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The tall brass tubes fitted to the 40IDS is generally referred to as a 'Booster Jet' it is a high speed enrichment circuit that functions at the higher engine speeds that were part of the 'S' specification compared to other early models.
The Accelerator Pump Jet is a small Aluminium Casting and there are two different designs depending on the type of carb.
The difference is the 'nose' length and they will have no impact on basic balance or idle.
The Accelerator Pump is the part of the carb fitted with the rubber diaphragm on the centre of each body.
Have you disconnected the drip links form the main transverse bar on the linkage?
The idle screw will then operate on all three chokes simultaneously so it is worth checking that all 3 throttle plates are fully closed when this screw is would fully out.
It can be quite tricky to set the ‘coupling between the two throttle shafts correctly.
The Air ‘Bleed’ or ‘Compensating Screw with the Lock Nut ( I think PMO call these idle air corrector screws) for initial set up is best screwed in until the just lightly touch the seat and locked. This will giv a slightly rich mixture for initial start up.
I would set the Idle Mixture Screw about 1.5 turns out.
The engine should start and you them want to adjust the idle screws so it will run and warm up.
You can then make a start on setting the Idle mixture screws and balancing the carbs.
Once it is idling check to see if any of the barrels is ‘spitting’ and open the mixture screw gradually until it stops.
Once the cylinder has stopped spitting I would open the mixture screw about another 1/8th of a turn.
This should mean that the Idle mixtre screws are wound out between 1 3/4 and 2 1/2 turns – more than 3 and it may need larger idle jets.
When all the cylinders have stopped spitting increase the engine speed to around 2500-3000 rpm.
Check the air flow with a synchronometer and balance the flows. I would find the cylinder with the greatest flow and open the Air Bleed Screws on the other cylinders to achieve equal flow on all 6 cylinders.
You may need to go round this procedure more than once as opening the air bleeds will affect the idle mixture settings and this needs to be dealt with carefully.
I would then slow it down to around 1200rpm and re-attach the drop links tying not to change the engine speed.
Check the air flow of each of the two carbs – and if each carb is fully balanced before attaching the drop links adjust differences by altering drop link lengths.
You can then make the final idle speed adjustment.
I assume you have checked float heights and pump jet deliveries.
I am sure that this differs slightly from other instructions but is broadly the same and I am sure everyone has their own subtle variation in how best to obtain a result.
i have replaced all the accelerator pump nozzles as a matter of course and also replaced the diaphragms in the pumps themselves as part of the refurb. Funnily enough, Larry at the Oil Analysis company wasn't familiar with the term "nozzles" and only recognised them once referred to as "jets" as per Webers exploded diagram. Different terminology for different folk.
Drop links were disconnected for tuning once the engine was warm, but as i say, i just ended up chasing my tail searching for lean best idle by ear. Hopefully, the colour tune will help matters,but i'm under no illusions about the prospect of doing the rounds, repeating the various processes until it's right. will post again once i've had another stab at it later in the week. Thanks for the invaluable advice from everyone so far.
Success at last! After much trial and error, the car is now running better than ever. I got a set of 32mm venturis sent from PMO via Larry at the Oil Analysis Co in the States. He is a very helpful guy and the service and rapid delivery were way beyond what i had expected.Once they were installed i took a punt on jet sizes based on suggestions from PMO and carefully checked and double checked things such as float height and accelerator pump volumes before re installing in the car. Next it was Colourtune time. What a pain in the proverbial it turned out to be from the installation point of view. The washer that comes with the Colourtune is a really loose fit and kept dropping off when removing it to move onto the next cylinder. I tried a healthy dab of heat proof grease which helped when installing, but not on removal and i ended up having to carefully fish around each time to rerteive it. It's also not easy to fit on a flat six given the deeply recessed plug holes and general awkward access, but once fitted it worked a treat. In hindsight, it would have been better to have six Colourtunes installed simultaneously, but i was being a cheapskate and only bought the one. Lesson learned!
I got things running reasonably, then went to checking and adjusting dwell, then timing, then more carb fiddling, then back to timing and dwell until i was happy. It is time consuming and i'm sure a pro could do it a hell of a lot more efficiently and quicker than me, but there you go.
Once this was done it was time for a road test. This threw up the need for more jetting adjustment, particularly idle jets, but eventually i was happy and the car was running great apart from at the top of the rev range through each gear i.e. just before you change up, and also at top end. Just a barely perceptible hesitation and slight miss that i couldn't nail. I knew the carbs, timing etc was now good so it had to be something else surely? This was when i noticed the coil was unusually hot to the touch. This got me thinking the problem may well be related and in fact i was suffering poor spark at higher revs because the coil was starting to fail. A new one fitted this morning confirmed my suspicions as the problem is gone and the car goes like a scalded cat without missing and pulls cleanly through all the gears right up to the rev limiter. Job jobbed.
Thanks for all the useful suggestions throughout the process, just thought you would all appreciate an up date.
Cheers.
