MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

TR parts and Triumph parts, TR bits, Triumph Car Spares and accessories are available for TR2, TR3, TR3A, TR4, TR4A, TR5, TR6, TR7, TR8, Spitfire and Stag and other TR models are available from British car spares and parts company LBCarCo.

Triumph TR6 - Out of ballance SU carbs.

74 TR6. Overhauled both SU carbs and re-installed and attempted to tune / ballance. Front carb is sucking so much more air then the rear one that it cannot be ballanced. Standing beside the car at idle, I can easily here the air flow difference. The front carb piston is visibly higher at idle then the rear one. I have replaced all vaccum hoses with no change.
What should I check, replace, etc.?
Thanks,
Jim
Jim Kinsella

Jim - Look at the shaft that is located between the two carbs and which, when they rotate, open or close the butterfly inside the throat of the carb. Remove the air filters to look in the throat to see this action when you hit the throttle. To sychronise both of them, you want them to suck the same amout of air. To get this, you will need to loosen or dis-connect the attachment for this rod - somewhere between the two carbs. Then when you zap the throttle, the butterfly in only one carb will operate. You will then adjust a screw on each carb till they both suck the same amount of air at an idle speed of about 800 RPM. If the idle is too low, adjust both screws to increse the idle. If the idle is too fast, back off on both screws.

With both air filters off and the engine idling at 800 RPM, I use a piece of old garden hose about 18" long and put the bottom end against the flange of the carb where the filter would be mounted. The other end of the hose, I hold to my ear. Then I move the bottom end of the hose forward and backward from one carb to the other to hear the "hiss". If one carb is hissing louder or more, it is sucking in too much air. In this case, back off the screw for that carb.

When the hissing sounds the same for both carbs, re-tighten the screw or clamp on the rod between the two carbs. Then check the "hissing" again. If the hissing is different again, it has happened by you tightening that screw or attachment on the rod. Loosen it and do it again till you get it right. Then put on the air filters and you are done.

Don Elliott, 1958 TR3A, Original Owner
Don Elliott

Don:
Thanks, but I have done this already. There is not enough adjustment to equalize the carbs. This is why I think I need to look elseware for something that may effect the intake imballance?
Jim
Jim Kinsella

Jim - You said you rebuilt your carbs. Did you by mistake screw one of the butterflys onto the rod backwards. Mine have a direction to them so that when they are closed, they are really closed. If one is on backwards, it will not close as it should.

Did you install new bushes in the body for the butterfly rods. If not, the holes where the rods go into the carb body may be oval and air is leaking in. If you did replace tham, did you ream them after for the correct diameter to have the correct clearance fit between the bushings and the rod diameter. This requires a reamer (like a drill, but a reamer has straight flutes, not helical - like on a drill). If the bushings are leaking, I've heard it suggested that you can wind elastic bands around the shafts where the rod enters the carb body to minimise the leakage of air. Note that this is only a temporary fix. It does not eliminate the problem. But it can help you to pin-point if the problem is here.

If one of the pistons is visibly higher, maybe the needle is off-center and this would prevent the piston from falling freely to the bottom. Same thing if the needle got bent. If you put in a new needle, maybe it's the wrong type - too fat ? and causing it to wedge the piston too high.

Lift the piston up and see if it falls down to the bottom or not. Remove the needle and try again.

Did you make sure that you put piston #1 back into Carb body #1 ? If you mixed them, the clearance may be different on each ?

Remove the tops of the carbs again. Are the return springs in ? If they are old, maybe one is too weak. Mine are still working after 43 years and 142,000 miles.

Never sand or file the pistons or the interior of the top body where the piston slides. Use solvent and a soft cloth to clean it. Occasionally you can use 600 grit sandpaper or finer, do it lightly, and not too much. The ring grooves around the piston are what is called a labyrinth seal and the clearance is critical, Make sure the grooves are clean. Use a pointed needle to remove any chips of carbon etc. and/or solvent with a soft cloth.

The piston is guided in a slot. Is something damaged here causing it to stop up a bit.

In the top cap there is a small hole to balance the pressure. Is one of them clogged with old gummy gasoline? you should be able to blow through it with no problem.

Let us know what you find.

Don Elliott

Don Elliott

You can also get a can of Quick Start and spray it around the shafts and other openings and mounting point on the manifold. Except the front opening of course! and if you notice a change in idle speed then you have a leak as the quick start will richen the mixture.

