Bob,
You mentioned that there is spark going to the plugs -- but were you able to
determine whether the plugs themselves are actually producing a visible spark?
If you removed those plugs, reconnected the wires, and then laid them on the
engine so that they could find ground, and still saw a spark, it would seem
you've completely eliminated that unless there is some way the current is
going to ground without creating a spark at the plug electrodes.
At any rate, it would be interesting to find out what you'd see if you used a
Colortune plug on one of the bad cylinders vs. one of the good cylinders.
If you're getting fire and compression, it would seem that the only variable
left would be fuel/air in or out of those two cylinders. Any chance either
intake or exhaust manifold is restricted on those two cylinders? #1 and #4
are connected via the tri-Y, right?...
The Weber sends one throat to #1 and #2, and the other to #3 and #4, right?
One more idea that's a bit far-fetched. Any chance the cam lobes for #1 and
#4 are very differently shaped from those on #2 and #3? You'd see normal
valve lash and get compression, but perhaps the valves are not opening very
far or for very long, which could affect power. You might find it interesting
to put a degree wheel on the engine and see what the valve timing is like for
each individual cylinder.
Duncan
(Texas)
On Aug 4, 2012, at 6:54 PM, robertten1@aol.com wrote:
> Thanks to all who responded to my problem here. I'll be heading to the
dyno
> shop on Friday next, hopefully to get baseline and a/f readings. This in
> hopes of solving the misfire problem a a little break-in time on the new
> engine.
>
> To recap : Removing the #1 or #4 plug wire there is no difference in
engine
> note. If remove the #2 or #3 plug wire the engine stumbles. I've checked
the
> timing, tried rotating 180 degs ( will not start ). Swapped the plugs
around
> and the same 2 cylinders misfire. Swapped the plug wires around and no
change
> in results. Checked and cleaned all the engine grounds and the connections
at
> the battery.
>
> I have swapped out complete ignition systems, one is Mallory Dual Point the
> other is a PerTronix conversion in the factory Delco Distributor. The
> PerTronix is all new parts the module, cap rotor, wires and coil. The
Mallory
> is as was before the engine rebuild. There was no noticeable change in my
> problem with either system. Re-checked all connectors and connections for
> both complete ignition systems found nothing faulty.
>
> I have done a compression test and all cylinders seem OK. I did a
leak-down
> test and nothing stood out there either. I had hoped If there was a problem
I
> would get some direction in one of these tests. Next I removed the valve
> cover brought the crank to top dead center, removed the plug to #1 cylinder
to
> verify and checked the lifters for #1 - both are loose ( suggestion from
Kas
> )
>
> I re-torqued the head, checked the valve clearances ( nothing out of place
)
> reassembled. Then changed from Platinum plugs to NGK V-Groove plugs and
> started the engine. Still a misfire at #1 and #4 ???
>
> I have checked the Weber carb, knowing it will need some tuning as I made
some
> changes to the engine during the rebuild. The biggest is a custom cam from
> Rick Cline. I found I need to lean the Idle Jets as both Idle adjustment
> screws could turned in all the way without changing the idle note. A 2
step
> leaner jet did result in backing these screws out almost 1 full turn. But
no
> change to effect the misfire problem.
>
> And yes, in all kinds of testing there is spark going to #1 and #4 plugs
just
> no change in engine note. A couple good zaps made me feel wide awake
> performing those tests, Hmmmm ??
>
> So I am going to order another rotor for the Mallory dizzy ( at some one
here
> suggestion ) as I grasp at straws for a solution to this misfire problem
>
>
> Engine - .'73 1500 Spit Bored .040" over (recessed blocked)
> A/E flat top pistons +.040
> Head - Milled .125" ( big valve head )
> 6.5 to 1 roller rockers Race Push Rods
> 10/10 crank polished and balanced
> Lightened flywheel @ 12 #
> Duplex timing chain set-up
> Cline Cam lightened and drilled lifters
> Tri Y Headers 2" exhaust
> Single Weber 45 DCOE 13 carb Cannon Manifold
>
>
> Stumpdified,
> Bob T.
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