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Triumph TR6 - adjusting carb mixture?

Last weekend at a car show in Canada, I was amazed by a Jag guy on how he tuned my carbs.
My ignition system was dialed in (so I thought so) and the vacuum on all three carbs were in synced. I just couldn't get the carb mixture right!
So... what this guy does is he cranks my distributor up until he hears the engine miss, then backs it off. He then brings the idle down to about 1200 rpm by adjusting the idle screws.
This is when the magic begins which I don't know how he did it. He listens if the carbs are too rich or too lean and adjusts accordingly.
My question is the following:
1)When he revs the engine, what is he hearing when it's rich or lean?
2)How does he know which carb needs to be adjusted?
If there is any other insights on how to do this the "old school" way, I'd like to know.
I hope someone out there can tell me how he did it.


my thought is that when he revs the engine he is listening to the air flow into/thru the carbs. I'd say he knows which carb to adjust because he's done it so many times he can pick up subtleties between the two carbs that only draw blank stares from the rest of us (or atleast me). I like his method, these cars are supposed to be simple!

c.a.e. emenhiser

I used to do what you described with my TR-250 back in '68, but alas, lad, like many skills honed to near perfection back then, they've long since gone by the by:(

Every time I had the Triumph serviced at the dealer, I'd drive a block or so away, stop, get out and adjust the carbs. The dealer just could never understand that it's just gotta feel right.
Doug Baker

Hi Benji
How ya doin'?
Yup, this guy has probably been adjusting carbs before you or I where born:)

"1)When he revs the engine, what is he hearing when it's rich or lean?"
He is listening to the carb (air intake). More air being sucked in= lean and visa-versa. How does he know if too little or too much air...??? That is his secret.
How to learn the "old school" way. Find a BL dealership and go work as a mechanic for a while.
Rick C

Rick Crawford

Just spoke to a MG guy. This is what he sez' after tuning the car:

Listening or putting my hand behind the exhaust:
-A consistent miss in the exhaust means it's running
-A inconsistent miss in the exhaust means it's too

What to listen for with carburetors:
-If it has a higher hiss, its running too lean.
-If it has a lower hiss, its running too rich. this true? I'd really like to hear from some of you guys or gals for advice.

I'm doing great now that my car hauls ar*e!
How's the stop smoking program working for you?

Have not had a smoke since going to the Hospital (2 months) and have not had a chest pain since the Angiogram (1 month).
That is interesting what the MG guys said. Will hold true for TRs also. Not sure on detecting a high or low hiss though.
Mine runnin' good also. Hate paying $1.19/ liter for 94 octane though. About $4.76/US Gal.
Rick C
Rick Crawford

That statement about doing great? Well, last night, I broke one of my roller rocker arms!! Time to call Richard Good and see if he will replace it.

Doug out there? I understand the CRS episodes(Can't remember s***) because I've been having them a lot more these days.
As per my previous listing, what the MG guy said makes sense but, does it sound right to you?

Rod Nichols...I'll see you at McMinnville.

Rick Crawford...
"That is interesting what the MG guys said."
Does that mean that you agree with the statement?

Don Kelly...
Stop talkin' about mirrors and jump into this thread!!


Never fooled w/the exhaust...too complicated w/o instrumentation. I listened to the engine and the carburettor intake, mainly to make sure that they both sounded pretty much the same. If not, I adjusted 'til they did and if the carbs sounded alike and the engine rev'ved smmothly, it was good to go. BTW, I've seen posts of top end speed with the 2.5L engine somewhere around 105MPH, but on one occasion in that TR-250 (and I do remember this, fortunately or not), I recall pegging the needle at 135MPH on a long stretch of open I-65. Don't know what that means today...maybe that my speedometer was way off!!
Doug Baker

As the mixture is made rich the idle goes up slightly and down as it is leaned back...a well trained ear can pick up this subtle change and the middle point should give the perfect tan coloured plugs. I'm getting better at it but for now I adjusted the mixture a 1/4 of a turn and after a run I check # 2 and # 6 plugs ( easiest to check ) and re-adjust as needed. Now my plugs are perfect .once it's done it should be fine for a loooooong time.
Charlie B.

I am not old school...I am way too young for that:). Do not agree or disagree. It is just plain interesting. Lets face it our carbs are pretty simple and I guess if you "tuned" enough LBS back in the old country well then listening to a hiss from the carbs and listening to the exhaust for a miss or irregular misses could give you a clue what the carbs are doing. I would be interested in hearing what some old school chaps say on his comment about listening to the exhaust.

I will add this though. Before I replaced the throttle shaft seals I had a consistent miss when listening to the exhaust. Following his statement would make sense as the worn seals would allow more air in thus leaning the carbs. The miss was consistent but not consistent like a dead spark plug.

Sorry to hear about a roller rocker..defective??

Rick C
Rick Crawford

My experience (with both MG/SU and TR/ZS) is that a steady miss is from a rich condition or burnt valve and an intermittent miss is from a lean condition.
Rick, check out our club website ( You really should have one of the ATDI tee-shirts with the RAF roundel. Only $15.00 American-$200.00 Canadian. Glad your health has improved, looking forward to another visit.
Mike Crane
mike crane

Hi Mike
How are ya?
Well that blows my theory out the door.
Hope you have put a few miles on you baby this year. I have only put on about 150 miles. Just got her on the road beginning of May. Tried to go for a ride every day this British Car Week. Rained yesterday.
Most definitely next time in Va, Wa. will call you. Went to your club WEB site and see that you will be having a meet at Fort Vancouver. That should be cool.
Please do me a favour and take a photo-stitch picture when you are at the Evergreen Air know what I mean.
Take care
Rick C
Rick Crawford

This thread was discussed between 25/05/2006 and 01/06/2006

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