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[Brynjaminjones]

I'm finally getting around to giving the Waggy some mechanical attention, as so far it hasn't had any at all (done well over 1000 miles in her now).
I currently feel a bit out of my depth having never touched a carburetted engine before, especially one with so many vacuum lines etc plus LPG.

I therefore need a load of general advice from all of you errm, more experienced people.   
These will probably sound like common sense questions to you lot, but treat me like an idiot please!
I've done a load of research on IFSJA, but a lot of this is LPG specific so I'm struggling for some answers at my level!


1. On petrol it starts up fairly easily with a few pumps, and seems to have plenty of low-end torque as well as a decent turn of speed. I did try flooring it from a start though, which caused the engine to immediately stall.
Is this calling for a carb rebuild?

2. On LPG it feels significantly slower. It's fine once the revs get higher, and can then move out of its own way just fine, but at lower revs it simply won't chug up hills like it does on petrol and takes ages to build revs. I've also had a couple of intake backfires (only small) when getting on the throttle reasonably quickly, as well as what sounded like an exhaust backfire at low revs when trying to accelerate quite hard out of a junction.

I know from what Kev has said that LPG will cause a loss in performance, but this is a night and day difference and doesn't seem consistent through the rev range.
I run it nearly entirely on LPG, so is there anything that can be done about this?

3. It struggles to cold start on LPG. I have to give it a good couple of sets of cranking for ~10 seconds before it'll think about firing. I do allow time for the gas to travel from the tank first and I'm not pumping the pedal.
Can anything be done about this, or is this the norm for old fashioned LPG?

4. The inlet tube on the air intake has a big flap/valve inside, which appears to be vacuum operated. This looks to be in a closed position and the vacuum line is missing. What is this, and could this be causing trouble?

5. I'm going to give it a general tune-up (plugs, leads, cap, air filter). Do I need to do anything special for these for LPG, or just go with normal bits like I do on our 4.0s?

6. At idle I'm getting very low voltage - low enough that lowering the window sometimes causes the radio to turn off! The alternator looks fairly new, so is this likely to be a bad ground or something along those lines?

Sorry to bombard with questions. I'm sure I'll find some more, but that'll do for now

[wildwood]

God knows why I wrote this down in my anaorak book of things to remember??

BUT.....
It says here ...... LPG on a 360 engine..... 10degree advance timing and remove vac advance hose.

Cooler spark plugs needed....

Also have written down IMPCO 425 carb....394 CFM..... Don't know how that is relevant
But maybe Tis a good one?

I think all other items you mention are part and parcel of the older LPG systems.....

I am sure other info will be forthcoming during the day......

[5536paulj]

I'm finally getting around to giving the Waggy some mechanical attention, as so far it hasn't had any at all (done well over 1000 miles in her now).
I currently feel a bit out of my depth having never touched a carburetted engine before, especially one with so many vacuum lines etc plus LPG.

I therefore need a load of general advice from all of you errm, more experienced people.   
These will probably sound like common sense questions to you lot, but treat me like an idiot please!
I've done a load of research on IFSJA, but a lot of this is LPG specific so I'm struggling for some answers at my level!


1. On petrol it starts up fairly easily with a few pumps, and seems to have plenty of low-end torque as well as a decent turn of speed. I did try flooring it from a start though, which caused the engine to immediately stall.
Is this calling for a carb rebuild?

Might be accelerator pump?  carb rebuild will help

2. On LPG it feels significantly slower. It's fine once the revs get higher, and can then move out of its own way just fine, but at lower revs it simply won't chug up hills like it does on petrol and takes ages to build revs. I've also had a couple of intake backfires (only small) when getting on the throttle reasonably quickly, as well as what sounded like an exhaust backfire at low revs when trying to accelerate quite hard out of a junction.

No idea about lag

I know from what Kev has said that LPG will cause a loss in performance, but this is a night and day difference and doesn't seem consistent through the rev range.
I run it nearly entirely on LPG, so is there anything that can be done about this?

It'll never be a rocketship on leg as compression ratio is too low, but it should run smooth.

3. It struggles to cold start on LPG. I have to give it a good couple of sets of cranking for ~10 seconds before it'll think about firing. I do allow time for the gas to travel from the tank first and I'm not pumping the pedal.
Can anything be done about this, or is this the norm for old fashioned LPG?

4. The inlet tube on the air intake has a big flap/valve inside, which appears to be vacuum operated. This looks to be in a closed position and the vacuum line is missing. What is this, and could this be causing trouble?

That's just to divert to warm air in the winter, shouldn't affect things much this time of year. But worth reconnecting.

5. I'm going to give it a general tune-up (plugs, leads, cap, air filter). Do I need to do anything special for these for LPG, or just go with normal bits like I do on our 4.0s?

