1970 Pontiac Lemans 350

Asked by Feb 22, 2019 at 09:06 AM about the 1970 Pontiac Le Mans

Question type: Maintenance & Repair

Sometimes during acceleration the car bucks.  Taking my foot off the gas stops the bucking.  This happens very intermittently but seems to be getting worse.  I have changed the plugs and wires and will be changing the  cap and router in the next couple days.  A previous owner installed an MSD part number 2601 ignition.  Last year I replaced the box because there was no spark.  Any ideas as to what could cause this bucking issue?

5 Answers

785

misfire from distributor?

200

Bucking sounds more like fuel related. Check the fuel filter. These older cars tend to develop a lot of rust in the fuel tank. 1970 should have a tiny filter in the carburetor at the inlet. Thats why most people add an additional fuel filter with a higher capacity to keep all the junk clogging up the smaller filter too quickly. Could be a tired fuel pump also.

87,445

Could be electrical or fuel related. Misfires cause a lag that feels jerky, but only if irregular, as in from some plugs, not all. So I wouldn't suspect it's distributor/points/condenser related. Multiple Spark Discharge units are really nice, but can be problematic, so DO have this checked. A lack of proper fuel pressure from a faulty fuel pump or component can do the same. Check to see if you have a dirty carburetor or clogged fuel filter, or a vacuum leak, including EGR/PCV. Have a mechanic check the MSD, then diagnose this and then fix it. This isn't something that sounds serious or expensive.

1 people found this helpful.
269,135

I would check the timing.

Hi Everyone First let me thank you all for your replies. I finally found what was causing this issue and thought I should post it in case in the future someone else has a similar problem. It turns out that the positive battery cable going to the starter was routed too close to the header. The insulation melted off and while the car was moving the bare wire would intermittently short out on the header causing a temporary lose of all power. The cable has been replaced and rerouted away from all heat sources. The car now runs great.

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