View single post by Esprit2
 Posted: 10-04-2018 05:20 pm
PM Quote Reply Full Topic
Esprit2

 

Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 575
Status: 
Offline
 The simplest way to know if enough fuel is reaching the carbs is to check the fuel pressure at the carb inlet. The pump's outlet pressure is ~3.8 psi, but with flow losses and the carb's higher elevation above the pump, the carb inlet pressure should be 1.5 - 2.5 psi. The carbs can probably handle 3.0 psi, but excessively high pressure can result in an overall rich condition that cannot be adjusted out. Get the pressure right before attempting any carb tuning.

Back at the tank, the fuel return line should include an inline flow restrictor that has a (?) 0.046" / 1.17mm diameter through hole. That works like a 'dumb' pressure regulator. The hole size is selected specifically for the J-H, it's stock fuel plumbing, and the carbs height above the fuel pump's output. Any changes to the system, or crud that partially plugs the bleed orifice, and the pressure at the carbs will be too high. If the bleed orifice is omitted, then there is an un-restricted, large diameter fuel bypass back to the tank, and the resulting fuel pressure at the carbs might be too low.

You can drive yourself nuts trying to diagnose the fuel system, or just check the fuel pressure at the car inlets. If it's right, relax. If it's too low or too high, then jump back into the diagnosis.

Without an anti-drainback valve, fuel in the lines will drain back to the tank when the pump is switched off. On re-start, it will take longer for the pump to re-fill and pressurize the fuel lines, but once done, the engine should run the same with or without the anti-drainback valve. The valve is more of a convenience item than a 'must have to work' item. It's best to have one, located back close to the tank end of the plumbing

Regards,
Tim Engel