I recently acquired a 1978 GMC motorhome, it has the UPP FWD drivetrain almost the same as a Toronado. This particular one is CA emissions, and is a one year only option for the Motorhomes. I believe the 403 died in 1979, so this may be a rare setup.

I don't mind the Evap canisters and will keep that portion.
A brief inspection revealed multiple disconnected, plugged, and/or broken lines and fittings, I doubt if much of the system is still functional.

I read through much of the 1978 supplemental manual about the function of most of the stuff, most of it is related to small vacuum advance adjustments due to coolant temps.

Is anyone familiar enough with this system to say if it's worth salvaging? I don't need to do any sort of Emissions or vehicle inspections for registration.





Thanks for any input!

oh yeah... it's in this...

 

Beautiful motorhome. If you want to delete the smog equipment just get an old style Quadrajet and HEI distributor. If you aren't prepared to spend the money on those parts I suggest returning the smog system to OE specs.

 

Neither your distributor nor carb need to be changed - this is not a computer-controlled system.

Before randomly trashing emissions equipment, you should first understand what each piece does. The evap canisters recover gasoline vapor. There is no reason to delete them, they don't hurt anything. Your engine doesn't even have EGR (it was not required on HD vehicles in 1978). The other vacuum lines all relate to carb pulloff diaphragms and the distributor vacuum advance. Removing them without recalibrating the distributor advance curves will likely result in the engine making less power (though I'm sure the "butt dyno" will convince you that there is an improvement after all that work). Frankly I would put it back to stock and be sure everything is functioning correctly unless you plan to undertake a trial-and-error tuning process to get the carb and distributor dialed in.

 

The evap and vacuum pulloff I will retain. It's mainly all the temp switches, vacuum switch and solenoid that I'd like to delete. I believe they're all related to the vacuum advance. Maybe I'll try replacing the advance with a single unit and just plumb it to timed vacuum like every year before this had.

The carb is specific to the motorhome, I may jet it up a bit depending on what O2 readings I get, but I have no plans of replacing it at this time.

 

Are these 350 heads? Stock 403 heads would be 4A.

192.168.100.1 192.168.1.1

 

I'm sure they are the original heads to this engine, I couldn't tell you the difference between 403 and 350 heads.