Maverick 4.2 carby LPG/petrol losing power and backfiring...Help!

[Davies90Maverick]

Hi this is the first time Ive posted here but is a great source of info so here we go.
I have a 1990 Maverick 4.2 carby petrol that is dual fuel. Just done a Palm Valley trip as its local to me as I live in Alice Springs, so lots of corrugation, rock hopping etc.
It has started to run like s**t. Very juddery at idle, juddery top end power and backfiring. These problems started on the way back (150km trip back). I have recently replaced the spark plugs and leads and is regularly serviced by me, oil filter, fuel filter, oil change etc. I have tried tweeking the idle screw and the mixture screw on the carby but just not getting anywhere.
It could be sucking air somewhere I suppose but just wondering if anyone had an idea of this as dont really want to put it into the garage if I can save some money and do it myself, however this is now pushing my knowledge as I am no mechanic but a "have a go" mechanic to save some money.
Anyone experience these issues with the same model? If so HELP!

Thanks

[taslucas]

Hi mate, have you looked at the distributor at all?

[threedogs]

re-check that all the leads are on and tight, You have an electrical problem IMO.
at night start the motor an look at the motor for sparks, easy to see
When you get a chance jump over to the intros and tell us a bit about yourself.
We have a member in Alice who may be able to assist you as well
you said it when you said lots of corrigations, you need to make your GQ territory tough lol
it may just be a loose lead

[Alitis007]

Does it run rough on both fuels??

[Davies90Maverick]

Hi all yes it runs rough on both. Went over the leads, couldnt see anything and seemed on ok. I spent the morning changing all the vacuum hoses and cleaned the carby as the air filter was off...seems to have sorted it but havnt given it a run up the highway yet or changed over to LPG, we shall see and I will put an update on shortly. Thanks all for the advice so far.

[Alitis007]

Hold you're hand over the carby so it chokes it or see if it still runs

[Davies90Maverick]

Right then, here we go.
I have changed the spark plugs, ignition leads, vacuum hoses, new fuel filters and even put in a second inline fuel filter. The carby has been cleaned with carby spray but not removed. It will now run fine on petrol or gas BUT NOT BOTH! I can get it to run fine on the petrol, no loss of power running fine, but press that magic change over button, will run on gas fine, change it back to petrol...bag of s**t again! Starting to think what have I missed? Getting very frustrated now!

[garett]

were the plugs really dirty ? like it was over fuelling. can try checking plungers are free to move on gas system, if they stick open it can cause duel fuelling and will run poorly

[taslucas]

Right then, here we go.
I have changed the spark plugs, ignition leads, vacuum hoses, new fuel filters and even put in a second inline fuel filter. The carby has been cleaned with carby spray but not removed. It will now run fine on petrol or gas BUT NOT BOTH! I can get it to run fine on the petrol, no loss of power running fine, but press that magic change over button, will run on gas fine, change it back to petrol...bag of s**t again! Starting to think what have I missed? Getting very frustrated now!

So after that what do you do to get it to run properly on petrol again? Could it be something to do with the fuel shut off solenoid?

[rusty_nail]

what about it being the points(i think thats what its called?) the thing inside the dizzy, where you adjust... im sure someone knows what im talking about? i had a problem with my old car doing what you describe. it ended up being the part im referring to and after that it ran fine. i noticed you didnt mention any work to do with that and its another very important part of your ignition system...

[4bye4]

Right then, here we go.
I have changed the spark plugs, ignition leads, vacuum hoses, new fuel filters and even put in a second inline fuel filter. The carby has been cleaned with carby spray but not removed. It will now run fine on petrol or gas BUT NOT BOTH! I can get it to run fine on the petrol, no loss of power running fine, but press that magic change over button, will run on gas fine, change it back to petrol...bag of s**t again! Starting to think what have I missed? Getting very frustrated now!

Mate your "magic change over button" will operate a gas lock off solenoid, which will control the gas into the motor. Is it possible that it is trying to run on gas and petrol at the same time. In other words is the gas solenoid operating positivly and shutting off the gas completly? The solenoid also has a filter in it on the inlet side.

[Davies90Maverick]

Hi all, Again cleaned out the carby, this time taking the "sight window" off and a load of s**t came out, took out the mixture screw, again load of s**t came out. Got the missis to run it at 3000 revs and set the mixture and idle high end, now seems fine on both. With the dizzy, I took it off had a look, gave it a spray with carby cleaner also but all looked ok. As it is now running fine on both I will leave it, however think its time to upgrade the ignition system with pertronix and a flamethrower coil next. Thanks all for your help. Anyone else had pertronix put in and are they as good as I hear? Thanks

[Davies90Maverick]

Oh one more thing, I noticed that I could see when running on gas threw the second fuel filter as its see through the petrol was still being pumped? would this be pumped anyway but just returned through some sort of return valve? or should it not be pumping at all? Thanks

[4bye4]

Check that the solenoid is changing over fully.

[taslucas]

I have the pertronix 2 and flame thrower coil. It made a very noticeable difference in economy and power.
I actually had a faulty module (from factory) so it missed and cut out a bit and was STILL more economic and powerful than standard.

[Davies90Maverick]

Hi problem continues intermittently now on both fuels. Now convinced its electrical, going to replace the dizzy cap and rotor button, then if this fails condensor?

[threedogs]

As I said in #3 you have an electrical problem, it may be spark timing and the way its delivered.
Do the coil , or the extended rotor button thingy this mod has been around for eons

[Davies90Maverick]

Hi all.
Today changed the condenser, dizzy cap and rotor button and points. It will now no longer start at all. It sounds healthy but just wont fire, what am I missing? Also Taslucas, how do I extend the rotor button which you mention as a mod?
Thanks