‘68 GTX 4-Speed Hemi Car Bucking

[Shadetree]

I wouldn't go by where someone else set there's. Sounds like your going in the right direction. Now make small adjustments one at a time.

Yes sir. I’m just wanting to see where others are pointing for a cosmetic reference, not the amount of advance. I’m thinking that it may be off a tooth but my understanding has always been that it doesn’t matter as long as you have enough range of motion to achieve the desired advancement.

 

[turbine68rt]

Yes sir. I’m just wanting to see where others are pointing for a cosmetic reference, not the amount of advance. I’m thinking that it may be off a tooth but my understanding has always been that it doesn’t matter as long as you have enough range of motion to achieve the desired advancement.

Easy fix. Intermediate shaft is probably off a couple teeth counter clockwise. With the timing mark at tdc the slot should be inline with the cam. Vac advance canister should end up pointing towards #1 cylinder to give plenty of room to adjust timing in both directions. I see this all too often at shows.

 

[AR67GTX]

37* total a bit much if accurate and what are the cam spec's. dadsbee think mentioned going to slow for the gears your in. I call it cam lope.

I second potentially too much timing for pump gas. If plugging the vacuum advance or retarding the timing were to help, it would more than likely confirm it. If no change then probably not the cause. If you get too much timing in the engine, especially with vacuum advance, cruising at 3,000 rpm’s on the highway could be firing your plugs off as early as 55-60 degree BTDC. As the plug flame spreads and combustion pressures rise and peak before TDC, it’s akin to that cylinder trying to kick back the entire engines rotation - thus the stuttering miss sensation. At 3,000 +/- rpm’s cruise your centrifugal advance may be fully in at the same time your vacuum is high and its advance all pulled in - everything advanced. Give it gas and the vacuum advance falls out reducing total advance and the engine accelerates smoothly.

However, this probably has little, if anything, to do with off-idle, low speed trailer hitching, especially if it has a pretty big cam.

 

[Shadetree]

I second potentially too much timing for pump gas. If plugging the vacuum advance or retarding the timing were to help, it would more than likely confirm it. If no change then probably not the cause. If you get too much timing in the engine, especially with vacuum advance, cruising at 3,000 rpm’s on the highway could be firing your plugs off as early as 55-60 degree BTDC. As the plug flame spreads and combustion pressures rise and peak before TDC, it’s akin to that cylinder trying to kick back the entire engines rotation - thus the stuttering miss sensation. At 3,000 +/- rpm’s cruise your centrifugal advance may be fully in at the same time your vacuum is high and its advance all pulled in - everything advanced. Give it gas and the vacuum advance falls out reducing total advance and the engine accelerates smoothly.

However, this probably has little, if anything, to do with off-idle, low speed trailer hitching, especially if it has a pretty big cam.

You are correct, Sir. That was the case, due to using the incorrect mark on the harmonic balancer. I’m currently running around 13 degrees advanced and the bucking I believe is gone. I failed to mention in the original post that I had the vacuum advance disconnected due to too much advancement but with much less advancement now, it may be an option and I plan to test that soon. Although I’ve never moved a distributor, just replaced them before, I plan to notate the current direction of the rotar button and distributor cap, remove the distributor, inspect everything and then relocate the distributor body one or two teeth to the right to allow for more range of motion and to be cosmetically correct. Anyone, feel free to advise me otherwise if I’m wrong. Thanks

 

[biomedtechguy]

If you ever consider changing the distributor and ignition system, I would highly recommend either the FBO setup or Progression Ignition.
The FBO system will allow more initial timing for the best idle performance and no "gas smell" cooler engine temps, BUT also limit total timing so you can run 20° at idle w/vacuum advance connected. The vacuum advance is also tunable.
The Progression system is simply THE best ignition system for any carbureated engine, and the tunability is basically unlimited.

 

[Shadetree]

If you ever consider changing the distributor and ignition system, I would highly recommend either the FBO setup or Progression Ignition.
The FBO system will allow more initial timing for the best idle performance and no "gas smell" cooler engine temps, BUT also limit total timing so you can run 20° at idle w/vacuum advance connected. The vacuum advance is also tunable.
The Progression system is simply THE best ignition system for any carbureated engine, and the tunability is basically unlimited.

 

[Shadetree]

That’s definitely a very user friendly setup! If I wasn’t dead set on a stock look I’d order one today! Thanks!

 

[Geoff 2]

The problem you have is caused by leanness, which in turn is caused by the big-ger cam. To confirm: engine idling, move choke blade towards closed position until engine sound changes. Wire choke in this position & test drive. If problem is better/fixed, it is leanness.
If you remove the carbs, I would expect that more than 0.060" of transfer slot is showing. At low speed cruise where the surging occurs, you are on the idle cct, not the main cct. So changing rods, jets will do nothing.

I suggest you check the above & report back for a fix.