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Triumph TR6 - choke and gag

Got a good one for you guys. My 72 Tr6 is running absolutely perfectly, after much work. The only fly in the ointment is that occasionally, usually after a hard run at high speed, it will lose all power and stall at stop signs. After a couple of minutes it will kick in at be fine again. One time I pulled the choke. It went pop and ran fine again. I'm bewildered(as usual). Any thoughts?
Joel

Joel
Vapour lock?
Rick Crawford

Rick; That was my first reaction too. The only problem is that the temp gauge reads normal. I still suspect you're right though no matter how sure I am that a temperature gauge could never give a bum reading. Riiiight!
Joel

My guess is that its getting unusually hot in the combustion chambers during prolonged high speed runs, which causes it to stall at tickover. Either the mixture is too lean or the ignition is too retarded. Using the choke will cool the mixture and help restarting, the 'pop' you heared being the mixture igniting (on a hot exhaust valve probably)while the inlet valve is still open. My first instinct would be to check the ignition advance curve with a timing light. Rubbish petrol- sorry gas - could also be a culprit if it is lacking in octane.
Peter Cobbold

Hi Joel
You may just have a plugged fuel line.

Lots of could be's but I went and played with a mockup of something. Pay attention all YE who are running lean and backfiring. Old guy might have answer.

From what you have described it sounds as though your tank isn't venting properly?

If vent line is blocked or partialy crimped somewhere or cannisters plugged. At high speed your fuel pump creates a lot of suction. Suction of gas creates vaccum in the tank that has to be replaced by air. If there is not enough air. Fuel flow will be restricted somewhat at full throttle after vacuum builds. Get it guys. Lean burn pop. Tank has a 1/8 id tube at top.

Not at idle not on rap raps. Enough air can get in. Just nice exhuberant high speed drive. When the pump slows on deceleration the vaccum in tank overcomes the pumps now low speed suction until the tank pressure returns to atmosphere. Gas in effect is now trying to go back to tank. Remember high school nature abhors a void. This all depends on the amount of blockage.

Now Rick has a problem lean and deceleration pops, Charlie seems to be lean does the choke a bit runs fine. Charlie and others also have a problem with diaphrams. I think the answer is here to. Joel seems to run fine until deceleration "sometimes"?? bet it depends on the level of fuel in your tank?

Now this is a lot of thinking and off the wall big time but picture this and please correct my theory. Remember all the fellows commenting on new fuel pumps resolved this problem. Just covered it up.

Float bowels are already lean starved due to restriction at full throttle? Deceleration what little gas there is is being pulled back by tank vacuum overriding fuel pump at low rpm stop light. Suction in fuel line. Suction closes float needle in bowel? No gas. Open your choke passages now there is greater suction in bowel. Pulls open float needle you get gas major lean pop and then OK.

I don't have conclusive proof of this theory. And at this point can't test. But its looking a ten so far.

Bill





B Brayford

And it's so simple to give it a test. Just leave the fill cap on the gas tank open and run it to see if there's any improvement.

Don Elliott, 1958 TR3A
Don Elliott

Yeah Don I was going to suggest that but hesitated. Any one trying this leave your smokes and Bic at home. With the venturi effect and filler cap next to your right ear you may just give a whole new meaning to "Roast Turkey".:)

Bill
B Brayford

Point well taken.

Roast Turkey or rather "chestnuts roasting on an open fire" - now that Thanksgiving is over - it's getting closer to Christmas. You can guess what "chestnuts" I'm referring to.

Please don't call this abuse to the attention of the web-master.

Don Elliott, 1958 TR3A
Don Elliott

B; I suspect you may be onto something. I Have a really strong gas odour when the car sits awhile. I suspect this would be consistent with a canister that is not venting properly. Think I'll take a look. Thanks.
Joel
Joel

Not that I have had a reason to have gas in mine for the last few years, but I remember when my tank was full (3/4-1/1) the fuel aroma was real strong too. Could this also be a plugged return system?
DonK.
DON KELLY

Another potential "stink pot" is the emission tank assembly rivited to right side trunk area. It should have 2 connections to it. One side does the loop around the trunk then to front canister. The other goes to the Gas tank. However. this is not true for all years. this is only for pre '72 cars. '71 had the most amount of junk on top of the tank with a total of 3 vent lines off the top of the tank. Anyway, this emissions tank as you can imagine has had a few years to collect a little gas and we know that gas does not age as well as red wine. The tank can easily be removed by drilling out the pop rivets and then examined. The tank sits in a "pocket" so it is not exposed to the outside of the car but it could develop a pin hole over the course of 30 years. For later years the seperator canister..Loose connection? pin hole/ plugged?
Don K, blow into the line at the carbon canister. Ya not easy to get at but with an extension piece of clear plastic pipe attached it would tell u if plugged or not.
Rick C
Bill B...very interesting thought. Good thinking my friend.
Rick Crawford

Took my expansion tank off and had it powder coated. Hope that took care of pin holes. I just remembered when I was under the car one time I noticed the plastic pipe that connects the canister to the tank, a section had rotted off. Probably from a gas leak.
Don K
DON KELLY

I had a similiar problem in my '72 TR6 - sudden loss of power during/just after high speed running. After several unsuccessful carb/ignition fixes, I loosened the fuel inlet at the pump. There was no gush of fuel like I got when I did this on my TR3 (after forgetting to clamp off the rubber section) - just an extremely slow seep.
To make a long saga short, the short section of pipe at the tank outlet was clogged with fine rust/mud/crud and virtually no fuel got through. In a parking lot with the left rear wheel off, I jammed a coathanger wire up the pipe and got it clear enough to think I had it fixed. (yes, fuel dumped everywhere) After a few more stalling incidents, I had to remove the 5+ foot section of fuel pipe that runs between the tank outlet and fuel inlet pipes. Reaming with a long piece of twisted copper wire cleared it up for good. I should have put in new line, but the car was my daily driver and had to be 'online' the next morning.
Check the 'at rest' fuel flow to your pump, as well as the fuel pump filter screen - mine was covered with rust particles. The DPO had let the car sit for 5 years, so that didn't help.
TR6s at mid-72 replaced the riveted emmission tank with a small metal can mounted just above the gas tank, right side. This can get loose and clunk around to simulate any number of expensive problems. But that's another story. Aloha
Jeff
Jeff Fetner

This thread was discussed between 28/11/2002 and 02/12/2002

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