6. At idle I'm getting very low voltage - low enough that lowering the window sometimes causes the radio to turn off! The alternator looks fairly new, so is this likely to be a bad ground or something along those lines?

How low? the std alternator doesn't start charging much until over 1200rpm.

Sorry to bombard with questions. I'm sure I'll find some more, but that'll do for now

Bryn, it's always worth rebuilding the carb as it's easy to do on your kitchen table and lighty's have rebuild kits if it's a motorcraft 2150. Sorry, know nothing about lpg. Idle mixture is pretty easy to adjust on a 2150 but I doubt that's your taking off problem. Make sure you have no vac leaks as it will run like crap, is that missing vac hose blocked off??

Paul

[JamesH]

Starting on LPG is always hard work as I understand it - that's why even the fancy electronic kits start on Petrol then switch over. I think it's a temperature thing but it's been a long time since I put LPG stuff in my head and most of it has leaked out now.

[bigjeepzj]

  you need to heat up the lpg to a gas so it burns better

[Brynjaminjones]

Thanks for the advice guys. I'm slowly getting my head around my first car that's not got the 4.0!
I have a feeling there's going to be an endless stream of constant fettling (and a stream of annoying questions on here to go along with that!).


I thought that the above was probably the case when starting on LPG. I've done some reading on Australian forums and from their advice have now found that holding the throttle very lightly open as I crank helps it start up much quicker.
This is such a different LPG system to that on the ZJ so still trying to understand.


I think I might head back to the LPG place to see if they can do some adjustments on the LPG system. It has an irritating habit of stalling if I get off the throttle too quickly whilst the engine is under load (typically reversing on full lock), always at the most inconvenient time.


The alternator is great once I'm above idle, but traffic concerns me as the voltage goes into the red even without the lights or wipers going! It does idle very low, but that seems to be the norm.


My other question you lot might not have the answer to, but worth a shot:
I need to put a new air filter in.
It's got the original filter housing, but inside is of course the LPG mixer. The pipes from the mixer protrude into where the filter normally sits, so the previous owner has simply hacked up a filter with scissors so it can fit around those pipes. This looks awful to me, and I'd be surprised if it wasn't allowing unfiltered air in. Is it possible to fit a bigger air cleaner, or a different type? I don't really know what the replacement options are for this style. I don't really want to have to hack up another filter with lots of bits that could get sucked through the engine!
Any ideas?

[bgbazz]

Any chance you could post some pics of the current set up...plus a couple of general pics showing the whole engine bay layout.
May help with suggestions.

[Brynjaminjones]

Any chance you could post some pics of the current set up...plus a couple of general pics showing the whole engine bay layout.
May help with suggestions.

Yup, will get some when I get home tonight as I'm in my neglected XJ today!

[wildwood]

Sounds like a bit of a mess under that filter.....

I know you don't want to replace any parts yet but just google IMPCO 425 carb (like I just did I)
I think that might be the long term answer to your woes!

[Brynjaminjones]

I think you might be on to something there Jez. The LPG place couldn't identify what brand the system on there is, which I didn't like.
There are lots of bits on this Waggy that have been questionably hacked up.

A good example is the front windscreen washer:
The switch had stopped working, so the previous owner simply extended the wires for the rear washer so they reached the front washer pump. This meant that the rear washer switch only operated the front washers, whilst the rear one no longer worked at all. 

I spent 5 minutes looking at the wiring diagram, looked under the dashboard for the control module, and discovered that it had simply come half unplugged. Plugged it back in and everything is like new again.

[JamesH]

Been there with washers before - crazy what you find sometimes. I can't offer any help with the V8 though I'm afraid, my knowledge just goes as far as remembering carb engines in crappy starter cars and how they always needed a tweak, clean and rebuild.

[5536paulj]

Thanks for the advice guys. I'm slowly getting my head around my first car that's not got the 4.0!
I have a feeling there's going to be an endless stream of constant fettling (and a stream of annoying questions on here to go along with that!).


I thought that the above was probably the case when starting on LPG. I've done some reading on Australian forums and from their advice have now found that holding the throttle very lightly open as I crank helps it start up much quicker.
This is such a different LPG system to that on the ZJ so still trying to understand.


I think I might head back to the LPG place to see if they can do some adjustments on the LPG system. It has an irritating habit of stalling if I get off the throttle too quickly whilst the engine is under load (typically reversing on full lock), always at the most inconvenient time.


The alternator is great once I'm above idle, but traffic concerns me as the voltage goes into the red even without the lights or wipers going! It does idle very low, but that seems to be the norm.


