How to balance carburettors on my 2000TC engine ?

Wilfred Oldtimer

Wilfred Oldtimer

Active Member
Good morning all,

I’m struggling with something.
My P6 has some forgotten maintenance, part of which has been taken care of now. All the fluids, spark plugs, cabling, electrical things, Etc..

Yesterday I noticed some locking on screws on both carburettors which weren’t tightened and also the screws itself looked like they have been turned a lot. For all I know these screws are supposed to adjust the mixture and rev. That’s what I read in the big book.

Curious and stubborn as I am I tried to see what happens when I turn these screws a little bit. They’ve already been touched and the engine is a bit shaking when idle, so what could I loose ?
I noticed some differences but no improvements, I marked the location so was able to put them back where they were in the first place.

I’m thinking of taking the car to a specialist for this adjustment, however isn’t there something I could do myself perhaps?

Many thanks for any advice,

Wilfred
 
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Which type of SU do you have? Mixture screws may vary depending on type - HIF6 carbs have recessed screws with a + slot, no locking, just firm to turn. HD6 or 8 will have a vertical screw on one side that alters mixture. HS types adjust mix by turning a brass nut underneath - up to lean, down to richen. Locked screws are the idle stops and the fast idle ones - these last run on the colde start cams(HIF) . Read the manual on setting up from scratch, its quite good. There will be pins with springs underneath the damper housings - push up until you feel some load (engine idling) then up 1/16-1/8" - if mix is good revs should rise a little then settled back; if revs stay up - rich; if revs drop - lean.
 
I recall theres an SU tuning /setup video and instructions on web but can't remember sites:( try web search for setting up SU carb(s) and U tube . theres a American guy showing a single set up but am sure there was. a dual carb too. its about getting air/fuel balance correct so both carbs pull in air and fuel at same rates. bit of a learning curve but not rocket science .good luck .
 
Thank you both, that’s useful information.
Now you mention, I remember seeing a short movie once where someone pushed up the damper and adjusting something underneath the carburettors.
In my situation there are two adjustment screws on one side of the carburettors. I will take some pictures today and post them.

Some additional information, I already cleaned both carburettors by dismantling them and renewed the oil with ATF. Compression of all four cylinders is 12.5 bar and the engine wasn’t even hot. :)

Cheers,
Wilfred
 
classicalgreen said:
I recall theres an SU tuning /setup video and instructions on web but can't remember sites:( try web search for setting up SU carb(s) and U tube . theres a American guy showing a single set up but am sure there was. a dual carb too. its about getting air/fuel balance correct so both carbs pull in air and fuel at same rates. bit of a learning curve but not rocket science .good luck .
Click to expand...

I found this interesting link:

tuning su carburettors - Google Zoeken
 
Just a heads up looking at your carbs. You have HS8 carbs for reference, unlike normal HS SU carbs you have two screws per carb. One is for idle speed and the second is for mixture. They have series of linkages so you can adjust mixture from above instead of the large brass nuts below the jet. Mainly because it’s very tight under the carbs.

I have one of these to help balance the carbs one of these. I think you’ll find this this video helpful on how to balance them.
 
Yes Wilfred, I was just going to suggest the same as Steve, but after seeing an STE Flow Meter, I'd opt for that. Does the unisyn fit without a length of rubber hose attached Steve?
 
From your photo it is obvious that someone removed the spring that supports the weight of the carbs (they should not be fixed firmly to the manifold). This in my opinion suggests that someone in the past tried to repair / fix / adjust something while obviously did not understand how things work and what does what.
I firmly believe that it is a waste of time trying to adjust or balance carburetors that have been tampered with in the past, so my suggestion is to take them out along with the manifold, clean and replace what is required, and then refit and adjust. Taking them out with the manifold is very easy, provided that you drain the coolant above the level of the cylinder head, and you have (buy or make your own) the inlet manifold gaskets. I would also advise you to replace the two O rings that seal the carbs to the inlet.
Here's how your carbs should look like: You will notice that they are not firmly tightened to the manifold, they are allowed to float, with the spring supporting their weight.

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Hi, that’s some surprising information..
Putting back the original spring won’t be of any help then I suppose :hmm:
Let’s figure out how I will solve this, your suggestion to dismantle the whole thing could be time saving at the end.

So, I can offer you a splendid cup of coffee whenever you happen to be in Breda :cool:

(Consider this as a joke)

Thanks anyway, also to the others who replied.

To be continued,

Wilfred
 
Please ignore this if I'm talking nonsense I'm new to TC's, and I'm not trying to start a flame war. But...I've just rebuilt my Carbs twice in the last year, and to my untrained eye, it looks like Wilfred's Spring is missing that's all. They may have decided it wasn't needed.

The Carbs press home to the manifold with 4 collared bolts. I've highlighted the top two here, the others are directly underneath. Once these are in place the Carbs are going nowhere. I understand that the Spring's function is to put a bit of strain when cornering. But I don't see how as the Carbs are solid, unless the whole assembly is designed to bend maybe to prevent cracking? I was puzzled by the manual's description, you might get the impression that these bolts don't exist and the Carbs are held to the Manifold by the Spring, not so. It also says the the Carbs should be level and vertical, I don't know how to achieve this after the bolts are in. Like I say, don't take my word for it!!
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This type of mounting the carburetors was used in order to cancel secondary vibrations, due to the mass of the twin HS8s being significant. It is a solution followed by other makers too on multiple carbuteror applications (i.e. Alfa Romeo) exactly for the same reasons.
The orginal bolts are shouldered, and even when tight, allow the carb mounting plates to move against the manifold. You level the carb assembly by adjusting the spring tension. If you read the manual, it's all in there.
In theory you could just refit the spring and back up the bolts, but probably the bodge was made to mask another problem (i.e. an intake leak), hence my suggestion to start from square one.
Thanks for the coffe offer, i would be happy to help whenever i can, and this is one of the easiest jobs on a P6. However, i doubt that i will be in your neck of woods anytime soon, if ever!
 
Good morning,

I know that the inlet part has been rebuilt once, apart from that I know very little history of this car. I don’t know whether they left out the spring by purpose or they lost it or whatever..
I will order one and put it back to be on the safe side then.

After this and prior to remove the lot I intent to try to adjust the carbs, in this way I can get some experience and probably be able to postpone the operation. I also sprayed some brake cleaner around the inlet and didn’t notice anything so I reckon there is no air leakage there.

About the Vacuum tool I got the Amazon link for, shipping costs to the Netherlands are about triple the price of the device itself. I happen to be in and around Midlands (Daventry, Solihull) the week of the 26th. Is there a shop somewhere to buy it ?
Otherwise I could stop on my way from and to Folkestone as I will be travelling by Eurotunnel.

This one:
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Thanks again.

Cheers,

Wilfred
 
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That’s weird, it costs 42.98 pound in the UK and 116 Euro in the Netherlands. Probably due to shipping costs. That’s why I wonder if I can buy it somewhere in the UK :rolleyes:
 
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