Advice needed before i I sell this piece of s*#%

Hey guys,

Desperately need some advice and or help please. Despite running brilliantly, my fuel consumption (Carbied RB30), has been getting steadily worse for some time... I just topped the tank up and it used a staggering 26.5 litres per hundred for low revs / stress 2wd suburban driving.

I cannot keep up with such huge fuel usage, particularly when it doesn't have the power / torque normally associated with that kind of fuel bill... It's no TB48. It also means that even with my long range (147 litre) tank, I cannot get more than the high 500 kilometre mark from a tank, which sucks!

I can't think what else to check, I've gone over the mix, (near perfect and carby only professionally rebuilt late last year), timing, vac advance, filters, new oil, distributor cap, rotor, new spark plugs correctly gapped, leads aren't old, took the foam sock off the snorkel, drove it hard, drove it gently, loaded, unloaded checked tire pressures, rotated tires, don't seem to have dragging brakes etc etc.

I must be missing something, but I can't think what could be causing such high figures all the time. I love my patrol and don't want to even consider selling it but nothing seems to improve it, best I've had for a while has been around 20-21 litres per hundred and not often...

Now I do have a 2 and a bit inch lift, and 32 inch BFG's (around 20k on them), and a rhino roof rack. It has a safari snorkel, and extractors, but otherwise is a stock engine. That said, these things haven't changed and my usage figures used to be somewhere around 17-18 MAX.

I have had conversations with a mechanic or two now, and had the car looked at, but they couldn't offer any other ideas, and I can't afford right now to start replacing parts that don't need replacing if it doesn't fix the problem. I don't expect to be doing any serious fuel economy runs, but it is ridiculous now and making me a bit crazy...

Sorry, rant over, Does anyone have any other ideas or can someone recommend a really good mechanic in Perth who can actually resolve the problem? I don't mind paying to have it fixed, but I don't want to pay for non-fixes. Please.........

Do you feel like you are filling it up more often? Maybe the odometer is reading wrong and you are actually travelling more kms than it is showing. Check the speedo againest a GPS.

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Thx mate, yeah speedo is slightly out, at 100 indicated, I am travelling about 103/104, that variance shouldn't make such a big difference I'm guessing?

Left-field... pinhole in a fuel line somewhere?

Fuel pump slowly failing?

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Originally Posted by mudnut

Fuel pump slowly failing?

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What economy do you get?

Anywhere from just under 14 Highway to around 18-19, offroad driving.

Maybe the fuel return solenoid is stuck open, making the fuel pressure too low, so you need to put the boot in it to get power. A dynotune or a fuel pressure guage might be the best guide to show whats up.

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Originally Posted by UncleFrosty

Left-field... pinhole in a fuel line somewhere?

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Thanks, I will look over the lines, I have replaced the hoses in the engine bay, feed and return, but never know, or maybe the hoses near the tank, I will look in daylight

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Originally Posted by mudnut

Anywhere from just under 14 Highway to around 18-19, offroad driving.

Maybe the fuel return solenoid is stuck open, making the fuel pressure too low, so you need to put the boot in it to get power. A dynotune might be the best guide to show whats up.

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Thanks mudnut, hadn't thought of the fuel pump or solenoid, the throttle response and power aren't a worry, it holds highway speed and accelerates pretty well for such a heavy vehicle. Regards the fuel pump, it's electric and in tank isn't it?

Maybe I'm tired but how would the pump slowly failing cause poor economy? Not doubting, just curious, and how would I test the pump?

I may have to find a dyno tuner in Perth that can work on Carbied motors, anyone know a good one?

Easy and cheap to replace. I just had to recently, because on a long trip mine failed then came good, failed then and we made it home. If it isn't giving the right pressure, the engine requires more fuel to run.
Also check that the pre-heat flap is closing off when the car is warm.
The fuel pump is in the top of the tank under the rear compartment. There is a cover that gives you access. Just lift the carpet and you will see it.

Hmm, I know that Carbie's are a low pressure arrangement, I wonder if I can get hold of a pressure gauge and check fuel pressure coming through to the carb? That would at least point to a pressure problem in the fuel system prior to the carb

Did you replace the points while doing that other stuff?
A good electronic ignition setup will help a lot with economy but ofcourse it would be good to find out what's causing the bad economy in the first place.

