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TR6 Running Rich - next step?

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Stan '75

Stan '75

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Thanks to everyone who assisted with getting my replacement fuel pump installed and connected. I've replaced the fuel filter and confirmed fuel is getting to the carbs. Starting with the metering needles at 1 1/4 turns off lean, I could not get the engine to stay fired. Moving 1/2 turn clockwise (lean), the engine will run extremely rough for 4-5 minutes. It will immediately stall if I attempt to add any throttle. I dialed the needles clockwise (lean) until they stop and while the engine improves slightly, it still will not stay running with any additional throttle. It also will not start with any choke. My idle rpm is around 250 and any attempt to adjust the idle screw causes the engine to stall. I cannot adjust any more lean and am out of ideas. Have I supplied enough data for your thoughts? Thanks in advance!
 
No tears in the diaphragms?
 
If those are ZS carbs with adjustable needles turning the needle adjustment screw clockwise raises the needle which makes the mixture richer.

To find the middle of the adjustment range which is the best place to start. Using the adjustment tool properly, turn the adjustment screw clockwise until it stops, then turn it counterclockwise 1 and 1/4 turns.
NOTE: If you turn more than 3 and 1/2 turns clockwise and have not reached a stop, then at some point in your fiddling the needle carrier and the adjustment screw have become disconnected.
 
All good ideas so far. Also the possibility of a stuck Grose-Jet ball valve or a needle and seat, depending on what's in there.

With the air cleaner off and the car running as best it can, put your hand over each carb's air intake one at a time, gradually, to see what changes, if anything. Speeds up, bogs down, stalls out, or nothing. Could narrow it down to a single carb being the offender, although this method tends to work better when the fuel supply is too low rather than too high.

I admit to being rusty and may be off-base here, haven't had fuel problems in more than a few years!
 
poolboy said:
If those are ZS carbs with adjustable needles turning the needle adjustment screw clockwise raises the needle which makes the mixture richer.

To find the middle of the adjustment range which is the best place to start. Using the adjustment tool properly, turn the adjustment screw clockwise until it stops, then turn it counterclockwise 1 and 1/4 turns.
NOTE: If you turn more than 3 and 1/2 turns clockwise and have not reached a stop, then at some point in your fiddling the needle carrier and the adjustment screw have become disconnected.
Click to expand...
Thanks. The stops seem to work fine and I start from the 1 1/4 starting point. I will doublecheck the adjustment screws.
 
BritBox said:
All good ideas so far. Also the possibility of a stuck Grose-Jet ball valve or a needle and seat, depending on what's in there.

With the air cleaner off and the car running as best it can, put your hand over each carb's air intake one at a time, gradually, to see what changes, if anything. Speeds up, bogs down, stalls out, or nothing. Could narrow it down to a single carb being the offender, although this method tends to work better when the fuel supply is too low rather than too high.

I admit to being rusty and may be off-base here, haven't had fuel problems in more than a few years!
Click to expand...
Britbox, I will try that next. Narrowing the carbs down is a great idea. After that, I guess I am tearing them down again! Thanks!
 
It seems to be SOP for the kits to not include the one part that has the most problems. Heaven save us from complete kits
that solve the problems and complete the job!!
Mad dog
 
mctriumph said:
It seems to be SOP for the kits to not include the one part that has the most problems. Heaven save us from complete kits
that solve the problems and complete the job!!
Mad dog
Click to expand...
I know this has been discussed before and opinions vary but aren't SU's just way less problematic than Strombergs? I heard someone mention that at a car show 8 out of 10 TR6's there had switched over to SUs :unsure:
 
karls59tr said:
I know this has been discussed before and opinions vary but aren't SU's just way less problematic than Strombergs? I heard someone mention that at a car show 8 out of 10 TR6's there had switched over to SUs :unsure:
Click to expand...
Interesting. I just received the 2 new floats I ordered. I'll install and advise. If not, perhaps SU's are in the future!
 
karls59tr said:
I know this has been discussed before and opinions vary but aren't SU's just way less problematic than Strombergs? I heard someone mention that at a car show 8 out of 10 TR6's there had switched over to SUs :unsure:
Click to expand...

I, too, have heard for many years that SUs were less troublesome. Never owned any, was always curious about them. I rebuilt my TR250's ZS carbs during the car's restoration in the late Nineties. As a Brit car newbie, I struggled with tuning (and synchronizing!) the carbs when I reinstalled them, but finally got 'em done. I never touched them again for two decades and about 50k - 60k miles, until 3 years ago the front carb got a stuck Grose-Jet valve and dumped gas into the engine -- yes, I changed the oil afterwards! Anyway, my own personal experience with Zenith-Strombergs reliability is very good, but probably because I've been lucky, and not a fuel system whisperer. Just one owner's very limited perspective.
 
I guess I've tested hundreds of floats from ZS carbs..I put a lead weight on them and drop them into the deep side of my swimming pool where they remain submerged for 2 sometimes 3 days while I'm working on the carbs they came from.
Only 3 in memory failed that test where they are recovered and put back unweighted in water to check for buoyancy
Here's a picture of 2 that failed. Notice the bracket goes into the float unlike the old reliable versions
ZS carb floats 002.JPG
If there is anything FLOAT related that is likely to cause a problem its the mounting clips for the float pivot pin.
This picture shows how I make that repair...notice the 2 screws where they used to be staked.
They are staked onto the carb and I find them broken loose from the stake much more often than a bad float.
TR6Bracketrepair001.jpg

BY FAR the component that causes more problems in the float chamber is the needle valves and Grose jets.
 
Photos are very helpful. Thanks Poolboy. New floats are installed. Today I'll fire it up and hopefully dial it in! Stay tuned...
 
If you are replacing the floats, you'll need to set the depth (height) and to do that accurately the carbs need to be upside down on the work bench.....without the gasket about 17mm from the rim of the float chamber to the highest point on the float.
ZS carb floatheight.jpg
 
I have fuel coming out of the front carb at the port that goes to the carbon canister. Sorry I don't know the name of this port. Should I assume the float is not properly shutting off the fuel when full and this is overflow out of the float chamber?
 
Yes, but the float may be doing all it can do...Usually it's the needle valve that is resisting the efforts of the float to shut the valve.
Try this:





  • Disconnect the fuel line at the carbs and plug them or use a cut off valve.
  • Start the engine and let it run until the carb runs dry.
  • Insert the red extension tube of whatever solvent you have into the carb's fuel inlet nipple. It does not have to be carb cleaner. WD40, PB Blaster, just about any aerosol will do.
  • Blast away but be aware that most of the solvent will come shooting back at you.
  • Be persistent. Blast them again now that you know what to expect.
  • While blasting, tap lightly but rapidly with a metal object such as a box end wrench on the wall of the float chamber in order to set up vibrations.
  • Feel free to follow up with a 20 # shot of compressed air
  • If you are lucky you will loosen up the needle valve.
  • If not, you should completely remove the carb and open the float chamber and treat or replace the needle valve and check for loss of buoyancy of the floats...that can exhibit the same symptoms.
  • If you do have Grose jets, skip the procedure I first described and just go ahead and replace them with the original plunger type needle valves.
  • Unless you are a dentist I would not recommend trying to take a shortcut by attempting to remove the float chamber and needle valve with the carb 'in situ'.
Click to expand...
 
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