TB42s missing, wont reve & back firing though carby

[GQ TANK]

TB42s (carby)

The truck has developed a fault.
The truck was running perfect- pulling well. On the way back from work it started playing up.


Its missing, wont rev and backfiring though the carby - will idle (LPG and Petrol)

I have replaced the peritonics, new coil, new dizzy cap, extended rotar button, leads, plugs, inlet manifold gasket check the exhaust - no leaks. checked and set the tappets. Checked that the dissy is in the correct position. I have a new battery

No bubbles in the water
No water in the oil

My gut feel is that it has done a head or cam

Im going to check the compression tomorrow - and run it with the rocker cover off to check that all the tappets are moving

Any suggestions?

[Drewboyaus]

Not sure but sounds a little bit like what happened to Evil on our recent Dargo excursion. His was running very rich and missing all over the place.....Pretty sure his is a very similar setup to yours.
Hit him up with a pm and see where he's at with it. Have a funny feeling he was going to rebuild the carby as a start.

[pearcey]

Sounds very much like a condenser

[mudnut]

Backfiring can be caused by: faulty EGR, ignition timing, valve clearances, damaged valve spring or sticking valve, intake leak, carby float level or thermostatic air cleaner system cactus. I hope it is one of the easy fixes for you.

[mudnut]

Lack of power is all above plus more to check : Fuel filter clogged, distributor shaft worn, faulty dissy cap or points. Incorrect spark plug gaps, dirty air filter, ignition coil, brakes binding, auto fluid low or slipping clutch. Wrong octane or shitty fuel, clogged carby jets. I would assume it is one fault causing both problems, but It could be multiple faults.

[GQ TANK]

Was running perfect on petrol and lpg. Now playing up on both missing, backfireing if IO try to rev it.

Timming right, new plugs - gap set correctly.
New leads, dizzy cap, new flame thrower coil new pertonics - old was doing the same, canot be fuel filter as both fuels are doing it. Tappets set, cannot be carby jets - both fuels, carby is NOT loose, manual / clutch has done less the 10,000km. swapped rotor button with my spare extend rotor. I have the air cleaner off and it still back fires. No condenser - running pertonics

[mudnut]

Yeah, I just copied it all out of my Haynes manual. So an air leak may be the go. Spray some wd40 around the inlet manifold and outside of the carby, and see if the revs change at all.

[GQ TANK]

I replaced the inlet manifold yesterday as I was thinking the same - no change. The carby is tight - no leaks.

I'm nearly at the point of thinking its the head or head gasket.

Im going to rip the rocker cover off it tomorrow and fire it up - make sure all the tappets are movning (had a round cam in my old rangie a few years ago)

[mudnut]

If it has a choke break diaphragm, it could be split, or even the auto advance diaphragm at the dissy. Did you check the manifold face against a straight edge before refitting it?

[GQ TANK]

More info-

Just done a compression test.

cylinder 4 is at 135 PSI
All other cylinders are at 150 - 155 psi

Also noticed number 1 drops down to 125 psi after short time - leaking valve?. All other cylinders hold there pressure for a couple of minutes

Also I gave it a run with the rocker cover off 0f looked like all tappets where moving correctly

[threedogs]

Yeah, I just copied it all out of my Haynes manual. So an air leak may be the go. Spray some wd40 around the inlet manifold and outside of the carby, and see if the revs change at all.
That was my guess
Ah ha Dual fuel I think you are running too lean causing it to back fire on the condenser there is a small screw with a spring on it turn that out 2 flats of the hex to make the mixture richer, remember where it was. 99% of all gas problems are electrical, be it bad leads[dirty] bad plugs ,electrical system needs to be on top of its game to function correctly
Does it do the same on gas as it does on fuel, gas is a PITB it drys out carbies allows for hotter running temps.
will melt an alloy carby to a puddle in 4seconds flat if not set right

[GQ TANK]

Tree dogs, thanks for the feed back - but its doing it on petrol and gas. I had a simalar thought - swpaed in my spare mixer - still the same problem.

[threedogs]

you'll need to hook up some vacume gauges, they'll tell you exactely what you don't want to hear
might be your valve seats are shot from the gas and recessed

[Petrolling]

Did you find the problem mate?
I've been have some trouble with my carby lately, they are sh*ts of a thing

[GQ TANK]

Not yet - i havepulled the head - notong sstood out as the issue - will be fitting a spare head his weekend.

[Bushy674]

Not to be presumptuous, but firing back through carb speaks to a timing issue, how's all your connections for your ignition system, I am bad for the KISS theory, it's usually the simplest of problems that cause the drama, or in this case I hope it's the simplest thing that's easy and cheap to fix! Best of luck!!!!