Mud-club
Vehicle & Technical => Defender => Topic started by: automania on May 10, 2007, 16:24:09
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got a v8 90 wth a dy lpg kit ftted. on overun it quite often backfres through the carbs, ts running on a single mixer, have tried altering the timing but hasnt made any dfferences. anybody experienced this? cheers
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try giving rangeroverblues a pm or thread in rrc/disco section, he is very very clued up on v8's and lpg systems :wink:
dan
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Several things that need looking at.
Mixture, could be a bit weak (like I'd put money on it TBH), possibly made worse by the system going out of tune.
Valve problems, LPG is very dry and can lead to valve wear. If you are unlucky like me it could also be caused by incorrect set-up for petrol, I could destroy an exhaust valve in about a minute with our first V8, 'till I figured out what the previousd owner had done (the donkey). Compression test first, though now I'm after a leak-down tester.
Timing, set it up for petrol, it will be a bit gutless and may sound a little hollow on LPG but should run ok. I run an ignition advance processor (had trouble with it mind you) because you can over advance the engine for LPG. Unfortunately that makes it harder to start and will damage the engine if left like that for petrol. LPG has an octane rating of about 112-115, unleaded is about 95 and 4 star 98 but LPG burns slower, so ideally a much higher compression ration and/or advanced timing, but like I say it isn't safe for petrol so set up as per the manual.
Carbs, you have stroms or SU, both should ideally have piston lifters for LPG as the variable venturi should be wide open. Otherwise it can cause some running problems and also premature needle wear, on account of there being no petrol on the needle to lubricate it.
Given that it's popping on over-run I'd look at mixture first (may need help with that) then your carbs. BTW have yuou noticed your MPG on petrol get worse since the LPG kit went on?
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sorry for the late reply been on a stag do then had computer probs. anyway, the mixture thing may be part of it as i have turned it down as much as poss to try to maximise mpg currently getting around 10 or 11 on 90% motorway use.
when i got the motor it ran fine on petrol, on fitting the lpg i noticed the prblem and so altered the timing slightlty opting for the bit at a time method, tho it seemed to make a difference at first it then seems to have got the same again. one strange thing with the ignition is the wires that come from the amplifier under the coil were near enough at full strecth, not sure what the crack is with that.
as for petrol mpg i havnt run it on petrol for ages. cheers again