rover 4.2L v8 lpg set up suggestions

[clive22]

I have a dual fuel 4.2 V8 out of LSE range rover in my county. It's running stock twin carb set up and the 10+ year old Impco LPG system bolted straight on that used to feed the old 3.5 engine. Crane cams ignition system fitted, came with engine. It has a 'torque' cam, but have no info on the specs - bought engine 2nd hand so no more info.

The performance of the engine on petrol,is really very good, pulls well and smoothly, throughout the whole rev range.

The lpg system is not so good: runs and operates fine, but beyond I guess beyond 2500+ rpm, really starved of fuel. Feels good 50% down on power, when revving on large throttle openings, but fine at low revs.

Anyone got recommendations as to what mixer is the best, which I am presuming is the cause of the performance loss on LPG. Or any other ideas as to what to do.

Use gas for highway and 'round town not after the ultimate set up just one that has reasonable performance, say 20% down on petrol.

I generally run it on 98 octane as its pre-detonates when the motor is hot on a warm day on 91.

Clive

[PhilipA]

One of my friends had a 4.2 Rangie, with twin Impco Right angle carby's? . Anyway they were attached directlt to/near the inlets of the strombergs.
IMHO it was still very weak at the top end and did not match petrol across the range.
Regards Philip A

[lokka]

Have you got any pics of the impco set up and some specs on them like mod numbers and such .

Sounds like its not getting enough gas flow maby it needs 2 condensers one to feed each carb .

I have a rangie with a impco gas carb on a butterfly plate its a 225 mixer fed by a impco condenser and now i have tuned it it runs fine and i get great power all the way to redline .

[bee utey]

Before you go any further find the power adjustment on the Impco mixer/s. It is a flat adjuster right next to where the 1 inch gas hose connects to. Look for "L" and "R" marks, move the adjuster pointer 1 or 2 notches towards the rich "R" side and test drive.

[clive22]

Thanks for the replies everyone.

The system is Impco 200 mixer.

Convertor is
Impco Cobra 700910

Will post up some photo's next couple of nights, camera not here atm.

Not expecting it to match petrol performance, but really is too weak at the moment. Old engine 3.5L was down ~20%, mainly at top end, this is down lot more then that.

Had a quick glance at Impco website seems this mixer is rated up to 160Kw, which would be a bit more but not much more then what this engine is rated at 150kw-ish (from memory) - feels about right to.

Bee Utey spotted the adjuster screw next to fuel inlet pipe, spring loaded adjuster. Will tweak settings to see if any difference. No point respecing & re plumbing mixers if it's only tuning. Thanks.

Economy is not to good either on gas 25-27l/100, steady 100-105 km/h - little wind, which is too high. Used to get 20-22 l/100 on old engine, similar conditions, which I always thought was about right.

Petrol consumption is fine under 20,on the dirt engine certainly feels good apart from the gas performance.

Clive

[Freestyler]

Hi Clive I run a 4.4 Leyland EFI in my county mine with an impco 300 carbie and is a bit the same but not as bad. I beleive after getting my fathers county going last week end (4.6EFI and Injected gas) that the gas carbie is fairly restictive on the air flow and holds the engines back. Also as far as I know the Impco 200 is only good for a 200Cubic inch engine! which would be too small for the 3.5 let alone the 4.2. I have fitted an O2 sensor t0 the exaust and have built a kit from Jaycar that tells me the mixture. If it is running lean it will bugger up the valves and seats fairly quickly
Tim