i hv a 70 fj40 that is stock. i just had the distributor rebuilt, new plugs installed and the carb rebuilt. unfortually the brakes lines broke at the repair shop and i had to tow the car home to repair (out of date spares). the mech was unable to test drive it before i towed it home but sounds great at idle. engine runs fine at idle and revs good. but when i drive it, whenever the rpm get high it runs really ruff and lacks power. lil bit of black smoke out the exhaust when running. any ideas, i am about to take it back in the shop. just curious if it sounds like something simple to fix.
thanks, sean

Black smoke means it's running rich. Either your carb is out of adjustment, or your losing spark at higher RPM's.:skull:

Running rich wouldn't generally be a problem like you describe at high RPMs. Two possibilities: The secondary isn't opening or the dwell angle is too high (point gap too large) so that the coil doesn't saturate at high RPMs. The points are easy to check, but the secondary isn't easy to check visually while the truck is moving. Usually, you can feel it "kick in". Your secondary vacuum diaphragm may have a hole. I haven't checked, but it may be possible to disassemble the secondary actuator to check the diaphragm without taking the carb off. If you paid someone to rebuild it, why not take it back and bitch.

So if the secondaries are closed at high RPM's your saying it will run rich????? Wouldn't you be running off primarys, low speed idle circuit???? Hummmmmm...........:skull:

Originally posted by ranger
So if the secondaries are closed at high RPM's your saying it will run rich????? Wouldn't you be running off primarys, low speed idle circuit???? Hummmmmm...........:skull:

No, I think the fact that it is running rich is unrelated to the poor performance as it would have to be seriously rich to cause problems and it should be rich throughout the RPM range above idle. Running rich causes more of a problem at low speed. The low speed idle circuit doesn't add much fuel once the primary butterfly opens and the vacuum difference above and below the butterfly drops.

could 80 lbs compression in the last 2 cylinders give my engine the above symptoms ? took it back in the shop and the mech said he can't get it any leaner. but he said the rear 2 cylinders are leaking and only 80 lbs compression. ???