TheSamba.com :: View topic - High Fuel Pressure and Carburetor Settings

Mon Mar 01, 2021 3:52 am

Recently rebuilt 1600 Dual Port, 34 Pict 3 carburetor, and after market fuel pump (JBUGS). When adjusting bypass screw, there is no noticeable change in rpm (monitored with tachometer). The bypass screw can be adjusted all the way and and out, with no response. The motor seems too be run very rich, and the oil has a slight gas smell, which leads me to believe fuel is being forced through the needle and seat.

I'm going to check the fuel pressure later this afternoon and purchase a fuel pressure regulator, if needed. Question is, can high fuel pressure, in addition to other fresh rebuild issues, cause the carburetor to be none responsive to bypass screw adjustments?

Any help is greatly appreciated.

Mon Mar 01, 2021 4:26 am

I'm going to guess that your throttle is too far open and the idle circuit is not in effect. This may be because the engine is a bit stiff but more likely your initial timing is not advanced enough. A vacuum leak could do that too.

Yes, check your fuel pressure.

Mon Mar 01, 2021 8:35 am

It's easy enough to pop the top of the carb to see what the bowl fuel level is. If it's within spec,
the fuel pump pressure is not to blame for your running issues. Non-responsiveness to bypass screw
adjustments is a typical result of vacuum leak, which includes improperly set throttle plate.