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Carburettor engine idle too high


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Richard

You have proved that blanking off the brake servo and the hose from the rocker cover doesn't make any difference, so that has solved that part of getting in extra air.

The next to do is to isolate the bypass air valves, this can be done by making  gaskets between the air cleaners and the carb body, that blank off the bypass port, the only holes in the gasket should be the 2 bolt holes, the slot at the top for the fuel reservoir, and then see how it runs, needs to be done on both carbs, this will surely eliminate the air going to the bypass valves.

Do you have a connection to the vacuum capsule on the distributor?, and where does that tube connect to the inlet manifold, some photos here would help please.

What is the timing setting in degrees BTDC, are you using a strobe light or just a static setting?

Have you disconnected the little short throttle rod at the carbs to see if the speed decreases?

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18 hours ago, poolboy said:

If the carbs are 74, then there will definitely be that nipple on the front carb...bottom as shown.

Please excuse the grimaced mug shot . . but yes, front car has a vent which I have overlooked!  Dizzy advance goes from the top of the rear carb, so should I plug this and see that occurs?

20210628_115859.jpg

20210628_115841.jpg

Edited by AarhusTr6
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+1

If that then reduces the idle speed, what has it brought it down too,  I would also disconnect the small throttle rod to make sure that is not opening the butterflies, then if still too high rpm, then make the gasket between the air cleaner and the carbs.

John

Edited by John L
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9 minutes ago, John L said:

+1

If that then reduces the idle speed, what has it brought it down too,  I would also disconnect the small throttle rod to make sure that is not opening the butterflies, then if still too high rpm, then make the gasket between the air cleaner and the carbs.

John

John

 

I so much appreciate the help, but am being fick . . can you advise or explain what part you mean, on disconnect the small throttle rod  - is this a part of the linkage?

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8 minutes ago, poolboy said:

AND .....You also have other problems...you are missing the THICK insulator between the carbs and the intake manifold. You must have those for the carbs to function properly.

See the parts in BA77

https://trf.zeni.net/TR6bluebook/40.php

I have those. . .in my garage I am embarrassed to say . .  So BA77 and BA78 (is this for heat protection?)

 

image.png.1ea8a9f3c999b2f061a6ab4712f909be.png

Edited by AarhusTr6
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1 minute ago, poolboy said:

Yes and to provide the space needed between the carbs' throttle disc and the manifold.

So this could be the underlying issue. . . 

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An open vacuum nipple on the bottom of the front carb is definitely a contributor to the high idle, but to be honest in all the years I've been fooling with carbs, you are the first person that I've encountered to have left off the thick insulators...so I can't answer...Just put them on and tightly seal that nipple and see where you stand...BOTH of those things need tending to.

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4 minutes ago, poolboy said:

An open vacuum nipple on the bottom of the front carb is definitely a contributor to the high idle, but to be honest in all the years I've been fooling with carbs, you are the first person that I've encountered to have left off the thick insulators...so I can't answer...Just put them on and tightly seal that nipple and see where you stand...BOTH of those things need tending to.

I am famous!  The first person in years to have left off the fat gaskets!   :-)

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Just now, poolboy said:

Maybe not THE first, just my first.

And you are probably the leading authority on TR6 carbs :-)  Still say I am famous!  Serious, thanks so much, I will give feedback 

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Thanks, but I wouldn't go that far....I do offer a ZS carb rebuilding service for fellow TR6 & 250 owners. Plus having a TR6 with ZS carbs affords me the opportunity to experience some of their malfunctions and fixes.

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You asked about the plugging the vacuum nipple on the top of the rear carb to the 'dizzy advance'

The short answer is "YES".

Unless the distributor has been modified by replacing the original Vacuum RETARD module with an aftermarket Vacuum ADVANCE module, a vacuum connection to the RETARD from that nipple on TOP of the rear carb is counter productive and would counteract the centrifugal advance once you are in a cruising scenario plus decrease fuel mileage.

For identification, if the nipple on the distributor vacuum module is pointing in the general direction of the cockpit, it's still the original vacuum RETARD module.....disconnect it from the nipple on the top of the rear carb and TIGHTLY cap that nipple on the carb.

If that nipple on the distributor vacuum  module is pointing toward the front of the car, then there has been the modification whereby the RETARD has been replaced with an ADVANCE and it's OK to leave the vacuum plumbing connected from the top of the rear carb to the nipple on the vacuum ADVANCE module

Retard nipple points to the rear, Advance module points forward..

 

4 hours ago, AarhusTr6 said:

Please excuse the grimaced mug shot . . but yes, front car has a vent which I have overlooked!  Dizzy advance goes from the top of the rear carb, so should I plug this and see that occurs?

20210628_115859.jpg

20210628_115841.jpg

 

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What we are trying to do here is to help you understand how the carb works.

If the butterflies are completely closed and the linkage to the throttle pedal is disconnected and not holding the butterflies slightly open the engine will not run, it needs air to run, so if the engine is running at the speed you are noticing there must be air getting in somewhere, hence asking to block off various pipes, so those not making a difference its not those, move on to the next. 

Do you have the workshop manual?, if not download it for free from here  https://app.box.com/s/3458383708b0fb05d75f   It will also give you the correct orientation of the carb isolator blocks, which seem to set a particular way, and all the other settings needed on you carbs to get it running.

The small throttle link, is the one that operates the carbs butterfly shaft, (the vertical one)that will make sure the the butterflies are closed, and that the slow running screws are then used to get the amount of air going into each carb are the same. 

John

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Thanks guys

Learnt so much, also that the insulators did not come back with the carbs, I thought I had new ones and now need to try find some before my roadtrip which I hoped for in 6 days . . oh man . . if I have to ship from UK, then its a delayed roadtrip.  or Is that a bodge too far to use multiple gaskets?

Thanks all, 

Richard

 

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My unnderstanding (from SUs) is the insulators are there to suppress vibrations from engine to reduce frothing of fuel in float chamber.

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13 hours ago, Peter Cobbold said:

My unnderstanding (from SUs) is the insulators are there to suppress vibrations from engine to reduce frothing of fuel in float chamber.

Correct.

Stuart.

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Hi

I am struggling to find these vibration spacers, Moss only have 1.   Does anyone know what material they are so I could try to make them?

Richard

So annoyed I mis-layed or did not see these missing

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22 minutes ago, AarhusTr6 said:

Hi

I am struggling to find these vibration spacers, Moss only have 1.   Does anyone know what material they are so I could try to make them?

Richard

So annoyed I mis-layed or did not see these missing

Im no Stromberg expert but I think the insulators are the same as the SU ones so Burlens should have stock.http://sucarb.co.uk/insulating-manifold-air-inlet-gaskets/insulating-gaskets/insulating-gasket.html

Stuart.

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1 hour ago, poolboy said:

That one in the BURLEN link is twice as thick as the one for ZS carbs which are 1/4" thick as opposed to the SU at 1/2".

New ones are a hard plastic..old ones were some sort of compressed fiber material.

https://www.goodparts.com/product/spacer-insulator-carb-to-manifold-175cd/

 

6mm ones are there as well http://sucarb.co.uk/insulating-manifold-air-inlet-gaskets/insulating-gaskets/insulating-gasket-11533.html

Stuart.

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