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Keeps running lean!

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Norton47

Jedi Warrior
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My 1974 TR6 rebuilt to stock spec engine has had a problem in that it wants to run lean. I used up all the clockwise adjustment in the needle and still lean.
Double checked for vacuum leaks and no really finds there.
I talked to a local Triumph shop and they say common problem.
They want to plug the bypass and plug the Idle trimming screw.
Then push the metering jet down into the body to richen it up.
But I don't know anybody else had to do this type of fix?

I tried the spacer fix that is in the Buckeye article on the WIKI and seem to have made some progress, I see black and sooty and dark brown on the back 3 and still to white on the front 3.
I added a 1/2 turn and will check on the way to work tomorrow.
Any other carb secrets to try?
 
Some of the folks who have non-adjustable needles find that the way to adjust mixture is to adjust the float height; might work for you.
If you feel like even more experimenting, you could change the diameter of the needle with emory cloth.
I'm not sure blocking the Throttle Bypass Valve would help, because it just taps whatever mixture that is in the mixing chamber part of the carb and slips it past the throttle disc. If adjusted properly it shouldn't be open, anyway, except during decelreation
If you screw the idle trim screw down all the way it will close off what very little air it taps off an open temperature compensator. That has so little effect on mixture, the book says you need a CO sensor to observe it's effect.
Are the carbs in sync, throttle shaft-wise ?
 
I have blocked off the bypass valve, but nothing with the idle trimming screw. I also snugged the tiny nyloc nut down inside the temperature compensator. These adjustments were to solve a high idle problem.
The diaphragm in the bypass valve can wear out allowing air to leak, causing it to run lean.
Just buy some gasoline compatible gasket paper(available at auto parts stores, it is usually a heavy black material) and outline the existing gasket for the bypass valve, also mark the mounting screw holes. Cut it out and punch or drill the screw holes. Reinstall.
 
I rebuilt the bypass valves and they both seemed to set up ok. I have them backed off now. neat trick on the gasket paper.
I think the bypass valves are just a possible vacuum leak that could affect the mixture.
Block anything that might be possible to allow extra air into the mixture is that shops practice.

I ran the car into work today. No longer white but still not brown or tan. A dark gray. This is with the spacer in and the mixture screw all the way clock wise. The spacer lifts the needle by it's thickness which is .060. It will lift the needle high enough it could raise above the screw that keeps the needle from turning.

As the Previous owner had various carbs on here, I am wondering if the main jet has been messed with. What is stock?
 
Another source of air leakage is the throttle shafts may be worn and bad seals.Spray some carb or brake and parts cleaner around the shafts bushings and anywhere else you suspect an air leak and the rpms will change if there is a leak.
 
Thanks for the stock number, that matches what I have. I have tried the leak check and it passes. I did have to replace the shaft seals though.
I took the carbs apart tonight and the metering needles are not marked. They seem to be undersized and have some wear marks on them. The book and TRF say they should be B1AF and 1/8" down from the shoulder they should measure .953 or so. These are .920.
So you would think it would be running rich. I did finally get it to run rich, but it just went way rich. This is with that spacer in to lift the needle.

Anyway got parts on order. Trying to decide if I should take the TRF and local shops advice and move the metering jet down to .125" below the bridge and install the stock needles.
Also wondering if I have a slight leak in the water line that heats the intake. The water level has never changed but all plugs being lean all the normal adjustment range and then some with undersize metering needles does not make sense.

I have isolated all accessory vacuum. The intake was surfaced and new gasket used when installed. I dunno, keep plugging away at it.
 
How do you know you are lean? Does the car sputter as if it is running out of gas? If you are lean, the motor will let you know right away. Are you using an AFR gauge to know how lean you are? Before you go out there to fix it, you should find out how far off you are. You may have to take the car to a dyno so that you can be told under rolling road conditions exactly what the carbs are doing.

I could be wrong.
 
I thought I was running lean, the AFR meter said otherwise. I would like to have a set of ZS's that run lean. All the people I talk to, and me, they are running rich. You set the needle for the right mixture at idle. Then, if you are running rich going doing the highway, you are running rich. You do not set the needle for the right mixture going doing the highway, or at full power, you set it at idle, and then find or make needles that are right at cruise, full throttle, etc. I think you will find yours is the same. I wouldn't even bother lowering the jet, I had to raise mine back up. There are not many needles available for ZS's. Lowering the jet does not change the steps on the needle, so you will still be wrong somewhere. You need to fork over 300 bucks for the meter. But, you can't really get the right needles, so, where do we go from here? WEBERS or EFI, or HS6's
 
I will try and answer both of the last posts with this one.
First a question, for Searcherman, how did you raise your jets back up? I understood it is a one way trip. Down only.

