when it’s warm and test.
Is the green plug (fuel stop solenoid) wired up?
Check fuel tank breather pipe
Check for air leaks
Is the wire to the fuel cut off broken?
Mixture solenoid gone bad
Choke lever return spring
Fuel pump
Float level setting
tps switch on a carb?
that ******* plastic cog with spring around it.....(?!!!)

Huge thanks for reading/helping/giggling.
I know an SU etc will fix but I wanna get this right first if I can. Must post a pic of the carb on Monday.

[Tramp]

I can't help much with the carb but it sounds like the big bump has disturbed some crap in your fuel lines which in then had made it to the carb. Hopefully I good dose of cleaning should sort it!

As for your fan, its a viscus coupling so it should turn all the time, but with no torque behind it (free wheeling) until it gets to a certain temperature. When the coupling engages, it will run at the same speed as the shaft. I think the way to test it is with an old newspaper, you ease it into the fan blades and when its cold the fan should stop and when the engines up to temp it should shred the paper!

[Darrell]

I had a bit of a hit offroading once and had the same problem afterwards. Turned out the inlet manifold gasket had starting leaking. The best way to test this was to give it just enough throttle to keep it running and then spray brake/carb cleaner around the inlet manifold. If it is drawing in air the revs will increase with the spray. Please be careful though as the spray is highly flammable. Yes the fan runs all the time but is just idling until the heat makes it run fully, this shouldn't make any odds to the warm up time as the thermostat will/should not allow water around the radiator until fully hot anyway. Some people suffer from overheating when offroading in the summer and remove the thermostat altogether so as you've not had it long it may be worth looking to see if you even have one.

[phayeser]

I meant to respond to this ages ago. Good to know the fan should run all the time. I shot the carb with loads of cleaner and drove home for christmas and back - 400miles without needing to lift the bonnett:}