ok well a friend of mine bought an 81 F100 (302) its in fantastic shape, and the engine was well taken care of. His problem is that when he runs it on propane it sounds and runs great, but when he runs it with gas it sounds like crap. Meaning it sounds like its going to die out when its idleing, it stalls when you put it into Park, rev's too high, and has hardly any power and spits out black exhaust that smells really strong of gas. he replaced a hose that goes under the carb to somewhere above his header, i believe it has something to do with telling the electronic choke that the engine is hot to open up the carb, after doing that it made the truck run a little smoother, but still stalled and spits out black exhaust. He started adjusting 2 jets under the carb i think it adjusts how much gas and air go into the carb. I suggested that it may be the termostat, or i read on here that it could be the ignition module or something along those lines.
anyone that could help, it would be greatly appreciated
-brAd

 

G'day Bradmur, Greetings from Brisbane, Australia!

Join the club of F100 users who have experienced the same difficulty.Thank goodness I am not the only one who has had this problem and I doubt we will be the last. When I bought my !981 F100 with a 351 Cleveland just over 18 months ago it was a dual fuel vehicle, with the LPG not operational.

It was running on petrol (OZ language), being very rough on that fuel, it was very eratic with a high idle of about 1200 RPM to keep it going as well as pre-ignition.

About 8 months ago I completed a rebuild of the LPG, with new tanks, new lines and electrics to suit, a new evaporator, carb top dissapator and air filter.

It is running very smooth and sweet on LPG with power to burn for my use of towing a caravan or camper trailer and heavily loaded with all the camping gear, tools, spare wheels and tyres, additional fuel, water, provisions, LPG for cooking, friges and lighting and a set of solar powered batteries which are needed to tour and explore outback OZ as there are no servos or corner stores out there.

Petrol, well? My problem was the dizzy. I sent the truck to a professional shop, had it recalibrated and, Hey Presto! It works.

The LPG I tuned myself not trusting all the mechanical monsters that lurk in electronic tuning devices and rolling roads, they cost heaps and make it run no better than my tuning techniques.

This is what worked for me on my V8.

You should have a restrictor valve somewhere in the main LPG supply line from the evaporator to the carb top. If you have not, get one put in.

Start the motor up, bring it up to operating temperature, up the RPM to 2000 by turning in the idle screw, slowly screw the in line restrictor in until the motor faulters, just like an air bleed on a petrol carb, then turn it out one half a turn, back off the idle to about 800RPM and make incremental adjustments as time goes by to that restrictor to ensure a smooth running, powerfull engine. You may find that you will need to screw it in rather than out.

The motor will then balance out its use of LPG accordingly. You should be able to smell a whiff of burnt LPG at the exhaust.

If you have the restrictor valve open to much the motor will just gulp LPG and you will get very ordinary performance and extremely poor economy. I used the trial and error method. Use you own judgement.

I have 2X75 litre LPG tanks with a usable volume of about 135 Litres. I get between 600 & 700 odd Kilometres on all types of running.

I consider that to be real good economy for a big 351 Cleveland V8.

Bear in mind your vehicle will use about 1/3 more LPG than petrol.

I hope this helps.

Les Bryant, Brisbane, Australia