Hi all. My friend has a Toyota 42-4fgc25 forklift with a Toyota 5r engine. The engine utilizes an Aisin carburetor and Aisin convertor/regulator. Recently he complained that it started to run rough and smelled heavily of propane. It would only run at half to full throttle otherwise it would die. It smelled like it was running super rich. After a few more days it wouldn't start at all regardless of what we did. Long story short after countless hours of troubleshooting we determined that we had a fuel supply issue. If you use an external propane supply (tiger torch forcing propane into the carb) with the carburetor intake pipe removed from the top of the carb the engine would run and operate properly.

As such we replaced the Aisin convertor/regulator assembly with a good used unit from eBay. After we installed the "new" unit we started the engine but only if the throttle pedal was at full throttle. It would run ok but die if it was allowed to "idle". We ran the engine at part throttle until it warmed then adjusted the idle. After the engine warmed it would idle fine and run properly. There seemed to be a lag in the throttle response but otherwise it ran as per usual.

The ambient temperature during this has been anywhere from 35*f to 60*f. Fast forward a few days and now it won't run again. It coughs but will not fire. It tries to start but will sometimes backfire and then just die. It's giving identical symptoms as the original issue. It sometimes seems like it will almost fire and other times just cranks. To date we have replaced the coil with an aftermarket coil, replaced all spark plugs, cleaned the distributor cap( non-points style ignition with magnetic pick up with vacuum advance), replaced the battery and tested the following components.

More to come...