Tach jumping past 2000 rpm and an intemittent skip

[biggziff]

1988 Baretta with the Volvo AQ131A. At 6 degrees BTDC the engine takes a bit of cranking to start. I've gapped plugs, checked and set timing and dwell so that they're pretty close to specs. When it finally does start it idles perfectly and takes throttle with no issues. At idle or up to 1500 indicated on the tach the tach is steady and the engine sounds great. If I run it up to a steady 2200-2500 the tach jumps around up to as high as 4000 (very quick jumps) and I can hear an intermittent miss in the engine. If I run it up to 3000 it will sometimes clear up and the tach will get steady for a bit before it occasionally does it again and the skip returns. The skip is hard to hear, but I can hear the engine clear and sound as if the RPMs rise a bit before it bogs very slightly again as the skip returns.

Also, when using the timing light the mark is jumping around from 6 to around 12 or so and back.

Coil maybe? I'm guessing as the tach gets its signal from the coil.

I've checked the spark at all plugs and used a touch spark tester to each wire and they're all firing.

Plugs look good, but I don't know how old they are. They're NGK B7ES and I can get the resistor plugs locally with no issue, but would have to order the non resistor plugs if necessary.

Maybe I should just put an electronic ignition in it and get rid of the points and condenser?

Thanks

 

[Don S]

Re: Tach jumping past 2000 rpm and an intemittent skip

Check your coil tower for cracks or carbon tracking, it could be arching to the negative terminal which would cause the engine to miss, and cause the tach to act erratic.

 

[biggziff]

Re: Tach jumping past 2000 rpm and an intemittent skip

Check your coil tower for cracks or carbon tracking, it could be arching to the negative terminal which would cause the engine to miss, and cause the tach to act erratic.

Thanks, Don. I don't see any arcing or evidence of same, but I'm going to run it tonight in the dark to see if I can see anything arcing.

Any other ideas? It does seem electrical. If I advance the timing to around 20 degrees it starts much better, but obviously I can't leave it like that. I've already had the distributor out and cleaned and lubed the advance and checked the shaft for play...it has none.

 

[biggziff]

Re: Tach jumping past 2000 rpm and an intemittent skip

Just went out and arranged the plug wires in the keepers so that they weren't touching each other and the tach jump went away. Maybe they're leaking enough to cause this issue. I'll grab some new ones in the AM.

 

[biggziff]

Re: Tach jumping past 2000 rpm and an intemittent skip

Adjusting the plug wires so they don't touch corrected my problem. New wires probably would have helped as well.