[Jason H]

Ok here is the deal: I have a 68 pontiac 350, I recently put on a NOS cheater syetem with a 100 shot. In the process I had to move the battery to the trunk, cuz I took out the inner fender wells. Anyways the motor was running fine before these mods. Once I had it running again I drove it a few miles. I drove it maybe 30 miles and then on the way back home I noticed the tach going nuts over 3000rpm. Then I drove it the next day and every time I went over 3000rpm the tach needle would bounce around and the motor sounded like it was missing. One big problem I have with this is that I have a TH350 behind the motor and a ford 9 ince with 3:89 gears in it. Do the math and 3000rpm is only 60mph on the freeway. And remember I can't even do 3000rpm/60mph.

Ok now for my troubleshooting. When I put the battery in the trunk I also mounted a switch to turn off the battery from the rest of the car ( right now it doesn't have the alternator wire going to it so it is not NHRA legal). Ok with the motor running, I kill the battery power which turns off the MSD 6A box and it still misses over 3000rpm. Which leads me to believe that it is not ignition. It might be the distributor which is a mallory unlite with vac advance. I tried playing with the timing, advancing and retarding and it made no diff. I pull the first three plugs on the driver side and I didn't notice anything but some carbon. I dont know if it might be a gas problem or what any ideas????
Please help.
Jason

[Jason H]

Ok here is the deal: I have a 68 pontiac 350, I recently put on a NOS cheater syetem with a 100 shot. In the process I had to move the battery to the trunk, cuz I took out the inner fender wells. Anyways the motor was running fine before these mods. Once I had it running again I drove it a few miles. I drove it maybe 30 miles and then on the way back home I noticed the tach going nuts over 3000rpm. Then I drove it the next day and every time I went over 3000rpm the tach needle would bounce around and the motor sounded like it was missing. One big problem I have with this is that I have a TH350 behind the motor and a ford 9 ince with 3:89 gears in it. Do the math and 3000rpm is only 60mph on the freeway. And remember I can't even do 3000rpm/60mph.

Ok now for my troubleshooting. When I put the battery in the trunk I also mounted a switch to turn off the battery from the rest of the car ( right now it doesn't have the alternator wire going to it so it is not NHRA legal). Ok with the motor running, I kill the battery power which turns off the MSD 6A box and it still misses over 3000rpm. Which leads me to believe that it is not ignition. It might be the distributor which is a mallory unlite with vac advance. I tried playing with the timing, advancing and retarding and it made no diff. I pull the first three plugs on the driver side and I didn't notice anything but some carbon. I dont know if it might be a gas problem or what any ideas????
Please help.
Jason

[george kujanski]

First, I don't understand when you say you kill battery power which kills the MSD box & the engine still misses over 3000 RPM. I thought shutting down the MSD box will kill your ignition.
Anyway, assuming your fuel system is not to blame, moving the battery to the trunk and associated wiring may cause noise problems at the ignition system, as evidenced by the tach going erratic. Do a test by connecting the battery back closer to your ignition system and see if the problem goes away.
By the way, disconnecting the battery from the alternator while the engine is running is a sure way to kill electronics in a car. Maybe not the first or second time, but you will kill something eventually.
Regards, George

[Old Man Taylor]

If you don't run your alternator through the switch it will keep the MSD powered and provide the spark required to keep the engine running. That is why NHRA tests it by turning the switch off with the engine running to assure it stops running. As George said, it sounds like electrical noise from the MSD box. I ran the MSD power through a large filter and I shielded my tach wires.

[Jason H]

Ok that might be the problem with the Tach, but what about the motor. It mill bog down, or miss once you hit 3000rpm. The motor is just fine until you hit 3000rpm. If I where to put a filter on the MSD box do you think that this will slove the problem?

[Old Man Taylor]

I doubt it. Do you have a rev limiter built into the tach? What kind of distributor do you have? Be careful assuming that the last change you did is what caused the problem. If it will do it in neutral, put a fuel pressure gauge on it and check what it is. Assuming it is getting adequate air into it, it can only be spark or fuel. If you can eliminate the fuel, you are down to one.

[Jason H]

I dont have a rev limiter. The distributor is a mallory unlite with vac advance. It does do it in every gear even park.
I will check the cap and rotor when I get home tonight and see if there is anything wrong there. It might also be a fuel filter.

[KS circutguy]

Buy and install a MSD-Noise Filter Part #8830.Around $28.00..
:-)Steve.

[Jason H]

You are all wrong. I got a chance to look into it farther. I played with the timing alittle more and finally just pulled the distributor. I got the distributor out and apart, there was a spring missing off one of the magnets. So now I just need to find one of those springs.
Thanks for your help you guys.
Jason

[george kujanski]

Original quote: "Ok that might be the problem with the Tach, but what about the motor. It mill bog down, or miss once you hit 3000rpm. The motor is just fine until you hit 3000rpm"

All along your tach was telling you there was a problem with your ignition since it is driven from the same circuitry that drives your coil.
Regards, George