If you disconnected the EGR make sure that all the holes are blocked off.

Make sure that the intake manifold is correctly torqued as well because that could be sucking air in. I am sure you had to remove it to rebuild the carbs. The Quick Start test will work here as well.

Just be careful when using Quick Start because it is compressed Ether and is very combustable and inhaling it will knock you out. Remember that is what they used to administer in the old days durring an operation.
steven

Great suggestions Steven and Don. Worked with it some this weekend, but no luck. Everything you have suggested seems to be OK. I think if the rear carb sucked with as much force as the front one does, the engine would idle no lower then 2000 RPMs!
I pushed the piston down on the front carb using the damper rod. The engine idled down to aprox. 800 RPMs and smoothed out. It takes quite a bit of force to hold the piston down, more then the spring could possibly muster up. Engine off, the piston drops to the bottom and operates as smooth as the rear carb. Again, everything points toward the front intake having much more vaccume then the rear one.
Is there something that ballances the intake manifolds?
If I had a valve problem in a cylinder or two, would she run as good as she does at higher RPMs? As long as I keep the revs up, she runs like a champ. Just don't bog her down or she bucks like a mule, back-fires and misses!
Thanks!
Jim
Jim Kinsella

Hey Jim

Re-reading your initial question, you said that you have SU carbs? did you add them as a modification because all TR6 (north american) came with Strombergs CD175.
steven

UH OH!!
Sorry guys! Definately Strombergs. Just getting into this British car stuff myself...
Can I still participate, or am I to be blackballed? :)
Jim
Jim Kinsella

Hi Jim
Ya you can stay...(I did the same thing when I was a newbe and was promptly corrected by my british friend who owns a spit with SUs).
After reading all the above excellent advice it still comes down to the fact that the front is sucking more air at idle. If your linkage is set up correctly as Don went through then it must be an air leak. Keep in mind that the piston drops down when you shut her off. There is nothing that ballances the intake manifolds other than you do not want a birds nest in there. Your question on the valve thing. How did she run when you first got her or is this a mute point (did she run rough before the rebuild)? Do you get blue smoke comming out the tail? Does it sound like she is banging on 5 instead of 6? I do not think this is the case or you would have said this. you do state she runs fine at higher revs. OK so back to the air mixture.
Your year of 6 has a lot more emissions control junk than mine (1971) so if I miss something, as I am not familiar with it, then consider it as possible air leak.
Where can air leak in where it should not???
1.The intake manifold.. is the intake/exhaust gasket new or reused??? Is the manifold torqued down? is it cracked?
2.The carb mounting Gasket and insulator.. Old or new? Carbs tight here?
3. I look at a parts catalogue and what about the air manifold assembly? Any air leaks where it attaches to the manifold? I do not know but are they compression fittings???air leak???
4. The carbs inside. Is there a pin hole in the Diaphram (we all know what happens if you have a hole in your diaphram:)
5. What about all vacuum hoses, plastic lines and clams? Do not forget to look at those little right angle sleeves..Cracked???
What Steven has suggested with the quick start sounds very logical. Never tried it for this purpose but yep, idle should increase if you find a leak. As Steven said, be very carefull with this stuff...no where near your throat or the carb throat. A very short "pst" will do.
Good luck and let us know what u find.
Rick
Rick Crawford

Hi Rick:
The engine ran so poorly for the previous owner that he parked it for 2 years! The ignition seems pretty solid, lots of new parts. It smokes slightly, some blue but mostly grey from carboration. Definately running on all 6. Lots of power and runs smooth when accelerating through the gears.
So...we are back to an intake leak. It must be on the rear carb because the front is sucking too much? Would a leak on the rear carb cause the front carb to suck too much? I say that it is sucking too much because ....stop, hold everything!
Just read a segment in The Vintage Triumph Regester called "The By Pass Valve Headache". Sounds exactly like my symptoms, only in one carb, not both..(the front one). Engine won't idle down because the stuck valve in allowing too much air to come in. Could be??
I will check this and do a starter fluid check of ALL intake areas and report back.
Great to have some help!!
Thanks to all.
Jim
Jim Kinsella

Jim
A further read for you is a MOSS catalogue, I have an old one 10/02/00 and at the back talks about ZS carbs. You might find it helpfull.
Rick
Rick Crawford

