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Triumph TR6 - How to get rich

For weeks I have been having a heck of a time tuning my TR6. Over the winter I rebuilt the carbs which seemed to work out OK. It wouldn't idle well though as the retard capsule was shot. After replacement the car would sputter and not run well at all. So I set the timing again, re-sync-ed the carbs to no avail. So far have replaced the points, condenser, coil, cap, rotor, leads and plugs. The timing has been set from 4 ATDC up to 28 BTDC. but still sputters. Runs better when colder, after about 1/2 hour running gets worse. After all this my opinion is the carbs are too lean. The plugs are very light brown and the lift the air valve thing causes the engine to stall. The needles are set to full rich, I even raised the float levels. I can't think of any other way the get the mixture richer. Could a weak fuel pump cause this? Sorry for the long post but I am very frustrated!
Chris W

I guess what I'm asking is how do you richen the mixture once the needle is set full rich? What causes this to happen?
C Wiebe

Are all 6 plugs white?
needles full clockwise?
if not carbs possible air leak in manifold.
Did you check for air leakes in carbs?
Did you replace fuel filter? Fresh gas this year?
I may be off on this but more advance seems to make leaner. 16 BTDC should be plenty to start.
Take a lok at the buckeye web site, excellent carb
tech article.
Ian Kinaid

OK - you think the carbs are too lean - sputtering? ANY air leakage that goes aroung the needle/jet will lean out the mixture.

1) My big thing is that when we "rebuild" our carbs, most of the time the butterfly shafts aren't replaced. The shaft is usually worn and is a great leak source even if the seals are replaced.

2) Put your finger over the hole on the carbon cannister. Does the idle speed drop? If so put a restrictor in the line. Maybe consider disconnecting the emissions lines...

3) Along the same line as #2, got a good seal on the valve cover cap? If you take it off, the idle speed should go up. Make sure it's closed tight.

4) I prefer the "early" gasket on the air by-pass valve. It has a solid region whereas the "later" gasket is split to allow constant air leakage. This only effects idle, but a number of small leaks will add up.

Brent B

Hi Chris

You might also want to check if you have good flow from your fuel pump. Intake lines not constricted. Vent lines OK. If you store the car crud in the tank, filter and lines will build. Change fuel filter and try a real good dose of carb cleaner in the tank.

If the fuel pump can't keep up it will cause lean problem. The only ones reporting rich are those who have gone over all the intake areas as well?

When you mention 1/2 hour of running I start thinking either fuel filter is really clogged or vacuum building in gas tank.

Let us know how you make out and what you find. Too many people are just dropping the ball after its fixed lately?

Bill Brayford

Chris W--How's the ignition side of the house? Replace your rotor.

Rick O.
Rick Orthen

Thanks for all the input!

Ian-I didn't check all the plugs, just one from each carb. The needles are full clockwise.

Brent-I didn't replace the shafts, but they didn't look worn. I did replace the shaft seals. I'm not sure which hole in the carbon canister you mean. I will check the valve cover cap. And I'm not worried about the bypass gasket as that doesn't create an air leak as only the mixture passes through. I've checked for leaks by spraying suspect ares with carb cleaner. Wouldn't there have to be a pretty big air leak to change the mixture at anything above idle?

Bill-I'm thinking maybe the fuel pump, but I don't know how to check it.

Rick-I've replaced points, condenser, rotor, cap, leads, plugs, and coil. The dizzy shaft and bearing are okay I think as the dwell remains constant at any rpm.

Could the timming be advancing too quickly? It misses more at low rpm and seems to smooth out more above 3000 rpm.
C Wiebe

Check for loose intake manifold nuts at both the carb and head sides.

Rick O.
Rick Orthen

Chris - I meant the hole on the bottom of the carbon cannister as the carbs normally pull air in through it to pick up gas adsorbed on the carbon. Better yet, just disconnect the hose from the carbs at the cannister. Does the idle increase? Now put your finger over the end - does the idle drop? I had a restrictor in the cannister inlet to get the idle speed down, but ended up plugging the taps on the carbs and routing the valve cover vent to a separate bottle to get the carbs richer.

