Running a bit rich...

[spandit]

Thing is, jets haven't been changed since I got the truck and it was running fine before.

I've now set it so the throttles close when I let off the pedal - makes it stall but at least it's not having the chance to foul the plugs. An imperfect solution.

I've also ordered some more 12mm braided hose to remake the balance tube that I'd cut, in case turbulence in there is a factor (although seems unlikely).

Once underway she runs beautifully, plenty of oomph, it's just initially I get a lot of popping/banging etc.

[Jim LaGuardia]

Two thoughts, 1 idle selonoids not working(#9 breaker) to bypass to test, remove them and plug the ports with 8x1.25 bolts, just hand tight only
If popping goes away you have isolated the problem.
2 Leaking float valve(look down top of carbs as engine is running) there should be no gas dripping onto the throttle plates.

As a last resort, I would pull the fuel sender and look into the tank. I once found 5lbs of sand in the tank of a truck that kept having strange running issues.

[spandit]

I've tried pulling the wires off the solenoids - the revs go up, until they're all pulled.

I have a clear fuel filter & it doesn't look dirty but I'll bear that in mind.

Regarding the float valve - I took one off & tried blowing through it whilst pressing it closed - didn't completely cut off. You could be onto something - I'll have a closer look

Thanks for reply. Learning a lot about these engines...

[spandit]

Had a look down the carbs today as the engine was "idling" (sounded like the Blue Man Group playing with dustbins) - couldn't see any obvious drips of fuel. Couldn't see anything, in fact - I guess the fuel is being atomized properly.

Will check the timing with a gun as despite my fancy-schmanzy ignition system telling me my timing is correct (and I can adjust it +-10º on the fly) it might be a factor.

Manifold gaskets are shot (4 on order) which is why I get a lot of popping when the revs change but wouldn't've thought it would make things so bad at idle

[spandit]

Think we're getting somewhere...

Spent most of today taking both carbs to pieces, blowing several hundred litres of compressed air through them and then reassembling. I also replaced the fuel hoses and filter. Sand blasted all the plugs thoroughly (after spending most of the morning making a new trigger wheel to bench test the coilpack)

After a bit of fettling, got her running and she sounded much better - no huge backfires etc. However, looking down the carb throats, the front one was wet with fuel - it was spraying out of the injection tube for cylinder 2. I couldn't remove the injector tubes when I stripped the carbs - didn't want to use too much force. Looking at the manual it seems perhaps the accelerator pump valve is at fault?