I have recently started putting premium 95 fuel in to get better fuel economy as i have been getting 150km out of roughly 24L or 3 quarters of a tank of fuel in my 1200 ute. I ran the first tank of 95 through it and it ran fine after putting in half of a tank of premium for the second time it was running as usual but all of a sudden when i start it and it wont start and takes several attempts once it does it bogs down and stalls i managed to get it going and every time i stop in first gear it stalls but will start again first go. it runs fine once you get past 2nd gear but when you are going back down through the gears it backfires and rumbles real bad. It has just recently been serviced it has all electronic ignition high performance coil new high performance leads spark plugs changed 3000km ago extractors and 2 inch exhaust and a weber 32/36 carby which i bought brand new and fitted about 5000km ago it all ran fine up until this. Is it a bad batch of fuel, fuel pump, or just cant run on premium fuel?

Thanks

150km with 24l of fuel thats horrible for any A series engine i would think the carby is jetted extremely rich.

i have a weber 34 adm and get more than 200km from 18 litres.

as for your other problem of stalling it seems that your float level could be to high especially if you start it and you have to keep the revs up a bit for few seconds because its flooded.

if the floats high and you take it on a hill you may see the idle drop and engine sputter.

but you said it was after putting in 95 octane but worked before so maybe totally different problem.

thanks

any engine can run on premium fuel

Sounds like something went wrong with the air/fuel system. Like a hose cracked. or the jets got plugged.

Does it idle normally? Or only with the choke knob pulled out?

yehh i know the jets are too big but it was still running fine even though it had a lumpy idle i was going to down size the jets but was thinking of putting a cam in so the mechanic said to leave them for now. Yeh only had to use the choke for like 5 secs if even that to start it but only on very cold mornings. As for fuel consumption thats why i choose 95 octane to get better fuel economy and after running two tanks i started getting this problem that why i thought maybe the higher octane fuel maybe the issue as it was already over fueling with the bigger jets now with the better fuel it cant handle it??

You could have dislodged crud in tank. Premium usually has additives to get octane up. Your not using ethanol fuel are you? That's bad for fuel hoses in older cars.

naa used just normal premium vortex 95 i was using normal 91 before all of this started happening thought id give the 95 ago to try and see if fuel consumption improves..

I run my A15 on premium 98 octane and it never caused any problems. my carby on the other hand runs really rich so after driving for a bit ( like 2000kms or so ) on long trips it will gum/ fuel up the plugs. this is heaps worse on short drives or lots of idleing. i would check your plugs and at least try clean em or better yet get new ones. as statded before ethanol will do bad things to your car but simple higher octane pump fuel wont hurt.
Avgas is to high octane for a stock motor though.

High octane fuel requires the exact same air/fuel ratio, hence the same jetting as regular octane fuel.

yehh rightoo..Could it be that cause the jets in my carby are already too big but it was running fine as it was tuned on 91 fuel that now cause its getting more richer and cleaner fuel that it cant handle it hence the reason of why its running bad and bogging down, hard to start, and really back firey??

High octane fuel is not richer. It still uses the exact same jets as regular octane fuel. The only thing high octane means is more knock resistance, hence potentially can take more spark advance.

It's not generally cleaner either (does not have more cleaning additives). But if the fuel station puts one or the other in comtaminated tanks it will be a problem.

The reason for "running bad and bogging down, hard to start, and really back firey" is most commonly caused by clogged jets. Easy to clean with a Hitachi, but more tricky with a weber. You have to remove the Weber, remove the top and dump the fuel out and spray the passages. Or you could try this: leave the weber on the engine, remove the top and suck out the existing fuel with a cooking baster. Then remove the jets and suck the passages below the jets too.