I have a ‘63 with a 327ci/300hp engine and a Carter AFB carburetor. I’m having an issue with it “bucking” when I try to slowly accelerate in first or second gear. I have adjusted the carburetor, checked all the plugs and wiring, reset the timing but nothing has helped. Any ideas on what the problem is?

 

Did this problem just start? Did you do anything to the car prior to this problem starting? Need a bit more recent history to help out.

 

One remote, but possible, cause would be a failing Ignition Coil.......

 

Perhaps it's the way you are driving the car. Need to slip the clutch at very low speeds in 1st to keep the revs up. At what rpm are you trying to accelerate in 2nd when the bucking occurs?

 

a 300 hp motor will never have that problem at low speed if the OEM cam is in place.

 

I'm with Leif . . . let's start here before we all jump to conclusions, shall we???

 

This doesn't sound right to me. The engine shouldn't buck at any speed. My '63 300 HP Vette never did. And even my solid lifter FI '60 takes off smoothly every single time.

 

It can be a bad or cracked spark plug, dirty plugs, old or loose spark plug wires, bad coil or condenser, rotor, cap, points, bad or old gas, clogged fuel system at the tank or filter, fuel pump ready to give it up, dirty carb or misadjusted choke or carb accelerator pump, trash in the carb, vacuum leak. It would be best to determine if it's fuel or ignition related and follow up. Good luck. Jerry

 

I too have a hard time imagining a 327/300 motor bucking or trailer hitching. I think I would look inside the distributor to see if some one installed real light advance springs allowing the weights to cycle in and out at idle speed. Also check that axial play in the distributor isn’t excessive. But still sounds strange.

 

When you set the timing, did you just check base or did you also check total timing and vacuum advance?

 

I purchased this ‘63 in an online auction and it was doing this bucking from the start. The dealer must have grout it had a carburetor issue since it came with a new one installed and another in a box. From the replies it appears I have a lot of possibilities to check. I’m far from an expert mechanic!

 

I would start with finding the correct carb and have it rebuilt by a person who knows what they are doing then go though the dist and make sure it’s up to OEM spec.

 

On the driving question the bucking occurs when I attempt to slowly accelerate to 2K to 2.5K rpms to shift into 2nd or 3rd. If I quickly accelerate through the gears there is no problem -except for dirty looks from neighbors

 

Look for the tuning paper written by SWCDUKE.

 

Well . . . that's not the answer I was looking for - but, we can work with it!

Question - can you tell if your car has new plug wires?

Let me tell you why I ask! A few years ago I did a complete tune up of my L79 - new plugs, new wires, new cap and new vacuum advance. After that tune up, my car exhibited the same "bucking" (aka "trailer hitching") at very low, steady speeds in 1st and 2nd gear just like you describe. It ran great at higher speeds and on the highway! I chased that problem for almost 18 months . . . we checked timing and advance multiple times and everything else we could think of without correcting the problem. One day I decided to pull the plugs and check them, and ever considered switching to another plug. That's when I found the problem!!! Apparently, when I installed the new plug wires, I didn't "snap" them all the way onto the end of the plugs! They were on there, but they weren't really "on there"! In hindsight, I believe that it was really tough for this old dude to reach over the fenders, way down into the engine compartment, and exert enough force to "snap" those new, really tight wires on all the way. I solved the problem with the help of a rachet . . . holding the tool in my left hand and putting the square end on the plug wire gave me enough leverage to snap the wires that last little bit! Problem solved - my car runs like a Swiss watch now!

It could be as simple as a bad plug wire connection!

Tom

 

It might help if you post good pictures of your engine from all sides. Something may stand out that may be causing the problem.

 

With the additional description I think this is a good possibility. Most bad plug wires I have experienced caused missing/surging under steady throttle and light acceleration. Yet it would accelerate cleanly with full throttle. Something with voltage and system resistance under different engine load conditions I guess.

 

the best version of this is the newest version where Lars and SWCDuke collaborated.
mail Lars and he has always happily sent a copy

I think this is his contact info:
To request articles, just drop me an e-mail to:
V8FastCars@msn.com

 

Try these.

https://www.corvetteforum.com/forums...tributors.html

 

Too much vacuum advance at low rpm?