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TR2/3/3A TR3 Running Rough Again?


Darth Vader
Country flag
I had Jeff at Advance dial in the Petronix dist in the Spring and that solved the black carbon fouling on the plugs.Car ran great all Summer idled great and pulled strong with a steady exhaust note.Recently I had let the gas in the tank get too low and rusty gunk clogged the filter....changed filter and blew out the line to the tank.Ran better but still running rough. Car has been running with a bad miss...runs rough on acceleration....better at idle....the plugs are badly carbon fouled again? There is a a bit of gas seepage near the jet area of the front carb(maybe the seal)? I'm wondering if some crap got past the gas line filter...past the electric fuel pump??? and into the front carb? Also am wondering if the dist rotor(has a nick in it) and cap contacts (which look less than new) might be complicating the issue? Only a few months on those? Or is it the dreaded Petronix malfunction? Any advice on how to isolate the problem?


Jedi Knight
Your black plugs suggest mixture too rich -- not what one would expect if you have gas tank crud impeding fuel flow somewhere -- UNLESS -- crud in the float needle valve is preventing the valve from closing. Do you smell fuel while driving? Is there evidence of fuel coming out the top of the float chamber?

Alternatively, black plugs indicate retarded timing. Check that, of course. It doesn't sound like your cap/rotor would play into this much...


Jedi Knight
Country flag
not a tr expert but have experience with Su's .Have you pulled the domes off to clean and check,or lifted a piston to see if it drops back with a click with damper out.Just a thought.


Country flag
Not sure exactly Karl, but it sounds like from what I hear that Jeff would know your situation best because he does that stuff every day. Having made that disclaimer, what I would do is keep a manual set around for comparison. I never used the electronic stuff, so I am not sure how difficult it would be to swap that around, but I speculate it would not be that difficult. Moreover it sounds like one needs a stock set for back up anyway. I doubt if any crud got past the filter because the crud would have clogged it first. I have had small pieces of stuff get into the jet assembly because I use the stock set up with just those brass screens for filters when they plug that that usually stops the fuel deliver, not letting the car start. But it is possible for a small piece to get through and hold the jet open and flood the system causing fouled out plugs. That is an easy fix by just lifting the bowl top off and pull out the jet and gently blow out the crud. If you have an electric fuel pump, and it is turned up past say 5 psi that can push too much gas in also. The SUs only need like two pounds of pressure. The reverse of that is. Have you tried driving up a hill and see if you run out of gas as the bowls go dry? However, there is an old sports car saying that what is wrong with your SU carbs is your Lucus distributor.



Great Pumpkin - R.I.P
Oddly enough, I was just looking at the same problem. Apparently, enough fine grit had gotten into the carb jet to erode the jet seals and cause them to leak, both out the bottom and into the carb throat.

So my suggestion would be to address the jet leak first, and see what that does for the rest of it. Of course, once you've had the jet apart, you'll need to reset the mixture anyway (which is the most likely cause of black plugs).

Another possibility worth investigating is whether the jets are returning up against the mixture nut after using the choke. It's not uncommon for them to stick down and cause extremely rich mixture. You can check by just pushing on the bottom of the jet. If it moves into the carb body, that was the problem.

If so, I suggest using some sort of polish to bring the surface of the jet to a shine. Original jets were quite smooth from the manufacturing process, but modern replacements are supplied much rougher, which can cause both rapid seal wear, and jet sticking. Ordinary toothpaste makes a suitable polish, or auto body polishing compound. Or pretty much anything sold as "metal polish". I tried some Mequiars Billet Polish this time, which worked about as well as polishing compound (for about 10 times the price :laugh: )


Darth Vader
if all was well untill you sucked crud from the tank I would say its all related to the crud getting thru the system and into your carbs, I would not touch anything else till you cleaned the entire fuel system out including the carbs,float bowls,seats,. Once that is done and you still have the problem then move to other systems, if you have crap in your fuel tank, best to take the tank out, clean it up, seal it too, other wise you risk doing it again

just my opinion



Darth Vader
Country flag
The problem was twofold: 1)AS Randall suggested the the jets wern't returning when I used the choke. 2)I actually had a bad spark plug in the #3 cylinder!....replaced the plug and all is well again. Thanks to all for their advice.


Great Pumpkin - R.I.P
Glad to hear you got it sorted, Karl.

karls59tr said:
I actually had a bad spark plug in the #3 cylinder!
A common side effect of mixture problems. Crud builds up on the plug, and then sometimes when it gets hot, it melts to form a conductive 'glaze' that can keep the plug from firing. Particularly frustrating when it only causes a misfire sometimes (like under load).
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