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Triumph TR6 - Power Loss
|I have a 73 TR6 and have owned 5 other TR's 3, 4, 4a, 250, and 7 (ugh). I recently rebuilt my carbs (175 CD's) and afterword could not get the same powerband that I had before. The car Idles well and the mixture and airflow are set correctly. But it seems to runs slightly rough during acceleration and seems to be very slow at the low end. It will eventually reach any RPM but has small power surges during acceleration.|
THINGS I HAVE ALREADY CHECKED:
1. Acouple of months before the rebuild I installed a Pertronix ignition and the car ran very well so I don't suspect that.
2. During the rebuild I replaced all gaskets, o-rings, seals, and both needles and jets. I have also checked all vacum hoses for leaks.
3. I regapped my plugs and they appear to be burning well.
4. I did a valve tune yesterday and was convinced this was the problem...but it still exists.
5. Replaced the fuel filter.
Any suggestions or Ideas?
suspect your Petronix. I changed out mine a few weeks ago because of exactly the same symptoms you described. Do yourself a favor and throw the old points back in just to see.
|Thanks Geoff I'll try my old points. I also forgot to add that it is backfiring through the carbs when RPM is above 1500 in all gears. Also what pug gap do you recommend?|
when my Petronix was in, I upped my gap to around 0.035 inches. When I through my points in, I automatically took the gap back down to the stock specified 0.025. Want to hear something funny: I am sure at the track the Petronix Ignitor may result in faster times, but around town, on the highway, even pushing at high rpms, you really could not feel much difference between the points and the Ignitor. When the Ignitor failed, I changed to something which really did make a difference: the MSD 6A ignition, which fires through the existing points, but oh, what a difference particularly at higher rpms. Multiple spark discharge (below 3000 rpms) and 1 lightning bolt above that. The only downside is that it calls for an external box, which was red, so looked at home in my Pimento red engine bay. Tried a spare Crane Cams XR700 that I had laying around and wasn't impressed. For some reason, I had to retard it quite a bit just to stop the pinging. Anyway, sorry to ramble, but just throw your old points back in without touching the spak plugs, just to see if the main symptoms of hesitation and power loss are eliminated: if they are, but you still have some low rpm backfiring, then adjust your plug gap.
Cheers and Regards
|Geoff--Did you upgrade your ignition cables (magnecor?) also with the MSD install? Just curious how important a performance factor cables are.|
I did not upgrade my plug wires. I supposed the already noticable benefits would have been even more apparent with increased wire size.
What is this MSD 6A ignition and where is it available from?
|Wayne - One of the things you haven't mentioned is timing.|
I use Petronix with a hotter coil and gap at .028 with no problem. Good luck. SC
|Thanks Guys for the info...I tried them all and still am getting a backfire through the carbs! I put in the points(which were pretty new... also put new spark plugs and wires in) and regapped from 035 to 028. I re-checked all my vacuum and breather hoses and they are all tight and in good shape. I spoke to two TR repair shops in Seattle yesterday and they insist that its timing...but I have retimed a number of times at various settings and it doesn't change the problem. I am getting a little frustrated. What timing setting is best for Points and Pertronix? Maybe I have the wrong setting info. Is it possible I have a bad valve erupting?|
sorry my suggestions were for nought. At least the nebulous area of electronic ignition has been ruled out. Time to look at the timing and the carbs themselves. On the surging/hesitation on acceleration, if feasible, pull over and see what type of fuel level may be in the carbs, could be that maybe one of the float levels is set low and one of the carbs not getting the fuel it needs on acceleration. Just out of interest, do you stall out when making a left of right u-turn? Before I changed to SU carbs, this is just one of the problems I experienced. Did you hook all the lines back up correctly - i.e is the vac retard (if you're running it) coming off of the correct port on the carb? Condition of the diaphragms?
If what you say is correct, and adjusting the timing has no effect on these symptons, then it is probably not the timing. Change the timing drastically (advance) just for effect, just to see. J.T. - you can look up the MSD site for all the specs and testamonials, and I actually bought mine used on ebay for about $80. Definately worth it.
|Thanks, Geoff; so much to learn so little time. Sorry for just taking and not contributing. JT|
|Wayne, some other areas to consider in your quest for smooth power:|
- Try swapping your distributor cap with a known good one (or hook up a timing light to each cable and verify regular firing)
- During the carb rebuild, did you replace all four throttle shaft seals?
- Air bypass valves reassembled with correct gasket orientations?
- Test run with carbs at or near full rich.
- Perhaps the distributor had been removed and replaced without proper indexing?
- Distributor bushings OK (no rock) and the advance mechanism free?
- Timing/plug gap: 4BTDC/0.035
- Bypass coil with spare one
|Thanks again guys for the tips. Sorry for the frustration remark...I have worked on TR's for about 25 years and have never had this long a time with a problem. |
Geoff, I don't have acceleration problems when turning however I retimed to 4 deg btdc (was 6 deg) and got a little better power. But unfortunately the carb backfire still exist while accelerating but it is less frequent. It seems if I push the pedal to the floor it reduces the backfire and some times smooths out. Of course I can't drive around that way in town.
Rick...I did replace the shaft seals about a year ago and bypass valve gaskets are correct. I have varied the mixture rich and lean with no changes in backfire, just power. I am going to inspect advance mechinism and see if indexing is a problem...
Geoff, how do I tell what my fuel level (Float level)is while running? How do you tell if the level is correct? This may have some merit if you can tell more on the procedure.
what I did to ascertain a float problem was 1 of 2 things. (1) I stopped the car as soon as I could after experiencing the problem, and unscrewed the float chambers and visually ID'ed the the fuel level in the rear carb was about half the level as in the front carb. But which one was right? (2)I unfortunately had to unbolt each carb and flip them over to measure the height at which the float fully pushed in the needle. Both seemed per the manual, but the paddle which contacts the needle in the rear carb was not sitting square. I straightened this out while still keeping the level the same and my problems disappeared. Turns out the float level in the front carb was right and the rear carb was running out of petrol. I later solved ALL my problems by switching to SU carbs...
This thread was discussed between 08/07/2002 and 18/07/2002
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