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IMPCO LPG cold start

The tunna runs a IMPCO L model LPG converter and a IMPCO 425 carb. I understand that the carb will flow 465CFM, so will suffice for this 308. I have run them in the past and shocked a few LPG disbelievers... No need to go to expensive gas research setups, these are cheap and very effective. I have a question though. When starting from cold, the converter just doesnt seem to want to give the engine what it wants and it will just turn over and over without fuel. If I lift the bonnet and give it a little purge, it flashes up with half a turn. Problem is that I dont want to have to lift the bonnet everytime it is cold. I have a fuel solenoid that I have wired to a button under the dash, which goes to open the solenoid when the ignition is on. Ths gas lines go from the top of the converter top the solenoid valve then straight into the intake manifold. The plan being that I can purge it from inside the car. It isnt working, can someone explain what i have done wrong here? It all sounds logical, but, doesnt work... Have I plumbed from the wrong part of the converter?




i tried to do the same thing, didnt work well meither so to make mine start better i put in a really good heavy duty battery make sure no air leaks anywhere converter carby and manifold and works pretty good still takes about 6 secs. was think a high torque starter.
but should work with the purging idea mabbe hook it up on the lpg carb there is a bolt you can undo it say ignition on it i think.
and also i cant c a real difference in gas research they both work the same way, so who nos why people would spend more 2 get 1.

[http://gallery.oldho...|MY SHED..MORE THEN JUST THE VK.COME INSIDE]

My understanding is that Gas Research will better meter the flow of LPG to the engine throughout the throttle movement. An IMPCO has only two circuits, idle and full throttle. The butterflys open further to allow more air, but the IMPCO doesnt meter it very well. The IMPCO is just a SCUBA regulator. Fact is though that the fuel ratio or stoichiometry of propane to air has a FAR wider tolerance than octane (Unleaded fuel) and can withstand this lack of good metering well. I suppose what lacks in the end is economy, but, Im prepared to live with that when LPG is only 60c/ltr. I do remember paying 15-18c/ltr in Melb only 9 years ago though!!


Hi MrPatchMan, can under stand what your saying about the metering of the mix etc, was thinking of putting Gas Research on my engine 202, but got conflicting stories, was told that would not realy achieve much as my Stromberg carby with mixer on top was just as good,he may be right,y/n
have you seen any figures of this?
Dynar might know from his mate with the Dyna tune, might have some figures of engines that he has done, with different set up for LPG conversion's on the same engines, that would be good to com-pair,so if you see this post Dyna,maybe you could ask him,would be great to know
Cheers, Jacks
QLD 4165
>Jacks shed
>Latest Update

Hi I have a IMPCO gas unit on a Crysler 360 and have the same probs you can get a cold start valve but it diden`t seem to help much I have installed a push to brake switch between the power suply to the gas which works as a primer if you push it several times it is like turning the key on and off this seems to help but still takes a few turns to start any way thats my 2 cents.


Impco model L needs vacuum to run, hence no gas flowing when you turn on the ignition.
I had the same problem with my torana. I sorted it by doing the following:-)
Fit a high pressure solinod into where the bank off plug is inbetween the water fittings.
Then plumb this to your inlet manifold.
Hook this new solinod to the switch on your dash.
Now, if you have a electric lock off device fitted (u need one for gas compliance) you be able to get a gas purge of about 2-3 seconds when you first turn on the ignition and while holding down the button on your dash.
The electric lockoff device will then open circuit, disabling the gas flow to your non running motor. (Electric lockoff is a rpm activated relay, under 400rpm the relay remains open circuit [expect for the initial 2-3 seconds when first switced on])
If this anit enough gas purge, simply turn your ignition on and off a couple of times while holding down the purge switch.

Your never late in a stroker 308
[http://gallery.oldho...|my shed]
Note:- not liable for this infomation, use at own risk.

Thanks, good info. Is that plug between the water hoses? Is this the one you mean? Easy done. Thanks.


I had the same problem,, if you want to contact me by email i can get you on the rite track,,,,(

are you sure it's the LPG side, if motor is turning over should be enough gas there to start, make sure your spark is at full strength, if the starter is robing you of your power to the dizzy etc then thats a problem,check with a meter
be careful with that purging bit, can be dangerous if not done correctly,can do a nasty backfire
some times it may fire just as you released the ignition key if this is so then problem is spark not LPG, just a thought
Cheers, Jacks
QLD 4165
>Jacks shed
>Latest Update

She has a gear reduction starter and an aftermarket hipo ignition, it sparks and turns real well with a brand new battery. As soon as it gets a whiff of gas from a manual purge, it fires (as described above). I really dont think it is either spark or starter. I can understand your thoughts though, sometimes we treat the symptoms rather than the cause...