My other question you lot might not have the answer to, but worth a shot:
I need to put a new air filter in.
It's got the original filter housing, but inside is of course the LPG mixer. The pipes from the mixer protrude into where the filter normally sits, so the previous owner has simply hacked up a filter with scissors so it can fit around those pipes. This looks awful to me, and I'd be surprised if it wasn't allowing unfiltered air in. Is it possible to fit a bigger air cleaner, or a different type? I don't really know what the replacement options are for this style. I don't really want to have to hack up another filter with lots of bits that could get sucked through the engine!
Any ideas?

Bryn, tweaking up the idle will help some of this stuff, I run mine about 850 rpm which is higher than recommended but keeps it charging and reduces stalling issues....

[Brynjaminjones]

Thanks Paul, I had wondered if that might help with some issues. It idles so low, even when cold, that I can't help but want to add a bit of throttle to stop it from stumbling. It currently sounds a bit like my Dad's Harleys that always seem like they're right about to conk out!


I'll give all of this stuff some attention very soon, but she's going into daily driver use soon whilst Emily's ZJ has a long overdue heater core replacement...

[5536paulj]

Bryn, idle screw is on the linkage where it meets the carb, best done with a small spanner, 8mm or thereabouts, give it a few turns!!

 

[Brynjaminjones]

That sounds simple! From your description, I assume it effectively just moves the default butterfly position slightly?


I keep getting myself a little confused about how the LPG mixer and carb work together without having disassembled everything or seeing a diagram.
I'd been thinking that the LPG mixer operated completely separately, but it sounds like the carb still impacts on it. Is anyone able to explain this to me? I'm not joking when I say I'm clueless about this!

[5536paulj]

I'm clueless on lpg too, but I think that turning the idle screw just cracks the butterflies open so should work for petrol and lpg? Have a go, you can always put it back to where it was. I would get it running sweetly on petrol first then tackle the lpg.

Basic tune up for these engines, for petrol is: 

1. Set ignition timing (8 deg BTDC), 500 rpm with distributor vac hose disconnected and plugged.
2. Set idle mixture (two screws on bottom of carb at front), start at about two turns out from fully screwed in and turn them out half turn at a time to the smoothest running point
3. Set idle speed

This assumes you have no vac leaks and plugs, leads etc are all good

Have a go at the idle first, might get you of trouble for now!

[Dave69]

Carb strip and clean maybe in order

i gather your running a single point mixer on the carb?

start on petrol first as this warms the coolant that runs through the LPG evapourator, with the warm coolant this little unit doesnt freeze up and stop the flow. Starting of LPG will cause the unit to start freezing up,with the V8 you should be able to swap ove after about 5 minutes.

with it being a single point mixer the engine will only take what it needs due to vacuum, if you have restrictors in the lpg feed lines to the carb try opening them slightly or restricting them to see what happens. as with petrol you can over fuel.

as for the tubes to the mixer, there is no way you can route the tubes without butchering the air filter in some way. With the mixer inside the filter the lpg pipes have to go through it

[Brynjaminjones]

Dave, cheers for that, I'd totally forgotten that your CJ runs on LPG.


I am indeed on a single point mixer with original Motorcraft carb. I'd definitely like to rebuild the carb but have a couple of questions:
1. Will the condition of the carb affect running even when it's on LPG? I wasn't sure about this which is why I've not looked at rebuilding it yet.
2. How do I remove the carb if the mixer is on top? Will I need to disconnect LPG lines to get the mixer off?


It's interesting that you say to start on petrol - I know that was always the advice on an injected system, but the LPG place near us reckoned I didn't need to bother. I had figured it must be the same as a straight LPG forklift.
From my experience so far it does actually seem to start okay on LPG now if I gently press the throttle as I crank, and driveability is good even when just started.


Would you think that adjusting the LPG fuelling settings is likely to improve the performance, or is it likely that this sluggishness is more an issue of ignition timing?


That's a shame about the air filter - it looks like I'll just have to find a better way to hack it up than the previous idiot!

[Dave69]

The only reason for starting on petrol as i see it is that it starts easily, the diffuser on mine froze and the coolant circuit became blocked (unable to strip and service unit)

The normal way a lpg set up can be done is use a wide band lambda sensor to set the mixture ratio, but never did this on mine. The jeep runs better on LPG than petrol as the jetting needs to be reset on the webber im using.

Take the filter off and yes disconnet the lpg lines to the mixer, nothing compicated there and no gas will leak as there is a shutoff relay in the diffuser.

If you look in detail the condition of the carb regarding jetting shouldn't make any difference as the mixer does all the work. As long as the butterflies are working correctly there shouldn't be a problem.

Have a read of the following to give you a basic idea on tuning an open loop system

http://www.diy-lpg.co.uk/articles/files/tuning-open-loop.html