Thread: Help required - Dual fuel won't run on petrol

Could be a worn cam but also could be burnt valves. Unfortunately the only way to really find out is to pull off the inlet manifold and look.
A quick and dirty way would be to take off the oil pump cover and look at the oil pump. If the cam is so bad it will not start , then the oil pump will be cactus from the bits of cam lobe in the oil.
Gee it would have to be low to not start. 3.5s will go with almost no compression.
Regard sPhilip A

I would check other things before changing the cam.
Somebody (LRH I think) posted a couple of good pages on vaccuum pressure a few days ago. I will try and find it again and post a link here.

Andrew

As with the others, before you commit to doing expensive cam work, here are some experiences I've had with a v8 of similar age and LPG (Admittedly the LPG was with a Holden).

1. Normal 84 RR V8 with CD175 strombergs - refused to start one day, only started with choke applied. Low manifold vacuum. Cause: Inlet manifold loose - despite new gasket 2 years previous - steel gasket damaged/useless. Remedy: Take manifold off, fit new ( and inexpensive) metal gasket and plenty of sealant. Cautions: Have imperial thread tap handy, very easy to damage threads on aluminium with steel bolts. If the torque on the manifold isn't right, air will still get in.

2. LPG dries things out like you wouldn't believe. Check carby's over ( Whatever they are, you didn't say what sort are on it). PS fluid is good for the float damper if you run CD's or SU's

3. You may as well take the manifold off anyway and check the cam and lifters. You'll be able to take pics and show (other) mechanics -

4. An 85 RR engine is now 21 years old. That means it takes more than usual vigilance to keep it running. All sorts of nuts and bolts come loose over 21 years, and things go wrong. Knowing that, be somewhat prepared with spare parts and know how the engine goes together and it will get a reputation for getting you home - not fault free, but what LR is.

I'm suprised it still runs ok on gas as gas needs good vacumm to draw it into the cylinder ? If its the original motor then it would definately need a new cam/ lifters /chain by now.

Thanks for the tips and I'll file them for next time.

Sorry if any confusion but it's a County so I presume Strombergs.

The 4.3L conversion was done I don't know how long ago but I'm guessing it had a full overhaul at the same time.

But the answer was...








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The adaptor plate beneath one carb was installed rotated 90 degrees from what it should be.

The manifold was vented directly to the atmosphere, so lack of vacuum and lack of effect from the carbs. The cause of the problem was the inexperience of the mechanic ( ) Why it ran on gas I don't know.

Now just need the gas certificate and I can register it tomorrow.

Steve

I think it could be the adaptor plate beneath one of the carbs. It may be installed rotated 90 degrees from what it should be.


I had an old V8 on duel fuel it used to play up on petrol due to the advance on the dissie to make it run on gas.

Is it possible to tune a V8 to run properly (no miss firing) on both LPG and Petrol?

Originally Posted by dobbo

I think it could be the adaptor plate beneath one of the carbs. It may be installed rotated 90 degrees from what it should be.


I had an old V8 on duel fuel it used to play up on petrol due to the advance on the dissie to make it run on gas.

Is it possible to tune a V8 to run properly (no miss firing) on both LPG and Petrol?

You've got me, Dobbo. What's the sound of one hand clapping?

Apparently it needs to have "limp home" capabilities on petrol to qualify for a Gas Certificate though it only needs to run on one to get a Safety Certificate - go figure.

I'll find out tomorrow how it's really running but the mechanic tells me it's fine on either. But then he didn't know how to reassemble the carbies, did he?

Steve

the vacuum doesnt run fuel into the carbs.....the fuel pump does this.....
if there is insufficient vacuum....you must have a leak in the inlet manifold....
as stated in the posts above......
what this means is that the engine is sucking in air which hasnt gone through the carby to get mixed with fuel....
so you have a very lean mixture which is too lean to burn.....
the fact that its running on lpg may mean that it is running too rich to compensate.......
meanning you are wasting fuel....


also running an engine too lean can lead to overheating in the cylinders and eventually piston meltdown.....

so check your inlet manifold for vacuum leaks........