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Triumph TR6 - High speed missfire

Hey guys; been working on the old Tr6. Runs well til I hit around 3000 - 3500 rpm then runs out of power. Shakes and misses like crazy. Have Pertronix electronic ignition so no points. Plugs have grey-white frosting with a little carbon around base of threads. Seems normal. Timing set at plus 8 degrees. Rotor and cap seem fine. Anybody got any ideas?
J. Stein

Grey/white may indicate a little lean? If you back off does it smooth?

Carb bowls may have some gunk in them that work up and block flow at higher volume. If Zs remove the drains a couple of times on each letting the gas flow out car off.

Restriction in the fuel lines filter or air vent to tank restricted?
Bill


Bill Brayford

Stale gas?
P H Cobbold

Bill, I think you may be onto something with the restricted flow. Gas is new. I do get a strong petrol smell in the trunk. May need to dig into the ZS's and check the adjustment. My mechanic has a nasty habit of shutting off one of the carbs to get the cars through smog. He then forgets to get them adjusted again. I suspect this may be it. Thanks.
J. L. Stein

I had the same problem with my '76. It drove me crazy trying to fix the problem. Ended up replacing the distributor, that corrected the problem. Although not sure, I suspect I was getting a wobble in the shaft at high speed
Mike Parkhill

By "plus 8 degrees" do you mean the timing is retarded 8 degrees? If so, it should instead be advanced that amount.

Rick O.
Rick Orthen

Sorry Rick. I meant advanced 8 degrees.
J. L. Stein

Some of the Petronix folks have had problems like yours (I haven't). Swap the old points back in and see what happens. Also, check that the brass thingy on top of the rotor is secure; if not, super glue it.

Rick O.
Rick Orthen

Rick, I dug into carbs this afternoon. Found that even with the needles all the way in she was still running lean. Immediately called my friendly neighborhood mechanic who suspects worn needles. 32 years old, I'd be amazed if they weren't worn. I hope it's the needles and not the shaft bushings. Thanks for the input guys.
J. L. Stein

J.L-If the needles were all the way in that would mean they were in the leanest postion. Also, worn needles and jets will produce a richer mixture.
Berry Price

Wait a minute there - needles "all the way in" WILL make it lean. And worn needles tend to rich up the mixture, not lean it. Needles are easy to replace, anyway.

Check those diaphragms (Jim D's favorite word) for holes! If they don't lift the air valves you'll run too lean. BTW - those are also simple to replace and you shouldn't waste your mechanics time with them. He'd only charge you $70-$80 for a $6 job.

Brent
Brent B

Now I'm really confused. I always thought it was the way you said Berry. I just went by Bentley. I quote:10. "Insert the special jet adjusting tool and turn it clockwise to enrich or anti-clockwise to weaken the mixture." When I raise the piston the call slows and stalls. Where am I going astray?
J. L. Stein

J.L.-The Bentley instructions are right, but when you said "the needles are all the way in", I took it as meaning that the needles were all the way in the jet. This would be the leanest setting. When using the adjusting tool, make sure that the outer part that engages the piston rod is not allowed to turn or the diaphragm will tear. The normal adjustment is about 2 turns up from the lowest setting. The shoulder of the needle will be about .060" above the bottom of the piston. If this adjustment still leaves the plugs white look for vac. leaks. The seals around the throttle shafts are suspects as are vac. hoses. The throttle shafts also could be worn, but the carb bodies have steel bushings, which shouldn't show much wear.Check out this site for a good detailed article on the carbs: www.buckeyetriumphs.org
Berry Price

Your correct. Only lift the piston by 1/4 inch slow to test. If your full rich on both and a slight lift of piston causes stall your not getting enough atamized gas into the air. The shaft bushings can be checked by spraying carb clean on them. If there sucking a lot and your lean revs should increase.

Worn needles will increase flow not sure of how atomizing would be affected. Not likely problem?

Did you check out the float bowls? And other stuff fuel line areas?

Good blast of carb cleaner down through needle passages. Drain bowls install plug and then again through needles fill bowls. Give 60 min. and drain. Blast carb stuff up from bottom and back through down needles. Try again.

Bill

Bill Brayford

J. L. - You still need to take the cover off the air valves and check the diaphragms for holes. Just pull out the air valve/diafragm assembly, hold it up to a bright light, and stretch out the rubber a bit. Any holes will show through. Start there before pulling carbs off the engine.

Sorry - I also didn't understand by "needles all the way in".

Brent
Brent B

Sorry guys, was just using the old "all the way to the right = all the way in ploy. Oh well. Thanks for all the ideas guys. Will try the carb cleaner, the draining and check the diaphrams. No I think I'll watch that 1958 classic "The Blob" and go to bed. Thanks again.
J. L. Stein

This thread was discussed between 06/11/2003 and 08/11/2003

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