Saturday, Mar 31, 2007 at 13:38
Well Godlike, the Archangel Gabriel is here to help (LOL)
Mate I have a 1981 Datsun(Nissan) bluebird which I purchased new and converted to LPG in 1986.
Have done all sorts of R & D projects on it re the LPG, and since around 1988 it has been 100% LPG. Why - because of too much playing around to make it work equally as
well on both fuels.
Don't despair at my solution because you obviously need dual fuel where I didn't.
In the earlier days of LPG dual fuel (1980's) the engines were produced with valves and seats designed for petrol only.
As an alternate fuel LPG has a few nasty qualities in that it burns hotter, has no lubricate in it and requires a colder spark plug set at a higher gap.
When all this is combined with a petrol set up something has to 'give' and after the initial tune to get both fuels to run at their best, the usual ( repeat usual) practice in the 1980's was to start on petrol and run on LPG (as it was cheaper) and switch to petrol before shutting down for the day. Plus maybe pump a tank of petrol through the engine whenever for lube purposes.
Also a 'lean' mix on the LPG to air ration can exacerbate the valve degradation.
ACCUMULATIVE AFFECT:
(1) In a nutshell the valve faces, valve seats and valve stem guides used to deteriorate much quicker leading to valve recession and then burnt out valves or seats (Exhaust).
The valve recession gives the symptoms that you describe both on petrol and LPG.
(2) I take it your set-up has a 'mixer ring' on top of the Carburettor. Over time where the user/s have elected to use LPG as the fuel of choice then the engine heat and 'dry fuel' absolutely wreck all of the Carby seals and make the Carby do strange things.
You won't notice it on LPG as it goes straight through, however on petrol it can be a real bitch.
CONCLUSION:
These are the two main sources of problems with this this type of setup and the first thing I would be doing is to
check the valve clearances (Costs nothing)
Then make sure the carby is work correctly - See if it is filling up with petrol, pumping/squirting when the accelerator is activated.
Also
check if it is a dual barrel carby (bet it is) and if so there are two jets underneath that people inevitable put back in back to front when they turn the carby upside down to work on it. (Has happened to Moi)
Air/vacuum leakages, will affect the smooth running of the LPG way before it shows on the petrol side of things. So I wouldn't be considering the warped carby just yet,
Hopefully this will give you something to look at.
AnswerID:
230851
Follow Up By: Godlike Chef - Saturday, Mar 31, 2007 at 20:10
Saturday, Mar 31, 2007 at 20:10
Thanks Archangel for the insight hopefully with some playing around I can get the problem fixed.
It's all a bit of a learning curve at the moment (but thats half the fun) fingers crossed I can fix it.
FollowupID:
491757
Follow Up By: Member - 'Lucy' - Sunday, Apr 01, 2007 at 00:35
Sunday, Apr 01, 2007 at 00:35
Good luck.
Remember.
(1) Valve clearances
(2) Carby
(3) Vaccuum (sucking air)
(4) Spark plugs and settings
FollowupID:
491793