The bypass valve on the front carb was the problem!! Just touching the screw in the bypass valve hole, almost stalled the engine, it reduced the idle (and the suction) so much! A few turns of the screw and she was purring like a kitten, well...sort-of. I need to start over with the tuning process now that the carbs are within ballancing range of each other.
Thanks for all the help, everyone. I look forward to monitering this site and learning more about this neet little British sports car!
Jim
Jim Kinsella

Hi Jim
Congrats Jim you solved it. The nice thing about owning a TR is that there is lots of info out there. (probably because we need it). The great part of this BBS is we learn from giving and receiving. I will keep an eye on my bypass valve.
Happy turkey Jim
Rick
Rick Crawford

Jim - Someday you'll be helping others who write in for help on this (and other) problems. Notice where all your replies came from ? Someday, you'll have to drive your TR6 up to Canada.

Are you planning to go to the VTR National Meet in Red Wing, Minnesota next July 16 to 19, 2002 ?

Check it out www.clubs.hemmings.com/mntriumphs/

I plan to be there, it's not far for me (3 days and about 1200 miles). A lot closer than Portland Oregon 2 years ago and Colorado this year.

Happy TRing.

Don Elliott, 1958 TR3A
Don Elliott

Don, Wow, you do some traveling! I will be doing good to make it to the local meets in 2002. Just
getting into this thing (neet British cars) and my TR6 is in no shape to travel...yet.
Jim
Jim Kinsella

Speaking of the air bypass valve, is there a way to modify the cover to allow access to the adjustment screw without disassembling the thing? Mine is a 72 TR6. Also, does the exhaust manifold heat rising under the rear Stromberg ever cause mixture problems to the extent that insulation is needed?

Thanks.
Rick Orthen

Rick O
Very good question. Lately I have been reading and web surfing on the subject of tuning ZS carbs. My 71 carbs also have (as I have read) an internal bypass valve adjustment. This is rediculous (typical british dry humour engineering). Jim I read the posting you mentioned above and imagine the time one would go through with on and off adjust on and off adjust...etc. Can someone out there in syberspace make life easier for us? Is this procedure of correct mixture adjustment carried out with the screw that one publication calls the idler trimming screw another calls It the mixture trim and the white TR shop manual does not even mention??? ( Not to sound dumb..I had a friend do the tuning while I sat inside at the gas pedel..now I wish to learn and do myself..he has SUs on his spit). Do not know answer on last question.
A side note to all while on the subject of carbs/tuning. A chap by the name of Ed Flexter has said to me that it is considerably more accurate to sync cars at the same time. He has taken a vacuum conection off of the carb to manifold spacer (drilled 1/8" hole for 1/8" short brass pipe) and uses a "mercury stick" with multy viles and can read both carbs and syncs both carbs at the same time. He said the mercury sticks are considerably more accurate than the unisyn tool. This sounds interesting to me. Any thoughts or coments welcome.
Rick
Rick Crawford

Really enjoyed this info on the carbs. Rick Crawford, can you do a bit more explaining about Ed Flexter's method of sync? Mercury stick? multy viles? Just a shadetree dummy here, trying to fix up my TR-6 [73] Thanks.
Les

To Rick and to Les - I can only guess, but it sounds like the "Mercury sticks" are "U-tube manometers" that are filled with Mercury. Like we used in High School and College Physics Labs. The glass tube is shaped like a "U" and the top end on one side has a rubber tube that is connected down to the fitting you mentioned. The "U" tube is filled with Mercury - considered very dangerous stuff these days. Then the vacuum in the manifold sucks the mercury up one side of the tube so you see the difference in the levels for the Mercury in that manometer. I gather from your description that he has a second "U" manometer connected to get a reading for the vacuum for the other carb. How he does this is anybody's guess. But when the differential in the Mercury levels is the same in both "U" tube manometers, the vacuum is the same in each carb - therefore each carb is sucking the same amount of air.

Not wanting to fool around with Mercury, I tried some glass tube manometers that I made myself way back in the early 60's. I used colored water. Because water is 13.6 times lighter than Mercury, each tube was about 3 feet long. They worked but they were really too long, got broken easily and I found that an 18" piece of old garden hose as a stethoscope was just as good.

See the details how to do this in the 2nd answer above.

