Missfiring, occasional backfireing & hesitation on LPG

[billyj]

14-15:1 is too lean under power, its fine under cruise but on power you want to be richer more like 12 ish, try richening the power side of your lpg and see if it helps

[dom14]

14-15:1 is too lean under power, its fine under cruise but on power you want to be richer more like 12 ish, try richening the power side of your lpg and see if it helps

Ok, cool. I'll do that. I did richened it to 12ish or so couple of days ago when I was trying to sort out the spitting and backfiring, then I smelt unburnt LPG & thought I richened it too much.

[Bidja]

Sounding good (plugs, leads, and then mixture).

Your impco gear maybe old build but when set good you can leave it pretty well alone.

IMO set it up for your preferred fuel and for sure keep other fuel bits in your tool box if you get stuck. If you run LPG majority of time, go that way, but is always good to cold start up on petrol then switch over to gas and is beneficial to occasionally run say 20kms on petrol every couple of months (your cal) just to keep that side of your sys all in a serviceable condition. LPG is a dry fuel compared to petrol. I guess you do understand this...

[dom14]

Sounding good (plugs, leads, and then mixture).

Your impco gear maybe old build but when set good you can leave it pretty well alone.

IMO set it up for your preferred fuel and for sure keep other fuel bits in your tool box if you get stuck. If you run LPG majority of time, go that way, but is always good to cold start up on petrol then switch over to gas and is beneficial to occasionally run say 20kms on petrol every couple of months (your cal) just to keep that side of your sys all in a serviceable condition. LPG is a dry fuel compared to petrol. I guess you do understand this...

Yeah, mate, but it is a 'contentious' subject.
Starting on petrol is particularly a good idea in colder climate as the LPG converter need coolant warmth to function properly(I reckon some of them are built that way, probably not all of them).
I believe(which means my logic may be flawed ) starting on LPG has it's own advantages when the engine's cold 'cos petrol has solvent effect(colloquially called "wash effect") and when cold start an engine on petrol the mixture is super rich and that can cause extra friction on the piston rings, and cause extra wear until the mixture is stoichiometric. Since the LPG is not a good solvent 'cos it is a gas in normal temperature it probably won't have that solvent effect. It is my belief a properly setup LPG system can extend engine life more than a petrol engine.

And I agree with you after having this dual fuel RB30 for over six years. Dual fuel may be a tricky idea, even with hightech units like dual curve units to adjust the difference between two fuel's combustion style. I prefer to tune it for LPG, but then again it's using a petrol carby to control the throttle and idling(partly).

LPG causing extra valve recession is mostly due not tuning/timing it properly, I think.

[dom14]

14-15:1 is too lean under power, its fine under cruise but on power you want to be richer more like 12 ish, try richening the power side of your lpg and see if it helps

It jumps to 12.5ish when revving high on low gear to get power with WOT, but not under 'normal' power/load.

Does that mean I should still adjust it to be 12ish under 'normal' power?!!

[billyj]

12-13 ish under wot would be a good starting to try

[Bidja]

Yeah, mate, but it is a 'contentious' subject.
Starting on petrol is particularly a good idea in colder climate as the LPG converter need coolant warmth to function properly(I reckon some of them are built that way, probably not all of them).
I believe(which means my logic may be flawed ) starting on LPG has it's own advantages when the engine's cold 'cos petrol has solvent effect(colloquially called "wash effect") and when cold start an engine on petrol the mixture is super rich and that can cause extra friction on the piston rings, and cause extra wear until the mixture is stoichiometric. Since the LPG is not a good solvent 'cos it is a gas in normal temperature it probably won't have that solvent effect. It is my belief a properly setup LPG system can extend engine life more than a petrol engine.

And I agree with you after having this dual fuel RB30 for over six years. Dual fuel may be a tricky idea, even with hightech units like dual curve units to adjust the difference between two fuel's combustion style. I prefer to tune it for LPG, but then again it's using a petrol carby to control the throttle and idling(partly).

LPG causing extra valve recession is mostly due not tuning/timing it properly, I think.

Thanks mate for your comments. Have run the Navara ute (petrol injector fuelling) for now over 10 yrs on dual fuel mainly LPG and always cold start on petrol. I live 620m above sea level on the southern tablelands, NSW and at this time of the yr the overnight temp is warming up to between 5-12 deg C but in winter we have frosts nearly every morning and gets down over night to below zero nightly, down to minus 5 degC and on occasion to say minus 9 degC. So yeh the converter needs a bit of warm water around it. Do understand that valve recession is probably the main downfall running LPG (stellite valve faces and seats or similar are of benefit). All the best on sorting it out.

[dom14]

Thanks mate for your comments. Have run the Navara ute (petrol injector fuelling) for now over 10 yrs on dual fuel mainly LPG and always cold start on petrol. I live 620m above sea level on the southern tablelands, NSW and at this time of the yr the overnight temp is warming up to between 5-12 deg C but in winter we have frosts nearly every morning and gets down over night to below zero nightly, down to minus 5 degC and on occasion to say minus 9 degC. So yeh the converter needs a bit of warm water around it. Do understand that valve recession is probably the main downfall running LPG (stellite valve faces and seats or similar are of benefit). All the best on sorting it out.

Yeah, many of the LPG conversions done on EFI engine within last ten to fifteen years were programmed with an auto switch to start always with petrol and automatically switch to LPG after few minutes, AFAIK.
No argument, "wash effect" wear or not, starting on petrol makes sense in cold climates as the converter freezes up easily with LPG when too cold. For warmer climates, I reckon starting on LPG is a good idea.

[Bidja]

Yeah, many of the LPG conversions done on EFI engine within last ten to fifteen years were programmed with an auto switch to start always with petrol and automatically switch to LPG after few minutes, AFAIK.
No argument, "wash effect" wear or not, starting on petrol makes sense in cold climates as the converter freezes up easily with LPG when too cold. For warmer climates, I reckon starting on LPG is a good idea.

All good mate. First eng I had modified to run dual fuel was a EFI eng about 25 yrs ago (early gas days) and at that there was not a lot known of LPG in EFI engines. Had a lot of distructive issues with backfiring and actually went to Lillydale, Vic (700km run) and had a new computer installed (retained Impco hardware) by LPGAS1. These guys were well regarded back then. Yes, auto switching for LPG run was a few yrs after that time. I have only ever run dual fuel using manual fuel mode select switching. Off to put in some vegi seeds before the rain.