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Triumph TR6 - 3 too lean, 3 too rich?

70 TR6, ZS carbs, Pertr EI.
End of last year couldn't get past having 3 rear cylinders too lean and 3 front too rich.
Rebuilt carbs over the winter whole 9 yards.
Now although nice idle and seems to run fine still can't get past white dusty plugs in rear 3 and sooty 3 in front. Have adjusted both carbs to max still unable to fix mixture. Have checked for leaks can't find any in carbs. Checked and adjusted float levels. Logic would seem to indicate something perhaps beyond carbs. Checked vacuum lines they're ok. Carbon canister is not plugged. Need some ideas? : )
Ian Kinaid

How do you syncronize them?

Does the '70 have temp compensators? Did you check that both opened at the same temperature?

Check that the air valve resistance is the same between the 2 carbs. Get to operating temperature, turn the car off, remove the air filter(s), and pull up the valves with your fingers. They should have the same resistance and fall back down with a 'click'. If one is harder to raise, get a dropper and remove some oil from the dashpot and add some ATF to thin it to where the resistance is the same. Also make sure the small vent hole at the top of the dashpot is open.
Brent B

Thanks Brent.
Sycn'd with standard sych air flow tool Unisyn loosening linkage, adjust to even air flow retighten.
Not sure how to check temp compensators opening at same time?
I will check on the piston lift tension and vent hole.

I will check
Ian Kinaid

There's an article in VTR about adjusting the temperature compensators.

Thought of another thing - recheck the syncronization up around 3000 rpm. That's more important than at idle, IMO.
Brent B

This is what I've found so far.
There was some difference in pressure on piston lift.
Then when I listened for click on drop, noted that rear carb didn't have definite click like front carb.
Took carb tops off, seems like there is a very slight
difference in diaphram tension, enough on rear carb to just hold piston off bottoming. So I think maybe I'll order a new diaphram to start with,it seems diaphram does not fit quite as nicely as front carb.
Now for theory if rear carb had a slightly floating needle and had a little less pressure in piston lift would this result in a more rich mix, higher needle height more fuel? the plugs read opposite?
Ian Kinaid

To get the needle higher the air valve also must be higher. When the air valve is higher than it should be than the vacuum at the jet is lower and less gas would be pulled through.

Remember, it's the damper that keeps the air valve from opening up immediately when you press the accelerator which opens the butterfly. That increases the vacuum at the jet and pulls more gas into the air stream for a richer mixture. When the air valve opens up the vacuum decreases which leans the mixture back out to where it should be for normal running.
Brent B

I just rebuilt mine this winter also, and has been running great. This past weekend I checked the plugs out of curiousity and found almost the same as you....front rich, rear are good. I haven't tried this yet (had to go back to work), but if you think the temp compesators are worth checking, it might be easier to switch them to confirm the diagnosis. If they're the culprits, the symptoms should be reversed.

Its just a thought. Seems easier than the procedure on Buckeye

I wonder if this is just a coincidence, or typical for these cars.

Good luck,
Mark H

great advice and ideas.
I'll be sure and post how it turns out.
weathers turning here so won't get back at it until next week.
Ian Kinaid

This thread was discussed between 26/03/2003 and 27/03/2003

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