I have a 1985 Holden Drover (Sierra) with headers and 2" exhaust and I'm still running the original carby with no problems. With the larger exhaust the engine breathes a lot easier and you can rev the motor longer and harder. I'm regularly revving the motor up to 7000 rpm. I could never do that with the original exhaust.
I suggest doing a compression test before changing the exhaust. If any of the pistons show less than 100psi I recommend that you fit new piston rings before fitting the new exhaust. Fitting a performance exhaust on a tired engine will only suck more power out of the motor.
I rebuilt my motor after 400k and now it goes like a bat out of hell and I'm still using the original carby. One of the downfalls of the aftermarket carbies is they suffer from fuel starvation on steep hills and in serious off road conditions.
If you're not happy with your original carby try overhauling it, overhaul kits are available. If you're not confident doing the job yourself take the carby to a carby workshop and let the pros overhaul it. Hope this helps.
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1985 Holden Drover Soft Top
Dual Batteries
Extractors & 2" Exhaust
Ported & Polished Head
2" Suspension Lift
75ltr Long Range Fuel Tank
150w Spotties x 2
4 Post Bullbar
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