Don Elliott, Original Owner 1958 TR3A
Don Elliott

Les
Sorry for long delay in answer (business getting in the way). Don is obviously more familiar with this than I. I did go to a motorcycle/snowmobile dealer and saw in a catalogue this item. Looked like a long ruler but could not tell from picture if "U" tube or not. Interestingly Don it did say Mercury filled! They come in up to 4 measuring units (all one piece). Motorcycles obviously have multy carbs. I look at the one with 2 and its price with CDN taxes was $CDN 140.00 Don read my last posting re this thread and you will see he had to drill holes so as to be able to read both carbs simultaneously. This drilling of holes bothers me and makes it useless to lend to a TR owner so as to do this "real time II sync". Any thoughts on how to adapt this unit to read off the throat of carbs without mod to carbs would be appreciated. Something like an "A" cup (any EEE Holley carb owners no laughing please) might work.
P.S. Any answer to my question re the Idler trimmer screw?
Rick
Rick Crawford

Rick - The two that I made years ago from the long straight glass tubes and rubber tubing were all secured to a piece of plywood about 4" wide and 40"long. I used small "U" clamps over the tubing.

I also cut out 2 plywood pieces using a gasket that goes between the filter and the carb body as a pattern. They also had the same-sized center hole and mounting holes as for the air filter gasket. I also drilled a small hole down through the edge of the plywood pieces to fit another piece of glass to act as a pitot tube, like for measuring air flow in the side-wall of a duct or a venturi which a carb is.

With the filters off, I mounted these contoured pieces of plywood onto the air inlets to each of the carb bodies, connected the rubber hose to one of the top ends of each of the "U" tube manometers, started up the engine and the manometers gave a reading on each carb inlet equivalent to the "hissing" you hear with an 18" piece of rubber tubing. My set-up was so long I laid it almost horizontally (like an inclined "U"-tube manometer) to get the readings.

Don Elliott
Don Elliott

Rick Crawford: Your 11/22 reply asked "Is this procedure of correct mixture adjustment carried out with the screw that one publication calls the idler trimming screw another calls It the mixture trim and the white TR shop manual does not even mention???" As far as I know, the idle trim screw on the front side of the carb was opened a turn or so on new engines only to provide a slightly richer mixture at idle to compensate for the extra friction in "tight" engines. It has no observable effect on broken-in engines and should be left fully closed.

I would still like to get an answer to my 11/21 post on adjusting the air bypass valve for the float condition without having to unscrew the whole thing every time. The bypass valve on my 72 TR6 does not have an external adjusting screw that I've seen on later TR's. I'd like to get my hands on a couple of the externally-adjustable valves and see if they would work as direct replacements.

Yes, the motorcycle world uses multi-sync gauges for carb balancing, but I don't know how much modification would be required to fit SU's or ZS's. Or whether they would buy you much in convenience.

Hope this helps you.

Rick
Rick Orthen

Bottom line...has anyone really compaired the performance difference between the "listening through a tube" method, and the manometer or sychroniser tool method? Or is it a mute point because this does not have to be set any closer then an ear can hear?
I am a firm believer in the KISS method of doing things!
Jim
Jim Kinsella

Jim - I too like to the KISS principle. Except for 2 or 3 times that I used that contraption I described (4 entries above), I have always used an 18" length of hose. I'm so Scottish, I still use the same piece of hose after 43 years that I cut off my father's garden hose (he's the one who came from Scotland). It works great (cannot be quantified), but I get 300 to 340 miles on a tankful (12 Imp. gals or 15 US gals) at 75 mph in overdrive (3000 rpm) on long hauls and I use that old piece of hose to equalize the "hissing". I check it once a year. My TR3A has 1991 cc displacement not like the others which have the up-rated 2138 cc engine. I always get 10% better mileage than they do.

Don Elliott, 1958 TR3A
Don Elliott

An alternative to the Uni-Syn is sold by JCWhitney (www.jcwhitney.com) in Chicago as part number 88NS2792N. This $30. part is advertised as not being flow restrictive (a downside of the Uni-Syn). Does anyone have experience with this unit?

