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Triumph TR6 - from too lean to too rich ZS carbs

Recently put my freshly rebuilt carbs back on 70 TR6 and now face what seems to be an uncontrollable too rich condition. Motor runs fine, nice enough idle. Get to the raise piston part of the tuneup get a rpm rise confirmed with very sooty plugs. Have the mix adjusted full CC, the bypass valve is fully seated. Trim screw is just about all the way out. Have not checked float height yet, was hoping to not have to pull apart.
Before rebuild complete opposite problem. bugger...
Any ideas to try for when we get a warm spell up here again appreciated.
Ian Kinaid

Hi Ian

Have you checked your choke cams are coming fully off. Something is preventing needle seating if you have full lean setting. What all did you change out?

You may be happy to know you probably have the only rich running Zs on the planet:)

Bill
Bill Brayford

I've read in several places that the float height should be 3/4". If the fuel level is too high (low float height) I suppose it's possible that by rebuilding the carbs and fixing any air leaks that by-passed the jet you now have more vacuum at the jet so more fuel is getting sucked up. That could be a reason for the two by-pass valve gasket types - the early type has a solid barrier, but the later has an opening to let some air through all the time. Try the "open" gasket if you're now using the earlier "solid" type.
Brent B

Ian,
I saw in the Bentley manual that a 'too rich' condition may be an indication the carbon cannister needs replacing. Maybe someone else on the board could explain why. My best guess was that a clean cannister allows some amount of air into the mixture, that was built into the design. If clogged, or in the cases of many cars, removed and plugged, would this make a richer mixture? Seems like the mixture has to be affected somehow.

I just ordered a new one to try to reduce the gas smell in my garage after a run.

I'm new to carbs just this past few months, so I'll just throw this out there for comments from some more experienced minds. I'm curious too, since I just rebuilt mine and use up most of the adjustment to lean them out.

Mark
Mark Hauser

Hi Mark,

Did you think about just replacing the charcoal in the carbon canister- rather than ordering a new unit? It seems to be just filled with aquarium type of charcoal. That's other owners have suggested and done with their canisters.

Aivars Berzins
Aivars Berzins

That would be great, as the replacement goes for around $100. Its backordered at TRF for now. I tried to find a way to pry it open, but no luck. Are owners cutting them open? I planned to dissect it when the new one came in, thinking I'd avoid the expense a second time. I was worried it was more than simply exchanging the charcoal, and if I destroyed it I'd be out of commission until a replacement came.

I didn't check with the BBS, because it seems like the most common approach is to plug it and forget it. As part of the fuel system, I wanted to be careful to get it right.

Mark
Mark Hauser

Hi Mark,

Out of interest I pried apart the canister from my 74.5 Tr6. The bottom part (where the single outlet is) is threaded onto the top part. The threads are under the first ridge from the bottom of the canister. About 1/4 inch from the bottom. I didn't discover these until I tried to pry it apart & realized it was threaded.

My only reason to leave it on is to have a place for my gas tank to vent to.

Aivars Berzins
Aivars Berzins

Hadn't thought of the carbon canister possibly being a
problem. worth looking into.

Also looking for a hotter plug than the N9Y I've heard the UN12Y was standard on earlier TR6's and is a hotter plug. Am I right thinging in theory with hotter plug and perhaps ignition may help convert extra rich mix into more burn, better power? Trouble finding those plugs so far. Also may try the pertronix mod and hotter coil. Thinking with a tight engine, fresh carbs that might do it.
Any thoughts? been there done thats?
Ian Kinaid

There really is no need to replace the charcoal. Just dump it out to make sure there are not obstructions and reload.

Rick O.
Rick Orthen

Rick,
How did you open it? I unscrewed the bottom a few weeks ago, and there was another screen under the removable filter. It didn't seem like it would come out without damaging it. My only other thought was to cut the case open, or drill a big hole in the side to dump and replace the charcoal.

How did you open yours?

Mark
Mark Hauser

Ian
are your air filters dirty (or frozen). No air same as too much gas (choke fully off, as suggested above ? Have had choke cable cover come loose from it's attachment point right behind pull knob on dash, so it looks like choke is off, but is not). I use NGK BPR6ES pluge with Pertronix El and coil (ballast bypassed) at 0.043 gap (same as most cars of the last 15 years which run 40'000 v systems. Instant starting and runs like a champ w/ clean exhaust
gases. Peter G
Peter G

Rick/Guys,
Never mind my last comment. I opened the canister last night. After unscrewing the bottom, what I thought was a sealed screen on the bottom came out easily once I pried the retaining ring around the edge. As easy as it turned out, its a little surprising these things sell for so much, when the cleaning can be done so easily.

Related to Ian's original question, the screen at the top just below the big port from the carbs/valve cover had its carbon granules pretty crusted over. They break free easily, but would definitely affected airflow a lot. Still don't know if its related to your problems, but wanted to share the observation.

Thanks for your patience with me on this canister cleaning. Guess I need to keep my glasses handier.

Mark
Mark Hauser

Mark--Yea, mine was crusted-over at the top too which would interfere with the whole air balance in the recovery system. I also wrapped a piece of filter material over the large port on the bottom; bleed air is drawn in through this port.

Rick O.
Rick Orthen

all testing done with air cleaners off.
will check out the carbon canister when warmer : )
Thanks for plug recommendation, I'll give those a try too.
Ian Kinaid

Nice day for tinkering.
checked float levels reset to 17mm. Seems to have helped rear carb. Still experimenting with front carb swapped out jet for a spare grose jet that seems to have made some difference still not as good as I'd like it but better.
Installed the pertronix EI easiest upgrade I've done so far : ) set plugs to 35 thought 43 was a little much? using Bosch 4216.

Ian Kinaid

This thread was discussed between 23/02/2003 and 16/03/2003

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