View Full Version : TR4/4A TR4A running rough question(s)

07-31-2006, 11:14 AM
My TR4A is running poorly and I am looking for some of you that are smarter then me to help me out. For background, the engine has only 800 miles on it since I rebuilt it (head to machine shop for new valves and seats, all bearings in the engine new, crank ground, cylinders honed and new rings). The carbs (HS6) were rebuilt and have new jets (0.100 inch) and new needles (standard TW). The thermostat is the 160-degree F. one. The entire ignition (coil, plugs, cap, rotor, points, condenser and ignition wire) is new (again this week). The plugs are NGK BPR6HS. The timing is set to 4 DBTDC static (but see my question below about this). Compression is good on all four.

The symptoms are: at idle it seems rich (when I do the lift the dash pot test I have to lean the carbs all the way before the engine responds the way the book says it should for the correct mixture. But, when I drive the car and accelerate hard the engine acts as if it is too lean (it misses and has no power, but if on hard acceleration I then pull the chock it runs a bit better). Also but, over all it is running very rich, in that it uses a lot of gas (compared to my TR3A with the same engine) and the exhaust is very black (in fact the back of the car is covered with black soot).

My questions are many but can be summarized into one. Does any one have any ideas what is up with this engine? One at a time they are: How does timing interact with apparent mixture (that is if my timing is way off can this make the mixture look right when it is wrong)? Can the cool 160 thermostat cause it to need to be too rich? In the Haynes manual it says to rotate the distributor counter clockwise when setting the timing but the rotor turns CCW as well so should the static timing not be set by turning the distributor clock wise until the points just start to open? Also in the Haynes it says to set the vernier one division mark on the distributor advance. I notice that the fourth mark is longer, so is ‘one mark’ four small ones (to the first long one) or just one small mark?

Any help would be much appreciated. This problem has been with me since last fall but I gave up on it then and put the car away for the winter and did not touch it again until yesterday when I replaced the entire ignition and started it up for the first time since last November.

07-31-2006, 07:51 PM
Did you rebuild the carbs?
Do both carbs react the same to fixture adjustment?
Are the needles installed correctly?
What is your fuel preasure?
Are you getting centrifical advance on the dristibutor?


07-31-2006, 08:11 PM
the answer to all your questions is 'yes' other then the fuel pressure which I never measured other then to make sure it delivers loads of fuel.

07-31-2006, 08:52 PM
When operating the choke, do the jets seat completely after the choke is pushed in?
With the jets adjusted up all the way, do the pistons drop and (clunk)?
Are the needles installed with the shoulder flush with the bottom of the piston? I worked on a TR4 with the needle installed to far up into the piston.
To much fuel pressure is something you might check. I run about 3 PSI.
Also check you PCV valve.


07-31-2006, 08:53 PM
For what it's worth I'd replace the coil(if you haven't already) it obviously isn't your entire problem....but if you coil is on the way out it can cause other problems.

07-31-2006, 10:24 PM
Has the cylinder head been retorqued since the rebuild? If not, check it, if low torque 50-60 lbs.,retorque to specs and then adjust the valves to specs because they will undoutedly be off spec. Their are some threads on the forum dealing with setting timing, maybe someone could help with that. Now you can try adjusting your carbs again.

08-01-2006, 03:05 AM
Adrio, here is my advice:

First, of course, make sure you've got a good distributor cap and wires. Do check those wires, and especially make sure they are well "booted" over the plugs.

Next, be certain you have clean points, filed flat if necessary. Pitting or chipping will affect your point gap and performance.

Set your point gap carefully.

Time the vehicle static only. Point the pointer over the hole in the pulley, rotor pointing to piston one, pull the rotor off, and rotate the distributor clockwise until the points just open. BUT do not eyeball it. Use a bulb from your front blinker lights, or another bulb, and an 18 inch wire. Rotate the distributor until the bulb just comes on (one wire end to the coil, the other to the bulb housing with the bulb bottom on ground--like the bolt on the valve cover).

After you've got it set so the bulb just opens, my advice is to turn the dial one more notch, like they say. After running the car, you may want to retard the timing using the dial. I retard mine just a bit and it runs better.

OK, now the carbs. After much agony, I just follow the manual and instructions. But, my personal opinion is that the piston lifting trick is too inexact and arbitrary. I'm not sure what kind of mechanical ear one would need, but I've had zero luck on that. So, I gently tighten up the
screws, all the way, then back off the number of flats in the manual (I'll get it in front of me if you need the number). Then, I go 2 to 4 more flats each side, a bit richer, not leaner. I'd rather be rich than lean. My car runs better (and I think cooler) that way. I think you'll notice what I mean if you experiment. [Or, you can lift pistons while wearing a white coat and pretend you're a scientist.]

Seriously, provided your carbs aren't leaking, and the jets are centered--with each piston falling freely after lifting it--and provided you're not sucking too much air from worn throttle shafts--and provided the floats are operating correctly--and provided you've used a sychronizer or other tool to substantially equalize the two carbs--just open those screws an equal, healthy number of flats and go for a ride. If I'd guess, I'd say you were too lean.

The thermostat is likely irrelevant.

Finally, if the car is missing after you've done all of the above, I'd check: a) the plugs for fouling; examine them closely; b)the plug wires for evidence of arcing against nearby metal (mine arced against the fuel line!!!); c) the flow of fuel to the carbs. Make sure you use a fuel filter at all times. Make sure there is no obstruction in the gas tank (I once had a piece of wood in there that caused nightmares until I found it); d) the wire from the coil to the distributor.

Good luck. Amateur advice from a long time TR owner.

Simon TR4a
08-01-2006, 12:36 PM
Hi Adrio, you've already got some good advice here, but I wonder if there would be any value in swapping parts over from the TR3a, one at a time, to try to pinpont the problem?

Also, I am not familiar with the needles you mention; my carbs came with SC needles, slightly richer than stock, I believe.

08-03-2006, 10:10 AM
Thanks for all the advice. I have solved it and the solution is a very interesting data point for us all.
It turned out to be the thermostat! It seems that when it was installed it fell down a bit leaving a large crescent shape bypass for coolant. The result was that the engine never got up to operating temperature (I guess between this and the other bypass I had way too much cooling). I have a picture of the misaligned part if I can figure out how to post it here.
Once I put in the new thermostat and set the carbs and timing the car ran great.
I must eat crow though, as I think in the past I have suggested at some point and some place that running without a thermostat is no big deal.

08-03-2006, 12:57 PM
I used to run my 4a all the time without therm. No Problems.
I (since resurrection) run with one in.

08-03-2006, 02:01 PM
Bizarre indeed Tomster. I think my TR3A has not had one since 1985. I will have to open the 3 up just to confirm this though. As they say all is well that ends well. I am about to go for a nice long hot summer day drive with the TR4A, this will be the final litmas test.

08-03-2006, 05:12 PM
Adrio ENJOY yourself !
Forget the past