I have been attempting to read the plugs. Do a drive over varied conditions, I have a 6 mile loop that includes up hill and down and a nice straight away. I stop the engine and declutch and pull over and pull the plugs. Usually 2,3,4,and 5.
Until the last couple times they always seem to be dead white.
Plugs are NGK BR6ES.
I did block off the bypass valves, and I replaced the needles as the ones installed were B1E's if I remember right. When I put the carbs back on, it wouldn't run hardly and when I tried to rev it, it backfired. Never had that happen. Started over looking for vacuum leaks. I noticed the 2nd and 3rd footballs were not located in the dimples of the intake manifold ears. So I loosened them and moved them and retightened. Now it would run and no backfiring. I still seemed to be running lean. I put the old needles back in as they are a smaller diameter. Lets in more fuel. They both run richer but the front 3 cylinders still are only getting to a dark grey while the backs are black and brown.
Put on a vacuum gauge, still under 17, kind bounces just like this one depicted on this website for poor rings.
https://www.therangerstation.com/Magazine/Summer2003/VacuumLeaks.htm
I got a new intake exhaust gasket and while talking with my guru, I sounded like I have probably over tightened the manifold fasteners. I pulled them off and found I have one broken football flange and one cracked one on the front two attachments for the exhaust manifold. Replaced installed the new competition gasket, which is much thicker and has no metal surface, carefully tightened the fasteners evenly working from the middle out. Shimmed the exhaust pipes to relieve some loading they were putting on the exhaust manifold.
Started it up and same vacuum reading. This is with all vacuum ancillaries blocked off. Reading is still under 17 and bounces like before. No change to the carb.
I also checked the output of the fuel pump which I just rebuilt. I did not have a gauge, but it pumps out steady flow and will push against a restricted hose. I would judge it would make a couple psi. I do wonder about the check valve. How long it would hold pressure.
As all of this was to get the car ready to go on vacation, I finally threw in the towel Thursday night at 10:30 and we left for Montana, Friday morning leaving the TR6 in the driveway.
I am contemplating the AFR gauge, I already have the bosses welded to the down pipes. I installed some narrow band AFR's but haven't had much luck getting good readings. They always say rich .8 to .92 when the plugs show white. I am also bidding on a snap on vacuum fuel pressure gauge as the vacuum gauge I have is of dubious quality. When I get back I will start over and figure this out.
 
Norton,

According to the Stromberg chart, the B1E should be much richer than the stock B1AF as it is a smaller diameter needle. What did you replace the B1E's with?

What is the base timing set at?

Did you spray the intake area and around all hoses, including booster hose with carb cleaner to see if the idle went up, as in vacuum leak time?

Just a few things to check when you get back. Enjoy your vacation. It will work out.
 
I fashioned a mandrel to support the carb body on my press and came up with a washer that just fits the shoulder of the larger diameter of the jet body, I then found an old alternator spacer that fits over the small jet protrusion diameter onto the washer. Now, I could gently press the main jets back in the upward direction.
 
Paul
I tried B1AF's but got a very lean condition.
I put the B1E's back in.
The brake booster is disconnected and the port plugged at manifold. I replaced both of those fiber washers and checked that fitting for tightness and leaks.
Base timing is set to stock number so it retards to 4 degrees ATDC if I remember correctly.

Yeah I am enjoying it, I did need a break before going back to the fray.

Thanks
 
I flattend a bolt head, and gently tap the jet in either directions, and I use a digital caliber to see where it is at. I have to remove the carbs to bring it back up. The problem is not the jet height, it's the needle profile. Anyhow, I think you need to cough up the 300 bucks for an A/F meter. And, the best gasket is a Payen. Anyhow, you are not going to get anywhere without the meter. Write the check dude. Plug cuts are for racers with years of experience, and then some more years. The thing is, once you see where you are, what are you going to use for needles? I have mine running good, however, I could make it alot better with a needle selection. I think I'll either do EFI, or webers, next month, we will see. I don't see any reason to go with EFI, if other people get Webers set up right, so can I, with the A/F meter. Webers look so cool............ And, the Repulican Party is lowering the price of gasoline so we will vote for them, and then, after the election, it will go to the moon.
 
I paid 3.62 per gallon yesterday.... thought it was a deal.... til I remembered that gas is ten cents per gallon in Saudi Arabia..........
 
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