My 79 has a peculiar problem, slowly over the past 12 months it has been getting longer and longer to get fuel to start, now taking 15 seconds or more of cranking before it fires. It has now developed a starving condition under wot, so i tested the fuel flow from the pump by removing ignition wire and fuel line at the carb, had friend crank engine, fuel squirted quite well, I put finger over flow and fuel had reasonable pressure behind it but I could easily block the flow. I suspect pump isnt producing enough flow/pressure to open non return valve in filter at carb, i removed the valve and put filter back in line, car no longer starves under wot condition, i dont blame valve though as i am confident pump should be able to produce enough pressure to overcome resistance of valve. So, is it pump? Why am i gradually getting less fuel flow over time? Not likely to be float level as I have checked it and I cant see why a bad float level would gradually get worse. For now i have left carb filter valve out. Heres my list of possibilities.

1. Fuel pump defective, maybe internal valves failing slowly.
2. Cam worn and pump not being activated enough (unlikely as cam is only 10k miles old)
3. Faulty non return valve in carb filter.
4. Clogged pickup filter in tank pickup.

Any ideas or thoughts about these possibilities?

Love to hear from Lars on this one.

 

Most likely, the (synthetic rubber) seal on your accelerator pump in the carb has deteriorated because of Ethanol in the fuel. Over that time, the accel pump has ceased to function, which is why you can keep pumping the carb but nothing happens. Eventually, what little vacuum the engine is making during the start cycle is causing some fuel to get into the intake manifold.

Remove air cleaner, (engine OFF, please) open choke plate manually, look down into the primary venturi and give a full-throttle pump on the carb linkage. You should see a full stream of fuel go into each side of the primaries. If you see none, or a very weak spurt, the accelerator pump in the carb is defective...probably only because of a bad seal on the end of the piston.

If that is your problem and you replace it, or have it replaced, make sure that the new one is "Ethanol capable". It should be made of Viton or some other alcohol/fuel resistant material.

 

Don't really see the accelerator pump being an issue at WOT. If we're talking fuel starvation and from what testing you've done I would conclude fuel pump is going out. Mine went the same way, slowly over time with fuel starvation problems at WOT.

 

Sorry. I read the initial post too quickly and didn't catch the "wot" part. Accel pump will only cause long starts and 'dead' conditions at the beginning of WOT.