What condition does it indicate?

How can it be corrected?

If this indicates a rich mixture (as it does smell somewhat strong while driving and in garage) please give me the simplified version of mixture adjustment for the Rochester 2GV. I'd prefer to adjust for daily economy if there's room for that consideration. The points, rotor, cap, wires, coil and plugs have all been recently replaced. The timing might need one more quick check as the points were just replaced last weekend (can this points break-in affect timing?).

Thanks,
Brian

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Brian Scott
1968 el Camino Custom
307-PG Purchased 11/01 w/81k (2 CA owner)miles.
"An eBay success story!"

[This message has been edited by madaboutabba (edited 04-02-2002).]

In most cases black smoke from the exhaust indicates a fuel mix problem,,,to rich...a carb. adjustment is usually the fix. Bluish smoke indicates oil is burning and white smoke is the worst,,,meaning in most cases you have water being burnt from a blown head gasket or cracked block for example. Black smoke is the best of all 3 to have if you gatta have one! Good luck...might look at this link: http://www.442.com/tech/rochester.html

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ACES #3355
ChevyTalk Silver Member
Metroplex Muscle Car Club
Assoc. of Proud SS Clone Owners
1972 Chevelle SS (clone),black/black 350ci



[This message has been edited by black72 (edited 04-02-2002).]

Again:
"...please give me the simplified version of mixture adjustment for the Rochester 2GV. I'd prefer to adjust for daily economy if there's room for that consideration."

In other words, is mixture adjusted leaner by turning screws inward (CW), or outward (CCW)?. Explain 'lean roll'.
What are pitfalls/hazards of a too lean mixture?
While avoiding a rebuild, any other basic adjustment to alter? I do believe that the choke is operating properly.
Also, are general lubricants (WD-40)acceptable for linkage, cable & hinge points? Other recommendations?

Thanks,
Brian

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Brian Scott
1968 el Camino Custom
307-PG Purchased 11/01 w/81k (2 CA owner)miles.
"An eBay success story!"

[This message has been edited by madaboutabba (edited 04-03-2002).]

Brian, A "lean roll" is this: on a two barrel dual plane manifold one barrel of the carb feeds 4 cylinders - I think 2 on the left and two on the right. Ditto with the other barrel. A lean roll happens when you reduce the idle mixture on one side of the carb. The cylinders that are fed by that barrel now see a lean mixture while the cylinders being fed from the other barrel are seeing a richer mixture. Thus, the engine develops an uneven idle because the lean cylinders are not producing as much power as the rich ones. As the engine runs this condition is referred to as a lean roll.

To answer your original question. Turning the mixture screws CW will lean out the idle mix while turning CCW makes it richer. What you want to accomplish is to have the screws IN as much as possible while maintaining an acceptable idle.

Start with a base line. This would be much easier if you have either a vacuum gauge or a tach. This also assumes that the engine is in a generally good state of tune regarding the ignition and also assumes there are no vacuum leaks. Get the engine completely warmed up then shut it down. Turn both CW until they just seat - do not apply undue pressure. Then back them out 1 1/2 turn each. Start the car. Turn one mixture screw CW until you note a decrease in RPM (or a reduction in vacuum) and an erratic idle (lean roll) then back that screw out about 1/2 a turn. Repeat same on the other side.

It may take a bit of fiddling but you'll get the hang. With a 2GV I'm not sure if starting with the screws out 1 1/2 is correct so if it runs like carp when you first start it you may need to turn them out instead.

As for lubs - just use carb cleaner.

With the engine completely warmed up make certain the choke is ALL the way open.


Happy adjusting....

Dan

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Awww, fer cyrin out loud, there's that IMPALA guy again.

http://photos.yahoo.com/bc/ss3964spd?d&.flabel=fld1&.src=ph

[This message has been edited by ss3964spd (edited 04-03-2002).]

Thanks for your detailed offering, SS3964spd. At this point, I'm just going to accept that my 307's rich smelling exhaust is just a product of the pre-emissions reduction era.
I printed your instructions and kept them nearby (along with my GM & Chilton), but I just can't seem to "get the feel of it". I started the mixture screws three turns out from full-seat, as specified, then gradually turned each screw back in at about 1/2 turn increments. I monitored the RPMs from my dwell-tach-voltage meter and eventually called it quits, returning to about 2.5 turns out from full-seat (lost track of what the initial position was, as I started fooling around with the screws a few days back).

As stated in the initial post, all factors of tune have been very recently replaced/adjusted. Might a full rebuild be in my near future? That would be quite interesting...!

Thanks,
Brian

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Brian Scott
1968 el Camino Custom
307-PG Purchased 11/01 w/81k (2 CA owner)miles.
"An eBay success story!"