[Silverback85]

Just rebuilt my 350’s top end with vortec heads,comp xe262 cam kit, and edelbrock dual plane intake and 600cfm carb along with msd street fire distributor. When you drive it or hold it at about 1200 rpms in gear it’s like it randomly drops a cylinder and same with driving it will be running fine then act like it’s missing on a cylinder then switch back to being fine again with no real pattern any ideas?weve tried carb adjustments and timing everywhere from 8 to 28 initial with no changes and are about to pull out hair out! Any help or ideas are greatly appreciated!!

 

[RWENUTS]

Could be too much fuel pressure and flooding a bit.
Eddy carbs don’t like more than 5 psi.

 

[Silverback85]

Yea my cheap in line guage reads about 4.5 psi but it may be off. It seems to be electrical the way it cuts in and out may start juggling power and grounds tomorrow see if it will act thought I should throw in the dist. Spark plugs and wires are all new as we changed them to try and fix the problem with no change

 

[ericnova72]

Is that MSD streetfire distributor new to the build, or was it used before the Vortec head and cam change without a problem??

600 cfm Edelbrock, or Holley carb??
If Holley, what is the list number on it?

 

[johnsongrass1]

A buddy just had a problem kinda like that. The rotor was arcing over to the screw. Nylons screws fixed it.

 

[Silverback85]

Originally after we finished rebuild we had a summit brand dizzy and thought it may be causing this issue so we tried the msd with no change still having same issue

 

[Silverback85]

What screws are you referring to? That makes sense but not sure what screw you mean?

 

[johnsongrass1]

Because it happening at throttle tip in you might need to look for trash in the idle and transition slots.
does it happen at WOT too?

 

[Silverback85]

No doesn’t seem to do it wide open if it does it’s not as noticeable

 

[chasracer]

So if you have it in neutral and just bring it up to 1200, the problem does not happen? What plugs and ignition wire were used?

 

[Silverback85]

No In neutral it will go up through the rpms with no issue it will occasionally have a small little blip but that’s it plugs are accel header plugs the shorty ones and wires are the 8mm accels too

 

[Silverback85]

Best way I know to put it in neutral is it will just occasionally skip a beat

 

[chasracer]

I would start with the basics. Check that distributor cap and rotor for carbon tracking, someone mentioned arcing to a rotor screw but you also said it happened with a previous distributor. Next I would put in either a used or new plug - one cylinder at a time. Then take one plug wire (long one) and replace one at a time. This type of issue is going to be tedious to find. Before you start on any of this, if you can put the engine in a dark place and at night, you might find an occasional arc to metal issue. I had a F-250 that I put brand new wires on one time and after two days started getting a misfire here and there - looked at it in the garage that night, had one heck of a light show going on. New just doesn't mean good anymore.

 

[Silverback85]

Thought this may be important if I pull a plug wire off the cap not any one specific and it’s idling in park it will have an occasional arc over to the coil that seems to line up with the blip we are having maybe every dist. Does this I’m not sure haven’t been around enough to know but thought it may be

 

[Silverback85]

Also when we switched dist. It ran good for probably 2 weeks without a hiccup and has started this back could I be frying modules?

 

[Silverback85]

Another thing my tac wire was ground out on my firewall it’s fixed now but could this be causing my module to take a dump?

 

[eric32]

I had the exact problem that you had to where I would start up my truck and while warming it up and holding it at a steady 1200 rpm it would drop a cylinder and go down a hundred rpm or so and then pick up again all the time I started it up. I could never figure out why and just left it as it seemed it did not have that problem while driving and in town once things were going that I could tell.

What the are talking about the screws on the rotor is the two screws on the side of the rotor that holds it onto the distributor that is on top of the mechanical weights. Davis Unified Ignitions uses plastic screws instead of metal ones on there distributors of the HEI versions to combat that problem.

Even with my other motor and with a different brand distributor it does it on the occasion but rarely and that is after I have swapped out plug wires and even distributors and ignition boxes and added grounds etc. I don't know what it was that made it do that on my old truck which I sold several years back but gave up on trying to figure it out. I tried to find the plastic screws to put in my distributor but nobody locally had them at the hardware store.

For me on my current and only truck it does not hardly happen at all so I just leave it be. All my plugs look good and all my wires are firing good and no problems ignition wise

 

[Silverback85]

Well I wouldn’t mess with mine but driving it does it like when your cruising down low it just drops on and off but guess I’m gonna try the screws it’s worth a dhot

 

[BogiesAnnex1]

Yes the tach ground it could be a problem.

Run the engine in the dark to look for ignition voltage leaks.

Shorty plugs can have problems with HEI and CD ignitions where the voltage is high and the external insulator short.

I’d check carefully for carbon tracks and insulator cracks both on the out and inside of the plugs.

Bogie

 

[RWENUTS]

Are you using the original type wire plug in on the distributor. The one that clips on.
Or just a female spade connector like this.

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I bought a truck that had one like that.
Would short out on the tach spade and misfire.