Gas saga continues

[Jhonno]

G'day fellow Landrover devotees
Further to my post in early Feb & helpful replies I have finally replaced the valley cover gasket bringing about some changes, no more backfiring, starts immediately when cold and hot except if you switch off before she is warmed up, then requires the removal of the air cleaner, prop open the mixer diaphram, switch off gas and spin her over till she starts, feel this is due to excess gas delivery, smell, :( high idle when cold 1500rpm. When hot, idle is approx 1000 in neutral, fluctuating 5/700 in gear with the feeling you need to touch the go pedal to keep her alive, on deceleration there is a hunting that wasn't there before, fuel economy has got worse down from 5ks per lt on a run to about 3, to town & back approx 32ks with a 3k climb 20 to 500mts to home, before about 3 now 2. The computer is disconected, air flow removed. Ckecked all injector Orings with petrol when manifold was off, checked all air hoses and vac advance can't find any leaks. I made a gasket for the plenum chamber, there wasn't one in the kit I ordered even though I asked for one :confused:.
Any ideas will be gratefully accepted and persued, before what little hair I have left disappears.
Thank you Jhonno

[PAT303]

Are the leads new?,dizzy cap good?.Do yourself a favour and take it to a dyno place and get the mixture right at idle and under power.Gas doesn't like lean or rich or weak spark,after getting it dynoed super glue both the screws so they don't move,it is common for that to happen.My 96 disco ran rough like yours does,dynoing it was the best $120 I ever spent on it. Pat

[Jhonno]

Cap is new, rotor new, leads less than 12 months old, it's an impco system and only has 1 air bleed screw on the mixer, adjustment makes no difference until screwed almost all the way in then she cuts out.
Jhonno

[PAT303]

Dyno's your friend. Pat

[bee utey]

Impco: there's a power adjuster where the gas hose enters the mixer, marked L-R, could be too lean or too rich. Both will wreck economy, lean will also wreck power. The 1 inch black wire reinforced gas hose is known to crack because its next to the exhaust manifold, causes lean mixtures. Replace it with the new cotton covered black hose. Good spark plugs are critical for gas, I swear by Bosch, part number WR7DC+, gap at 0.8mm as supplied. Timing: a standard 3.9 will run much better when set at 10 degrees BTDC at idle, never had a problem with pinging on petrol. If you do you just use premium unleaded. Thermostat: if its in poor condition, it will be partly open when cold/cool/ causing the converter to stay too cool. Then when you turn off it will flood the engine with excess gas! I replace thermostats every 2 years regardless. Make sure your converter warms up quickly, idle your engine warm and check. Water hoses might not be flowing well enough, rectify if needed. The gas solenoid should be screwed right up against the converter inlet. If you want my opinion of Impco, its the "Boston Strangler". major power loss at low RPM, not seen with fixed mixers.
Hey, here's a fun one, when I get to refit second hand kits from the wreckers I often see a mixer ring with only 38mm bore size. I usually suggest to owners to chuck it and use a 45mm bore mixer. My first choice is a mixer made by AMR in Melbourne, part no. M352, needs a little modifying, then AMOS after that. Any gas equipment can run OK for an old fella, but if you want to keep some go-motion you have to do it properly.

[bee utey]

One more thing, if you remove your Impco mixer and shake it, you might hear a noise like loose screws. Yes, its loose screws, causes over-rich as the diaphragm doesn't lift enough. Carefully take the lid off and replace the screws in their holes with loctite. Also if the diaphragm is very old it won't run lean ever. You might need a new one.

[Jhonno]

Thanks for the tips bee utey.:)

The power adjuster was set midway, leaned it off to approx half way to full shut off, made for a much better idle and cut down on gas smell, just went for a test run, no loss of power, runs beautifully on the road, pulled up to the Mt Warning car park like a dream, stopped and let her idle in gear for while no problems,:D now after the hard pull home she's back to bad idle in gear below 1000 rpm, hasn't cut out but feel she wants to,:confused: still has a high pitched whistle from the mixer at around 1500 rpm.

No loose screws inside the mixer, the diaphragm isn't what you would call hard though not in top condition, will order a replacement.

?? Is it possible that the backfiring may have upset something in the converter to cause this problem, prior to that she started and ran great with the power adjuster in the middle position.

I am an old fella and I do like plenty of go.:twisted:

[bee utey]

I think your backfire might have distorted/slightly torn the diaphragm, replacing it sounds like a good idea! I don't think the backfire would have reached the converter, however to test for leakage you pull off the gas delivery hose and energise the ignition, gas will run from the converter if it is damaged. Remember also to reduce backfire damage there is the old "beer can cooler" trick, perforate the adaptor pipe to the engine and slide on your least favourite beer cooler sleeve, minus bottom of course. Cheers!

[Jhonno]

Rang for a new diaphragm from impco distibutor in lismore, picked up another bit of useful info.

When a backfire happpens the diaphragm is slammed back against the cover, slightly bending the fixing plate, this causes a very rich mixture. Pulled it apart this afternoon and sure enough it was bent, hammer and dolly, back together & test run, whistle has almost disappeared, idle still not great but better, maybe a new diaphragm will solve the problem, will test the cold start tomorrow morning, still running the same power setting, she actually seems to be pulling better than ever.

Thanks for the beer cooler, may now have a go at setting her up on duel fuel, the cost of replacement airflow meters is prohibitive, haven't had a backfire since replacing the valley cover.

JML

[bee utey]

Good tip, I'm not an Impco fan, I usually heave them when they give too much trouble, this should help fix a few instead. Remember once you have fixed the damage to retune the idle, usually they run about 1/2 way in. As you screw it out it should idle leaner and slower, then turn it in to just maximum idle speed, should be around 3% C.O.
You can also fit a backfire protection flap to the Air flow meter, I get a metal flap type from my local wholesaler for around $80, fits on the 70mm dia. outlet, much more expensive than the beer cooler but more reliable.

[scarry]

Dyno's your friend. Pat

Its the only way,or you will be fiddling with it for ever,& possibly damage other components:(

I have had a fleet of vans on LPG for18 yrs,& trust me,once set up properly on a dyno,they are fine.

LPG is very touchy & is affected by manifold leaks,airflows,etcLocating faults is very difficult without proper diagnostic equipment,unless you have lots of time & like getting frustrated;)

Good luck