Rick
Rick Orthen

Jim
This thread sure has continued since your original solved problem. OK Jim and Don the KISS approach is always acceptable to me. Maybe if I was racing my 6 then one could say, yes the "full blown" sync of the carbs would help. It would be interesting to DYNO the 2 methods. My only goal is to try to keep the engine running at its' peak performance for a long time and a long quality time. So...you have sort of convinced me on the sync issue. I will, however, use a unisyn tool.
Rick O, I read a MOSS catalogue (Tech tips--Dealing with ZS carbs)and it talkes about these idle trim adjusters and basically says do not touch and is not for air/fuel mixture adjustment. So now I know they do nothing. Read further and it talkes about the bypass valve and also says more or less the same thing..do not touch. Maybe you should just replace the diaphragms. After reading this, it looks like the bypass valve is used in "engine breaking" and really does not need adjusting other than what Jim discovered. Maybe Rick O you and I are lucky we do not have adjustable ones.
So back to where Jim started this thread and the tunning process. My question is ..how de we adjust our air/fuel mixture? This same MOSS Tech Tip talkes about 3 methods (looks like depends on year of your carbs). I know the procedure of lifting the carb pistons and listening to engine RPM changes. Don is a special tool required to adjust the jets down below the piston dampers? Even a special "glass spark plug" can be purchased to get this issue dead on (sorry Don & Jim..had to throw that in here :). How do I determine which method to use to adjust mixture. Don do you have the easy external brass mixture screw? Us later models of TRs do not have it. Don I know this is rather MORE important when doing altitude changes as you have mentioned in another thread. I simply want to tune my engine to best performance (and economy). All help appreciated here guys.
Rick C
Rick Crawford

Rick - I have a TR3A with SU carbs. If you remember, this thread started as an SU carb problem. On my SU's, I have a small tool that is available from Moss and all the others. It is a short (about 2" long) open end wrench stamped out of about 1/16" thick sheet-metal with the opening fixed (about 5'8") for adjusting the brass hex nut on the bottom of my SU carbs. To make it leaner, I crank the nut up which puts the top end opening higher around the tapered needle. This make a smaller annular opening, hence less fuel (leaner). I sometimes remove my air intakes for better access to change the rich/lean settings, but it's not essential. It is also easier with these off, because I can snap off the coil spring that pulls back up on the choke setting after manually going off the choke when starting. This spring gets in the way of the adjusting wrench mentioned above a bit when adjusting for lean or richness. After I got back from Colorado, I pulled the plugs and they are sooty dark brown to black around the edges and a lighter brown on the center tip and near there. I also push up the small plunger on my SU's to check if the richness is correct. I do this after I put the filters back on in case the flow restriction of the wire gauze filter element results in less air going into the carbs than when the air filters were off.

Don Elliott, 1958 TR3A
Don Elliott

Rick C. You asked how to get the mixture adjusted [I presume you're talking ZS carbs here--if we're talking SU's here, disregard this post]. You have to unscrew the dashpot piston on each carb and insert the ZS adjustment hex wrench until it engages the adjustment screw. On the other side of the screw is your metering needle (the jet is fixed on ZS's), so when you turn the hex, the needle moves up (rich) or down (lean) in the jet orifice. When tuning from scratch, I normally turn the hex all the way right (Right = Rich) till the needle bottoms, then left (Left = Lean) two turns. This is usually a good starting point. From there, do the piston lift routine looking for a slight momentary increase in rpm with immediate return to stable idle (850 or so). You have to make small hex adjustments to the needle to achieve this condition. If your rpm drops with the piston lift, then you need to Right = Rich the hex by 1/8 turn increments. Left = Lean if the rpm surges, and so on.

After the mixture's about where it should be by the piston lift, lean the hex just a smigen to account for the paper air filter restriction (not necessary if you did all this with the filters in place). Next, balance the carbs. Hopefully you won't have to readjust the mixture to get equal carb flows.

Drive the car some, and then read a spark plug from the front three and rear three cylinders. Only then will you know the mixture is right. You can also use the Colortune setup as well, but reading the plugs is more convenient.

The problem with the air bypass valves is that you never know if they've been adjusted properly. I know how to adjust them, it's just extremely inconvenient to do unless the adjustment screw is accessible from the outside of the valve cover. I think I've found some used ones that I'll use as replacements.

Rick O.
Rick Orthen

Boy, this thread has gone a long way! Thanks to everyone who has participated. Can someone change the title of the thread to read: "Out of ballance SU carbs. (Actually ZS carbs, not SUs)"
I don't know if it can be done, but it may help others in the future.
Thanks
Jim
Jim Kinsella

This thread was discussed between 16/11/2001 and 10/12/2001

Triumph TR6 index