Carb Needle Conundrum

[Bryan Boyle]

OK...conundrum time for me. 

I'm planning on doing a complete overhaul of my carbs; I did the diaphragms and most of the gaskets a couple years ago to get the buggy running, but figure it's time to do a complete strip down, soak in a carb cleaner bucket, blow out, and replace everything including that funny little o-ring on the needle adjustment screw in the air valve.  It's sucking the oil out of the dashpot, so, guess it's past its sell-by date.

Have a set of Joe Curto's rebuild kits, updated floats, new viton o-rings for the modified secondary-to-head, base, and lots of spare gaskets.

So, currently running euro needles, but picked up a new set of the fed needles (photo below).  Going to try these and see how they work.  The euro needles are in good nick (they were new and came with the car and I used them to get the car running initially), so can go back to them if these aren't to my liking.

So, what's the conundrum?

All the instructions (hard copy, youtubes, web searches) say, as the primary setting, to have the base of the needle even with the bottom of the air valve.  So...do they mean to have the teflon (assuming that's what it is...) washer (indicated by the red arrow) even with the base of the air valve, or the brass sleeve (indicated by the green arrow)?

Thoughts?  I realize this is down in the weeds...but...fiddled around with it last time (the euro needle set I have has the washer, too), and have never really been satisfied with how the carbs run (no, didn't replace the butterfly shaft seals last time...built the tool in the workshop to set the seal this time...)

TIA.

[jbcollier]

That’s a very lean needle (not much visible taper).

I’d ignore the plastic washer myself and fit the bottom of the brass holder flush.

You will also want to:

Check the throttle shafts for play.  If there is play, change the bushings and shafts.  These are CRITICAL.  If there is a lot of play, change the throttle butterflies as well.

Check the valve adjustment.  Tight valves mean you will never get it running right.

Seat the idle bypass screw.

Seal off the accell valves by making a gasket with no holes except for the retaining screws.

I would convert to adjustable needles using dashpots from a US TR6 or TR7.  If you do so then setting the needles is a breeze.

Get it running. Warm it up.  Check the throttle sync.  Once it is close, check your idle mixture.  Use a small screwdriver to lift the dashpot 3 to 5 mm.

Engine revs up a bit and stays up = mix too rich, lower the needle.

Engine immediately falters = mix too lean, raise the needle.

Engine briefly revs up a bit and then falters = perfect idle mix.

The needles are spring loaded to one side so the needle constantly rubs against the needle jet.  It doesn’t take much needle jet wear and it hard to set up properly.  If the needle jets have not been changed, just change them.  This proceedure is not in the manual.  You HAVE TO HAVE A PRESS, you can’t knock the out.  Mark the needles orientation as some are handed (not on the TC IIRC but still good practice).  Measure the needle jet depth from the bridge.  It should be 3.00 mm ± .05 (yes, it is THAT exact).  Carefully and slowly press it home checking its depth frequently.

[Fotog]

Slightly off-topic, but John, when you mention "tight valves", can you clarify?  I ask because if the clearance measured between the cam lobe and the valve tappet is tight, the valve itself will be, let's say, opening more fully, or "not so tight".  And vice versa.  For me, there's a possibility of confusion, and I plan to go through things completely soon to make sure my tuning is optimized.

I guess that tight valves means to adjust for clearances cam-to-tappet on the high side of the range.  Exhaust is specified as .009"-.011", and I should shoot for the .011".  Correct?

Can you elaborate on just what we're trying to achieve?...more certain closing or opening of the valve?

-Vince

[jbcollier]

A “tight” valve has less than the specified clearance.  You are right it will open a bit more and for a bit longer.  That means it will be closed less which affects the intake vacuum which is critical for a proper idle with constant depression carb.

[Fotog]

Thanks.  I understand that we want clearances cam-to-tappet at the high end so the valve closes more fully / longer.

