<VV> More details on rough running at WOT

[Daniel Kinzelman]

Hello

I'd like to thank those of you who have been consistently responding to my 
queries on getting my engine running right.  I have performed a few more 
tests and would like to update you all and see if this brings anything to 
light.  I'm sorry this email is so long, but I want to make sure all 
relevant details are included.  My car is a 1966 Monza coupe with a 110 
horse engine that has aftermarket dual exhausts, an electric fuel pump from 
the Source, and a Pertronix ignitor.  To my knowledge, the engine is 
otherwise totally stock.  Joe Potts has been assisting my attempts to 
diagnose and repair the problem.  We recently replaced a bad inlet valve on 
the passenger side carb which was preventing my car from running, but the 
miss is on the other side, and has been bothering me since I purchased the 
car last August.
We ran a compression check and found excellent compression on all cylinders 
(average 140-150 psi).  The miss appears to be exclusively occuring on the 
left side of the engine.  Someone suggested bad plug wires or carbon 
tracking, so I tried a cylinder balance test on that side.  Each cylinder 
that I grounded seemed to result in approximately equal loss of rpm and 
increased roughness (I didn't try the passenger side plugs at all).  I don't 
know what carbon tracking looks like, but I pulled the rotor cap, and it 
looks clean inside.
Some people have suggested poor fuel supply as the source of this problem.  
I have a transparent plastic inline fuel filter with an electric pump.  
Therefore, I can see the condition of the fuel supply, and I don't see 
anything indicating fuel starvation at idle or the little bit of throttle I 
gave it during the testing.  In addition, the fact that the miss only occurs 
on one side of the engine seems to indicate that any fuel supply problems 
must be downstream of the T-fitting.  Also worth noting is that due to the 
in line filter and electric pump, the inlet stones on both carbs were 
removed before I purchased the car, and we did not replace them.  We have 
removed both carbs and set float level and drop to specifications, and 
replaced one inlet needle and seat.  The float bowls looked reasonably 
clean, and the driver's side jet is marked 50.  We neglected to check the 
passenger side jet, and we did not dissasemble the venturi cluster or 
accelerator pumps on either carb.  The pump shot looks good on both carbs, 
and the inlet valves appear to be holding fuel pressure very well.
Currently, the car's idle is inconsistent, usually very poor (very lumpy), 
especially when cold.  There is a constant, severe pulsation in the driver's 
side exhaust that can be clearly heard and felt if you hold a hand in front 
of the pipe.  When I open the throttle, the left exhaust kind of thumps and 
the miss appears to get worse.  Under load, the engine runs worse as the 
throttles are opened more.  At a certain point, (maybe 50% throttle) it gets 
really rough and acceleration is very poor.  At this point, I can actually 
increase the acceleration by lifting off the throttle a little bit.  There 
is no obvious valvetrain noise, and the cam gear does not appear to have 
slipped.  I performed a hot valve adjustment on the engine without any 
noticeable results for better or worse.  I am running the proper oil level, 
and the problem is present when I run either midgrade or premium gasoline.  
The engine does not ping.  The vaccuum advance seems to hold a vaccuum very 
well, and I recently replaced most of the vaccuum tubing.  We have not 
checked the centrifugal advance to see if the weights are installed 
backwards, but my understanding is that the centrifugal advance doesn't come 
into play until fairly high rpms (2 or 3,000 if I understand correctly), and 
this problem occurs at from idle to redline.  I have tried advancing the 
timing, but that didn't help either.
My plans at the moment are to swap carbs from left to right to see if that 
moves the problem to the other side.  Please let me know if you have any 
thoughts on what my next step should be if this doesn't work.  Although the 
car is functional right now and gets me where I need to go, it's very 
frustrating to drive in its current state.  Thanks for all your help and 
advice.

Dan

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