V8 Running LPG woes

[gbmoto]

Hi All

Have recently bought a V8 90 running LPG.

I have owned a few Landy's but this is my first with more than 4 cylinders.

When purchased I was told it would not run on Petrol as the needles and jets (twin SU's) had worn due to the dryness of LPG.

I had heard this before, and would like the dual fuel option, so replaced the needles and jets with new ones.

It will now fire up on petrol but once warm chokes up and will not take throttle.

It does seem to run very well on LPG, but maybe a little lumpy (not familiar with V8 so may be expecting too much!)

Trouble is if I stop after a short journey ( a couple of miles ) it is a swine to restart on either petrol or LPG

What is the traditional V8 starting technique, I have been told lots of throttle, but that feels wrong.

Starts OK on LPG when warm but still has to turn over a bit before firing.

Any ideas?

[heath robinson]

Most LPG carb setups have the timing half way between the optimum points for both fuels. This means that neither is perfect.

RPI's sell a device to alter the timing between gas and petrol, as there's quite a difference. This little gizmo also works as a spark amp. I had similar problems as you before I got it, and found life peachy after.

This is probably a good place to start looking. Hope that helps.

Jake

[oakesy]

First off welcome.

1. For the V8 type check your two SU Carbs pots for oil make sure they are not empty. Because running on LPG can empty the dampers chambers. Hence the jets being worn.

2. Useful tip for V8 on warm up is to feel the heat coming through the window vents. When they warm up, this will be okay to transfer to LPG. Your ideal Idle revs should about 800+ for the LPG to be cosy.

3.When was it last serviced both LPG and Petrol side.

4. Should try and avoid starting on LPG as the gas has not had chance to warm from the water system. Hence the feel of the vent as a indicator.

5. How are the LPG unit setup. Tank sideway or forward looking on the rear bench seat. Is the regulator flat or side on to the front wing. Also the mixers a single to the air inlets or one on each side of the carbs.

It is important for LPG that the Petrol usage in good condition first as this lubes the carbs. As when you switch over P-N-G you should feel a struggle in Neutral twice as each carb emptying then the flicking to Gas manually will be instant. Make sure when not using for more than few hours return to Petrol.

[Quagmire]

Is this an open loop system (no feedback) or a closed loop system that has an oxygen(lambda) sensor in the exhaust controlling a stepper motor after the vapouriser?

My family run three rover v8's on gas, and my advice would be thus:

Get the car running on petrol sweetly first, and then get the LPG sorted. When you say it won't take throttle, does it just bog down? How have you reset the mixture after reassembling the carbs? Did you balance them? I have the SU manual if you need a copy...

Troubleshoot one thing at a time. Make lots of changes at once and you won't know which made the situation better or worse. Ask me how i know!

Don't buy silly things like Magnecor leads, or whizzy spark plugs. Just ensure you have a genuine/good quality set of normal leads and plugs. Route the leads carefully to avoid crossing each other or leads touching. Buy more spacer thingies if you need to. Make sure the silly screw cap things on the spark plugs are not loose, and that all the plugs are gapped correctly.

Ensure your dizzy cap and rotor arm are in good condition. If you need to replace them, then make sure you buy genuine as these are the best.

My starting technique on gas requires a little throttle to start when stone cold first thing, but anytime after that for the rest of the day i can start it standing outside the truck. I have Megajolt though so have massive sparks.

Lean mixtures or too much ignition advance can cause tricky starting (i think).

The fact that it is hard to start on both fuels would seem to point to an ignition type fault, so i'd go through these first.

So is it just short journeys that make it hard to start? I.e. it starts better from cold or really hot, than it does from just warm?

As for the lumpy running, on petrol mine idles so smooth you can put your hand on the dash on not feel any vibration. On LPG idle is not quite so good (mine sits at 600rpm, so a tad slow), but i believe this is down to the fact that the crankcase breathers feed back into the carbs after the mixer plates, rather than before.

One thing i will say is that once you get it sorted you'll love it! I certainly love mine :)

[gbmoto]

Wow, so much good info so quickly, Thanks chaps.

In answer to the various questions

The tank is mounted behind the central bulkhead, across the chassis.

The regulator looks like it is sitting on it's side.

Carbs have been topped up with oil.

The lpg system has a mixer between each carb and the manifold.

I don't think there is a lambda sensor, it is an Italian set up, not sure how it works!!

From cold it starts second turn with full choke, choke in immediately, then have to change to LPG pretty soon.

Starting from warm on lpg is fine, seems to start OK on petrol if the throttle is floored!!

I like the idea of the amplifier, but also am attracted to megajolt (a lot! )

But I think my first port of call will be ignition timing for petrol, sort the stuff I understand first.

LPG is not so important as it is not a daily driver.

But when it runs well it is fun, first Landy I have had that gives me the option of overtaking people!!

[heath robinson]

I would definitely second what has been said about filling the pots on yer carbs, and getting new, genuine ignition bits, dizzy cap, rotor arm and coil. According to many people that I've talked to, aftermarket "Extreme" coils are death on a stick, and the only thing you should use is the lucas original.

I can't praise the ignition amp highly enough though, my truck starts on gas every time (Although I know it's not advisable...) even in the coldest weather. The difference between running a half-arsed setting for both fuels, and getting it spot on for each is massive. IIRC it's about 8 degrees different!

Megajolt would obviously solve this for you, so if that's the direction you're heading in, I'd say get it as soon as you can.

Good luck!

[mickeyw]

Hmmm! I'm a tad puzzled by this talk of not running gas at startup.

I've been using gas for 9 years now, first on a carbed V8, and more recently on two Efi V8s. I have always started from cold on gas with the carbs and never experienced any problems. The important thing is not to hare off up the road giving it too many beans, otherwise the vapouriser will ice up, causing the engine to cut out.

Drive off sensibly and you shouldn't have any problems, assuming your system is set up correctly. You engine will like you for being gentle when cold too