Amazon: Setting up a Stromberg on ex-LPG car

[riczito]

Hi all,

My Amazon 121 came from Holland, and was a bi-fuel car, with an extra LPG system. I had the LPG tank, the pipe work and the electrics removed before I took delivery of the car, as it wasn't homologated for use here in France.

The car is a late 1968 model with a B20a 2 litre engine and a single Stromberg carb. It always starts cleanly from cold (less so from hot), and I never need to use the choke, which I'm told is an anomaly. Also, it drinks fuel at quite an alarming rate.

Recently I met some Volvo enthusiasts and they suggested that the needle and jets used on these LPG-equipped cars are different from regular cars, which might account for the fuel consumption, hot starting and chokeless cold start issues. They suggested I change the needle, the jets and set the carb up properly for petrol-only. Can anyone confirm this diagnosis, and if so, which needle and jets should I be looking into?

Many thanks,
Ric

[Rustinmotion]

Originally Posted by riczito

Hi all,

My Amazon 121 came from Holland, and was a bi-fuel car, with an extra LPG system. I had the LPG tank, the pipe work and the electrics removed before I took delivery of the car, as it wasn't homologated for use here in France.

The car is a late 1968 model with a B20a 2 litre engine and a single Stromberg carb. It always starts cleanly from cold (less so from hot), and I never need to use the choke, which I'm told is an anomaly. Also, it drinks fuel at quite an alarming rate.

Recently I met some Volvo enthusiasts and they suggested that the needle and jets used on these LPG-equipped cars are different from regular cars, which might account for the fuel consumption, hot starting and chokeless cold start issues. They suggested I change the needle, the jets and set the carb up properly for petrol-only. Can anyone confirm this diagnosis, and if so, which needle and jets should I be looking into?

Many thanks,
Ric

This one?

[Nullifie]

Hi Ric,
only driving on LPG the jet and needle (and piston) in the carb aren't functional (they could be removed from the carb if never driving on petrol). So no special needle and jet is used for LPG. But driving on LPG results in a clearly quicker as normal wearing of needle and jet (no fuel flow seperating them from each other). The gap between them eventually will get way out of the gap needed for petrol driving and results in a very high petrol use, not having to use the choke and bad starting hot on petrol (too rich).
So rebuilding the carb (at least new jet and needle, and I assume also the throtle valve axle and bearings) will have to be done.
succes,
nullifie

[riczito]

Originally Posted by Nullifie

Hi Ric,
only driving on LPG the jet and needle (and piston) in the carb aren't functional (they could be removed from the carb if never driving on petrol). So no special needle and jet is used for LPG. But driving on LPG results in a clearly quicker as normal wearing of needle and jet (no fuel flow seperating them from each other). The gap between them eventually will get way out of the gap needed for petrol driving and results in a very high petrol use, not having to use the choke and bad starting hot on petrol (too rich).
So rebuilding the carb (at least new jet and needle, and I assume also the throtle valve axle and bearings) will have to be done.
succes,
nullifie

Thanks very much for the explanation ! This aligns exactly with the symptoms my car is exhibiting. I will rebuild the carb as you suggest.

Thanks again !

[Burdekin]

Start with setting the fuel mixture at idle as per the Volvo green book instructions and then see how things go. If it’s set to run very rich at idle then it’s going to be running rich when normal driving as well, even if the correct needle is fitted.

Consider a wide band O2 sensor and gauge fitted to the exhaust, makes it easy to set idle mixture accurately and then check air/fuel mixture when driving. You can use this to ensure you have the correct needle fitted.

[Burdekin]

Also I’d recommend only buying carb parts from Burlen in the U.K., especially the diaphragm. I’ve bought aftermarket ones and they’re not good. I personally replace the diaphragm annually and keep a spare in the car. If the car is new to you it’s a good idea to replace it. Make sure when you screw the carb top back on after replacing the diaphragm that the alignment line on the carb top matches with the line on the carb body. See attached photo. It’s a 5 minute job. Change diaphragm and set the fuel mixture at idle and see how she runs then.