Upping my economy record :)

[threelitre]

Hi!

Finally I get the adjustments of my LPG installation to where I want them: The problem up to now was rather high consumption in and around town (I got up to 260kms/160miles from my 31l tank). So I took some time to fiddle with the adjustments (lean out until car starts to loose performance or show reluctancy when picking up). The first go delivered me 300kms/190miles on about 28l in and around town - very satisfactory for LPG. But on the Autobahn it was too lean, the car was far from being happy at rpm above 3000. So I enriched the mixture bit by bit until I found it cruising OK: Result: 380kms/240miles with just 27 litres (for just under 10 quid!! ). I have not been driving quick (around 70-75mph all the time, mostly on cruise control), but I am pleased. LPG will usually get consumption figures about 10-20% worse then petrol, so I think I can be happy with the results now. The car is still not pulling as good as it was before at faster speeds, but the engine is not complaining, so it seems I am close to the 'lean' spot, where the engine has slightly less power then possible, but is most economical.

There's also still an unresolved problem, probably someone of you may have the answer: When running on LPG the feather sprung needle of the SU carb will wear out the jet quite quickly (several 100km will see the mixture to start getting rich, several 2000-3000 will see a carb that is nearly not adjustable). I tried to fix the needle in the piston, so that it doesn't slide along one side of the jet all the time, but I don't seem to have got it fitted stiff enough, since the jet still wore out further. I considered thinking about something like screwing the jet down as far as possible while not using petrol or fitting a modified cap, that has something that can be used to lift the piston instead of the damper. I even thought about changing to an old HS6 carb, which has a fixed needle. Any ideas? Basically I do not run the car on petrol at all, but being a bit perfectionist I want it to run perfect, when it should do. Ideally by just flicking the switch from LPG to Petrol...
(the last 12 Months or 11k miles have seen me using less then 1 tank full of petrol - so I am not really desperate to find a solution).

Regards,

Alexander

[tony]

alex have you any pics of the lpg system under the bonnet, and how it connects to the engine ?
how does it turn the petrol off ?

[threelitre]

Yeah, I have been promising these pics since June... OK, here they come:

The 1st shows the vaporizer in the back and the gas pipe entering the carb in the front. There is nothing special inside the carb, the gas pipe is just cut off in front of the carb's entrance. Simple, but does work.

The 2nd pic shows the 2 solenoids on the bulkhead. The one on the left sits between fuel pump and carb and shuts of fuel when the car runs on gas, the right one is to open and close the supply of LPG.

The tank is in the spare wheel well and has a volume of 42l (with about 32 useable).

This very easy setup has some disadvantages, some of them hard to avoid with a carb on the engine:
No automatic changes between LPG and petrol. When changing from LPG to petrol there is a short time with no traction when the float-chamber fills up. Other way round the float needs to be emptied first, before LPG can be opened. So best make these switches on an open road, like a motorway. It can take up to 1km to empty the carb of remaining petrol after closing the solenoid. Another disadvantage of the location of the fuel solenoid is that the petrol in the pipes gets boiled for months or so before it is used eventually - it may well be diesel or something like that and the car may be very reluctant to run! All this can not really be avoided on a carb'd engine. The advantage is that this car can be started on LPG all the time (up tp -7 C without probs).
I did describe the SU-HIF specific problem further up already...
Then the SU carb has one advantage if you allow the piston to move up and down just as if it is running on petrol: The mixture will enrich slightly on acceleration from low rpm, a typical weakness of not lambda controlled LPG installations. I still have the (also typical) slight leaning off at higher speeds, but it's running fine! And a manual choke is a good thing, since this can be used to control the higher idle rpm needed in cold winter mornings...

So far, I have saved about 700 quid in 12 months and am happy with the result...

Regards,

Alexander

[G Force]

Hi, Alexander, with regard to the needle wear issue, if you do not want the needle biased I think all you need to do is file the top of the grey collar (that holds the needle in the dash pot piston) flat, as the little nodule on top of it is what tips the needle over. The needle is biased to maintain acurate fuel metering at low piston hight, so you could experience the odd idling/light throttle anomalie on petrol.

Other carb probs associated with lpg can be floats wearing out and needle valves wearing or even dropping out due to the vibration of the float etc. when not in petrol.

Cheers Gary

[threelitre]

Hi, Alexander, with regard to the needle wear issue, if you do not want the needle biased I think all you need to do is file the top of the grey collar (that holds the needle in the dash pot piston) flat, as the little nodule on top of it is what tips the needle over. The needle is biased to maintain acurate fuel metering at low piston hight, so you could experience the odd idling/light throttle anomalie on petrol.

Obviously, this was my first try, after I found the mixture getting too rich. But this worsened the wear dramatically, since the needle now randomly scuffed along every side of the jet and did not only slide along one side. So after a couple of 100kms the carb was rendered not adjustable... (see pic for the jet new and after this attempt). 2nd stage was trying to fix the needle. I fitted the needle to the collar using some engine sealant (to withstand fuel and lpg), this helped, but still not perfect. Although the needle feels quite solid now, it seems to virbrate enough to wear out the jet again. A friend has an old SU HS4 on his LPG-car and has no such problems at all, but his carb has the traditional, fixed needle. So I will probably solder one needle to the filed collar to see if this helps. Problem is to get it centered exactly...

The biased needle's main effect is to make manufacturing quicker, since the adjustment of the jet vs. needle can be handled much easier (i.e. non existent anymore). The area of the opening between needle and jet will always be the same, regardless if the needle is centered or off-center. Only small effects, like slightly different pressures in front and back of the needle will affect the flow, so I don't see a reason for noticeable running problems between these to variations.

Other carb probs associated with lpg can be floats wearing out and needle valves wearing or even dropping out due to the vibration of the float etc. when not in petrol.

I guess that the float or the needle may sometimes stick a bit after being unused for a long time. But I can't imagine that the float needle will drop out. The Maestro isn't that rough! And looking into the carb, everything is perfect, even after more then 10k miles.

Regards,

Alexander

PS: I already thought about dumping the petrol tank and fit a 2nd LPG tank instead

EDIT: Forgot the pic of the jet... Guess which one is worn out.

[G Force]

[QUOTE=threelitre]I guess that the float or the needle may sometimes stick a bit after being unused for a long time. But I can't imagine that the float needle will drop out. The Maestro isn't that rough! And looking into the carb, everything is perfect, even after more then 10k miles.

Hi, I saw this happen on a regular basis when british gas ran Ital & Marina vans, as they were all lpg converted. Obviously it did not happen on every van but did present on a high number. If you have not used petrol for 10k miles then you have done well not to have any problems.

Cheers Gary

[threelitre]

I did use petrol on the occasional basis, but not more then 1 tankful in this time. Basically I try not to use it at all - but at least once a year I have to: for the emissions test Last time in September. On one day each in July, February and last years October I had to use petrol for driving some distance, since I did not come across a LPG station... Other uses are occasional tests, if the system still works, and mostly it does only work after (yet another) retuning of the carb. Currently I am thinking about fitting a new jet, buying a new needle and keep the needle in the car to fit it before using petrol. Although I would like to find the perfect solution where no wear occurs and I can change from LPG to petrol any time I want, the need to run on petrol is currently VERY rare and is predictable - so I guess a needle and a screwdriver in the car will suit...

Alexander