The Stovebolt Site Forums The Shop Area Engine Shop 216 still misfiring...help

I have replaced the points and condenser on my truck with a new Petronix HEI and coil

Set Timing on the ball. (I have tried many settings. This seems the best).
Vacuum is steady at 20
New plugs, wires, cap and rotor
I gapped the plugs a little bigger (.042) due to the HEI and it seems a little better.

My dizzy seems very solid. There is no side to side play on the shaft but there is some rotational play on the linkage to the vac advance.

I have random misses on all 6 cylinders.

What do you guys think?
Will a valve lash adjustment help? (I do have a slight valve noise)
Do I need to replace the bushing on the dizzy? How do I do this?
Is there supposed to be play in the vac advance linkage?

What else would cause random misses on all cylinders?

Hy rust bucket 53, could your fuel be contaminated? Is your float level correct? Does it miss at all r.p.m.s, more under load, or just at idle? I think we need more info, otherwise we're just firing in the dark, and you "miss" a lot when you do that.

A lean mixture will cause random miss. Is the centrifugal advance working as well as the vacuum. Disconnect the vacuum line and watch it with a timing light. Vacuum advance can be observed by just revving it up and see if it pulls on the distributor when the vacuum goes up. There is a little play in the vacuum linkage.

Guys,

I will check to see if it misses at rpms other than idle. I never really looked at that. I do not have the ear or "feel" to discern missing under a load. I can really only confirm the random miss on all cylinders by using a timing light on each wire and watching the light blink and miss randomly. Since I increased the spark plug gap it is a little better. (Gap went from .035 to .042)

I get a popping out of the exhaust associated with this as well.

The fuel system is all new. New tank, new lines, rebuilt carb, gas is a few months old as I don't drive it much. The carb could be suspect as I have had some difficulty with it. But I am pretty sure the carb is rich if anything. My plugs went from black to grey/white when adjusting the carb with only little change in the missing.

The vac advance seems to be working ok when you rev the engine. There is a little play in the linkage which allows about a 2 degree change in timing if you take up the play.

I have been fussing with this all summer. I have a replacement carb on the way that I will rebuild and try to see if it will make a difference.

Will valve adjustment cause this???

Thnaks for the help.
Rich

Also I have carbon in the tail pipe (black powder in the tail pipe)

I also get some wet black spray out of the tail pipe if I rev the motor when I first start up.

It runs better after a drive but the random missing does not change.

I don't know much about 6 cyl, but that sounds pretty minimal.

Black in the tailpipe could be too rich fuel mixture and/or oil burning. What is your idle speed (without any choke)when the engine is at operating temperature? Pull the spark plugs and look at their color and wetness. Make sure you are not running the choke too much.

Plugs have been good lately ...tan color. Oh and the compression is also good.

Below is from a post a few months ago
cyl 1 120# plug is tan
cyl 2 120# plug is tan
cyl 3 110# plug is black
cyl 4 110# plug is black
cyl 5 110# plug is tan
cyl 6 118# plug is black (little oily)

Idle speed at full temp is 500rpm. Any less and the misses seem worse.

I don't think I am burning any oil (very little exhaust smoke). The plugs are dry for the most part. I do have one that was a little wet (oily) back when I first started to tear into this but that seems to have resolved. (which takes me back to valves again)

I will take it out on a highway run tonight and then check all the plugs when I return to see color and dryness.

I have only been driving this truck this summer and probably less than 100 miles.

There is no history on this truck I have no idea how long it sat without running but it was probably a long time based on the condition of the truck and engine when I got it.

Should I adjust the valves or keep driving and see if some of this resolves as the engine comes back to life? I would think with some good plugs and some bad there is a valve issue.

Ran it out on the highway for a few miles and then back to the garage for a look at the plugs. Still some tan some black. very little oil on any of then.

I regapped the plugs to .045 started it and checked the timing. right on the ball. the missing seems better by timing light. instead of missing 1 every 5 or 6 strobes it was more like 1 every 10 or 20. and some barely missed at all.

Still have the popcorn sound at the exhaust.... any suggestions on what casues that besides miss fires?

Rich

I'd adjust the valves and since you have a vacuum gauge use it to set the timing, just set to hightest vac reading. If this doesnt work Id go through the tune up proceedures in the old shop manual. Also I have a mini HEI, instructions suggested plug gap .060-.080, plug type extended tip type plugs.

Best of luck
Jim

Jim, i did set the timing by vac at one point but over the last few weeks I have been tweaking here and there. It do not stop the missing.

.06 to .08 seems aweful big for a gap. ?extended typ tip plugs?

I have instructions I found on line for valve adjustment. I could not find it in the manual. Is it trus there are only 2 engine positions to adjust all the valves. That doesn''t seem possible

My instructions say to set the engine rotation so the bb is at the pointer then

The first two rockers should be slightly loose, but not to worry, take your feeler gauge and unfold the .006" and .018" blades, fold up the rest and tighten the nut so they're not sliding all over, see if the .018" blade will fit between the tip of the rocker and the 1st valve then see if the .006" blade will fit between the #2 valve; if not, take a box end wrench and loosen the locknut on the far end of the adjuster, fit your screwdriver into the slotted screw and adjust until the feeler gauge blade just lightly fits with a slight drag be aware that the angle you hold it at has a great effect on how accurate the adjustment is. Once you've got it where you feel it's good, hold the screw from turning and tighten the locknut again with the box wrench then re-check the adjustment. Be aware that if you use an open end wrench, you'll not only strip and ruin the locknut but you'll soon have professional mechanic's knuckles - bloody and scarred for life. It hurts too. You don't need to really crank the nuts down tight; a tiny bit more then snug will do.

Once you've set the two front valves, count down the valves from front to back. There are 12 of them and the next one to adjust is #3 to .006" (this is an intake valve) then on to #5 .018" (this is the #3 cylinder exhaust valve,) next is #7 to .006" (this is the #4 intake valve) then on to #9 set to .018" (this is the #5 cylinder exhaust valve.)

Set down your tools and relax for a moment; you're halfway through.

Now turn the engine one complete revolution until the steel ball lines up on the pointer in the window again; you're now on TDC cylinder #6, so let's do the other 6 valves in this order, working from front to back: valve #12 to .018", #11 to .006", then #10 to .006", then #8 to .018", next is #6 to .006", and lastly #4 to .018".

Is this right only 2 engine positions to adjust all the valves???
I got this off Deve's site. He is usually very reliable.
Rich

I adjust mine with the engine HOT and running (you need to run the motor for maybe 15 minutes or more beyond water temp getting hot), slowest idle I can get. First I go for the exhaust valves, being carefull just slip the feeler gauge in and if it's not tight I'll adjust a little until feeler gauge just begins to stick then move on. Also watch for bent pushrods etc while you're in there. BTW do this at your own risk, you can break stuff if you get carried away.

I've cut down a spare rocker cover to keep the bleeding of oil to a minimum.

I love my HEI and it's set up as described and those numbers re. point gap are from "The Boss" he knows his stuff.

worn or sticky valves could also cause the miss.

I knew the plug gap need to be larger I never imagined .06 to .08 but it is easy enough to try.

On the valve adjuistment it is really only 2 engine positions TDC and 180 degrees off TDC as in my instructions abover? I have only done this on 8 cyl engines long ago but remember many different engine rotations.

What is an extended tip type plug?

Yes, it looks like Deve's valve-lash adjustment procedure is correct.

Here is another rendition

Tim

Thanks Tim