Bogs down... sometimes

[Bonz]

My great '80 SG has begun bogging down occasionly when cruising at highway speed.

It will be running well, then I realize I am dialing in more and more throttle to keep speed up, then she just sits there plodding along for awhile and begin to lose speed. Then she'll start to pull hard, then bog, repeat. Most times a quick downshift will get the revs up and she is fine and I can get back into 5th with no probem, other more rare occassions I have to slow down, then accelerate in a lower gear and then things are fine, like nothing was wrong to begin with.

Many times this doesn't happen at all and she runs fine.

I haven't had the carbs off yet, so yes, that is going to be done regardless. I've been just putting up with it for now.

What should I look for? Main jet clogging, float height issues, possible timing advance issues?

Thanks!

[Rhumba]

Check the gas cap air vent. Vacuum may be building in the tank causing fuel flow problems.

[tarzan]

I would go through the carbs and make sure all passages are clear.Clean all parts well.Replace o-rings under seats and possibly needles and seats.Also if it still has brass plugs blocking the pilot screws ,you should drill the plugs out and remove the plugs.I bought a drill and easyout kit with a center drill on one end and a easy out on the other end at sears.It worked slick because the center drill is just long enough to break through the plug.Then flip it around in the drill and the easy out end is about 1/4" long,so it didnt hit the screw and would start turning the whole plug, and you can just pull on it while its turning and the plugs come right out.
You may also need bowl gaskets but a lot of times they are still good.I also recommend doing one at a time so you dont mix parts between carbs and you always have a reference if you cant remember how things go.
Then reassemble them and install.Then sync,adjust pilot screws,then recheck sync.

[TopCatGr58]

Hey Hbonser,

Could be carbs, could also be fuel flow, could also be PU coil wires?? If you have the Octy still, it may be sticking or not opening all the way, or a vacuum leak so it's not opening? Changes in rpm and gears could increase the vacuum allowing more fuel to flow filling the bowls back up?? As mentioned, could be vacuum lock in tank due to clogged gas cap vent? Could also be PU coil wires partially breaking, changes in rpm flexes wires to remake contact, etc.!? But could also be partially clogged pilot circuits in carbs?

Have you gotten some Sea Foam and put it in for a few tank fuls?
T.C.