Try the carb cleaner spray test on the seal area if the shafts. They rarely look badly worn, but can nonetheless leak.
Brent B

Chris, for a lean condition related to the carbs and not any other source like a leaking brake booster check that the temperature compensators are closed at normal operating temperature. Buckeye Triumphs has details to follow to test this item. Also make sure that the fine air adjustment screws are seated closed. I have seen situations where the screw was tightened all the way in but would still leak air due to the needle being worn or the threads needing retapped. If you are out of adjustment on the mixture needle and still run lean with everything else sealed you may have installed the new jet tubes too high in the throttle body.
Jeffrey Palya

I have had a very similar situation regarding the lean mixture (sputtering inside 2500rpm under load). About half way through the carb tuning process I decided to follow the KISS (Keep It Simple Stupid) route and checked the fuel was a mess. My plugs were okay up front but light in the rear so I figure I'll still need to adjust and rebalance the carbs. The car has been up on jacks all week so I have yet to be able to try it out and see if the filter replacement worked but I will report back (I promise Bill!) to let everyone know if it worked out.
Josh Tarnow

If I remember correctly a long ago post was about the back 2 plugs being different than the front. The poster couldn't get the plugs to match Anyone recall the answer?

Jeffrey-The temp compensators do remain closed at normal temperatures. The trim screws are fully closed. If these leaked are, would it actually be enough to effect the mixture past idle? I didn't touch the jet tubes when I rebuilt the carbs, but have thought about pushing them down in the carb body slightly. Do you know if this can be done through the top of the carb with the air valve removed and the carb still attached to the manifold?

Josh-The fuel filter flows lots af fuel. I haven't checked the output of the fuel pump as I figured this problem would cause poor running at all engine tempuratures not just 20 minutes after its been running a while.

Interestingly the spark plugs are all even at a nice light tan color, probably meaning the mixture is alright.

Does anyone know what kind of compression readings are typical for a 76 TR6? And how to check for valve or head gasket problems? That is the dirrection I am going next to track this problem down.
C Wiebe

Hi Chris

To do a compression check that will narrow down problems. Good compression is around 165 to 175 within 10% all 6. That will drop with milage.

Take the car for a run 10 minutes to get everything warmed up.

Remove all 6 plugs. Have someone spin the engine you want about 4 compression strokes for each cylinder. Try to use the same turns on all. Mark down each one. Cylinder and comp. If all are even most important and above say 130 your great.

Get an oil can any thing that will squirt a few shots of 30 weight into the cylinders trying to get to the back through plug. You want a fair amount depending on the oiler. I use the old train type with a squirter handle. 3 shots about right. Not critical.

Do another read.

The oil will seal most ring problems and raise the overall compression reading. If any are low you have valve or head problems.

Give the readings.


Bill Brayford

Well I did a compression test

At least they're even. I didn't get a chance to do another test with some oil squirted in, but I go back and do that and post the results.

C Wiebe

Chris don't frown thats not bad at all. Very common. And engine will run fine. Your 75 is a lower compression engine original as well because of emissions.

Is your compression tester a screw in type?

Bill Brayford

I missed a few things I take for granted.

1 thing that will improve readings.
Block the throttle wide open when testing.
Block temperature affects readings so your probably right on the money across board.

Make sure that engine is spinning fast let it go 6 turns or more just to be safe. Just try to get even # each close.

I should have mentioned as well make sure thermostat has opened and coolant in rad is hot. Evens out block temp. If your stat wasn't quite open they sometimes open just after you shut off car.

Remove the coil HV wire? Little safer.

Compression is based on atmospheric pressure. And compression ratio. The 175 comes from a manual for Britain and is aproximate. There cars have a much higher comp. ratio. Older pre 73s as well.

So you likely have a good reading for a thirty year old car. That hasn't had total rebuild? :)

Only thing you might try is to do a fast reading since your experienced now. After the problem has shown up? Trying not to let the engine cool down to much. Just to absolutly prove out no cracks or gasket problems. And I don't think you will find anything. But will set your mind to rest.

Sorry for the missed items Atmospheric pressure between my ears!! :)

Bill Brayford

Chris - Something you might want to consider is disabling the temperature compensators. Mine LOOKED closed, but apparently leaked. I ended up sealing the valve plug/seat area of the compensator with RTV silicone, and tightened down the adjusting nut 2 turns. That lowered the idle speed and riched up the carbs a bit, and I'm quite happy with the performance.

If it doesn't work for you, disassemble the thing, clean out the RTV, readjust to 145 deg F or so, and put them back in.
Brent B

I drove it until it hot and sputtering and did the test. I took off the cap and wires but did not block the throttle open. The tester was a screw in variety. I let the motor spin 6 times for each cylinder.

I also adjusted the valves previously while the engine was cold. Some were a bit tight, but it made no difference in the running car.

I'm glad the compression reading were all even but am still frustrated that I can't find the root of this problem.

I'll keep trying. Chris
C Wiebe

I think a quick way to confirm your 'too lean' diagnosis is to run the car and gradually pull out the choke. On these cars, its not really a choke that cuts airflow, its a control that opens another port to let more fuel into the mixture. So if you're right about running lean, pulling the choke some amount should smooth things out.

