Okay so my 1973 240z (all smog gear removed) wont go above 60mph in 3rd or 4th gear, kind of hits a wall. Pulls strongly through RPM range in 1st and 2nd up too 5000 rpm (didn't try any higher), change to third and all acceleration ends. Doesn't seem to be hunting for extra fuel, just stays where it is.

I've checked my timing (with a strobe) it's set at 10 degrees @ 800rpm.I've tried advancing/retarding it with no improvement. I've got a new petronix ignitor (had one before replaced it as test) with new 3 ohm flamethrower coil (no ballast resistor). Just put in new NGK sparkplugs, re-checked SU float levels are correct, made sure damper oil is in dashpots, and that pistones are freely moving.

I know I've a rusty fuel tank but I cleaned rust residue out of rear pump filter, and changed front filter for testing. All to no avail. I'm guessing I have to get my tank cleaned but was just wondering if anyone had any other ideas.

Gary

Oh and its got 3 screw round tops not flat tops

Check that the vacuum advance mechanism works.

E

I hooked up it up with a mityvac and the plate moved freely and held position. So I think that's working, thanks for the suggestion

Two words: Fuel Pump.

That is exactly how my 71 acted when the fuel pump was bad. It ran strong, at any RPM so long as the car was moving less than 60 MPH, then it just as you say, hit the wall and would move no faster.

Thanks Walter, will give that a try.

Try shifting into second gear........

Oh I'm so funny .

Yep fuel pump related IMO.

Edited November 28, 201014 yr by Unkle

Final filters in the float bowl lids clean? Could be partially plugged especially if you're fighting rust issues.

Very good Unkle. Thanks Bruce checked those filters when checking float bowl levels. I guess I'm going to have to bite the bullet and do the gas tank & fuel pump.

Changed fuel pump, no change

Did you check your throttle plates? Spray carb cleaner on them while the engine is running to see if the car stalls. A few people pointed that out in the past as a possible problem =T

When you say you "rechecked float levels and they are correct" what are they set at and how did you set them?