1987 Samurai JX with OEM engine and Hitachi carb. New fuel filter, fuel pump, and accelerator pump. Sea Foam was run through the fuel system. Air filter is clear. Carb secondaries are opening. Choke appears to be working properly--closed when cold and open when warm. Timing at 12 degrees BTDC because I live at 4,000' elevation. New NGK plug wires. Starts immediately, idles well and spins right up through the RPM range. Actually has good power and acceleration for a Samurai.
It does have a weird thing that seems to happen only at highway speeds 55-65 MPH. I can be driving down a flat section of highway for several miles at 60 MPH and everything is fine. All of a sudden the RPMs will start to drop off and the speed will drop by about 10 MPH with a noticeable lack of power. I'm not going up hill nor into a headwind. It just kind of loses power all of a sudden as if it is gas starved. However , it does not buck or surge or stall. I have tried backing off the throttle when this happens thinking that if it is running out of fuel in the carb bowl this should give it time to refill. That doesn't seem to do much. Eventually, after a few minutes, it will climb back up in RPMs and have full power again. There is nothing that gives an indication when or where the power loss will happen.
The previous owner had taken 2 of the small hoses coming from the fuel tank and joined them together. My guess is it was done to bypass the fuel vapor capture canister that is located near the fuel filler neck. All other lines on the fuel tank appear to be connected properly. I checked these lines on the fuel tank thinking that maybe it was not getting vented properly causing too much vacuum and a loss of fuel to the carb.
Any ideas what might be going on?
Thanks!