At least you'd be sure that lean mixture is the cause of the problem.
Mark H

Decided to do a slow read of thread.

I like Brents thinking on temp. compensators. The ball seal is poor at best in any I have seen?

If your problem is fuel mixture unless pump starvation. A starved carb will not run any better unfortunately. Marks idea should give you a better running car.

Charlie was over last weekend with his 75 has a slight lean prob and funny running at initial throttle. Quite white plugs. He was using choke for better throttle response. We noticed a change in RPM when I played with the anti run on valve at the bottom of the cannister? Charlie set carbs full rich to test on way home but I havn't heard how that worked out?

I don't know much about that valves effect off or on idle? Never taken one apart regarding internal workings of canister as far as air metering. Most Americans it has no effect, this one seems to. Canister is usually hooked up on american cars to a thermostat valve that opens at temp.??? That is the hole under the canister or under the run on valve that Brent mentioned before. Check those curved lines to it as well for leaks if you have.

Now as for Josh and the fuel lines.( Havn't heard fom you Josh) We store these cars or leave sitting quite a bit over winter in the North. Very few add Sta-bil or drain fuel system right? If system drained do you oil spray inside of tank to prevent rust? Our new and improved gas goes somewhat crap in 2 weeks.

Taking the fuel line off and watching flow won't tell much if there is a lot of crap in tank. Particles will float unless under suction, and filter will flow fine. When the pumps sucking volume and speed all come rushing to the inlet blocking after a while? If you shut down the engine for 3 to 5 minutes still hot does it run better on restart? If it does may be a good indication.

Checking fuel pump question.

Pump has about 2.5 psi. If you take off line and put a line into a gas can you should have good and even spurt every 2 revolutions. Won't likely show a particulate blockage though. Take off line to tank plug and add a line with a filter into a clean gas can and try.

Chris try to go through the whole thread and look at anything you may have missed. As Josh mentioned simple things are the worst.

I know an old guy with a hot truck that ran like crap all of a sudden sometimes about a year ago. Sputtered stalled etc.. Changed fuel pump. Reworked ignition. Ripped hair out. Decided it had to be the carb. that was shot. Bought an Edelbrock performer. That was it $400 bucks ran like a dream. Moose next door came in. Needed a rochester Carb. filter long after parts store closed. Hey I put a new one in that no good carb before I took it off. Grabbed a wrench and wow loook at that perfect filter. "IN BACKWARDS" some old guy with bi-focals that resembles me put the thing in?

$400 dollar fix for a $2.00 problem. Don't tell my Wife. :)


Bill Brayford

Hi Guys,
Bill, the car ran the same on the way home,pretty good but when she is hot (driving for 40mins or more) It sputters a couple of time when pulling away from a stop and sometimes in 2nd ( but not all the time !!) I advanced my timing a bit and re-balanced carbs, reset idle, BPV are set from fully turned to the right and then turned back 5 turns for now,
Temp comps open about 135 per my wifes turkey thermometer etc, She ( the TR6 )starts instantly when cold with about an inch of choke though I have to leave it on till she's warmed up ( 5-10mins) then runs great till I pass that 40min mark. My plugs are a light tan colour and the car has lots of power and cruises the back roads and highway's just that annoying sputter / hesitation and I can't figure out why my mixture has to be so far to the rich side ...*&^&*%@$%$^^( aggh)

Any tips will be appreciated /
I still love my TR6 !
Charlie Ballard

Maybe try adjusting the temp comps to 145 F or 155 F, or maybe bypassing (disabling) them all-together (my choice). Sure sounds like a temperature related problem...
Brent B


It running well again! Thanks everyone who posted with suggestions to help me out.

Invited the father-in-law over (a TR3 owner in his youth) to hash it out for a day.

No matter what we tried nothing worked. We did discover a lot of bubbles in the gas as it squirted out the gas line as we were checking the pump. We couldn't find any leaks so we thought the gas may be boiling (it was a very hot day and the motor was hot from sitting being reved constantly). We wrapped the gas line next to the motor with foil to make a heat sheild. The car stil missed. Anyone else have a problem with bubbles in the gas?

After we had tried everything I got to thinkng. The book says set the popints gap to .015" or a dwell of 35. With .015" the dwell measured at about 30 and the car ran poorly. When the dwell was adjusted to 35 the car ran okay but missed when warm. We though maybe the dizzy shaft got a touch loose when hot and the made the points float sometimes. So we closed the point gap to .010" and voila, no misses!!

I'm very happy again!

Thanks, Chris
C Wiebe

This thread was discussed between 27/04/2003 and 06/06/2003

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