Outer Limits 4x4 Board

Ok, got my lpg setup finished,runs ok but in need of a tune. Problem i am having is that it is a real biatch to start on petrol, i almost flatten the battery trying to start it. Seems like it is not drawing fuel properly into the carbs at startup, i have twin lpg mixers which are bolted in front of the carbs that would be reducing airflow. So do the strommies use vacumn for their metering ? would the gas mixers cause them to run really lean? even with choke its hard to start, but once running its as good as it was prior to the gas setup.I have checked the usual suspects, cleaned and re gapped the almost new plugs, leads are new 8mm topguns, timing has been checked, fuel pump is fine and the fuel shutoff is opening when on petrol. Any ideas ?

what is your timing set to ? 6 degrees ?

how are the diaphrams in the carbys (not that it would make it hard to start but workth checking)

Tom

In a carby set up fuel runs from your tank through the fuel lines, into a bowl in the carby and then into the carby itself. If the bowl is empty the car wont run. The fuel bowl is there to take into account different engine needs eg when accelerating more fuel is required. When starting a petrol car it is necessary for this fuel to go from the bowl into the carby, down the manifold and into the cylinder before it is ignited by the spark plug and kaboom, rattle rattle rattle ah she's idling. This process, depending upon the condition of your car may take a couple of seconds to any number of cranks of the engine. Delivery of fuel from the bowl is a mechanical process not an electronic one.

When you run on lpg and you hit the ignition switch your fuel supply to the engine is more instant as the fuel is supplied as soon as the solenoid is powered.

Your car wont run with petrol and lpg in the system together. In most LPG applications (all that I know of but I'm leaving my self a margin for correction) it is necessary for the fuel float or bowl to be empty before running on LPG is possible (remember petrol is supplied mechanically). Yor lpg system will therefore run your petrol supply out before injecting lpg.

What all this means is that it is possible your problem is due to the fuel supply at the time of starting. Are both fuels being injected at the same time? This will cause extended cranking to run out one fuel supply over the other. Your LPG may escape quicker with the air cleaner etc off. Alternatively is there not enough petrol in the carby float on starting, causing extended cranking while this fills up?

here is a test for you - Next time you drive it, make sure it is running on petrol when you turn it off. Then when you next try to start it, make sure it is again on petrol. Make sure you havent tried flicking to gas at any stage as this will mix your fuels. If the car starts better in this situation the problem is likely to involve the amount of fuel in the float before starting.

Therefore to rectify when having run on lpg when you turn off and to start on petrol, make sure you sit with the ignition on for a few seconds and allow the fuel float to fill up. In my last rangie with lpg I could hear the fuel pump running and then stop when enough fuel had been delivered and it was only then that I attempted to start the car.

If the test doesn't resolve the problem then - I kunnano

Carbs were rebuilt about 4 years ago, timing is at 9 degree's. Once started it runs great and as plenty of power but since the conversion its been a bastard to start since- on gas it starts instantly.

TRobbo wrote:In a carby set up fuel runs from your tank through the fuel lines, into a bowl in the carby and then into the carby itself. If the bowl is empty the car wont run. The fuel bowl is there to take into account different engine needs eg when accelerating more fuel is required. When starting a petrol car it is necessary for this fuel to go from the bowl into the carby, down the manifold and into the cylinder before it is ignited by the spark plug and kaboom, rattle rattle rattle ah she's idling. This process, depending upon the condition of your car may take a couple of seconds to any number of cranks of the engine. Delivery of fuel from the bowl is a mechanical process not an electronic one.

When you run on lpg and you hit the ignition switch your fuel supply to the engine is more instant as the fuel is supplied as soon as the solenoid is powered.

Your car wont run with petrol and lpg in the system together. In most LPG applications (all that I know of but I'm leaving my self a margin for correction) it is necessary for the fuel float or bowl to be empty before running on LPG is possible (remember petrol is supplied mechanically). Yor lpg system will therefore run your petrol supply out before injecting lpg.

What all this means is that it is possible your problem is due to the fuel supply at the time of starting. Are both fuels being injected at the same time? This will cause extended cranking to run out one fuel supply over the other. Your LPG may escape quicker with the air cleaner etc off. Alternatively is there not enough petrol in the carby float on starting, causing extended cranking while this fills up?

here is a test for you - Next time you drive it, make sure it is running on petrol when you turn it off. Then when you next try to start it, make sure it is again on petrol. Make sure you havent tried flicking to gas at any stage as this will mix your fuels. If the car starts better in this situation the problem is likely to involve the amount of fuel in the float before starting.

Therefore to rectify when having run on lpg when you turn off and to start on petrol, make sure you sit with the ignition on for a few seconds and allow the fuel float to fill up. In my last rangie with lpg I could hear the fuel pump running and then stop when enough fuel had been delivered and it was only then that I attempted to start the car.

If the test doesn't resolve the problem then - I kunnano

Ah, yes i know the process( sarcastic voice), i have converted cars before, i'm talking about cranking for about 30 seconds after waitng till the electric pump has reached pressure, but still nothing till i almost kill the battery.

With that timing do you get any pinging when driving on petrol on hard acceleration, particularily up a steep hill?? Have you tried, as an experiment, starting the car on petrol with the timing close to standard? If so any change in symptoms?

The timing is the same as it was prior to conversion, but i will check it again - bit cold for working outside at the moment!

I start mine on gas.
0.5 seconds, and it's running.

Yeah it starts on gas first crank, the problem is when on petrol it takes a long time to start - this seems to be fixed for now, gas tuning is taking longer as i want to get it running pretty good before i take it to be complianced.

Hmmmm.
Interesting!

Is it hard to start on petrol when cold or when warm, or all the time?

The mixers should not cause a restriction to the air flow, as they should be roughly the same size as the carby inlet.

I have found that after running on gas for a while, mine plays up on petrol (it runs very rough).
Faultfinding is difficult (as you have found out), but if I leave it pressurised with fuel overnight it runs OK.
Can't explain this except the needle & seat must like it.
If I run for ages on gas, and then switch to petrol, it runs very rich.
My guess is the fuel bowl is over full.

But this maybe irrelevent, as I have SUs.

Funny enough, last monday after i fitted new rad hoses and thermostat, i couldnt get it to start on gas, found out i had an air lock and the converter froze up. I topped up again with more coolant ,left it over night , topped up again and it wasfine. An after it was left overnight again, it started on petrol without any hassles. If this is going to be reqular then i will fit the 450 holley and sprintgas new gen mixer i have sitting in the shed !