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The float level ok?

Tank leaking?

Any smoke and colour from the exhaust at idle, cruising or accelerating?

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Originally Posted by Patrol'n

Thanks mudnut, hadn't thought of the fuel pump or solenoid, the throttle response and power aren't a worry, it holds highway speed and accelerates pretty well for such a heavy vehicle. Regards the fuel pump, it's electric and in tank isn't it?

Maybe I'm tired but how would the pump slowly failing cause poor economy? Not doubting, just curious, and how would I test the pump?

I may have to find a dyno tuner in Perth that can work on Carbied motors, anyone know a good one?

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Check the float level of the carby from the slight glass while idling and revving. There is no easy way to check the float level while taking off unless
you setup one of those el cheapo inspection camera. But I reckon idling & revving test for the float level is good enough in many cases.

I would've thought a low fuel pressure would cause lean running issue by making the float too low, and the high fuel pressure vice versa.

What you can do is to take the first spark plug out and check it for soot build up, clean it and put it back and drive for few minutes and check the
spark plug again. If it's building up soot in no time then you know you have a carby rich running issue, which easily translates into a fuel economy issue.

Another thing you need to make sure is the auto choke. Check to see whether the auto choke open up completely after few minutes or warming up. You need to remove the air cleaner to see of course. If the choke is not opening up then the continuous rich running will mean poor fuel economy.

3km/L is pretty crappy fuel economy for sure. You have to find the culprit and fix it, 'cos it's not just about the fuel economy. It is saying there's something else is wrong with the engine for that poor economy, so it's a good idea to find out before taking off for any long treks.

Compression test also might be a good idea to find out whether the head gasket is on it's way, 'cos that can affect the fuel economy as well.

As a relative noob, what difference does the float level make to running, how do I adjust it (if I need to), and what level should it be at on the glass?

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Originally Posted by Throbbinhood

As a relative noob, what difference does the float level make to running, how do I adjust it (if I need to), and what level should it be at on the glass?

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Typically it's the half way mark as you can see from the sight glass.
You obviously have to take off the top of the carby and take the float out & carefully bend the metal hook either direction depending on whether
you wanna raise or lower the float. You can do that without pulling the carby out of the engine, but I prefer to have the carby on the bench 'cos it's
lot easier and you won't lose any small bits and pieces as it can happen while working with on the engine.
Few trials may be needed get the float level right.
It's too easy to quickly pull the carby out in RB30 & TB42, so it's no problem.

As I understand, too low float level mean the possibility of fuel starvation on high revving or when loading, and too high float means possibility
of running too rich & flooding.

Float level in mine's is quarter high atm 'cos mine has an issue of running too rich which I temporarily 'fixed' by lowering the float.

One of my spare carbies are beyond help by the looks of due to excessive wear.
There is a time eventually we have to replace the throttle body due to wear.
It's not easy to rebuild a worn throttle body 'cos the mechanical throttle shaft is bound to wear out eventually.
They can also warp over many years, but you can machine it(or sand it on the glass sanding table) to fix that.
Since the throttle body is not available to buy on it's own, a new carby or a good used one is the way to go.
Used ones are a waste of money unless you get them super cheap. Couple of years ago I paid $100 for a used one.
Waste of money with the piece of crap from the wrecker.

Ebay is selling brand new ones for around $300, so it's a waste to spend good money on used ones.

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Interesting stuff! Thanks Dom! Mine's running fine so I wont touch it, but always good to know :)

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Originally Posted by Throbbinhood

Interesting stuff! Thanks Dom! Mine's running fine so I wont touch it, but always good to know :)

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Yeah, don't touch the bastard if it's running good. :)
What I would recommend you though is to spend couple of hundred bucks to get a wideband AFR gauge kit and use it to tune the carby(AFR mixture) or even cheaper get a Gunson Colortune plug(fifty bucks) and use that. Gunson & AFR gauge is the best investment so far for me, 'cos I use the Gunson to tune the bike carby as well.
Mine's running like crap 'cos of the dual fuel challenge, so I don't have a choice but fiddling with it once every few months. I will be going EFI sometime in near future. I am not kidding myself though. EFI also comes with it's own set of challenges with dual fuel and other electrical issues. I'm only considering EFI 'cos of the 'need' to go turbo in future.