Wasted spark and LPG conversation for classic...

[m_c]

AJ has answered that, however a forklift may never had had one fitted, as I'd guess gas probably doesn't need as strong a spark to ignite, and also wouldn't generally be expected to have to start in sub-zero condition as most forklifts get kept inside.

One way to test if it would help, would be to connect the ignition system to a separate good battery, and then crank the engine. If it improves things, then fitting a ballast would be less work than fitting a complete new system.

 

[knighty]

apparently (from a mate who used to fit lpg conversions) you need a better spark with gas than with petrol

will a ballast help once it's up and running or just with starting?

once it's up and running it bogs down and dies pretty easily

it's much better once it's warmed up... but even revving it flat out it'll bog down and die when it's cold

I think the problem is more LPG than spark, but figured I quite like the forklift so might as well sort both problems at once

 

[carbon]

When I was having problems with mine it would start from cold and run for about 10 seconds then stop, maybe about 15 minutes later it would start and run ok. Changing the plugs corrected that. Is the thermostat faulty? On mine the the gas converter is part of the cooling system and needs the heat from the cooling system to stop the converter from freezing.

If there isn’t a ballast resistor then the coil should be 12v. With a ballast resistor coil the resistor is bypassed at start and provides 12v to the coil for a better spark at start then it works at a lower voltage when running. Running a ballast coil at 12v continually probably will damage it after a while.

 

[carbon]

Does the distributor have a vacuum advance hose? Is this damaged? Or is the distributor shaft seized and not allowing the timing to change with engine speed

 

[knighty]

vacuum advance hose to distributor is fitted, looks like it works as it should, no leaks I can find

here's a photo from the internet, pretty much the same as my setup

the lpg evaporator has a water feed/return, it gets good at hot once engine is up to temperature

lpg is fed from the other valve, it's basically just an on/off valve which is vacuum controlled

the lpg feed to the carb from the evaporator is vacuum controlled too

I've searched and can't find any vacuum leaks, replaced the diaphragm in the carb


I've been swapping bits on it for years and can't find the problem, it can have it up and running awesome one day... then it's useless again the next day :-(

 

[m_c]

That does sound more fuelling rather than spark related.

My knowledge on LPG stuff is pretty much non existent, but does it have any kind of mixture adjustment screw?

And stupid questions, you are using a forklift gas bottle, and have the gas bottle on the right way up?
I'm aware some setups need the a liquid draw off, whereas others need a vapour draw off. IIRC the arrow pointing upwards is vapour draw off, and downwards is liquid draw off.
The two I dealt with, always need the bottle on the 'wrong' way up...

 

[carbon]

Is there a solenoid valve to turn the fuel off? In mine that has a filter inside and I would say lpg is not the cleanest of fuels and it may need cleaning

 

[mike 109444]

Not sure if this is like yours but Mustie 1 does give very basic explanation of how it works. There are three videos on this machine.

 

[minimutly]

apparently (from a mate who used to fit lpg conversions) you need a better spark with gas than with petrol

will a ballast help once it's up and running or just with starting?

once it's up and running it bogs down and dies pretty easily

it's much better once it's warmed up... but even revving it flat out it'll bog down and die when it's cold

I think the problem is more LPG than spark, but figured I quite like the forklift so might as well sort both problems at once

This is correct, lpg normally runs a Smaller plug gap from normal.
The cold start and running issue can be due to the gas not vaporising - on initial start it should, all being well, but if the coolant temp isn’t high enough, or not circulating through the vaporiser, it will eventually freeze. Result, no gas.
If it was my forklift I’d start it and let it tick over until the bypass coolant pipe gets to 40 degrees or so before driving it around. Maybe a minute or two?

 

[jsf55]

A follow on from AJs post worth testing too see which coil is fitted and if it's right

Ballast Resistors, Resistance and Coils

What is a Ballast Resistor and what does it do and why? A Ballast Resistor is an electrical device that reduces voltage to the coil so that more energy is available for the spark plugs during start…

blog.simonbbc.com

 

[Seadog]

That sounds like complete bulwarks to me.

 

[Jack_K]

Do you know someone with an old engine analyser? The stock ignition system should be all it needs unless the distributor has something really wrong with it.

 

[knighty]

That does sound more fuelling rather than spark related.

My knowledge on LPG stuff is pretty much non existent, but does it have any kind of mixture adjustment screw?

