Timing related question...

[philo_beddoe]

Is it okay that the idle drops when we plug the vac line at the dist. When doing the timing? 

[blazer74]

Yes


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[blazer74]

Adjust your idle accordingly when setting timing, then readjust idle after unplugging your vac line and reconnecting to distributer.
You are removing vac advance when vac line is plugged to dist causing your idle to drop.


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[philo_beddoe]

Thanks,,,amazing as it seems, coincidently, plugging the vac line to the dist. just happens to bring the idle to 500 RMP which is just about the same as NOT plugging the dist. vac line and putting it in drive, which obviously drops RPM also.    Does this sound normal?

I did set the timing while the dist. vac line was plugged and rpm was at 500 rpm, factory specs recommended. Gonna do a full test drive today.

[enaberif]

Thanks,,,amazing as it seems, coincidently, plugging the vac line to the dist. just happens to bring the idle to 500 RMP which is just about the same as NOT plugging the dist. vac line and putting it in drive, which obviously drops RPM also.    Does this sound normal?

I did set the timing while the dist. vac line was plugged and rpm was at 500 rpm, factory specs recommended. Gonna do a full test drive today.

Another tip.. vac advance for distributor on manifold not ported.

[philo_beddoe]

Ok, what do you mean "not ported"?  Vac line coming from carb base (below throttle plate) and connecting to manifold or dist.?

[Irish_Alley]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=28857.msg241110#msg241110

[enaberif]

Ok, what do you mean "not ported"?  Vac line coming from carb base (below throttle plate) and connecting to manifold or dist.?

Ported is a vac line that sits above the throttle plates and only gets vacuum when the throttle plates open. Manifold means a constant source of vacuum no matter what the engine is doing.

[philo_beddoe]

Ok, I understand fully.  I probably have that nipple on the carb blocked off. It is on the carb right?

Also, I have a lot of connections on this M4ME carb. Sure would love to see a diagram as to what they are all generally for. The ones I know are the vac for the dist., pcv valve, exhaust to charcoal canister and in the back..the power brake booster.  There is one nipple in the back on top center that I have blocked off, and two in the front that are blocked off, lower right and upper left, (facing the engine).  Does this sound about right as far as my connections??   Thanks again.

[Irish_Alley]

http://forum.73-87chevytrucks.com/smforum/index.php?topic=11934.msg89184#msg89184

[Irish_Alley]

and MODEL M4MC/M4ME/4MV CARBURETOR

[philo_beddoe]

That's a major help? Thanks!!

[philo_beddoe]

Ok, so which nipple on the carb is port and which is manifold??  And once I re-attach, do I need to make any adjustments? Wont the idle be low?

[Irish_Alley]

rule of thumb if you have a port and at idle theres no vacuum that means its ported. if you have a port that theres vacuum at idle it manifold  but set your timing with the vacuum advanced hose plugged and set your idle the same way. then plug it in and youre good

[philo_beddoe]

Now that makes sense!  Hey, thanks again.   BTW, that is how I did the timing and idle rpm.

ps. wow, over 8k posts, where do you find the time,,,,and w/family!  Lord bless!