Here goes - '71 fasty (twin manifold balance pipes) came to me with mismatched carbies - one emissions-style 70s carb and one mid-60s model (big mixture knob, idles throttle-valve open).

That was never going to work, so I switched out the worse one (in this case the later one), found a near-match (apart from the number of transition ports) for the earlier one, had both carbs' throttle-bodies rebushed, whacked a kit and a clean-up through them, set 'em up according to the mid-60s workshop procedure ("Look, Listen, Do It Better" bulletin off TheSamba), and, while they needed a monthly regime of twiddling around to keep the idle even, the whole thing has worked okay for a few years.


Until now. Bothered by a sudden super-rich, boggy, misfiring idle condition, I pulled the passenger-side carb apart, quickly finding out that it had eaten the throttle-body gasket wall that seals the idle fuel drilling from the barrel. Replace gasket, too easy, right?


Yep. Reassembled, set it all up again to initial starting point, idle speed screws at "contacting lever +1 turn, mixtures at closed +1.5 turns, started it up - rich, boggy and a bit fast. Pulled the driver's-side carb, disassembled, found nothing obviously amiss (except it leaks slowly out of the float bowl plug). Float bowl fuel height seems okay.

Long story short, this thing is now idling with BOTH mixture screws completely closed and is still blackening its plugs. Performance off idle is surprisingly okay. Colourtune confirms both sides are burning yellow and super-rich. And it diesels horribly for about eight seconds on shut-off, which tells me the amount of black in the heads is probably off the scale.

Any ideas before I go completely insane and start building a fuel-injection system?

I am assuming that you have checked---- float levels,accelerator pump discharge nozzles (these have a habit of coming out and the engine eats them,the engine then runs exorbitantly rich as the fuel is sucked out of the orifice),the idle jet bleeder holes (the gasket often blocks these),fuel pressure,idle jet cut off valves (these come loose and allow fuel to feed in after the electro magnetic valve shuts them off? these are a few of the things that can give your symptoms particularly the dieseling.

Cheers for the reply. As stated, float bowl fuel height is fine. Both accelerator pump nozzles are there, both squirt (although I didn't check how much each, seeing as we're talking idling).

Know what you mean, though, since I once had a nozzle-less '69 bug that dumped a pumpload down the inside of the throat every time you hit the pedal. One carb had no full-load enrichment circuit, so I sealed the opposite carb's suction tube off with solder. Both electromagnetic cut-off valves work, were tight in their holes and I cleaned the tips out with compressed air.

Didn't check fuel pressure because bowl levels look okay and I don't have a gauge. Of your suggestions, that leaves idle jet bleeder holes - are you talking about the small holes adjacent to the main mixture port in the throttle body, or is there an idle air bleed jet (apart from the one that faces upwards from the float bowl side - they're checked + clean) that I've missed somewhere?

Another thought,are the ball bearings still in the accelerator pump discharge ports,these prevent the fuel being sucked out. The air bleeds are the holes facing up above the electro magnetic jet.
With both screws fully closed the fuel has to be getting past something,try another shim under the needle & seats.

Cheers- gave float bowl needle valves another shim each, still to test. But this just gets more hilarious. Adjusted fast idle cam rods to spec, i.e. 2.3mm gap between idle stop screw and butterfly lever with choke fully closed, top of fast idle cam.You'd think, wouldn't you, that this would give you at least similar butterfly-to-inner-surface-of-throttle-body gap both sides? Well, one side looks nearly shut and the other side is propped so far open that the edge of the butterfly is pretty much flush with the bottom of the throttle-body (choke fully closed). These babies have been seriously messed with. I'd be right in assuming I need to throw the manual over my shoulder and adjust until they at least look similar? And if so, do you have specs for butterfly gap, either hot or cold? Wish I had a Uni-Syn.......

PM your email and I will send some details,photos and any info that I reckon will help. Without a balancer you are only guessing,another way is to listen to the suck from the venturi with a tube but this takes a lot of expertise. I have a spare balancer if you are interested.

Okay, I'm throwing this one open - I've developed a theory about what's going on with these carbs. I think one or both of the idle mixture ports have been mashed around and distorted by being screwed in too tight - i.e. widened until there's no way to lean out the mixture enough without opening the butterflies so far that then the transition ports kick in and even more juice goes down the throats.

On the screw-full-closed setting one needle valve is hanging out into the throttle body throat about 2mm and the other one nearly 4mm. I'm starting to think that the best way around this might be to get a pair of matched late carbs that at least idle with the throttles fully closed, so I can fight this battle on one front at a time.

So, to anybody who has a late pair of matched stocker PDSIT Solexes in the shed - preferably in SA - and would like a few extra bucks, check my post in the Buy and Sell Parts forum.

And cheers to Grumble for his input....

Halle-freakin'-lujah - we're sorted. This has turned into a cautionary tale about trying to be logical and methodical when all you want to do is start kicking things.

Long story short - it was both float bowl needle valves. At some stage, an aftermarket pair of needle valves has gone into the carbs as part of a rebuild.

And these replacements, despite being slightly longer than the standard Solex babies, must have a hugely raised seat height compared with the originals. And, yes, I checked the float bowl height of both carbs on the bench, some time between balancing the accelerator pump strokes, cleaning jets, clearing emulsion tubes and generally dismantling and reassembling everything a dozen times.


I'm guessing that the float bowl levels looked okay on the bench because I was filling them by gravity feed through a plastic tube, which doesn't take into account that the fuel is actually being pushed in there at four or five psi by a pump.

Anyway, these needle valves are currently sitting below no fewer than four aluminium washers each - a few more than anything I've read suggests they'd ever need - but the car has been totally transformed. Not only can it now keep its spark plugs clean, but driveability, acceleration and idling smoothness are far, far better than they've ever been since I've had the car.


So a big thanks to Steve in the Hills for selling me enough parts that I could match up two throttle-bodies that actually look the same - that certainly can't have hurt - and to Grumble for sending me some carb jetting documentation and words of encouragement.

Yeah, mate, you nailed the nature of the problem a couple of posts ago. Cheers, guys.

A happy Type 3 auto is a pretty sweet and cruisy thing to drive.