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Trouble on Petrol.......

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A little trouble with the truck this morning. Being a little low on LPG, I decided to give the girl the run to Sheffield from Manchester on unleaded.

Going on to the M67 from the M60 there is a sharp rising slope, and I thought I detected a problem in third gear. Then I had to wait until the snake pass to test further. Sure enough, in third, while climbing hills, just as she reached 4000 engine rpm, she stutters slightly, drops to about 3800 engine rpm before going back to 4000, then stuttering again etc. Some sort of fuel starvation perhaps….?

Now given I’ve been driving it on LPG for weeks, and over the same route every working day, I stopped in one of the lay-bys, and switched to LPG. A couple of miles further along the road, and there I am heading uphill in third, with the old girl fairly screaming (but managing without any problem) at 7000 engine rpm.

Any ideas folks? All help gratefully repaid in beer if I ever meet you… :P:P:P

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Often in dual fuel vehicles the timing is advanced to run better on LPG. You may find that when you run on petrol it is too far advanced and you are getting pinking (pre-ignition) at the higher revs under load and this is causing your issue. Did you also notice a feint knocking noise (amongst all the other noises of a V8 Defender hurtling down the motorway :lol: ).

If this is it, maybe worth trying higher Octane petrol which may calm it a bit, or backing the ignition off a tad.

Option 2 is if you are on carbs, IIRC some people have reported the (carb) pistons drying out when run only on LPG. Not sure of the full story (grown up maybe along soon), but maybe worth check of oil levels in the dashpots on top and their smooth movement.

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twist the little plastic caps off and fill to the top of the inner tube (becomes obvious when you take cap off) and fill with ordinary engine oil. When running on lpg they do use some oil from the dashpots cos the lpg doesnt have the lubricating properties of petrol, keep an eye on it, just add it to the list of regular checks like oil/water :P

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Well, I opened up the dashpots last night and they were very dry. So duly topped them up and headed from Sheffield over the hills to Manchester running on petrol.

Still sputtering at 400 revs in both 3rd and 4th gears....really does feel like petrol starvation....also used a bucket load of petrol yesterday for the distance covered....half a tank for 85 miles. Not happy.

She is in my very-trusted garage today for final electrical split-charge work and one or two bits, so my man will have a look at it today.

thoughts please....fuel pump?? filters anywhere?? mucky carbs??? I really dont know, any advice gratefully received.....ta.

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If it's using a lot of petrol I wouldn't think it was filters but could be wrong, could be the needle valves in the carbs (or one carb like mine does) sticking part open and overfueling but then it wouldn't propperly run at low revs.

Are both vac pipes on the dizzy?

And it could also be spark related, like mucky pick ups in the dizzy cap or dirty, burnt plugs or owt ta do with the sparks.

Run out of ideas now :lol:

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Update........my man tells me that the fuel filter was "quite badly blocked", for now it has been removed and is running like a very speedy swiss watch....... :P

Split charge system all installed, all electrics finally tidied up, all works complete.....for now......

Picture of new dash later this evening - bet you cant wait!


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It sounds like the floatbowls are not holding enough fuel for some reason, then starving the engine until the valves open and fill up the bowls with fuel again.

They don't hold much anyway as they are on a tilt.

just a thought. :)

Don't like to gloat but :i-m_so_happy:

Glad you got it sorted, mines back on the road after a rotor arm failure (keep one handy) and keep on revin' :lol:

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I'm still curious as to why you'd need to rev it that high unless you were towing a house up a cliff or something. :huh:

As earlier, I was testing it to try to determine if the problem was one of petrol or lpg or both. Indeed it turned out to be petrol only, and I await a new fuel filter. Now running like swiss watch.....

Normally i keep to 5000 revs! :blink:

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