Vince

[Bryan Boyle]

That’s a very lean needle (not much visible taper).

I’d ignore the plastic washer myself and fit the bottom of the brass holder flush.

You will also want to:

Check the throttle shafts for play.  If there is play, change the bushings and shafts.  These are CRITICAL.  If there is a lot of play, change the throttle butterflies as well.

Check the valve adjustment.  Tight valves mean you will never get it running right.

Seat the idle bypass screw.

Seal off the accell valves by making a gasket with no holes except for the retaining screws.

I would convert to adjustable needles using dashpots from a US TR6 or TR7.  If you do so then setting the needles is a breeze.

Get it running. Warm it up.  Check the throttle sync.  Once it is close, check your idle mixture.  Use a small screwdriver to lift the dashpot 3 to 5 mm.

Engine revs up a bit and stays up = mix too rich, lower the needle.

Engine immediately falters = mix too lean, raise the needle.

Engine briefly revs up a bit and then falters = perfect idle mix.

The needles are spring loaded to one side so the needle constantly rubs against the needle jet.  It doesn’t take much needle jet wear and it hard to set up properly.  If the needle jets have not been changed, just change them.  This proceedure is not in the manual.  You HAVE TO HAVE A PRESS, you can’t knock the out.  Mark the needles orientation as some are handed (not on the TC IIRC but still good practice).  Measure the needle jet depth from the bridge.  It should be 3.00 mm ± .05 (yes, it is THAT exact).  Carefully and slowly press it home checking its depth frequently.

All good suggestions, JB.  I'm thinking, at this point, these might be due for more attention than I can devote...especially when considering the probably wear on the jets, etc., over the years.  I don't see any maintenance receipts in the voluminous records I have stretching back to the delivery of the car to the original owner...so thinking that perhaps sending the carbs off to Joe Curto for a complete overhaul may not be the worst thing.  Side benefit: will force me to attack the other pending tasks (clutch, head gasket, transfer tubes, rear suspension) since the car will be laid up for a couple months while the carbs are in process.

Only question is whether I wait till after the Brits at Bristol show this June to start the tear-down or bit the bullet and miss the show this year.  Decisions, decisions...

[2766R]

Bryan, You will not be disappointed if you send them off to Joe Curto.  A bit pricey but well worth it!
Had mine done back in 2015; no problems to date.  Bypasses all the emissions nonsense.  I have adjustable needles, done back in the day.  I'm sure Joe can hook you up with that mod as well.  They looked brand new when I got them back.  He's not terrible far from me so I dropped mine off and picked them up.  Quite the affable fellow, old school shop but an artist!  Some pics:

Gerry 2766R

[Bryan Boyle]

Bryan, You will not be disappointed if you send them off to Joe Curto.  A bit pricey but well worth it!
Had mine done back in 2015; no problems to date.  Bypasses all the emissions nonsense.  I have adjustable needles, done back in the day.  I'm sure Joe can hook you up with that mod as well.  They looked brand new when I got them back.  He's not terrible far from me so I dropped mine off and picked them up.  Quite the affable fellow, old school shop but an artist!  Some pics:

Gerry 2766R

WOW.  Now, that's what I call nice. 

Not worried about the price...good results make the price worth it.  I could spend days fiddling with it, but, I talked to him yesterday, and he seems to hit all the right buttons.  When I described what was happening with my set, he zeroed in on worn jets and clogged passages (which, considering the crap they pass off as gasoline these days versus what was around in the 70s with varnish deposits, oxygenates, and such isn't surprising) as the main cause.  I forgot to ask whether he put them on a flow bench to at least set them up alike to give a baseline when I reinstall, but, pretty sure he'll match them as close as possible...

He has a good rep...which the turn around time indicates that he's not grasping for business. 

Next on the list is sending out my S2 master cylinder for overhaul/resleeving/modificataion to use remote reservoirs.  Figure Apple Hydraulics is a better choice from what I hear vs White Post.