backfiring

[[email protected]]

i have an EA82, in my L series wagon and have a backfiring issue, when idling and rev the motor quickly there are a few backfires each time you take the foot off - smooth increase in revs then foot off seems ok, maybe a quiter pop. whilst driving when coming to an intersection slowing down in gear, mostly (3rd), the same problem and quite a few loud cracks of backfiring- seems the more revs the louder and longer the backfiring goes. cant see any exhaust blackening from any leaks on the pipes, motor is standard carby and distributor, hoses all seem to be connected- unsure of 100% accuracy in hoses to fittings, timing is correct and is lpg fitted, any suggestions of how many turns out the mixture screw should be and exact timing to reduce the backfiring or any other factors that could be the problem

[El_Freddo]

Are you running primarily on LPG or petrol? The best timing for LPG is advanced compared to Petrol as it has a higher octane rating. The only problem is that when running on petrol it will be sluggish and backfire. 98 premium might help with this...

Other than that I'm stumped.

Cheers

Bennie

[steptoe]

by backfire, you mean exhaust not intake backfire?

Can you discern if it is on one fuel, or the other or both. What brand names model names appear n your LPG converter with heater hoses running through it

Bennie is sort of on right track with ignition timing differences for LPG, it likes a lot of advance down low revs and not as much up top revs so is hard to cater for without modding the distrbutor. I braze up the advance slots outer ends to limit the max advance to about 28 deg in total, with initial at about 12 deg. If you set standard dizzy to 12 initial you are likely to get more than 28 total.

LPG gives fuel savings and those in turn go well spent on new plugs and leads, dizzy cap and rotor every 40 or 50 thousand kms to be on safe side of things. Reduce plug gap 0.2mm less than spec for petrol

Wonder if your problem lies in any pollution control reed valve thingys?

[[email protected]]

el freddo has a fairly good idea of the lpg v petrol situation. i use petrol 91 octane around the town and lpg on longer trips lpg- the car goes ok on lpg, no or very little (exhaust) backfiring but switch it to petrol and lots of backfiring heard from the tailpipe on decelleration- fairy loud too and sluggish whilst on petrol.. the lpg regulator has ZAVOLI, italy stamped into it and my timing is at 8 deg..

standing at the front of the car, bonnet up and idling the exhaust sounds fairly loud- maybe the head/exhaust joint gaskets may be leaking just enough to be letting air through, i cant see any blackening there though - would this contribute to the problem if air or exhaust is leaking from the gaskets. i think it has those gaskets silver top and bottom crimped to a black centre gasket, nuts are tight but i have seen them leak from between the silver and black part before..

plugs, leads, dizzy cap and rotor are all in good order i did replace those but set the gaps at specified gap- what gap do you think i should set them as

also i have a ticking from the passenger side head, sounds like a dry tappet or similar, would one of the lifters be clogged up therefore not opening the valve properly and that being a cause to backfire and the sluggishness on petrol or not. i didnt hear this noise previously but have detected it after not using the car for a while. ok i will await for some points of view on the above

[RSR 555]

Sorry I'm no expert in Gas/LPG side of things but it sounds like it is extra unburnt fuel in the exhaust. Have you changed the exhaust system? as I feel this maybe because of no back pressure, also check that your catalytic converter is still intack as I've seen them broken up from LPG. It is very hard to tune a car for ULP and LPG at the same time unless you have a EFI system. My best suggestion would be to tune it to what ever fuel you use the most but ensure the other is not running too lean