Triumph Repair: Triumph GT6 Tuning, delco remy distributor, manifold vacuum

Question
QUESTION: Howard,
I came across your email detailing issues with ignition tuning your GT6 MkIII.  I have a 69 GT6+ and having a similar problem.

In your post on 4/27/07, you mention that at the factory setting your car performs like a DOG.  What mine is doing at the factory setting is failing to rev. above 3000 rpm.  It is almost like I have a rev limiter on the engine.  Especially in 3rd and 4th gear.  Is this how yours was behaving?

I have gone through the normal tune-up parts: points, plugs, wires, cap, rotor, condensor and to no change.  Additionally, I bought a 2nd set of carbs and rebuilt them.  There was no change in performance.  Also, for the GT6+, I have not been able to find a dwell setting.  For 67-68's and 71-73, I can find them.  I use the same .015 point gap, but I use a delco remi dist. and different points than yours or the 68's.  There is no way I can set the point gap at .015 and get a dwell at 40-42.  Mine is always 32-36 deg.

So, my 2nd question is: How is yours running at 12deg BTDC?  I have not tried that on mine as I was trying to set everything at the factory setting.

3rd question: What is your manifold vacuum?

To recap:
Please explain DOG in more detail
How is yours running now with 12deg BTDC timing
Do you know the dwell setting for a 69 GT6+ with a Delco Remy distributor
Do you know the manifold vacuum level

Thanks,
Mike Cave



ANSWER: Hi Mike,
If your car seems like it has a rev limiter and just levels off at 3000 RPM do a vacuum test under those conditions and if the manifold pressure goes down to or close to zero, suspect a partially stopped up exhaust system. I tested many brands of street cars on a dyno and I found that all of the ones I tested other than some "wild cam" engines would never drop below 5 in. hg. at full throttle, full load.

To be sure if you get the zero reading take a short piece of steel brake line or such and drill a hole in the exhaust pipe close to the front. Measure the piece of brake line and drill the hole just a slight bit smaller than the OD of the piece of line and drive the piece of brake line into the pipe and put a pressure gauge on the line (a fuel pressure gauge works great) Run the gauge out from under the hood and place it under a wiper arm and drive the car to the point it goes flat and read the gauge. It should not exceed 1.5 PSI. Some cars like some GM cars claim they can handle up to 3 PSI but I found all the British cars I tested could only handle up to 1.5 PSI. Any more and you have a stopped up exhaust. You can remove the brake line and install a large short sheet metal screw to plug the hole or weld it up if you have the equipment to do so.
Let me know,
Howard


---------- FOLLOW-UP ----------

QUESTION: Well Howard,
I think I solved the problem.  I reset the timing and the rev problem went away.  It really acts like a cliff.  The factory setting is 4deg ATDC.  I was maybe 6 ATDC.  I set it at 2BTDC and it runs great now.  I decided to do this since the previous person said his ran great at 12 deg BTDC.  It also solved the warm running that crept in since the last tune-up.  I got a vacuum gage and it reads normal for the car too.

Mike


Answer
Great Mike, Factory settings in 69 on most British cars were for emissions, not for good running. So it may be ok to run a more advanced timing just as long as you don't get the pinging noise of detonation. In which case back off the timing a little. You should also check to see the advance system is Ok
Glad to hear it is running good.
Howard