Latest mystery.........

[texasmike]

So, everything has been going well, truck running good so I decided to reinstall the original 195 degree thermostat and put in a new temperature sender to get a more accurate reading. While under the hood, I thought it would be a good idea to check the Q-jet mounting nuts and torque to 11 ft-lbs. Now, the temp gauge is dead on the mark before 210 but the truck seems to be running a little rich, with black smoke when it is revved up from idle. Any ideas what could have happened??

 

[Snoots]

Put the old temp sensor back in. You didn't use teflon tape on the new one did you? Carb's running rich. I'd say go back to the carb and check for cracks in the base plate. Then check all vacuum hoses.

 

[texasmike]

Thanks Snoots. The temp sensors come with the tape on them and I don’t see how 11 ft lbs could crack the carb base sitting on a thick gasket.

 

[texasmike]

Could raising the operating temperature (180 to 195) of the engine make it run a little richer, not quite as much as Elon ? Should I try turning the air/fuel mixture screws maybe a quarter turn and which direction do I need to turn to lean it out a little?

 

[Snoots]

Turn them in. Use a vacuum gauge connected to the manifold, not ported. Go for highest vacuum.

It's easy to crack a bottom plate IF your gasket does not have the phloenic spacers in the bolt holes. Just sayin'.

 

[texasmike]

10-4 and thanks.

 

[ReefkoiC10]

Id guess if the baseplate was Loose enough that it had a vacuum leak then you sealed that thing, it suddenly got rich since it has less air coming in (no vacuum leak now) maybe its been that way and was tuned to match and make right by a previous owner IDK just another thought for you

 

[Conejo_K10]

Where did the 11 ft.lbs torque come from? That seems high.
The downside to q-jets is the top which warps if over torqued. Once warped the fuel in the bowl leaks into the primaries.
Every q-jet I've rebuilt has had a slight warp. I typically check the top with a straight edge.

 

[texasmike]

The 11 ft-lb came out of my Chilton GM 80-87 shop repair manual. Do you think I should back the hold down bolts a bit to see if that helps or is it too late?

 

[Snoots]

Depends on the age of the gasket. If it's old it may not 'spring' back. Back 'em off and see. Couldn't hurt.

 

[texasmike]

Thanks, the gasket is about a year old and I backed the bolts out but it didn’t seem to make any difference. I’m going to leave it alone for awhile before I go to the trouble to replace it. Too darn hot down here right now.