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TR4/4A TR4 misfiring under load, fouling plugs

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Had exactly the same symptoms. Mine was solved by changing to Bosch platinum 4032(WR7BP) plugs. Champions were good too but NGK always fouled on mine. Changed the plugs and I was done.
 
Interesting. This is my second set of NGKs with very little mileage on either set. They get pretty black pretty quickly, but I've also been changing/adjusting a lot. I'm definitely going to double-check the timing. I do feel like it might be off. I'll run it around for a little while after that and see how the plugs look, but that's good to know.
 
There are many things that could be causing your problem. Poor starting from cold , long warm up , backfiring through the carbs are symptoms of being too lean or a vacuum leak. The sooty plugs however, mean the ignition system is suspect as you don't have enough fire to burn the fuel pumped into the engine. The coil usually fails when it gets warm and breaks down inside causing misfiring as do the wires so that's probably not it. Of course a bad valve could cause this but that's too much work . The points just break the current at the proper time and if they gradually close you'll have this kind of problem so you'd check these right after you've checked the carb. dashpot oil. The condenser however, ramps up the voltage to the plugs so the fuel will burn and the engine will fire quickly and run smoothly and will cause the exact symptoms you describe. Any British Car wrench after checking the oil in the carbs dashpots would have changed your points and condenser and probably be off burnin' rubber by now. I don't check condensers , I replace them and throw the old ones over the hedge. Some parts aren't cost effective to wonder about , just replace them.
 
Thanks, Brinkerhoff. Point made, point taken. I will, indeed, change that condenser while checking the timing and vacuum advance.

One question, KVH...or anyone for that matter: You mentioned turning the dial one notch toward advanced. When I set the advance, I followed the suggestion on https://www.macysgarage.com/myweb6/ign-timing2.htm where he said,

"Just turn the external thumbscrew in the “A” direction (advance) as indicated by the arrow. There is a reference line through the middle the thumbscrew, and one complete turn is equal to 8 degrees of adjustment. Therefore, note the position of the reference line and turn the screw ½ turn in the “A” direction to set your ignition timing at the factory recommended 4 degrees BTDC."

Compared to your suggestion of one notch, a 1/2 full rotation would put me at quite a bit advanced. I just want to verify how much I should be turning the advance thumbscrew.
 
We've discussed this before; I believe the comment on Macy's site is wrong. Unfortunately, the "one more notch" comment is misleading.

The book is correct though. Sorry I don't seem to have a photo handy, but if you look at the vacuum advance module where it attaches to the main distributor body, you should be able to see some small grooves, kind of like the marks on a ruler. There is a larger groove in the middle (you may have to advance the thumbwheel/vernier to see it) and smaller grooves to each side. There is also a kind of corner on the dizzy body that serves as a pointer.

Each small groove represents 4 degrees of ignition advance. So if you set the timing "straight up" (TDC), you then need to turn the thumbscrew far enough to move the advance by one small mark to achieve the "book" 4 degrees BTDC timing. It takes more than one full turn of the thumbwheel to move it that far.

Note however, that it is common for people to modify the centrifugal advance curve to require more initial advance. I understand that when Jeff at Advanced Distributors does a rebuild for a TR2-4, he always installs a curve that needs more like 12 BTDC for proper operation.

Personally, I prefer to do the "road test" mentioned in the book. Get the engine thoroughly warmed up (even overheated a bit is better), and then floor the throttle at about 30 mph in 4th gear. The book says it is OK if it just barely knocks under these conditions, but I prefer to back off just a bit (about 2 degrees or so).
 
Well that's why I was confused. The manual mentions those marks on the vacuum but I didn't see them on my unit and since I was going off of that Macy's article, I didn't bother with unscrewing the thumbscrew enough for them to show. Look like I'll be resetting everything tomorrow!
 
Most of the time it is electrical. Try replacing the condenser. You should always has a spare in the glove box with a set of points. Another thing to check on the carbs is the choke enriching jet. They tend to get a build up on them and will not fully return with the choke pushed in so your running rich. About every 5 + years I have to take mine out and polish them. It will work great for a year or so and then slowly the choke cable starts to get harder to pull. I would get ride of that ballast resister too and go with a good Lucas sport coil.
 
Hi Tom,
Essentially, a full, correct tune-up (champion plugs, new wires, points, condenser) with proper advance, timing, and valve adjustment got it going really well. Of course, this took me a couple tries to get it all right, as you can see above. I also cleaned up the carbs really well and centered the jets. With every little thing I did, it got better and better so it's hard to say what was most contributing to the sputtering. Luckily, none of it was too expensive.
 
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