And stupid questions, you are using a forklift gas bottle, and have the gas bottle on the right way up?
I'm aware some setups need the a liquid draw off, whereas others need a vapour draw off. IIRC the arrow pointing upwards is vapour draw off, and downwards is liquid draw off.
The two I dealt with, always need the bottle on the 'wrong' way up...

it has the proper bottle on and it's mounted right, tried multiple bottles to make sure that wasn't the problem - we've had bottles where the arrow on the bottom of the cylinder wasn't pointing in the same direction as the pickup tube before

Is there a solenoid valve to turn the fuel off? In mine that has a filter inside and I would say lpg is not the cleanest of fuels and it may need cleaning

no solenoid valve, it's a vacuum operated valve

Not sure if this is like yours but Mustie 1 does give very basic explanation of how it works. There are three videos on this machine.

oh that's the exact same forklift... I'll watch those later when I'm home :-)

This is correct, lpg normally runs a Smaller plug gap from normal.
The cold start and running issue can be due to the gas not vaporising - on initial start it should, all being well, but if the coolant temp isn’t high enough, or not circulating through the vaporiser, it will eventually freeze. Result, no gas.
If it was my forklift I’d start it and let it tick over until the bypass coolant pipe gets to 40 degrees or so before driving it around. Maybe a minute or two?

warm doesn't help much - the evaporator doesn't freeze up - had that problem once years ago and fixed it, it was a blocked water hose

Do you know someone with an old engine analyser? The stock ignition system should be all it needs unless the distributor has something really wrong with it.

no engine analyser... timing is spot on by the book, checked with timing light etc.



I'd put a new valve/evaporator/carb on it but I begrudge spending time/money on those when they might not fix the problem

the only thing I think the problem could be is lack of vacuum... but there's no leaks anywhere, compression test is good etc. etc.

 

[CompoSimmonite]

I swapped the valve/evaporator completely, it was better after the swap but not totally right

Was it a brand new evaporator or a secondhand unit. As I said before the diaphragm need changing every so often so if a secondhand item then you can't eliminate the evaporator

 

[Melvyn Best]

Have you checked and adjusted the valve clearances,? I know you say it has a weak spark but I always check the basics first when looking for the cause of non starting , it’s surprising how often it’s something simple. If you have a suitable port a vacuum gauge is a very underrated diagnostic tool

 

[knighty]

Was it a brand new evaporator or a secondhand unit. As I said before the diaphragm need changing every so often so if a secondhand item then you can't eliminate the evaporator

always brand new

Have you checked and adjusted the valve clearances,? I know you say it has a weak spark but I always check the basics first when looking for the cause of non starting , it’s surprising how often it’s something simple. If you have a suitable port a vacuum gauge is a very underrated diagnostic tool

no vacuum gauge... I'll order one

any idea how much vacuum it should pull under normal conditions?

valve clearances etc. were all checked when the head was off (head off because was looking for problems, made no difference to how it ran)


EDIT: will something like this be ok? https://www.ebay.co.uk/itm/403977517510

 

[Melvyn Best]

Should be fine, I did have a chart somewhere showing various vacuum readings and what caused them which I found very useful . A younger brother brought a Renault 20 that was an absolute pig to start , ran badly and had no guts. After connecting a vacuum gauge I diagnosed the problem in 20 seconds . After checking and adjusting the valve clearances all of the problems had disappeared( apart from the fact it was a Renault)

 

[dobbslc]

Does the carb itself have a heating circuit running off the cooling system? Maybe worth checking a pipe isn't blocked. It sounds a bit like carb icing to me.

 

[knighty]

Does the carb itself have a heating circuit running off the cooling system? Maybe worth checking a pipe isn't blocked. It sounds a bit like carb icing to me.

no, but the inlet manifold does

carb doesn't ice up at all

once the engine is up to temperature the lpg evaporator is hot to the touch

 

[Melvyn Best]

Does the engine start on lpg , I’ve not had a lot to do with lpg powered engines but I think the ones I have worked on started on petrol until they had warmed up . Do lpg engines have any form of enrichment device like a choke ? I used to look after an old diesel Mercedes taxi that was well past its sell by date that had huge problems starting from cold , it really needed an engine rebuild, just to keep it running for a few months I fitted a Kenlowe Hotstart which was plugged into the mains on a timer overnight so the engine was up to temperature every morning which cured the cold starting issues