View Full Version : TR6 TR6 Misfiring

01-22-2005, 03:49 PM
I have a TR6 that is a 1976 with the smog removed, a set of '73 carbs and a single vaccuum distributor. The car idles o.k., but I can't seem to get the carbs rich enough. Floats are set at about 17mm and I've looked for air leaks. Idle is o.k., but when I accelerate, the car pops. Head was rebuilt, and car was recently ringed. These problems were pre-existing. Car was purchased a year ago and I haven't been able to get it roadable because of the poping (backfiring?) One carb diaphram was replaced due to a small tear. Didn't seem to make a difference. Car is set to run at 4 degrees after at 750 rpm. I actually recorded the sound, but don't have the ability to post it on the internet. <font color="red"> </font> https://www.brannenconsulting.net/cars/car%20images/hathaway%20hunter%20front.jpg sugestions greatly appreciated. This is for a Hathaway Hunter bodied TR6.


01-22-2005, 04:35 PM
Lee, how are you running a car in Cal that has the pollution removed? Try running centrifugal advance. Plug us your vacumns on the carbs (don't have to plug the distributor, just for looks) and turn your distributor to 8 degrees BTDC at 1000 rpm. Just the opposite of vacumn advance. What do your plugs look like? Also might try a colder plug, open the gap and run a hotter coil. Have you adjusted your valves at all?

01-22-2005, 06:05 PM
Hello Lee,
if you still have the original Triumph distributor (Lucas) then the timing should be set with the vacuum advance diconnected. (that doesn't matter if you are setting it statically), with a strobe at 750 rpm, I suggest that 8 to 10 degrees BTDC is a basic starting point. If you don't get any pinking at that setting, it may take a little bit more advance. If you set it at 4 degrees after with the vacuum connected then I'm sure it will be way too retarded.

Good luck,


01-22-2005, 07:55 PM
As you can see from the pic, the car is not a stock TR6. It is registered as a 73 TR6 for registration purposes only. The long block is off of a 76 though. Car came from PA and was never completed. The engine is a bit of this and that, so I can't go by stock tuning procedures. I'll try caping the manifold vaccum, cleaning the plugs, regapping them, and then re-timing. Thanks for the help and I'll let you know how things turn out.

01-22-2005, 10:55 PM
Changed the plugs, set the ignition to TDC static and 8 degrees at 1000 rpm. Disconnected and plugged the vaccuum advance line from the rear carb. Car runs fine until about 2500 rpm and then starts popping. If you just accelerate, it seems to be o.k., but if I hold it at 2500 rpm it pops. Will try going over the valves again. 10mm cold. Any other suggestions?

01-23-2005, 12:05 PM
Hey, Lee. My first reaction is that it's running out of gas at higher rpm's. Check the fuel filter(s); if there's not one inline, the top of the fuel pump has a screen.

Disconnect the fuel line and route to a can, then pull the priming lever a few times. It should give some healthy squirts. Start the engine for a few seconds and confirm you get a good flow.

If that's all OK, then the problem is likely the carbs. The by-pass valves could be bad - you could try blanking them off by putting a solid piece of gasket paper in place of the regular gasket. As a last resort, reducing the float height is a good way to richen up a carb if the needle is backed out all the way. A couple mm can make a difference.

01-23-2005, 04:01 PM
Have you checked the camshaft? If you have a worn lobe it will pop back thru the carb like a lean mixture problem. Just a thought. /ubbthreads/images/graemlins/grin.gif

01-23-2005, 05:02 PM
Hello Lee,

what advance do you have at 3,000rpm, look for about 32 degrees, maybe a bit more. By the way the valve clearance I take was an error, it should be 10 thousands of an inch (0.25mm)


01-24-2005, 04:59 PM
I had the same problem after I did some major engine rework and removed and reinstalled the distributor. I had set to 4 deg. BTDS (with retard disconnected) but found that it was not advancing enough under power (later TR6's had a vacum retard). After abandoning retard and letting it centrifugally advance, it's running well (go figure).

01-25-2005, 06:51 PM
The fuel line is my guess also, but I can't seem to make a difference. I replaced the line with a new copper line, replaced the hoses, just put in a new filter. I'll work on that angle again this weekend, and may even drain the tank and flush it out (though it is a custom aluminum unit).

01-25-2005, 06:53 PM
Don't want to tear up the engine for that, though that also is a possibilty. The po told me he bent a lifter when he forced the engine through after bending a valve. Hope this isn't it.

01-25-2005, 06:57 PM
32 degrees? Nowhere near that. Around 20 degrees at 3000. If it is supposed to be 32 degrees, with static at 8 degrees, then maybe my distributor needs to be rebuilt. Easy enough, and I hope that is it!

Dave Russell
01-25-2005, 07:31 PM
Hi Lee,
Yes, Alec is correct. If it is a somewhat standard distributor, you should be able to turn the rotor (with your hand) in the direction of distributor rotation, &amp; have it advance about 20 degrees against spring pressure, then return to its original position when pressure is released. The advance mechanism may be stuck or have missing springs or something else. If it is stuck, try putting a couple of drops of oil in the top center of the shaft, under the rotor, &amp; working the rotor back &amp; forth to free it up. If this doesnt work, you will need to remove the point mounting plate &amp; investigate further.

I wouldn't worry about fuel or valve problems until the timing is working correctly.

01-26-2005, 04:51 AM
Hello Lee,

my 2.5 engine (P.I. distributor) has 14 degrees mechanical advance, this is 28 degrees engine advance plus static advance was where I got my figure from. Some 2.5 engines may have less than the 14 of the P.I. engine. If you remove the top plate of the distributor you will see on the beak of the rotor the advance figure stamped on it. Some distributors may require more than 3,000 engine rpm to get to full advance.
I would say that 20 degrees is not enough advance at 3,000 rpm. Just try swinging the distributor with the engine running to see if it helps your misfire. That tells you if you are on the right track or the problem is somewhere else.


01-26-2005, 02:41 PM
I had the same problem with my '76. Did all the things that everyone has mentioned. Found out that I had a little water in the tank.

01-30-2005, 04:03 PM
Thanks, got the distributor cleaned up and had my wife hold it at 3K. Wobbles a bit, but holds at about 32 degrees. Still pops. Replaced plugs, condensor, rotor, fuel gauge, cleaned in-pump filter and cleaned out pump. Next?

01-30-2005, 06:38 PM
LeeC, well to me it sure sounds like a valve train problem. Check for a broken spring or weak one. I would do a compression test also. Wayne

01-30-2005, 07:50 PM
Two last things on the fuel system. Sounds like you're running it in the garage rather than on the street. If you drive it around the block, does pulling out the choke (to richen the mixture) make a difference?

Next, try disconnecting and plugging the air line to the brake servo (making sure there's no hole worn in the line itself). A large air leak there could cause too lean a mixture and popping. You can do a similar check with the lines to the carbon cannister, but those generally effect just the idle quality.

03-06-2005, 01:25 PM
Thanks for your help. And I feel really, really dumb. Seems I dropped a nut into the valve assembly when I replaced the head. That little nut floated arround and sometimes (not all the time) found its way on top of the lifter. Guess I'm lucky it wasn't a bigger nut or it would have lifted the valve enough to hit the piston.

Seems to run o.k. now, need to get some miles on it to find out.