Genuine help from you experts needed!!

[Forkie]

So firstly Happy New Year to all that may be left on here. Secondly i really do need your help!
To recap - finally got my 2500S Auto back on the road 12 months ago , albut a week or two. Had many a teething problem, most of which i posted up in various sections as applied to ' various' sections - rear luggage light staying on, fuel tank wiring issues, spare wheel tyre size etc - all these issues now sorted. The main issue that i have had from the start - as in returning to the road after 14 years - i still have - a complete lack of top end power/ no acceleration.
I initiallally thought i had an auto box issue. - not changing up into 3rd. Since changing all the worn components - it is so smooth a change up now i have to ' feel' it , not hear it - and yes it is going into 3rd.
So , to be basic,my symtoms are as follows - starts spot on, cold ( with choke) or hot (without choke). Settles down to a normal idle speed. No missfiring. No 'kangarooing'. Drives perfect to 30 mph. Normal temp showing . Push it to 45 /50 - thats when the problems start. No power felt after that speed. No kickdown felt. On a flat road, at 45/50 - floor the throttle - nothing happens. On the road, 45/50 feels like 130 - harsh, with more noise than speed, and just not smooth at all.
As soon as an incline is met - the power just dies, even moreso.
One p.o., now on 48k. Laid up 14 years, although engine was ran periodically. Previous to the lay up , did not show these traits. Dashpots still clean. Oil level in dashpots good. New coil. New battery. Points checked. Valve clearences re-checked. Leads new, but 15 years old. Same with ngk plugs. Auto box oil drained 3 x cycle / new filter. No smoke from brand new full S.S. exhaust system.
Suspected carb imbalance - ok rear bank, weak front bank. Awaiting a ' Gunsons Colourtune ' kit. Plus i intend to do a compression test on the cylinders.
Any thoughts on any of the above would be greatly appreciated.

Regards, Nige.

[johnnydog]

It's difficult to suggest any specific points to check, but...
Sounds like your lack of performance is definately carb related. Have you checked the basics such as the piston movement - that they rise and fall smoothly and freely with a gentle clunk, the operation of the throttle linkages, the kick down cable and the adjustment of the throttle cable, and ensured there is no silt in the float bowls? Whilst in the float bowls, I'd check the operation of the floats, and that they are allowing fuel through when 'open' ie when the fuel demand is greater - easy to check by blowing through them yourself with the top off whilst raising / lowering the float by hand. Have you changed the fuel filter (just before the pump), as that could well be partially blocked - it may let sufficient fuel through for the car to idle, and run at low revs, but then starve it of fuel when the demand is greater. From its period of inactivity, it also could be dirt in the fuel tank that is restricting the metal pipe that exits the bottom of the tank. It may be worth disconnecting it when the level is low, draining the remains of the fuel and before replacing the filter, blowing air through the fuel line between the tank and the filter to ensure no contamination in the fuel line.
Ideally, it wouldn't be a bad thing to strip the carbs down and ensure all us well in that department as that definitely sounds where your issue is.
I've never had a 100% success rate with Gunsons Colortune - maybe it's me, but I find setting them up by ear gives a much more satisfactory result.

[Forkie]

So yes piston movements i have checked, with the lifting pin, both free and 'clunk' back down, although the rear one 'feels ' slightly heavier than the front if that makes sense, but no drag. I also removed them to check for deposits but they are still as spotless as they were when i cleaned them years ago. Both cables checked and appear ok, but i will recheck. Again, regarding float bowls i cleaned them years ago so i would not expect anything in them but again will recheck. New filter and n.o.s. pump so again all clean. Fuel tank was emptied many years ago and has had no fuel in until she went back on the road, looked fine inside when fitted new sender unit. Fuel line had been plugged both ends whilst dormant. So as it looks, all fuel system looks, and should be clean ( whilst laid up engine was being run from a new fuel can, and always let the carbs run out of fuel so as to not leave fuel go stale inside).
So i dont think the issue is dirt. But will look at the floats. I have never used the Colourtune, it has been suggested to at least give an idea which as to each carb maybe ok or not, as not sure if rear one rich or front one lean. Now its on the road-ish , the plugs indicate that the front maybe lean.
I am puzzled in that i know years ago i removed all that side of the engine to renew all gaskets and the metal link pipe under the manifold, but kept it all together as such, and not making any actual adjustments to the carbs, and it wasn't like this before. I am wondering if i have not put some part of the linkages back quite right, but all appears ok. Seems like a lot of re-checking may be a good idea....

[Forkie]

What size is the nut for the mixture jet under the carb - just before Christmas i was having a look see and thought i would sus out what size spanner i needed - which led me to this question - how do you guys get a purchase on it? I tried everywhich way to get something on the rear jet and whichever position/ angle i tried i got nowhere. I assume the elephants trunk has to go for starters? I tried turning with finger and thumb but could not budge it.

