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Triumph TR6 - Wierd missing problem - help.

Hey there all. I'm new to this BBS. I've got a 74 and it's in nice condition. I had a misfire problem at cruise speeds and a mechanic found it to be that emissions valve. He disconnected it and it no longer does that. What's going on now though is that if I've been driving her for a while, and then I get in some traffic where it's stop and go. She'll start to warm up a bit (not even to the half way point), and when I start off in 1st gear, she'll bog down. Like there's not spark or air or fuel or something. Volt meter shows no problems there. It's a new sport coil. I'm not sure. I think the mixture is good (been working with that for a while). Maybe it's smog crap. What other smog junk can I rip out of there without hurting anything? Oh yeah. I can blow through the problem. In other words, it bogs, I hit it & it blows through it and performs. Again.. any thoughts would be appreciated.

Frank - California USA
Frank Garay

Frank, I don't know your problem, but am willing to correspond - I like a challenge. I drive a 74, a little less smog stuff on lt, but most of this can come off, with ease and performance gains.First try disabling items,one by one, until problem changes - this is how you'll know your car, a great confidence to have. Peter G
Peter G

Hi Frank,

I also have a 74. Here are some of my guesses:

1.) The dampers on your carbs are low or empty. This could cause the stumble when you step on the gas, i.e. the trottle isn't damped so the fuel mix goes too rich before the carbs can respond to the change.

2.) If you adjusted the mixture before removing the emmissions valve (I understand this to mean you removed the EGR valve?), then you will have to adjust again since I think your system will now be running lean. The EGR mixes in some air with unburnt fuel into the flow and removing this causes more clean air to be drawn in from through the filters, but this clean air does not have the fuel mixed in that the EGR fumes have.

3.) At some point, you said your TR was running great, but did not knock on wood, or do whatever you do to avoid jinx'ing the car. The pennance for this is to wash and wax the car 3 times. :)


Thanks guys. Okay I'll work on this. Yes the EGR was removed. I do notice now that the plugs show a very lean mixture. I've been fattening it up but maybe I have to go further? Also I attempted to pull the choke while it was doing it to see if it helped and it didn't. But I'm not sure how the choke richens the mix. I'm thinking it's by reducing air flow, not by adding fuel, so maybe it's not a good way to trouble shoot it. Thoughts?
Frank Garay

Frank - A marathon runner finishes near the top of the field because he breathes more air with less effort than the others in the race. The same with your TR6. If an engine breathes more air, it will go faster with less effort. There are test devices called air flow meters at repair machine shops which help the mechanic to improve the breathing (into the engine and out) by all sorts of little improvements with the head, valves, cam, etc.

You don't want to cut down on the breathing ability of your TR6 engine. Think of it as an air pump which does the work of carrying a bit of gas into the cylinders which then explodes to keep your air pump (engine) going.

Don Elliott, 1958 TR3A
Don Elliott

If you have not done so allready I would very carefully check your fuel supply to make sure that there isnt anything blocking the lines. I had very similar symptoms to you caused by a piece of crud in the line at the fuel filter that intermitantly blocked the fuel supply starving the engine of fuel resulting in a severe unpredictable bog while running perfect at other times. I would check and replace the fuel filter - check also the fuel pump for clogs and proper operation and of course the carb to make sure no orifices are plugged. Apark Plugs may possibly be invovled too: years ago before I got smart and started using NGK plugs I had misfiring and rough running caused on two separate occasions by using NEW sets of champion plugs - of course having just put in new plugs I thought the problem had to be eleswhere and spent hours looking for the problem before I figured out it was the plugs!
Good luck

I'm with you all, however, the problem is when it warms up past the 1/4 mark on the temp indicator. It's heat related... so ponder that one and let me know what you think.

Frank Garay

Disconnect the vac retard (do 74's have that?) and strobe the timing with some decent advance.

Rick O.
72 TR6
Rick Orthen

Could be the temp. compensators on the carbs aren't functioning properly. There's a good procedure at

that might help out.

Also, next time you have the air filters off check that the carb air valves are not sticking. With the engine off lift and drop each carb valve with your finger. It should hit with a good "click". Then lift both valves up to max position and release simultaneously. They should hit (click) within a fraction of a second of each other. If not, there's a sequence of things to do to get it moving again.
Brent B

Now that i am driving my wonderful, beautiful TR6 everyday,I am noticing how temperature sensitive it is and will replace these frickin ZS's with real carbs as soon as I can afford it. Not the cars fault, mostly the attempts to satisfy the emmision requirements of the times.Peter g
Peter G

my '72 had sort of the same symptoms,I was losing air through the carbon canister,block off the hose and see if that helps.

