Running rich....

[Milner62]

Hi Guys,

I need some advise/help..
I have a freshly restored matching numbers (NCRS TF) 66 427 (390) roadster. On initial cold fire up the choke comes on using the bimetallic strip technology. That all works fine as as you would imagine, it's rich until the choke turns of which it does. When warm, we adjusted the air/fuel and this was done by a friend with a lot of vintage Holley tuning experience.

The result is a car that drives beautifully! No flat spots, great throttle response and the HP you would expect from a 427.

So....the question. When I drive the car for 20 or so mins just around town, pretty normal stuff, when I return, I have a little soot on the rear fenders below the bumper. The car is a side pipe car. We think it still maybe running rich although it doesn't smell like it. Our thoughts are that this maybe normal and part of the 427 side pipe fun from 66 or maybe the jets are too big or something else? The carb is the right carb for the car!!

Any help would be greatly appreciated.

All the best
Dan

 

[Oneball]

You don’t know what part of the cold-warm or on/off throttle deposited the soot. Far better check would be to pull a plug after a long run and see it’s colour.

 

[Roscobbc]

Old school method of checking whether cruise mixture is correct is to find a favorite bit of road - (ideally with convenient lay-byes) drive at, say a steady 50 mph in top gear - snick in to neutral and cut the ignition at the same time. Coast in to the above mentioned lay-bye with the 'dead' engine and pull one spark plug out of each cylinder bank. The colour of the centre electrode will give you a clue to how rich/lean the engine is at 'cruise' - centre electrodes should be a pale to mid coffee colour. There may be darker carbon deposit visible on the outer part of the plug. Problem is that this deposit could be from an earlier engine running condition when at lower speed or idling so it best to carry out this test immediately after installing a set of plugs new (or cleaned and 'gapped' plugs).
What is the carb? Holley? is it vac secondary or mechanical - if the latter are the secondary 'squirters' correctly sized and adjusted? - whether vc or mech are the primary and secondary jets correctly sized?

 

[Milner62]

I checked the plugs last night after a runs and all look coffee brown. Not sooted up. Funny thing is that if it wasn't a side pipe car, you would have no signs....
Carb is the factory Holley.

 

[Roscobbc]

Whilst the plugs on mine come-up with the colour's I previously noted (so primary jetting is probably spot-on) - continuous urban driving is a different matter. Couple that with a rather large carb needing the largest 'squirters' available with the cam installed does mean (on my car anyway) that the plugs will tend to soot-up with extensive urban driving. So much so they have shorted-out and 'lost' spark at times and required replacement.

 

[Oneball]

Get it on a rolling road, if it’s a new engine and it sounds like it is, for a small outlay it’s worth the effort, where are you based?

 

[Milner62]

Thanks for the comments. For the rolling road, sounds interesting. I'm in Berkshire near Reading.

 

[Roscobbc]

Rolling roads are no doubt the best way of establishing certain parameters (fuelling at WOT for example) - but a Holley (or Rochester for that matter) is not exactly the most technologically advanced product on the market - it sounds as though the OP car is jetted just fine - black soot etc is typically what one would find on any non injected non ecu controlled vehicle from 50 years ago. If the engine is a 427 cu in (390 hp L36) its exactly the same engine as my '68 originally came with and very forgiving with carburation.

 

[Milner62]

Rolling roads are no doubt the best way of establishing certain parameters (fuelling at WOT for example) - but a Holley (or Rochester for that matter) is not exactly the most technologically advanced product on the market - it sounds as though the OP car is jetted just fine - black soot etc is typically what one would find on any non injected non ecu controlled vehicle from 50 years ago.

Agree.....Maybe this is simply 1966 standard. I don't expect it to be super clean, just that I have 1 sign seeing a little black soot on the read fenders after a run. As said, it all seems fine, runs right, plugs good Etc.

 

[Roscobbc]

Mine always had carbon deposits on the rear panel, under valance and bumper after even a short run (and still does) I have had complaints from people following too closely in other vehicles about their eyes watering if I use the 'loud' pedal too often.....

 

[Milner62]

Mine always had carbon deposits on the rear panel, under valance and bumper after even a short run (and still does) I have had complaints from people following too closely in other vehicles about their eyes watering if I use the 'loud' pedal too often.....

OK - Thanks! Sounds like I may be OK and just part of the usual quirks of an older car. I'm used to this having other American v8 powered vehicles. Appreciate the comments!!