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TR2/3/3A 1961 Triumph TR3a

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danger2nature

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Hi all, I'm new to the BCF. I bought a 1961 TR3a from my uncle last year who did a complete restoration on the vehicle and enjoyed it for 10 years himself. He has relocated across the country so even though he is only a phone call away, its been difficult to tinker with and fine tune the car without him. After putting the car away for the winter, I had to have the carburetors rebuilt and tuned this spring. It runs great until I come to a stop, and the rpm's are at around 1,000 then it wants to drop out and stall...…even when the car is hot and has been driving for an hour. If I pop the choke it hops back up to 1,000 rpm's and idles fine. My mechanic cant figure it out...and said I should invest in Weber carburetors. I'm mechanically inclined, but still green when it comes to this car so any advice on the problem I'm having or the Weber upgrade would be appreciated! Thanks,

Brian
 

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Nice looking car. If your mechanic thinks you need to convert to Webers to solve your problem, you might want to find another mechanic. Big money for the Webers and far more complicated and difficult to tune, IMO.

As for the idle issue and stalling, my first guess, and it's only a guess, is that you have a vacuum leak around the throttle shafts. Ask the rebuilder if he did the shaft bushings. Lots of other things it could be, float level height, dashpot oil low, a sticky piston to mention a few.

Tuning SUs is quite easy. You don't really need a synchronizer tool either. Here are some instructions. > Tuning - Multi - SU Carburetters <
You can also find instructions on this and other forums.

If your car did not come with a factory service manual, that might be a good investment to make too.

Tom
 
I have a 1961 TR3A and it has SU's. I agree with Tom. Definitely stay with the SU's. You may need to check out the ignition system as well as the fuel system. Check the points, plugs, spark plug wires, coil. Also, if you don't have a fuel filter before the fuel pump it would be good to add one.
Bob
 
I have not heard that one for a while, about buying the Weber’s--- heck I wonder what that would cost??? 4K new, and what kind of guarantee you would get. Heck I think he would be adjust things for a long time because driving these cars is driving old school American 1950 with all its fixing and worse gas. But that is what a tr4 is, right. Anyways I agree with Tom; it probably needs shafts and some fine tuning on the points and plugs probably, but the carburetors are simply and great and easy to maintain and if that was not done probably twice in its life; it needs it anyway to run better.

steve
 
If Webers are 4K you could get a new pair of SUs from Moss for about $1200.00.

Do you have a British car club locally? Someone there should be able to point you in the correct direction.

David
 
Two things happen when you pull the choke. This mixture is enriched and the idle speed in increased (if it's set up properly) I agree that throttle shafts are a good place to start.

Anyone who thinks that Webers are easier to tune that SUs obviously has no clue how to tune an SU.

The beauty of a Weber carb is that it's infinitely adjustable; the curse of a Weber carb is that it's infinitely adjustable. My friend has Webers on his Super 7 and has been trying to get them properly adjusted for 20 years. He's got it close, but still not perfect. There are just way too many variables with those carbs. They look really nice, but I've never seen a set work better than SUs on a road car.
 
If your mechanic is the one who rebuilt your SU's I would suggest his tuning skills are poor and that is probably your only problem. You say you are mechanically savvy so look up all the info you can find on SU's and understand how they work then have a play with it yourself. The adjustments are usually quite small to make a big difference to the way it runs give it a go.

Graham
 
Just wanted to share my opinion. I agree with the previous posts listed here. Your description matches what I experienced on my first TR. Right down to the need to pull the choke to get it to run without sputtering or stalling. I have owned 5 TR's and needed to replace the throttle shafts on all of them. The first TR3 I owned, came with brand new Weber carbs. The previous owner paid about $900 for everything to swap out and replace the original SU's. First thing I did was switch back to the SU's after rebuilding. Still trying to sell the Weber's (Haha). If you stay with the SU's, once sorted out, they are really great.
 
Hi, I had a similar problem with my TR-3a. Mine would typically idle at 800, drop to 400 and die. Sometimes it would slow to 400l then return to 800. Once above 800 RPM, it was fine.

Issue was a worn out distributer mechanical advance. I had the stock Lucas DM2 distributer. The flyweight springs were broke, and the "toggles", that connect the springs to the weights, were worn.

I found it by putting a timing light on it and idling for a couple of minutes. I allowed to go thru the speed up and slow down cycles. Keep the timing light on the while checking. The timing was shifting from 2 btdc to 10 atdc at idle, on its own. A new distributer fixed the problem.

You could also check it by twisting the rotor and releasing it. It should snap back to where it was. If not, look at the advance.

Good Luck, Roy
 
"99% of all SU carburetor problems are electrical." True in the 1950's and true today. Thanks Roy.
 
Attached are two pages instruction for adjusting SU Carbs for TR3. This is out of the Haynes Carburetor manual. The sections and figures I note on Page 1 are the key. First of all, as mentioned above, be sure to thoroughly check out the engine electrics. And also, balance the air flow of the carbs, see figure 5.11. I found Figure 5.9 very helpful in conjunction with the items marked (w), (c), and (r) in section 5 in the first column. It takes some time and close listening to decipher the sound of the exhaust but it is very accurate. ( I did not find the section about pushing the lifting pin helpful at all, just didn't seem to work right). I also closely observed the color of the electrodes on the spark plugs. Over quite a long time of tweaking and driving I found the best setting for the jet adjusting nut (see figure 5.7). If the spark plugs were too black, I'd turn the nut clockwise to lean the mixture, (i.e. 1/2 to 1 flat at a time and then drive). If the spark plugs were too white, I'd turn the nut counterclock wise, (i.e. 1/2 to 1 flat at a time and then drive) to richen the mixture. Once the spark plug electrodes were a nice shade of brown and the exhaust sounded right (Fig 5.9), I found that is when it ran the best. As I mentioned, it took me some time before I reached where I wanted the carbs to be.
Bob
 

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Thank you all so much for your replies to this thread! I have a lot of tinkering to do to figure this out but I'm amazed at the wealth of knowledge available on this forum. I'll stick with the SU's and start troubleshooting! I"ll let you know how I make out. Thanks again,

Brian
 
In addition to other good suggestions you've already gotten, take a look at the vacuum line that actuates the vacuum advance. It goes from the underside of the front carb to the distributor. Mine was not seated properly at the carb and was leaking. I had to file some material off the carb to get it to seat. Somebody must have put a non-original fitting on it at some point.

I tested it from both ends with a vacuum pump. With the pump attached to the carb end, you should be able to see the advance move as you pump. The advance should not leak down. With the pump attached to the distributor end, you should be able to stick your finger down the throat of the carb and cover the hole that the vacuum line goes to (air cleaner off, obviously). Then crank the pump. It should hold vacuum when your finger is on the hole, then release it when you take your finger off the hole.
 
When the carburetor is at idle there is no vacuum because the throttle is closed, when you say crank the pump do you mean open the throttle, there is no pump as such on an SU carburetor and as Brian said, his problem is at idle so vacuum advance doesn't come into it.

Graham
 
The pump he is referring to is the vacuum pump that he is using to test for leaks.
 
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