Hi,MrPatchMan, glad you see my point,
in some cases they will say it doesn't do that when running on Petrol, meaning it's the LPG thats the problem,
'Gas/air mix is much harder to ignite than a petrol air mix for LPG, good to see you have a good ignition set up,
have you a pics of the set up please,
BTWB, you can fit a special switch that primes the engine as soon as the ignition is switched on, with a short burst of gas for about 5 seconds, so hence it primes before cranking,(lot safer) just a thought ,
incidentally what's the static setting of your dizzy when on LPG, do you disconnect the vacuum advance as well
Cheers, Jacks
QLD 4165
>Jacks shed
>Latest Update

Jack, I have used a large aftermarket coil and a brand new hall effect dizzy that was regraphed for the tunna. I havent opened her up yet, so, I havent disconnected the vac advance, no. The regraphing should have all the advance come in real early though. As far as pics go, they wont help, the dizzy looks fairly stock and the coil is behind the dash (wouldnt fit on firewall).
I also have an aftermarket CDI type amplifier, which isnt wired up yet and may not be, as I am happy with it as it stands... Still, when she is on the road, I am sure I wont be able to help myself from fiddling.


yes i mean the plug bewteen the water fittings.

for those that dont own a impco model l, the large vapour line from the mixer to carby, it simply doesnt flow if there is no vacumn.
You see, if mrpatchman was to disconnect this hose, turn on the ignition, no gas would come out. thats his problem.
its a major pain the arse.

will try get a pic of my primer up tomorrow

Your never late in a stroker 308
[http://gallery.oldho...|my shed]

Hi v8slrtorana, that can be a problem reason being unlike Petrol starting, the fuel is there on demand so to speak as its in the fuel bowl, however a leaky fuel bowl will take some cranking to get it to fire as well
with LPG, it does not stay there so hence not on demand, has to be given a signal, the signal comes from thr vacuum that the engine creates when the starter motor is activated,
now if the starter motor is sluggish then the vacuum is to weak to send signal to converter, so hence no start,
further problems, are now accelerate as the starter motor wears out along with the ring gear, this intern may create a backfire as well as a flat battery,
Note:when he used a better battery he got more revs from starter, so more rpm = more vacuum from engine = a quicker response to signal to converter, which = release of gas to mixer and Waller ignition
so in essence,
LPG cold starting, needs heat for the converter to stop the LPG and converter from freezing up, it does not have to be a cold temp outside, infact converters will freeze up at 25c,if the air outside is very moist,
you need good vacuum to give a signal asap to the converter, also need a good ignition system, and correct spark plugs and gap,
get all of this and no problems with LPG
the more we talk about LPG the more we learn, as it will be used more and more, the rewards, will save you heaps, will also give a longer life for your engine as well
Cheers, Jacks
QLD 4165
>Jacks shed
>Latest Update

Nice to see some more alternatives for gas systems...

Love the tonner if you've got anymore photo's of her
Send em to my mail below

Cheers ALLAN

Check out my old tonner i used to have in my shed'll like

>E-mail Free_Styler1
>Allan's Carport

i did the same for a mates 350 chev only i put in a delayed relay to the start circuit that way the solanoid opens delivers gas but even if cranking it stops in around 5 seconds but lets in enough gas to get it started tho i plumed the line into the actual carb not the manifold.

Seems i forgot to take that pic. (try tomorrow)

There is a another method of priming a impco model L.

Its via a vacuum operated soliniod connected to balance port on these convertors.
These soliniods are low pressure design, the 2 ive seen are made out of plastic. It has a 3/16 vacuum fitting on 1 side, a 3/8 male threded fitting on the other side.
A tee is screwed into the balance port on the convertor (AKA the port that says DO NOT PLUG)
The primer soliniod is screwed into the tee.
The 3/16mm vacuum pipe is fitted to vacuum port on your carby.
The other side of tee is connect via a 3/8 vacuum hose to the balance port on your carby.
So thats the mechanical side, heres the wirring side,
Connect the primer soliniod to earth, the feed wire goes to your gas computer, i kid you not.
So im guessing if you dont have a computer, you just connect the primer soliniod to your starter circuit??
More investigation required.
Ive seen two of these low pressure primer soliniods, when i orginally had the cold LPG start problem, i went and brought one of these primer soliniods from a LPG installer, he told me fit it to the converotr, i took it home, tried to fit it, couldn't understand it, couldnt make it work, then i just checked it in the glovebox.
Im current in the process of converting the vl to dual fuel.
The gas system i took out of another vl has a impco gas computer and the cold start primer system mentioned above.
I would like to change my torana to this system, but untill ive finished my vl conversion, ill stick with the pressure primer system.
Ill keep u all up to date with the vl conversion, and attemping to fit the new primer to the slr.

Jacks, yep, froze a convertor once before, took about 5 minutes with no water, 35deg day humidity of 80%

Also the system i fitted to my mums HJ, is 202, hole drilled in side of carby, runs a complexe type convertor. Ah, i think the brand is a Landi convertor, as soon as the ignition and gas circuit is switched on, the gas flows from the main vapour fitting to the carby, no vacuum req.
[http://gallery.oldho...|landi setup]
A impco L convertor is dubbed a simple convertor.
The reason for the convertor freezing is because of a 'change of state' being we a converting liquid to vapour, thus the need for heating the convertor.
Thats why canadians have MASSIVE convertors, for more heat exchange.

