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Triumph TR6 - Running Lean

I have a 74 1/2 TR6 with a fresh carb rebuild, no egr and everything else is attached and stock. No matter what I do I'm still running lean. Anyone out there have any ideas? By the way I was running lean before the carb rebuild also.
C Anderson

C--If you are a registered member here, you can do a search on ZS tuning issues; I suggest you do that first. There are many things that could cause a lean mixture, such as: needles out (try cranking them full right = rich), temp compensators stuck open, vac leak through throttle shaft bushes or through any of the vac hose connections, failed brake booster diaphram. Can you maintain an 800 to 900 rpm idle? We'll help you out any way we can.
Rick Orthen

Hi Rick
I am a new registered member here and I did a search on the carb tuning before I did the rebuild. I followed the instructions from a link I found here, Buckeye Triumphs. Anyway my needles are cranked full right temp compensators checked, shaft seals replaced and checked with carb cleaner while running and no vacuum leaks. I idle between 800 and 900 a little rough though. My vac retard is still attached and I've played with timing between 4 deg atdc to 4 deg btdc. I'm thinking of trying a bushing as suggested in that article at http://www.buckeyetriumphs.org , a small thin bushing that the adjustment nut fits on but and the needle fits through. Or maybe I should change to Gross jets I don't know much about them.

Curt
C Anderson

C--Looks like you're onto all the possibilities. An obvious question I forgot: what's your evidence for the lean mix (plug read, piston lift, exhaust popping, stumbling performance, other)? If it's piston lift, don't go by that alone.
Rick Orthen

Also, don't know much about Nelson's needle bushing, but it sounds like that would make the condition leaner since you're extending the needle further down in it's jet. Maybe I don't fully understand the concept however.
Rick Orthen

How's the output on your fuel pump? If you recently rebuilt the carbs with new float valves, the Grose addition isn't really needed.
Rick Orthen

Well letís see, I've got new float valves, and new fuel filter. I stall on piston lift, I have exhaust popping, and I have a Gunsen color tune with a very blue flame. My plugs read lean but my performance isn't all that bad, I think. But I've only had this car 5 months and it's been lean since the first time I drove it. I'm mechanically inclined but this is the first time I've worked on a car. I have in my youth rebuilt air conditioning compressors that make this look easy. I was hoping I missed something obvious. I was able to lessen the exhaust popping by adjusting the bypass valves but I seem to have all the gain I can get from that. Oh yes the car came with a Monza exhaust. Iím going to find different mufflers soon, to noisy.

By the way the bushing fits under the adjusting screw for the needle raising it up, and allows the needle to be raised up through the bushing.
Thanks, Curt
C Anderson

Hey C,
I always had a lumpy rough idle when I had the retard attached. When I removed it along with the EGR the engine ran better and reved freely up to the redline and could maintain an even idle.
steven

Hi Steven
I thought I might remove the line and plug it up long enough for a test drive. Did you remove the mechanism or just cap off the vacuum line?
Curt
Curt Anderson

Curt,

If I follow your post from 8 August, 1544 Zulu, you checked the shafts of the carbs for vacuum leaks, but did you check the manifold itself? While not an everyday occurance, TR6s have been known to require tightening of the manifold to the head or have the gasket replaced. The mounting mechanism is somewhat clunky with the three bolts through the manifold and all those little "football" clamps. If you wind up pulling the manifolds, check the mounting faces for flushness. You can get warpage there that will cause a leak if it has been running with the manifold loose for a while. Also check around the insulating spacers between the carbs and the manifold. I had one of those develop a hair line crack on me several years ago with an MGB and it pretty much drove me crazy trying to chase down why I was running lean.
SteveP

Curt
Now I know of 3 TR6s in the Seattle area.
Curt a quick question for you. Do you recall the direction of turn of BPV to lessen the exhaust popping on deceleration?
Thanks
Rick C
Rick Crawford