[johnnydog]

Yes, any adjustment to the mixture really neccitates the removal of the 'elephants trunk'. Otherwise its like trying to decorate your hallway through the letter box...
You should be able to turn the mixture adjusting flats quite easily with your forefinger and thumb; no need to use any type of spanner. If you can't, I would say you need to investigate why.
Visually, whereabouts is the top of the jet relative to the bridge?
I take it you checked the piston raising and falling with with your finger and the damper removed? Doing it by the lifting pin doesn't really allow for much movement. You could try slackening the three screws a little on the dash pot of the 'stiffer' carb, and although there isn't much jiggle room, a miniscule movement can make a lot of difference to the free movement of the piston. And when nipping them up, try a little tightening it by bit in sequence until tight (ish). Although they aren't as sensitive as Strombergs in this respect, but it's worth doing rather than tightening each screw fully at once.
If someone has been in there before, could they have odd / unmatched springs?

[Forkie]

No way i could get any movement on the big jet nut by thumb/finger. And i take it when you suggest to raise the piston with finger i assume you mean through the opening when elephants trunk is removed? If so no, everything is still ' together' at the minute, when i have the Colourtune in my hand i will then allow a whole day and try and go through all the suggested things, and more, to try and gain some ground on it. I think doing a bit here and there may not be helping. I will measure the springs as well.

[johnnydog]

Not questioning anything you've've said in any way , but I am assuming of course you are trying to adjust the mixture using the correct part of the carburettor?
The green arrow is the mixture adjustment, whilst the red arrow is the securing nut for the jet assembly to the carburettor body, and once the jet is fitted, doesn't need to be moved.

I asked re the position of the jet relative to the bridge to give an indication of the adjustment setting currently.
As a very rough starting point prior to any adjustment, the jet needs to be approx. 1mm below the bridge on each carb, but if you can't move the mixture nut up (anticlockwise as looking from above to weaken) or down (to richen) indicates excessive wear to the jet / needle, and they ideally need to be replaced. If the hole in the jet looks anything other than round, then they are both worn (this occurs in part due to the spring loaded bias of the needle).The throttle and choke linkages need to be set up equally, and the air intake balanced prior any mixture adjustment is carried out.

[Forkie]

John - no offense taken at all. You are the guys that have run these since new, you know what you are talking about, i would much rather be called a clown and get things sorted!!!!
But yes, the lower nut - green arrow - IS the one that i have tried moving by hand , which will not budge ( i have only tried the rear, not the front , jet nut). I was brought up on S.U. carbs, with Austin /Morris variants, and got my head around them ' back in the day' as a youngster and was able to ' keep them going' but they were always in single form. 30 years later , i find myself back with S.U.s but in twin form - i think that might be the issue here !!! As in setting a pair up together.
I do think my issue here is as i previously mentioned , as i have not ' altered ' the carbs in any way since was last on the road, but merely ' removed them' - have i not fitted the linkages etc back as they were ....
But again, you have given me more info for more checks. I may be tempted at the weekend to pop the tops off again and look at the bridge settings, although its gone blxxdy cold out there now!!!!
As an aside - when i removed the dashpots a couple of days ago and withdrew the piston and jet, the jet on BOTH looked everso slightly off center - like a very slight bend in them both. Not sure if that is normal. 30 years ago is a long time to think back to

[johnnydog]

The visible top of the jet on the carburtettor bridge is rarely 'dead central'. Usually when the jet is assembled in the carb, it is centralised relative to the piston and needle position during the gentle nipping up of the nut (red arrow) whilst continously raising / lowering of the piston. When you removed the tops, I presume you mean piston and needle rather than piston and jet? The needle does lean to one side - it has a sprung bias to one side which is one reason why the jet wears 'oval'.
I'd be tempted to take both carbs off the inlet manifold, bolt them to a thin strip of wood (utilusing just two of the holes) to keep them rigid and complete with the linkage in situ if you prefer, and investigate why the adjustment nut is solid. They are easier to work on as a pair with a support, and to work on the jet area whilst supported. Otherwise deal with each carb individually whilst separated from the throttle and choke linkage.
Sounds like you really need to strip them down for a clean / check over.

[Forkie]

Yes i deed indeed mean piston and needle ah so slightly bias to one side - the needle (!) is normal - thats something anyway! Ok so the jet nut should be free enough then to be able to be turned by hand , so that is of concern as you say. Cannot see why it appears solid, they are really clean with no horrible age related build up of rust or crud . I like the idea of removal and bolting them to a piece of wood - makes perfect sense. I think i will definately remove the tops again over the weekend, check the spring heights and have a look at the jet to bridge positions, and for ovality ( in that instance i assume you mean the hole in the center where the needle drops into). I will also see if the front jet is movable whilst there. At least if i do that and report what i find with those checks it may give some more info.
Would you expect issues of serious wear at 48,000 miles? I cannot see them not being the original carbs that were fitted at the factory.