I have the dreaded Aisan Carb fuel draining out to the bowl problem. 85 Toyota 4x4 22R extra cab, single owner never wrecked... It drains overnight when the motor is shut off. I've serially plugged all the point where fuel can leave the bowl, and have determined it is coming from the Accel/Aux. Accel pump jet in the primary barrel. I've estimated the "drain rate" of fuel leaving the barrel to be 3/4 (three fourths) of a drop per minute. which explains why I can't find the leak visually. even with fluorescent dye and a black light. But at that rate, no fuel will be visible in the bowl sight glass overnight. I did much of the testing with a cold engine, only running the engine only long enough to refill the fuel bowl. So Heat is not the problem... although it does make it drain faster...
The only thing I have found that is suspicious is the "levelness" of the carb. Side to side it is level, but there is a significant lean front to rear, The top valve cover front to rear has a 3.25 inch drop per foot, the stock manifold has a front to rear drop of 1 in drop per foot" Indicating Toyota did engineer the manifold to have less front to rear lean. The rearward manifold lean makes the fuel level higher at the barrel a quarter inch higher at the barrel jet than it shows in the sight glass. Which makes siphoning or capillary fuel movement easier...
I machined an angled riser/spacer, to place between the carb and the manifold. (it has a quarter inch rise across the 3" manifold gasket). This reversed the lean to a slightly higher rear to front to levelness. It slowed the drain rate down by 50% but didn't stop it. The Carb mounting bolts, through the Manifold, won't allow for a spacer with more lean, with out major modifications...
Is my my carb mounting the problem? Does anyone have a Asian carb that doesn't drain off that could check their carb level?
Anybody discovered the solution?
I just replaced the carb with a new one, it drains at the same rate. Back to the drawing board...
I figured out a way to check the deceleration fuel cut solenoid for leakage. During a carb rebuild, with the top layer removed, back you mixture screw out so it doesn't protrude into the primary barrel. Cover the hole and the fuel enhancement slot (just above the needle hole) with a piece of scotch tape, then place another piece over the mixture screw hole (outside of carb) to seal it. Use another small piece to cover the High Altitude Compensation air supply hole on the top surface.. You can now use a handy vac to pull vacuum from the remaining idle air supply hole. It should hold air almost indefinitely... (Inspect your taping for bubbles and leaks)
