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TR2/3/3A TR3 Running Rough - Cause[s]?

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TEXAS_TR3A

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Guys,

Have something strange happening with my 3. After about 20 minutes or so, the car will begin running rough when it is hot outside, sputtering under any more than 25% throttle. Sounds like a rough running old VW Beetle. Very little power.

Up until that point it runs great from idle to full throttle acceleration. Took it out to our local Triumph club breakfast two weeks ago and it ran great for the 10 minute trip each way, but the outside temp. was ~80F and a not 95 as it was tonight.

Any ideas what might be causing this? Could it be something ignition related? Coil getting hot?
 
Coil crapping out (and generally you can feel the coil and tell....if you can't touch it, it's bad OR an external-reistor coil with none), condensor, bad or no fuel tank vent (easily checked by pulling over, cracking the cap, re-sealing, and if it goes another 10 minutes, bingo!), issues with carb float bowl vents, any power lead in ignition circuit breaking down and increasing resistance after being under load for a longish period of time (easily checked by having a known good running voltage at the coil, then checking it running when "crappy").

Probably a dozen others, to a crack in the intake runner of the head opening up under heat, a valve starting to seize in a guide, but check the easy and accessible things first.

In troubleshooting guides, overheating ALWAYS lists a loose impeller. I went 37 years in the industry before seeing one, and the complaint was a leak, not overheating.
 
Is the rubber grommet gone on the front of engine where the fuel line crosses over the top of the water pump. That has been a source of vapor lock on these engines dating back to the Roadster.
This will sound silly, but put a couple of wooden clothespins on each side of the tubing and see what happens. Today we have better ways of getting ride of this, it just looks funny. Not all cars had this problem, for some reason they got rid of the hot air under the hood (bonnet) better than one just like it.

Wayne
 
Yes I think it is most likely ignition also, and yes I would start with the coil. I had a problem like that once and it was the vacuum advance. Do you have another complete ignition system you can swap in?
Steve
 
I had a simular problem a few years ago. When it got hot..100+ my TR3 would spudder like it was out of gas. I found the rear float bowel at 140 degrees the front at 120. I istalled a heat shiel and no more problems.
 
See? Dozens of things, and the list will get longer by morning.
Start eliminating.
Take a voltage reading cold running on the coil, when it acts up, do it again.
Crack the gas cap.
Feel the coil.
Look for the grommet.
Keep a spray bottle with water, soak the fuel line and filter bowl, even the carb float chambers.

When you find it, it will be obvious with readings/temp/gascap/water/etc.
 
Thanks guys for the troubleshooting guidance. I can rule out gas cap as I got gas in the middle of the rough running evening drive and ni improvement. My new carb. heat shield came in a week ago and I'll get it installed once carb. gaskets arrive.(Carbs were rebuilt las year) Picking up a new Multi-meter in the morning to check voltage as my old one crapped out, and will check out the grommet then too and try the clothes pin trick. No back-up ignition system to try so I'll have to take it step by step and hope I can figure it out before replacing parts prematurely.
 
Do you have electronic or stock ignition? My TR-6 would do the same thing in hot weather with Crane Electronic ignition. I sent the unit back to the factory - they checked it out & said it was fine. I re-installed it and the next hot day, it sputtered badly again and I barely made it home. Back in went the points and into the drawer went the electronic kit. No trouble since even on the hottest day although it runs hot in traffic when you idle too long.

PD
 
Stock ignition from what I can tell. It has probably been 10+ yeas since it has been touched. The car belonged to my Dad and I don't think he changed it to electronic at any point. He was a stickler about originality. (a good thing) The symptoms you describe sound just like what I am experiencing though.
 
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