Having some issues that I have never had before with my '68. Replaced the 20-year old EB 1406 carb with a new exact same model 1406. Set Idle screws settings correctly with Vacuum gage. Engine starts fine and idles relatively smooth. However, when driving her the engine surges in all four gears. I figured it was either vacuum or possibly the electric choke not fully opening once warmed up. Vacuum lines replaced and electric choke reset based on EB recommendations, but the engine still "surges" up and down while driving. Can't figure it out.

Any thoughts would be appreciated.

Sounds like a vacuum leak somewhere.

Bob, agree with that. I am thinking up some troubleshooting options to identify the problem. Maybe cap-off all vacuum lines and see if that makes any difference? It is set up EXACTLY like it was with previous Carb. Really pissing me off.

Maybe something stupid like the PCV valve

New parts don't mean good parts.
Put the old one back on and see if the surging goes away.

Jeff, agree that is certainly an option. Will look at other possibilities first.

Check the throttle spring
When I had the surge issue it was the throttle.
The spring setting had throttle partial open so when you shift the throttle surges.

Ditto on the throttle. Maybe something not working correctly or sticking. Is it all the time or sometimes? Warm? Cold? Both? Does it surge right away or does it work up to it. If you tap the pedal does it settle?

I second on putting the old one back.
That said why did you take it off to begin with? leaks?

Frankie, the old 1406 was at LEAST 20 years old and pretty ugly compared to the rest of the engine compartment. Got a good deal on a new chromed 1406.

Guys that have mentioned the throttle spring here...are you referring to the simple spring on the drivers side of the carb that provides tension to the throttle linkage? Having a hard time understanding that would cause a problem. You saying maybe the spring is too weak and therefore allowing a weak tension while driving?

Yes, was not enough spring tension, in between gears / neutral significant increase in rpm.
Moved spring over a slot and problem went away.

Spring tension too light... spring tension too much... throttle arm sticking... etc. It is a pretty simple system and doesn't require much fine tuning but it can make a difference. Especially if something is bent or sticking.

OK thanks folks. Will play with it once this ice storm passes through.

Did you find anything out?

Too darn cold here in Nashville to do anything out in the garage. Hopefully it warms up next week.

Did you check the air in the tires?

What'sup John!

I solved too hot/cold garage by rerouting an empty bedroom duct into a floor vent, punched a hole in the cold air return plenum, and ran a pipe against the wall, dropping to the corner. Works great, especially the a/c.

After you reinspect and try blocking all vacuum including the booster, you might end up trying the old carb.

Update when you thaw out.

Hi ,

Usually a lean condition will cause a surging at "cruise" throttle. Since this appeared after replacing the carb, I would check for two issues.
1 . Check for any minor vacuum leaks.
2. I would think more likely the new carb is jetted more lean than the old one.

Bob

I thought I read the 600cfm 1406 is to small for the 400???