Hi Rick

The bypass valve is a spring-loaded valve you turn it counter clockwise to increase tension on the valve, clockwise to release. I started with the valve tension maxed out and slowly opened it. I got to a point that my idle speed increased, I assume because of air flowing through the valve and then tightened it back one turn. You have to be careful not to over tighten it (I set it with the valve off the carb during a rebuild) as it is a screw with a hex head nut in a hexagonal shaft as you turn it counter clockwise the nut moves down the screw in the shaft and compresses a spring, which pushes the valve closed. If you turn it counter clockwise too much youíll push the nut out of its shaft. I think itís probably good for about 10 to 12 turns counter clockwise from all the way open but I didnít count. I opened mine about 4 Ĺ turns.

Good luck, Curt
Curt Anderson

SteveP
Very good thinking. I checked the manifold and found all the bottom nuts loose. I shouldnít be surprised considering some of the other things Iíve found on this car. I donít yet know if that was my problem, havenít driven it yet but at least it was something to try that I hadnít thought of. The insulating spacers and gaskets are good. I looked them over when I rebuilt the carbs.

Thanks, Curt
Curt Anderson

Curt--How in the world did you get a screwdriver to the bypass valve on the rear carb?
Rick Orthen

Rick O
Try one of those tiny"jewelers" screwdrivers..you know...the ones that come in a plastic flip case for 2 bucks.
Rick C
Rick Crawford

Rick O
Maybe I misunderstood your question. The tiny screwdriver works for the BPV adjustment screw. A stubby screwdriver will remove the back BPV. You will have to disconnect the throttle linkage...move the throttle arm and this will allow the vertical linkage arm to flop out of the way.

Curt ..Pulled the back BPV off and yes it is about 12 turns from a stop to a stop, it will not thread itself off. I set it to 4 turns then set the front to 4 turns. Thanks.
Rick C
Rick Crawford

Rick O

Be careful not to turn it too far counter clockwise, no it will not thread off itself but if the nut turns all the way out of itís shaft, it may turn free and you may have to remove the valve to get it back in.

To adjust it I used a cheap 3 or 4 inch screwdriver and cut the handle half off.

Curt


Curt Anderson

Oh yes SteveP

I tightened the manifold and checked the carb gaskets and spacers but I'm still running lean.

Curt
Curt Anderson

Curt all I can do is commiserate. Mine does exactly the same thing. The motors strong 180lbs across the board. Seemingly good condition carbs, broke em down, cleaned, replaced the ususal suspects, replaced filters checked for leaks still seemingly lean. However runs great. So for now I have learned to accept the things I cannot change, at least while its driving weather here in IL. Frustrate myself again when it gets cold out.
I'll be watching closley to see how you do. Please let us know.

Thanks Ian.
Ian Kinaid

In the days of leaded gas, I only had to look at my tailpipe to know if I was running rich or lean. If the tailpipe was black, it was rich. If it was gray/white, I was running lean. Today, with unleaded, that won't work. Now, I remove my spark-plugs and exam them visually. Black = rich. Gray/white = lean. Light beige = Right On !

But I have a TR3A with SU carbs. What do I know about TR6's ? Very little.

When those TR6 owners with "the supposed problem" say they are running lean, how do they know ? What says your TR6 is really running lean ? What tests have you done that tell you that your TR6 is running lean ?

Maybe you don't have a problem.

Don Elliott, 1958 TR3A
Don Elliott

Have you checked the vacuum line to the brake servo unit? (also all other vacuum lines) I had the same problem, was driving me nuts until I found that I had a bad brake servo unit with a big vacuum leak. Try pinching off the lines one at a time while the engine is running to see if it makes a difference.
Dan Alesandro
Dan A

I can't find any vacum leaks, and I borrowed a vacum gauge that reads 22. I have no idea if this is right or not. I talked to a mechanic with experience and he sayed that you just don't have enough adjustment on Stromberg carbs, he see this all the time. I found a set of SU HS6 carbs on Ebay I'm going to try.

Curt
Curt Anderson

This thread was discussed between 07/08/2002 and 23/08/2002

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