'72 tr-6

Great advice guys. I've discovered something else. My number 2 carb wont hold it's dampening oil. I fill it to the proper level, make a run, and then when I check it again, the oil is like... gone! Could this be the diaphram? What would go bad to cause this? So I'm thinking it's not heat realted. What should I fix?

Frank Garay

There's a rubber "O" ring at the bas eof the damper pot. Check that. I had a problem with loss of power under load at one time too. It ran great when I started her up but under load -> lots of misfire. The problem (I think) was in distributor shaft had sheared.

No damper oil could explain the stumbling at startup, since the oil is supposed to ease the transition when you step on the gas pedal.

I would suggest rebuilding both carbs if you haven't done this lately. It is pretty easy. I followed the instructions on

Am now thinking that as my idle that keeps rising on it's own,is possibly just the brand new engine breaking in.Could this be i? Feel very restrained,having to 'Gentle' the engine for a 1000 or so miles, when I want to stomp it. Peter G
Peter G

Regarding the rising idle, I've had that problem twice in the past. Once was due to the carbs not being in sync, and when one was resting against the fast idle screw, the other was held open a little. The second was more recent and discussed on a previous post a couple of months ago. The bypass valve was defective and allowing mixture to go around the throttle plate. Mine are older (71) and not easily adjusted, but it can be done. Your 74 may have the external adjustment.

My solution was to bypass the bypass completely, and the more I drive it, the more I'm convinced it was the best thing I've done. I'm very happy now with the ZS carbs. I've only bypassed one, since the other is still working. it just involved replacing the gasket with a solid one with no holes.

To test the bypasses, you can remove them in place, and put a piece of masking or duct tape over the holes exposed on the carb body. You'll know if it worked right away. The front carb is easy, getting to the three screws on the back carb is a little tougher. I'd do one at a time so if it works, you'll know which one is bad.

Whether you bypass them or not, this would help you determine if they're part of your problem. I'd try the bypass before buying new carbs though, just to see if you like it. The reason I tried it was because one of the comments on why people like SU's was because they have no bypasses, so this just moved my ZS's in that direction.

Mark H

Thanks Mark, I will check that out. Got a book on Stroms - I like to know the theory behind how something works. Once I understand that, usually, I can figure it out, but not always. Any tips appreciated.Actually happy this car ran at all. Took quite a gamble - could not drive it, really knew nothing about it's 'major'mechanical condition, had sat for 10 yrs. New engine, bolted all the old stuff back on, and she fired right up. Was stoked. And not too many weird noises on the road. Peter G
Peter G

Bryn hit the proverbial nail on the head. you damper oil is making your back 3 cylinders think they are 2 stroke. The replacement of the "O" ring is very tricky as u can do severe damage to the damper piston wall!!!! The WEB page Ignatius refers to has the repair outlined (Zenith Stromberb Tech Tips) but it has a major flaw in it. In a past thread I did a correction to the repair steps. go to ARCHIVES and you will find Aug. 2002 "TECH-TIP CORRECTION". The "O" ring is available from any auto supply. While just back there trying to find my thread I found my old "rough idle/popping on deceleration" volumes one and two that Don K enjoyed so much:) Some thoughts on the BPV there. Ha Don, still have to deal with this one this spring.
Frank, if you do not have the carb adjusting tool (MOSS 386-310) or the carb synch tool (386-200) ...GET THEM! "must have" tools for any owner of ZS carbs! But useless tools till you fix the leak.
Rick C
Rick Crawford

If its theory you're after, check

In the technical section is a group of articles on theory, rebuilding, and adjusting. I started with no knowledge at all about carbs and successfully rebuilt mine just by following the steps. Worth a look.

Mark H

Thanks Rick! I'll try to find the thread. I ordered the replacement part today and it will be in by Friday. I just dont see how to get the retaining clip out of there.. I do have the mixture tool. I've ordered the syncronizing tool. Do I need a special tool to change this O-ring?

Frank Garay

Hi Frank

Nope no special tools other than the mix. Go to the Buckeye page provided by Mark and have a read. And this one by Brent specific to your problem.
Be carefull and lay out and catalogue in your mind how it came apart.

The choke on this type of carb adds fuel to the mixture through ports in the choke mechanism richening. It does not block air.

From your comment on running lean plus blowing through. Fix the damper first. One carb popping open on throttle may be cause.

Peter you should stomp on it a bit. Breaking in the engine should be done much like you intend to drive it. If you plan to run flat out don't baby it between 30 and fifty? Thats my opinion.

Bill Brayford

This BBS is great - thanks guys, Peter G
Peter G

Thanks Bill. Once all parts are in I'll let all know how it turned out.
Frank Garay

Thanks for everything guys!!! O-Ring replaced, Carb's sync'd, Mixture adjusted & spark plug gap widened - She's running excellent!!! All of your help was great!! Thanks again.

This thread was discussed between 03/03/2003 and 22/03/2003

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