GQ RB30 (carby)- Not Idling on LPG but ok on Petrol

Hi all,

Was doing a bit of maintenance trying to fix one issue and seem to have created another.

The engine was having issues on LPG with splutering and missing until reaching about 2ooo rpm then it ran fine. Ddin't have the issue when running on petrol.
So today I changed the spark plugs and that seemed to get rid of that issue but now I have a problem with the engine not wanting to Idle when running on LPG.

Running on petrol is fine (and better now with the new spark plugs) and idles fine but as soon as you go onto LPG, it coughs and slows sown till it eventually stalls. If you restart, it takes about 5-10 seconds before it dies again. If you touch the accelerator, it runs fine and even accelerates fine but as soon as you stop at lights or take time changing gears....it stalls.

Prior to changing the spark plugs and just checking the timing, it was running on LPG fine, in fact it ran extremely well on LPG...about 550km per 90ltr tank.

Other things I did prior to this, rotating the distributor to check timing, adjusting the Idle screw (runs at about 850-860rpm) and went to adjust the fuel mix but noticed the mix screw seems to have been locked off (it may not be but not familiar with this carby and cannot finds answers anywhere). The screw has a 'U' shaped bar attached with the open end facing towards the rear of the car. The pipe coming from the carby to the left of the mix screw sits at the open end of the 'U' shaped bar and this seems to stop the mix screw from being turned. There is a slot for a thin screw driver but after trying, it didn't seem to change the mix screw....but i could be wrong.

Since this afternoon (after putting the bits and peices together) it won't idle on LPG and it is also back-firing when the engine is under back pressure (going down hill) and reving at about 1200-1300 rpm.

Don't know how to fix this as I'm not sure if the mix screw has moved or whether it even affects LPG....but it sure is annoying to fix one issue, only to have another one appear.

If you need a photo of the carby showing the Mix screw I'll add one.

Cheers
Paul

:1087:

Hello, Paul, and welcome to the forum. Check all of the electrical connections done by the gas installer. Especially and scotch locks and spade connectors. My neighbour's car was playing up on gas and we found a wire to the gas solenoid wasn't crimped properly. Other than that, when was the last time the system was tuned by a mechanic using a CO meter?

Hey Mate
Mixture screw on carby won't change gas mixture. Normally there is an adjuster for the gas, where the gas hose joins the top of the carby. It's a pretty agricultural adjuster. Well is on mine at least. Mine has a cable running into the cabin which is pulled to open mixer to let more air in when running on petrol. When doing some work on the motor some time ago, I reconnected this cable. Didn't get it quite right, when shutting it mixer wasn't closing properly, letting to much air through and car cutting out when switching to gas. Don't know if this helps worth alook.

Quote:

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Originally Posted by fourj

Hey Mate
Mixture screw on carby won't change gas mixture. Normally there is an adjuster for the gas, where the gas hose joins the top of the carby. It's a pretty agricultural adjuster. Well is on mine at least. Mine has a cable running into the cabin which is pulled to open mixer to let more air in when running on petrol. When doing some work on the motor some time ago, I reconnected this cable. Didn't get it quite right, when shutting it mixer wasn't closing properly, letting to much air through and car cutting out when switching to gas. Don't know if this helps worth alook.

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Thanks Fourj for the info. I did move the adjuster at the top of the carby where the LPG connector is....just remembered....but I did also try putting it back to where I remember it being before I touched it. Weird thing is that it runs fine and drives fine, just won't idle now on LPG.

Serves me right for tinkering :)

I may just have to take it in for a tune-up.

Can anyone recommend an LPG mechanic in the Heathcote/Engadine/Sutherland area south of Sydney?

Cheers
Paul

Quote:

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Originally Posted by mudnut

Hello, paul, and welcome to the forum. Check all of the electrical connections done by the gas installer. Especially and scotch locks and spade connectors. My neighbour's car was playing up on gas and we found a wire to the gas solenoid wasn't crimped properly. Other than that, when was the last time the system was tuned by a mechanic using a CO meter?

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Never heard of 'Scotch Locks'...what are they?

Cheers
Paul

The scotch lock is the lazy way to join wires. It is a tiny plastic case with one or more metal teeth inside. You place the wires inside, fold the top over and use pliers to crimp it. I have looked for an image to post, but have been unsuccessful. The join can fail if subjected to vibration and /or moisture. I recommend soldering all of the joints and using heat shrink or liquid electrical tape to seal them.

Thanks for all the info guys. Have finally worked out what it was.

Looked up a diagram of the Impco 300A and after looking at the components in the diagram I realized I must have turned the idle/tuning rod. So after a couple of minutes I had it running and Idling properly again on LPG.

FYI....Its a very precise tuner on these machines. About 1/16 of a turn between 'tuned' and 'out of tune'...

I have attached a copy of the PDF with a blown-out diagram of the Impco LPG kit in case any one is interested.

Glad to read it was an easy fix.

Quote:

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Originally Posted by mudnut

Glad to read it was an easy fix.

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Thanks. Hopefully if someone else has the same issue, the PDF diagram of the Impco 300A will come in handy.

By your image I assume you have a GQ LWB? Get the chance to get out much?

Have some other issues with my GQ that I'm trying to nut out....more to do with the drive train and transmission but I'll post those up soon as I work out how I'm going to describe the issues.

Cheers
Paul

Other things I did prior to this, rotating the distributor to check timing, adjusting the Idle screw (runs at about 850-860rpm) and went to adjust the fuel mix but noticed the mix screw seems to have been locked off (it may not be but not familiar with this carby and cannot finds answers anywhere). The screw has a 'U' shaped bar attached with the open end facing towards the rear of the car. The pipe coming from the carby to the left of the mix screw sits at the open end of the 'U' shaped bar and this seems to stop the mix screw from being turned. There is a slot for a thin screw driver but after trying, it didn't seem to change the mix screw...

:1087:[/QUOTE]

Does anyone know how to adjust idle mix screw, my carby has the same thing on it, wont let you get a screw driver in there and seems to cover the adjusting bolt, can anyone tell me if it comes off or not..thanks.