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TR2/3/3A TR3A running on two cylinders

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Bremer

Bremer

Jedi Hopeful
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I have a problem where I would appreciate the forum members' input.
I was doing a tune-up on my 59 TR3A (with an early TR4 engine) and noticed the following:
- When pulling the leads off the #1 or #2 plugs at idle, the engine sound or speed does not change.
- When pulling the leads off the #3 or #4 plugs at idle, the engine stumbles and almost dies.

This led me to believe that the engine runs on two cylinders only (at least at idle). The first question is whether this conclusion is actually correct.

Things I have done to diagnose the problem:
- The plug ends of the leads do spark when held against ground.
- The plug gap was a little wide, I reduced it to 0.025''. No difference.
- Swapped leads and plugs between cylinders. The problem does not follow either.
- Checked compression: All between 100 and 108 psi. (I believe my gauge reads low since two other engines have been checked with similarly low readings)
- Ran the engine with the valve cover off: All valves move approximately the same amount (eliminates wiped-out camshaft).
- Measured lead resistance: Appears to be around 10 kilo ohm for all of them. This compares with about 300 ohm for new ones that I had ordered (not installed yet because they came without terminals that fit into the distributor :m).
- Loosened throttle shaft connection between carbs and increased front carb idle throttle setting, thinking the carb might starve cylinders 1 and 2. This moved the problem to cylinders 2 and 3, i.e. when pulling those leads the engine did not stumble.

Other observations/information:
- There is a point just slightly above idle speed where the engine rocks so much in its mounts that it's impossible to adjust throttle settings with a screwdriver.
- It had failed the emissions test (mandatory here for everything that drives on BC's roads) with high HC and CO at idle as well high CO during the driving test. It passed on HC and NOx in the driving test, where NOx was extremely low.

Sorry for the long message, just trying to provide all info that might be relevant.
Comments welcome! :smile: Thanks very much.
 
It sounds like a fuel mixture/idle setting issue to me. It's either running very rich, or it could have a lean miss - both cases will raise the HC and CO. Another possiblity is a burned valve, although I do not think that is the case since you can change the cylinder that is affected.

I would start by balancing the carbs and mixtures.

John
 
My first thought when I read the description of the problem was that perhaps the needle valve (or grose jet) in the front fuel bowl is stuck closed. Easy enough to check -- just undo that top bolt and lift the lid off the bowl and see if there is fuel in there.

I have had a grose jet stick closed and got the rare 2-cylinder TR engine as a result.
 
All good points. I forgot to mention that I also adjusted the float bowl heights (7/16'' bar under the fork), and the valve was freely moving. Actually, the float was, well, floating in gasoline when I removed the lid. I also swapped #1 and #2 cylinder leads with no results.
I'll continue diagnosos tomorrow with a focus on fuel mixture. Till then, keep it coming!
 
another way to check if you have spark is to use a timing light on each plug wire, if your light strobes on each wire you have spark just dont try adjusting your timing unless you are on plug number one hehe

Hondo
 
I chased a similar problem with my BE a while ago.It turned out to be a short in my low tension coil lead from the points. Everything indicated fuel and carbs until I found and fixed the problem.
Though, it seems you have identified your issue is fuel related. Be sure your carbs are synched at idle with a vacuum gauge. Ensure you have the appropriate amount and type of oil in the carbs. Check for intake leaks around the intake manifolds and carb shafts. I do this by spraying with carb cleaner or such and listening for changes in RPM. This could lead towards a resolution.
 
I had a similar issue once and it turned out to be a carbon track between two posts inside the distributor cap. the result was it was trying to spark two plugs at the same time.
 
I would have a look at that compression as well. 100psi is a very tired engine. I've just rebuilt one that had 135psi on all four and that was due to broken top rings.

Paul
 
Quick update:
I have excluded the ignition side of things. In fact, all four exhaust manifold tubes get hot, i.e. it does run on all four cylinders. So why does engine speed not change when the #1 and/or #2 leads are pulled? My theory is that this is caused by the fact that the carbs are not balanced at the moment, the rear carb draws more air than the front one. Cylinders 3 and 4 are doing all the work and driving the other two. These are still firing but don't contribute, so they are not missed when they are disabled.
So I'm left with a carb synch task. I'll get to that on the weekend.
 
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