Weber questions

Picked up a '76 308 GT4 with dcnf 40's. Carbs may just need a complete rebuild but I thaught I would first post for potential fixes. Car has single dist. elec. conversion and I installed new plugs gapped at .36 before the 100 mile drive home.
Car starts and idles great.
Hesitates a little at low rpm when first taking off.
Mid range is great. 65-80 in 5th ran flawless. I can't state the rpm because the tach is disconnected because it reads double since the single dist. comversion. My guess is 2500-4000 in all gears is pretty good.
Bogs down at higher RPM in any gear and pops/backfires. This is probably above 5000 rpm. Not sure if that means too lean or rich?

Also, when coming off throttle and engageing the clutch for a gear change up or down, the rpm doesn't immediately drop, it is quite slow to come back down. Engine braking will bring it down.
Any thoughts or suggestions from you Weber experts? Just thought I would see if I can do any adjustments before I decide to send them out for a rebuild.

BTW, I removed the air box to see if anything was binding to cause the high rpm when shifting and could not see anything being held up. The linkage would spring back but the rpms still dropped slowly.

First thing I would look at is Distrib advance operation. idle, 3500, 5000, idle.

Regards, JRV

Doug,
Agree with JRV 100% as to checking the distributor for proper advance...I spent quite a while chasing my tail, thinking that I had carb problems with my BB, only to find that the distributor advance weights were seized.

Secondly, unless you're running a MSD box, or similar high energy ignition system, .036" gap on the spark plugs is too wide. This too can cause a miss at high engine speeds...

The RPM "hanging" between shifts is a typical symptom of a seized/sticking distributor advance...

Regards,
David

I appreciate the info. Yesterday was my first day with the car after a 100 mile drive home. I realized the air filter was trash. Car runs better now but still has the bogging down/popping at higher rpm. Is that too lean or rich? The car also still comes off rpm very slowly, when I put in the clutch to shift, the rpm does not drop. On another board someone suggested the bearings in the carbs. I figure I will work my way to a carb rebuild if necessary, No reason to do it if not needed. They were rebuilt once in the last 9 years and 4000 miles.

Doug,
Although the bearings in the carbs are a possiblity it would be the last place I would suspect a problem. However, you can verify the integrity of these bearings by manually moving the throttle linkage in the engine compartment...and watch the carb butterflies.

As to rich or lean...Who knows, as the distributor advance function must be verified first...Once this has been verifed, and/or repaired, further diagnostics can be done.

Regards,
David