I agree to having the best ignition system you can afford with LPG.
I have crane CDI system, accel spiral core wire leads, best money spent.
LPG just doesnt like a [Naughty Pottyword]ty ignition system.

Your never late in a stroker 308
[http://gallery.oldho...|my shed]


I think what you are describing is an electronic feedback system for the LPG system. They use the signal from the oxygen sensor to determine if the mixture is rich or lean. The computer then modulates the vacuum signal at the balance port to try and keep the mixture at the stoichiometric ratio. The mixture is mechanically adjusted so that it runs rich, and applying a vacuum to the balance port leans the mixture out. The Tee-piece that you talk about has an orifice in the leg vented back to atmosphere that allows the negative pressure behind the diaphragm in the converter to return back to zero when the solenoid switches off.

Impco mixers that are designed to use this system have "FB" in the part number e.g. CA225FB. You shouldn't use a standard 225 or 425 mixer with a feedback system because they will run predominantly lean.


My HZ V6 conversion

ive got a excuse for no pics, will do 2morrow

bf6379- i think your correct there, it does make sense to me,i will check carby model 2morrow, please if you have more info could you post it or email me trentonbarfoot@aapt....
However, the LPG installer supplied me this soliniod as a primer soliniod. (in the case of the torana)

Your never late in a stroker 308
[http://gallery.oldho...|my shed]

the leaness and whatnot is denoted by the color of the diafram in the top of the gas carb you may want to look up what one u have yellow black and red are all different mixtures at diff revs

I took some photos of the Impco model L convertor on the torry.
This one is setup with the pressure primer soliniod
[http://gallery.oldho...|pressure primer]

Here is the other system i was trying to discribe.
The black soliniod is what a gas installer sold me as a gas primer.
[http://gallery.oldho...|other soliniod]

Your never late in a stroker 308
[http://gallery.oldho...|my shed]

i have a landi gas convertor & lately it freezes up when i start in the morning & if car has sat for 10 hrs or so,i can start it,idle for 2-3 mins but as soon as i take of & change gear it freezes up & wont start,i switch to fuel,drive bout 1 klm & i can switch back to did this bout 2 years ago & i stripped down the convertor,cleaned it out & was fine,tried doing same other day but no difference,any ideas?

the reason it freeze up is because there is no warm water going thru it , as DAVE said check how you have the water hoses going to the converter , also the water passages in the converter could be blocked thru corrosion flush out the converter with a garden hose, if its not blocked and the water hoses are connected correctly you probably have a thermostat that is opening too soon so try fitting a thermostat around 86-90 degrees..

THAT IS one of the reason they recommend you start your gar on petrol , so the water gets warm enough so the convertor wont freeze over and stop the gas from flowing , after you have driven a km or sop on petrol the water has warmed up enough to stop the convertor from freezing ...

what sort of car and engine are you talking about.???


Sounds like either a hose routing issue (rearrange the order the heater hoses are in) or it has air in it.


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I have lived with faulty solenoid power supply for over a year now.

An LPG specialist and LPG Holden dealer were unable to diagnose problem.

Either or both the tank or the engine solenoid close unexpectedly when engine running and often cannot start because soelnoids do not open.

Sometimes both shut together, sometime the front then another time the back. Sometimes both fail to switch on or both will switch off at same time.

The problem has slowly over the last year or so I can only drive a few KM's before car stops and I have to switchover to petrol.

Car is '98 VT commodore factory fitted Impco 225 system.

Any help gratefully accepted thanx

John P


had a dodgy fuel controller awhile back sadly was a brand new one its the thing that sense the pulse and if it has pulse turns on the lock offs check to see if and where it is sensin pulse and make sure all connections are good

one thing to note is becouse it was factory fitted u may need to go to another dealer to get a new fuel lock off controller.

more involved than what i can bring my fuzzy mind to entertain right now but you get the idea

I have a Impco BRC system on my Suziki Grand Vitara V6 2.7litre , started to stall. after about 40,000 kilometers (no problems before that). Stalls Mostly when
cold (on rare occasions when hot). when engine stops steering and brakes fail. Car would stall running on both petrol or gas. I put the car on a Dyno, then on an Oscilloscope, problem not found, auto electrician could not find the problem. Spent
eight months trying to get car fixed. Car is now undriveable. Have compression failure with the engune. Everyone has taken my money, and no one has taken responsobility. Suzki has voided the waranty.Car pruchased new 2 years ago. Lasted a year before stalling started.

Does anyone have any information on "IF" the Impco system can destroy an engine???
and what damage can LPG do that Unleaded Petrol wont do. any information appreciated.
Would like to hear from people who have a Holden Comodore or Holden Rodeo with an
Impco BRC installed and working.

Any help and comments appreciated.


hold throttle flat to floor will help heaps must have good crank speed if electric fuel lock off is used crank for 5 seconds turn key to off then on again and crank can change spring in converter if still having problems

The problem with cold start can be solved easily if you have a dual fuel setup.

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