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View Full Version : TR6 Depth of the metering needle in the air valve piston



Got_All_4
02-18-2017, 01:31 PM
Last winter I installed new dash pot seals in my Stromberg carbs. Since that time I've been running lean despite that I turned the adjustment to full rich. I need that proper distance to set in the needle. One of my customers told me that his father made a tool that slipped over the metering needle then smack it with a hammer to set the proper depth of the measuring needle to the top of the air valve piston. He never had any issues with tuning his cars.
We are having a record warm weekend for 4 days in the 60s (already had the TR7 out this morning) and was going to try to make one of those tools today if I can get that proper depth. Mine are flush to the top of the piston. Unfortunately his father has passed and the tool never found. Also I don't have a Stromberg manual.

poolboy
02-18-2017, 07:48 PM
For a fixed needle the normal position is flush with the bottom of the air valve.
I guess you'll have to do some experimenting if you want to vary from that depth...You may even have to shorten the needle carrier.

Got_All_4
02-18-2017, 08:31 PM
These are the adjustable needles. How far does a needle move from full rich to full lean?

Merlin63Tr4
02-18-2017, 10:50 PM
Have you seen this article, it might prove useful.
https://www.bowtie6.com/other/zenith-stromberg-carburetter-repair/

M.

poolboy
02-18-2017, 11:07 PM
These are the adjustable needles. How far does a needle move from full rich to full lean?
When you can no longer turn the adjustment screw clockwise, that's the maximum richness.
I should add that once fully clockwise (rich), you can only turn the adjustment screw counter clockwise(lean) 2 and 1/2 rotations 'safely' .
I say 'safely' because at that point, the needle carrier is hanging onto adjustment screw by less than a full thread and any more counterclockwise turns will disengage the threads..

Here's the components you are dealing with...notice the # of threads on the adjustment screw....about 1/8 of an inch is all you have to work with from full rich to full lean.
BTW, on the far right you'll see the adjustment screw with the shank of the allen wrench adjustment tool inserted into the adjustment screw.
https://i233.photobucket.com/albums/ee300/poolboy_album/TR6NEEDLE2001.jpg (https://s233.photobucket.com/user/poolboy_album/media/TR6NEEDLE2001.jpg.html)

poolboy
02-18-2017, 11:21 PM
Here's the 2 piece adjustment tool along with the carb's air valve that has been removed from the carb for picture taking. The diaphragm has also been removed.
https://i233.photobucket.com/albums/ee300/poolboy_album/TR6CARBADJUSTER003.jpg (https://s233.photobucket.com/user/poolboy_album/media/TR6CARBADJUSTER003.jpg.html)
And here you'll see how the barrel of the tool engages the air valve. Hold the barrel tight so that the air valve can not rotate as you rotate the allen wrench... If the air valve rotates, the diaphragm will probably rip open.
https://i233.photobucket.com/albums/ee300/poolboy_album/TR6CARBADJUSTER001.jpg (https://s233.photobucket.com/user/poolboy_album/media/TR6CARBADJUSTER001.jpg.html)
https://i233.photobucket.com/albums/ee300/poolboy_album/TR6CARBADJUSTER002.jpg (https://s233.photobucket.com/user/poolboy_album/media/TR6CARBADJUSTER002.jpg.html)

Got_All_4
02-20-2017, 12:20 AM
Ok thanks the articles were helpful. I inserted the allen tool and was able to engage the threads and pull the needle up to full rich. I've got to wonder if it was ever engaged in the first place because this came from the middle carb which I was never able to richen up. Going to have to start over and pull all the pistons and go to full rich on the other 2 needles. Then hook up the color tune and slowly lean it out.

poolboy
02-20-2017, 11:35 AM
Using the colortune you'll probably want to see it indicate a little rich when idling ...if you get a blue flame at idle, you'll probably be too lean for it's own good at high speed under load such as when you are actually driving your car as opposed to reving it up in neutral while observing the colortune's reaction.
On my rebuilds I set the needle in the middle of it's adjustment range (1/1/4 ccw from fully cw), which suits most engines; but I include a note suggesting to drive 300 miles as is, then pull the plugs for mixture evaluation. I also ask that the last 50 miles the rpms kept 2000 or higher even if it means using lower gears and by all means avoid stop and go traffic and idling as much as possible during that last 50 miles.
From the mid point that the needle is set, you'll have the option of raising or lowering the needle as much as 1/16 of an inch to zero in on the sweet spot.
There's usually very little, if any, change required, at least according to the feedback I get.

Roger
02-20-2017, 01:58 PM
Then, of course, there's the height of the jet in the carb body, which from my observation can be variable.
I've just rebuilt the 175s on my Lotus Europa TC, and have set the new jets outer diameter flush with the carb body. The car ran a bit rich before the rebuild, and the jets were different heights. We'll see how we get on once it's running again.

poolboy
02-20-2017, 05:16 PM
There's usually no need to have both adjustable needles and adjustable jets, but if one feels the need or desire there's this:
https://i233.photobucket.com/albums/ee300/poolboy_album/ZS%20adjustable%20jet%20001_zpskfwqfgrn.jpg (https://s233.photobucket.com/user/poolboy_album/media/ZS%20adjustable%20jet%20001_zpskfwqfgrn.jpg.html)
Plus there's a fairly decent selection of different needle profiles for the ZS carbs...maybe not as many as SU carbs, but there are close to 100 listed, although not all are considered 'adjustable'.
In reality, it hasn't proven difficult to work with the B1AF needle and a fixed jet in the TR6 engines...that's about the extent of my experience although YMMV.

Got_All_4
02-21-2017, 01:19 AM
I'm hoping there isn't much difference from before I changed the seals out. Id did each piston separately so not to mix up the parts. I've probably got 15k on the rebuild and the engine ran awesome. last 2 time I used the power tune I had a hard time seeing the flame.

poolboy
02-21-2017, 10:05 AM
The ZS carbs don't rely on matched bodies and air valves like SU's. The difference is the diaphragm that the SU's lack, rather SU's depend upon the annular space to 'contain' the depression...It's that space that generally needs to be preserved by keeping the SU air valve matched with the SU body.

Anyway, as far as mixture, start in the middle, then evaluate.

Got_All_4
02-22-2017, 12:46 AM
Yep I remember doing the timed drop test for my SUs. Anyway put everything back together tonight. The front carb was almost at full lean. Took some effort to turn the mixture tool but went all the way to the top and backed off a half turn. Took for a 12 mile ride. Much better. Idled fine now but had some slight missing upon acceleration. This spring I'll start over with balance and tune up and get it dialed in.