Hot Rods Skipping sbc

I’m running a stock 305 sbc hei ignition 2 barrel Holley carb . I’ve run this for 5 years and always has the same skip at take off and in second . It skips at idle . I’m at my wits end . I’ve changed the carb, spark plugs cap coil wires ,full distributer and rechecked timing and fuel system.ive even tried premium no ethanol gas but always has the same skip. I don’t know what to check next.


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Probably a valve not seating , does it still have exhaust valve rotators ?

 

No. Also it’s not a constant skip . At idle it will run fine for a few seconds then have a skip then run a second and then two skips .., repeat


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Pull one wire at a time and let it idle ,see which is the skipping cyl. Lippy

 

Let it run at night in the dark and see if anything sparks.

You say it does it in 1st and 2nd ............only? What transmission are you using and does it have a lock up converter ?

 

IME , its a valve that does not always seal. Carbon / warped/ bent , whatever , just doesn't always seal.

 

I'd hook up a timing light and watch the timing marks at idle and fast idle.
If it is an HEI distributor with mechanical centrifugal advance I'd expect the timing to be dead steady..
It would be most enlightening to test all 8 cylinders but marks will have to be added to the damper every 90°.

A worn point distributor with worn bushings can have a really crappy idle and wandering jumpy timing.
Magnetic or optical pickups in place of the points are less sensitive to worn bushings.

 

What is your vacuum gauge telling you? Best tool in the box for finding running problems.

 

I did this and replaced no. 1 and no. 5 spark plugs as they looked suspect. The car ran and idled great so I took it out and ran the piss out of it today 100 miles and at speed on the expressway and when I parked it still idled good and ran good , best it’s ever run. I’m still not convinced it’s fixed.We will see what tomorrow brings .


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Many new parts...plugs, condensers and more, never work right even when new. Easiest way to rule the plugs out is to switch them for cylinders that seem to be running well, to see if the problem follows the plug.

 

I'm hoping you're gonna replace the other 6 as well ??

 

The reason I said to do it that way is to isolate the cyl's that are skipping. Once you know which they are, then you can dig deeper, Lippy

 

I forget that people don't do ( or know) basic diagnostics before asking for help sorry ..

 

Sorry I was directing that to the OP.

 

Well today brought rain so We will see what happens later this week I guess.


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Try unhooking the vacuum advance sometimes the wires under the plate will loose contact when the plate moves.

 

Ok skies cleared up so we went for a 50 mile cruise. End result everything is running great . I’m still confused as over the past five years I know I’ve put new plugs in every year at least 3 sets of wires , 2 coils 3 distributer modules 2 sets of caps and rotors checked timing constantly, gone through the carb twice and nothing ever fixed it until now . It’s so weird I think I have to chalk it up to being 2020 . But thank for the advice guys.


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So now we are done right

 

Sounds like you are trying to fix it with a parts cannon. You need to find someone with some diagnostic skills.

 

We put 130 miles on it today , we did a Back The Blue rally still runs like a top.


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Update: I’m out of work right now so I decided it’s time to rebuild the engine. I tore it down and found no. 1 and5 had broken rings but over all everything else had the usual wear from being 190 plus thousand miles . I did a complete overhaul honed it out new rings bearings cam lifters all new gaskets timing set even took the heads completely apart for cleaning and new valve seals ( no more smoke on start up) . Got it back in all hooked back up and fluids filled. Now I’m ready to fire it up to break it in.


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Grounds, good grounds. Engine to frame, engine to firewall (if it's a steel car). Grounds. Do you see all the ground stuff they sell for the "tuner (import) types". Broken rings are't going to cause a "skip"; loss of power, oil use, yes. I say the skip is electrical. I am Butch/56sedandelivery.

 

Yes I also cleaned all the ground connections. Thank you.


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I hope that after 190k miles you bored & honed , or st least checked the cylinder taper & the piston wear ...did you grind the valves & seats & check the guide clearance ? Flat tappet cam ? Did you use a moly assy lube & break in additive ?

 

At what cold temperature outside would you fire an engine after a rebuild not heated from an outside source?


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Heat wave It’s 47 degrees today !


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