Diagnostic help please

[AustinJim]

I'm still resurrecting a 78 Spitfire and now that I have the engine running (most of the time) I need help diagnosing it's condition. I'm getting black smoke in the exhaust all the time it's running. It seems to come out in puffs so I guess it could be related to one cylinder but I can't really tell. I'm trying to get a reading on the condition of the engine. It also idles rough.
I've attached a photo of the plugs. I installed new plugs then ran the engine about 10 minutes at about 1,000 rpm. The plugs in the picture are in order: cylinder 1 is on the left then 2,3, and 4.
Compression:
Cylinder...Dry....Wet (oil)
1..........110....125
2..........115....130
3..........115....120
4..........115....125

I'd like to hear any opinions on this engine.
Thanks!

 

[SilentUnicorn]

Jim,
what do you have for an ignition system? what color is your spark? Looks kinda rich. Is your choke working? what kind of condition is the carb in? Compression looks good.

mark

 

[AustinJim]

It's been converted to a solid state ignition... no points and a module on the firewall labeled "Luminition". I'll check the color of the spark this weekend. Can't tell if the choke is working or not. It's a water choke. How can I tell if it's working? I also don't really know what shape the carb is in. It looks fine from the outside. I've removed the float chamber cover when adjusting the float. There was a little debris in the bottom but no corrosion in the float chamber. I've thought it might be running rich too. The carb is at ZS (150 I think).
Thanks!

 

[SilentUnicorn]

Spark first, cap and rotor up to snuff?

have you read this? https://www.theautoist.com/weimerisms.htm chapter 3 section 2.

mark

 

[Banjo]

I agree. First, make sure the ignition is in tip top shape. Then I would definatly make sure the choke is opening all the way and that the carb is trimmed right.
If it was puffing blue smoke, then you'd be looking at oil. But you have black smoke, that's a rich condition, or partially unburnt fuel from an ignition problem (either way it's gas, not oil). From the looks of the plugs #3 isen't doing much at all (#1 and #4 look kinda sooty, or, rich). Is #3 damp when you pull it out? You may have a bad wire, or a cracked dizzy cap.
The compression numbers are a little low, but are even ,and are acceptable, so I don't think that's the issue.

 

[Bugeye58]

Jim, those compression numbers arent all that bad, as the engine should only have a 7.5:1 compression ratio.
But, running the engine at 1000 RPM for ten minutes isn't really going to show you anything. Find a good stretch of road, and run at 65 or so for about 15 minutes. Then, shut the ignition off, at speed, and pull over and look at the plugs. This way you should have taken the choke out of the equation, and get a good solid read of the plugs.
Also, check and make sure the valves are adjusted correctly. Bad valve adjustment will effect the burn, and could cause an intermittent miss, and puffs of black smoke.
But, by all means, check the cap, rotor, and wires. Start it after dark and spray a mist of water from a bottle on everything around the area and see if you notice any arcing.
Jeff

 

[Alan_Myers]

Hi Jim,

You said you adjusted the carb float.... are you sure you got it correct? I am not certain it's the same with ZS carbs, but with many SUs too high a float can often cause flooding and an over-rich condition. Might be worth a double check.

Cheers!

 

[AustinJim]

All,
Thanks for all the great suggestions! Now I have plenty to do this weekend! The wires, cap and rotor are all new but I know that doesn't mean they're ok. I've adjusted the valves but I'll double check them. I know a poor float adjustment on ZS carbs can cause flooding but I think I have it adjusted ok now. One thing I don't know how to do is to adjust the choke correctly. The book I have is just not clear enough. There's an index mark on the choke body but I don't know what it should be matched up against on the carb body. Also, how can I tell how far the choke is engaged, if at all?
Thanks!

 

[AustinJim]

I just found the article that SilentUnicorn referenced above. It seems to tell me how to adjust the water choke so I'll give it a try tonight.
Thanks again!

 

[myspitfire]

In my opinion first thing i'd go out & buy is a manual choke & get rid of that water choke,You can disconnect the auto choke easily & hookup the manual.Then replace the rubber diaphram in the Stromberg its probably torn.Your problem is fuel related an easy fix.ALWAYS with Spitfires its usually some small thing causing problems.Go buy a Bentley shop manual;Every Spitfire owner should have one they explain things clearly & explicitly for any novice mechanic.,from beginning to end.My Bentley is for 75-81 Spits but you can get one for yours to their about $40.00 a wise investment.As long as its black smoke & NOT blue you'll be ok. Ken

 

[Bruce Bowker]

1st and 4th ( especially) plug look very rich.
Bruce

 

[ydh878g]

I have owned several Mk4/5 Spitires, one problem with the later cars was the WAXSTAT choke assembly which replaced the earlier manual choke. If your car has this you will see a large jet assembly below the carb body centre and no manual mechanism. These WAXSTAT chokes faile with age and often give a very rich mixture, your mixture sounds very rich. I would replace these WAXSTAT jet assemblies with the erlier manual jets. I believe that Rimmers and Moss in the UK do a conversion kit and maybe some suppliers in the States (I have only been here 2 years so not sure where to try)

 

[AustinJim]

I checked out a couple of the suggestions this weekend. The water choke was way out of adjustment creating the righ mixture. After adjusting it I'm only getting a little smoke on acceleration. I misted the plug wires while the car was running but found no arcs. Still haven't had a chance to check the spark color.
Thanks again for all of the suggestions!