Hi guys,
OK as you may know I run my 351 on LPG only, and I have done since putting that engine in. When I first got the Fairlane the engine came out of, it ran fine on both petrol and gas but previously my car had only run on gas, so when I installed the 351 I only hooked the gas up - the petrol side of things hadn't worked in my car since I've owned it, like 12 years or something. Anyway, with LPG going up and up with the excise etc. its now at a point where petrol's cheaper (at least around Adelaide) if you use the `LPG more than 50% of petrol' rule. That, combined with my tank needing an inspection in 2013 anyway, is making me consider just pulling the gas system out and running it on petrol.

So....given that the carby (600 holley) ran fine on petrol 2 or 3 years ago but hasn't had petrol thru it since, do you think it'll need a rebuild, or just run petrol thru it and see how it goes? Obviously I'll need to pull out and clean out the tank, fuel lines etc but I'm just curious about what you all think about the carby...I will probably end up just running petrol thru it and see how it goes but yeh, just seeing what you guys think.


Gaskets would of shrunk from drying out.
Will need a kit at least put through it.
LPG at the moment is expensive because its the Northern Hemispheres Winter and our price is set accordingly.
It will get cheaper over Winter.
Duel Fuel Style setups are always crap. Fit a 425 on your 600 baseplate and get the ignition curved for gas only and it will use less fuel.
Also curious what other LPG users think generally about the notion of using petrol over LPG ..what are you thinking about the excise and pricing? Has it got to the point that there's no advantage to LPG?

if you use the `LPG more than 50% of petrol' rule.

The excise is 2.5 cents per year until it reaches 12.5cents. It's currently at 5c and will be 12.5c in 2015.

From the feedback I get my customers are using on average %30 more LPG then they would use petrol, with EFI vehicles fitted with impco or venturi systems.
With carby engines the ratio favours LPG a little more as carbs just don't get the mileage that EFI, but it doesn't effect the LPG.
The break even point with my AU was when LPG was at 76c petrol had to be 24c/L dearer to end up with the same running costs. Any more then that was money saved.
If you are looking at petrol at $1.38 LPG at 80c is still a decent saving.


A 351 should have a 425, not a 300. If you decide to stay LPG find a second hand mechanical secondary holley base and fit a 425 straight to the base, the 300 through a full carb body like you have is not very efficient.

Then setting the correct advance curve in the dizzy will improve both power and economy if it hasn't already been done.

A carb base, impco425 and tank test should be able to be had for under $1000. Calculate the savings based on the %30 usage rule, you only need to save 19.32 a week to pay off $1000 in 12 months but you'll get ten years from the tank and easy 5 years from the 425 before it might need a $50 diaphragm.
Id'd rather spend the money on the gas system to save $1000-$2000 a year then spend money fixing the petrol and paying that extra in fuel. Petrol isn't going to get cheaper, it might fluctuate a bit, the trend will always be up. Just wait till gillard puts carbon tax on fuel. (cos we all know the mole will do it one day.)

Basically you take the elephants truck setup off your original carby and through it over your left shoulder.
Remove the throttle body base from your existing 600 Holley and fit a 425 Impco mixer to it.
This is the 425 Mixer
http://www.ebay.com.au/itm/NEW-IMPCO-42 ... 27cdf65d3e

Existing convertor should be fine.

Cool! If I was to just bolt this on and hook it up I suppose I'd have to get the gas re-tuned? Like adjusted and so forth?