TR6 TR6 Hesitation

[wingsandwheels]

New member here. Thanks 77midgetmkiv.

I'd appreciate any thoughts on a problem that's driving me nuts..

Car is an early 1974 TR6, 42K miles, bone stock w/ all emission controls in place and appearing to function (incl. egr, thermo switch, vac retard, evap cannister, etc.). Carbs are newly rebuilt and the car has new points, cap, rotor & condenser, TRF 'repro' green plug wires, NGK iridium plugs and a Bosch 'red' coil.

The car hesitates under moderate to full acceleration at low RPM's, <1,800+/-, in the higher gears. The problem worsens as the car warms up.

I noticed the problem developing a while ago then it worsened. I checked & adjusted the mixture using the lift the air valve method and it seemed to be lean even with the needles at the rich stops.

I also flushed coolant and noticed that the Fail-Safe thermostat was locked open...I though the car ran cool ever since I put it in. Replacing that brought the car to a proper temperature but exacerbated the hesitation problem. I've never had an overheating problem.

I had the carbs rebuilt by Apple Hydraulics (it was time aside from this problem, nice job by the way) and the mixture still seems a bit lean, I'm close to the rich stops, but the plugs are OK, light grey/tan w/ light deposits. I checked and didn't see any obvious intake leaks (brake booster, vac retard system, line to carbon cannister). The hesitation is still there, but much less and, except for that, driveability w/ the rebuilt carbs is excellent.

I am not sure that the vacuum connections to the thermo switch are correct, does anyone have a diagram? My switch has 4 ports. Not a lot of good reference material for that.

I can't think of what else to check and I am leaning back towards the ignition system, but aside from the diustributor itself, which seems fine, and the thermo switch connections I can't think of anything else.

Thank you.

 

[piman]

Hello WW,
the hesitation seems mixture orientated to me, as your remarks about it being worse when hot. I'm assuming Stromberg or maybe S.U. carburettors. Forgive me if I'm teaching you to suck eggs, but is there oil in the dashpots, and the dampers in good condition? If that is OK, then perhaps a few degrees more advance?

Alec

 

[AltaKnight]

I agree that it's likely a mixture problem.
If you're at the end of the adjustment on the needles then you will have to tweak the float levels to further enrichen it.
FWIW I had the opposite problem with mixture too rich, ran great but burnt a lot of gas or more accurately sprayed it out of the exhaust in the form a black smoke etc.
I managed to remove the float bowls in situ (tricky, 6 screws) and slightly bend the float tang to adjust it(make sure you bend it the right way).

 

[wingsandwheels]

Re: TR6 Hesitation-Solved

Solved! The distributor cap itself was the culprit.

After going through the fuel, intake and ignition systems I went back again and followed the spark path.

The distributor cap contacts were partially fouled w/ plastic from the cap itself. When I first installed the cap, a new production Lucas, I noticed that the molding around the inner contacts was a bit sloppy w/ bits of cap material standing proud of the contact faces, some on the faces, etc. I removed some w/ my findernail but didn't think much of it (figured it was a new part). When I took a real close look yesterday, what I first took for normal contact wear, oxidation & carbon were actually smears of cap material across the contact faces...essentially a dielectric layer across parts of three contacts... Swapped back to an old Lucas cap I had around and its a new car! I assume the rotor was just touching the plastic around the contacs and deposited it on the contacts over a few thousand miles.

After confirming it was the cap, I also threw out the TRF repro wires, some had weak grips on the plugs, didn't hold the dizzy cap too well, generally weak terminals. Certainly not TRF's usual standard.

I also have to say I am a not quite happy w/ the "new" Lucas quality as of late....

Thanks all!

 

[Guest]

Re: TR6 Hesitation-Solved

I buy caps and rotors by the pound and keep spares (matched sets) in the boot, tucked away in a nice niche, along with a couple of "C" notes for emergencies. Anyway, when I get a new cap and rotor, I will install same, run for a few tanks of gas, and figure I have some good ones. I have had more than a few brand new caps and/or rotors go bad out of the box and on the road. New doesn't necessarily mean good. But these new/broken-in matched sets are guaranteed to keep me rolling.

Bill