1976 2.7 Bucking when warmed up.

Hi, I have a 1976 2,7 Targa which I tinker around on and enjoy the rides when I have them but I also have this "BUCKING" problem especially when she warms up and after changing gears. Once the gear is changed and I increase excelleration she is ok until I reach cruising speed in any of that gears then she starts bucking again. Very frustrating. Any thoughts. Thanks

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[Casey at Pelican Parts]

Bucking can be many different things, but in my experience this is usually caused by a bad distributor (too much play in shaft up and down), or mis-adjusted idle or fuel mixture. Assuming your cars maintenance is up to date...Check the basics first, fuel pressures, check for intake leaks, check the fuel mixture, check and or adjust the ignition timing, then set the idle.

- Casey

[rockreid]

fuel pump.

test fuel pressures.

[OsoMoore]

When I had my mechanical advance mis-adjusted, I had some light bucking. My 79 SC needed more than 5 degrees advance (presumably due to a compression increase during an earlier rebuild).

[stlrj]

Too rich?

[Targalid]

My guess is too lean. When the car is warming, the Warm Up Regulator (WUR) sets the mixture rich by the cold (low) control pressure during warmup. As the WUR raises the control pressure during engine warm up, eventually the warm (high) control pressure is reached which is the lean setting. This explains your observations: it bucks when it is warmed up, a sign of a lean mixture. If this is a new problem, you should check for a vacuum leak first. Also, if you live in a northern climate and can only now drive the car with the onset of warmer weather, wait until you have run out the old gas and refilled the tank a couple of times before you change any settings. Try injector/fuel system cleaner such as Techron. If you cannot find an unmetered air leak you can adjust the mixture richer by turning the mixture adjustment screw clockwise. Don't do this unless you have exhausted other approaches. It was working fine before right? There is a great post on this forum called CIS Troubleshooting for Dummies. You should read it if you have not yet done so.

CIS Troubleshooting for Dummies

[john walker's workshop]

Try removing and plugging the small side vacuum hose on the warmup regulator.