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To my tired old eyes, your plug looks fouled with a combination of oil and fuel deposits, in other words, incomplete combustion. This could be caused by a lot of things, including retarded ignition timing, lugging an engine in high gear and improper spark plug heat range.  This occurance is also not unusual if you have been doing a lot of tinkering, and this includes swapping spark plug leads and squirting carb cleaner in every direction.   Since you have not fully disclosed the condition of your engine, at least not in this thread, is it possible the combustion chambers are laden with deposits that have been loosened up with your latest handiwork?  (I might have suspected a crankcase blow-by issue, but for your picture showing no connection from the valve cover breather and the carb.)  How did the the plugs you replaced look?  Dry and worn or wet with deposits?  Those old plugs may be able to tell you a lot.    How many miles on your engine?  Does it consume any noticeable amounts of oil?  Do you have any recent compression numbers?  (None of this information is a necessity, but the more you know, . . . is generally a good thing.)


Looking at the plugs after twenty minutes of spirited driving might give you a fair indication of engine health.  So might a .25  mile run, if the engine was built specifically for that purpose.   But you mention twenty minutes of engine "running."  That is not necessarily the same thing,  If you are constantly throttling up the unloaded engine, you are engaging the accelerator pump and flooding addiitional fuel to the cylinders - which is a naturally rich condition.       


I just read Daron's post and agree with his suggestion about double checking the distributor and the possibility of low temperature fouling, meaning you might consider a hotter heat range plug - as suggested a BP5ES.  (I have run both numbers on my '02s going mostly with the "5s" when the majority of the driving is city traffic as opposed to the open road.  The '5s tend to look extremely white (as in overheated) on my cars after long hightway trips.  The "6s" tend to look tan and the engines are less prone to pinging on pump gas with the cooler plugs.)  There is no question that a worn distributor, or one with a gummed up centrifugal advance can impact the full range of engine operation.  To be clear, I was only focusing on your rough idle, as you did not mention any other engine issues.  Of course you should have a rock steady timing mark, but if misfiring is present, it can cause an erratic mark.  Since the idle circuit affects idle as well as low speed part throttle operation, inclusive of 1400 rpm, some mark jumping is understandable.  However, the mark should be stable at higher rev ranges.  Did you have a rock-steady timing mark before the tuneup and carb rebuild?


if your engine is past its prime, (not saying that it is) and carburetion is determined not to be a primary issue, you might consider employing the "Big Dog" timing method mentioned early on in this forum.  Recommended timing settings are great as a baseline for most fresh, up-to-spec M10 engines,  but so many engines in 40+ yo cars can't claim that mantle.  





Hi Roland,


I did keep the old plugs: Bosch W7DC. They are very cruddy - lots of oily soot on each. So that doesn't bode well.


The history of the car is a complete mystery to me - I bought it on Ebay from a guy in Lancaster, CA, who delivered it on a flatbed, although it did run, it wasn't highway safe. There was a Title, a few receipts, that's it. It hasn't been off jackstands since I drove it onto my property at that time. The car was in very shabby condition indeed, so I have no idea of the engine mileage, or oil consumption. Based on the wear on the original driver's footwell carpet, my guess is that the car has done a high mileage. It's fine: I bought the car as a project/challenge, and I didn't pay much :D  

I added an oil pressure gauge, so I know that the oil pressure is good - around 30 after warm up. I never checked dynamic timing before the carb rebuild.


When I check the timing again tomorrow, I will see if the timing mark stabilizes at higher revs. The engine does rev very freely, and sounds great when doing so  :)


Thanks as always for your encouraging advice.

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Stock plugs are W8's... Bosch heat range scale is colder in lower numbers. a W7 is a colder plug. NGK plugs...lower the number hotter the plug. I don't think plug gap will solve the issue but something to pay attention to when you fine tune.

I don't think float level is the issue either but it needs to be ruled out.

You will eventually establish a baseline. you are getting there. 

A different distributor will certainly give you another piece of information. FYI there is a bosch distributor shim kit available, but I certainly agree, yours is starting to look pretty hosed from some butchery.


How old is the petrol? Get some fresh in the car !


Have fun wrenching today. :)

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I think the question regarding “cam” is shorthand for asking whether you have a modified engine with a non-stock camshaft.  A different profile cam can provide more power or torque.  A typical tradeoff is a “lumpy” idle.  Some wilder camshaft profiles make a “liveable” idle a virtual impossibility and should be relegated to the track or back woods.  Although I cannot be sure, your cam is probably stock.


Since you are dealing with an unknown history, nothing would surprise me with you car.  Occasionally, the surprises are good, sometimes not.  In suggesting your idle could probably be improved, I was assuming that your engine was middle-of-the-road condition, an overall good runner with niggling idle and transition roughness.  You mentioned “the engine used to run alright before” and something about a high vacuum reading.   Did not intend to mislead you, but the suggested remedies are typical and relatively inexpensive.  They may work fine, but there are no guarantees, especially when tossing out advice long distance regarding an engine that may or may not need additional work.  I agree with the others that it is wise to start with a baseline and work from what you know about the engine.  Something I do not think you mentioned is compression.  If you have an issue there, fuel and ignition mods amount to wishful thinking.  If your car drives well, it is unlikely you have a compression issue, but it is good to know as a starting point.  Even as a starting point, it is still no guarantee of a perfect running engine.

A neighbor brought over a similar purchase (not 02) with a so-called recently rebuilt engine, with receipts.  Car looked good and ran well but something about the exhaust was not quite right.  The neighbor was unhappy about the smell of burning oil.  The neighbor was even more unhappy when “someone” noticed a spark plug anti fouler jammed between the firewall and frame rail and he said that was enough.   After several tune ups and followup visits to his mechanic, he sold the car to another neighbor.  The new-new owner immediately dismantled the “recent” rebuild and discovered a few new parts in the valve train and enough gasket sealant for three engines.  He also said he discovered one or more of the oil control rings was either missing or improperly installed.   Good compression - and smoke.   Go figure?

Some things can be fixed with adjustments.  Lack of compression and wear are something else.    Mike referenced valve train noise, but viewing your video in a loud room made it unclear to me that the valve train seemed unacceptably loud.  Since you are not dealing with hydraulic lifters, sound similar to a sewing machine is normal.  Excessive clearances caused by improper adjustment or wear usually results in excessive noise.  I have no idea if there is a decibel measurement for unacceptable valve train noise, but even an untrained ear should know it when he hears it.  Valve train noise and other earmarks of valve train wear is a subject beyond this post, discussed countless times on the forum.

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Hi Roland and Daron,


I realised based on the feedback that I really need to drive the car a bit before pursuing this any further - it may just be that it needs a good run  :P


To that end I had to replace a couple of the tires, which I did this week. I also got hold of 55 and 60 idle jets from Ken and installed them, and re-timed the engine after my repair of the distributor. Now I'm all set for a spin round the block, and perhaps further, but some dude has parked in front of my gate, and I can't get the car out!


I'll report back when I have more news  :)

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