Group A Carb with T28 Turbo?

[Leloby]

First post!

I've just bought a 1986 Ph1 and I've narrowed down the hesitant idling and take-off to the carb, or at least the idle screw/jet screwed holder (amongst other possible things). I have receipts in the folder for the car for a group A carb and T28 turbo and that's what I think is on the car.

Total newbie here, as you've guessed.

The idle screw had lost it's rubber O-ring and it wouldn't idle at all except on a held-throttle of over 2Krpm. I've since sealed this while I wait for an O-ring and it is better but still hesitant on initial throttle - like it is drawing too much air.

The whole system seems to be hanging on this screw/jet..?

I've read the stuff about a standard carb being best for a T2 turbo but would a standard carb swap still be the best thing to do given that I have this bigger turbo or should I look to getting the Group A carb fettled?

[GTphil]

Depends on what spec the group a carb is, if it's the bigger venturi then a standard carb will be much much better if you keep the boost low until it's set up it will be fine.

However it may just be a fettled standard carb that someone has just said is Group A.

Only way to tell it to measure the venturi (that's the main bit that the air/fuel goes down to towards the throttle butterfly) and see what jets it has in it

I run a standard venturi carb with a t28 and reasonable boost if the carbs set up correctly it will be fine.

The screw on your picture is the idle jet, this gets full of crap easily and needs cleaning out sometimes on more than one occasion, if it didn't have the rubber o-ring in place then it defiantly won't idle well.

You will need to adjust the idle speed and the C/O mixture screw also more than likely.

[GTphil]

https://www.rtoc.org/boards/showthread.php?t=4734

this worth a read

[Leloby]

New poster! (less than 10 posts)

Brilliant help thanks.
I'll get the lobster off and have a check.
I had the same problem with an old AX GT I had and it's all starting to come back to me now.
Cheers!
PS, boost is low but it has new pistons and liners and I'm taking it easy for now.

[Brigsy]

From looking at your pic the turbo looks to be standard matey.

[Leloby]

New poster! (less than 10 posts)

Thanks. That's why I posted the pic - just in case it wasn't.
In that case, I'll replace the carb with a standard one if this one does prove to be non-standard.
Cheers.

[Leloby]

New poster! (less than 10 posts)

Here's the carb pics. It's 47.5mm wide. Car won't start today at all!

[Adey aka Ewok]

the venturi, the part that gets adjusted is the insert at the bottom of the carb you can see, it has 25 stamped on it. That the part that get made bigger on so called group a carbs measure the smallest diameter on that bit, 25mm is oem, bigger is bored out.

[Trevhib]

"Hesitant on initial throttle."

Check that the accelerator pump jet isn't blocked. It's a very common problem and causes this exact fault.

[Brigsy]

Its hard to tell in the pic but that looks like a standard venturi in the carb. Get a fuel hose clip fitted onto the fuel pipe.

[Trevhib]

It definitely has 25 stamped on it Jon, and there doesn't appear to be any sign of it being bored out.

[Leloby]

New poster! (less than 10 posts)

Could be getting somewhere then thanks. I took the hose clip off to check the fuel pump was OK - will replace asap.

Cheers.

[Trevhib]

Now who can fill in the numbers

1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.

This needs to be put in the RTOC article. Who has the permissions to do that?

[GTphil]

That's ace Trev, great for a beginner. I will let someone else fill in the list as I probably won't be able to

Your Air corrector jet looks to be smaller than standard also, that's the small removable brass jet at the top just under the carb top. That venturi looks to be standard (most definitely a good thing) but again only way to be 100% is to measure. I have a board out one that's still got the 25 stamped on it

The smaller Air corrector jet will make it richer for more boost.

[Jonny5]

1.Pressure feed/main body.
2.Upper carb body/choke mechanism
3.Upper to main body gasket
4.Throttle lever/lower body
5.Main to lower body gasket
6.Base gaskets and spacer plate
7.Main fuel inlet filter
8.Needle valve
9.Float
10.Emulsion tube
11.Accelerator pump jet
12.Air corrector jet
13.Main jet
14.Idle jet
15.Accelerator pump diaphram
16.1st stage jet and diaphram
17.Idle speed screw
18.Mixture screw
19.Throttle stop screw

Any good? Few might be wrong..

[Trevhib]

Cool.

Isn't 10 the accelerator pump jet? As in, the thing that needs checking is clear in this case?

[GTphil]

That's my best shot, question marks mean I'm not sure

1.Vacuum reference
2.Carb Top?
3.Carb Top Gasket
4.Throttle arm
5.Carb to Carb Base Gasket
6.Carb base to manifold Gaskets/Plastic Spacer
7.Fuel Inlet Filter
8.Needle Valve
9.Flote level devise (feck knows what this is called)
10.Accelerator Pump Jet
11.Accelerator Pump Ball Valve?
12.Air Corrector Jet
13.Main Jet
14.Idle Jet
15.Accelerator Arm/Diaphram/Spring
16.Enrichment Block/Jet/Gasket?
17.Idle Speed Adjustment
18.C/O Mixture Adjustment Screw
19. Fast idle Adjustment Screw

Maybe it would have been better if I had left it to someone who actually knows what everything is called

[Leloby]

New poster! (less than 10 posts)

This is brilliant!

I've cleaned up and blown through all the jets I can and it's running and ticking over OK now - so thanks very much guys. All I need to sort out it the mixture screw setting and I think that's best left to the local rolling road guys.

Great stuff.
Cheers!

[Leloby]

Carb on the blink again. Accelerator emulsion tube completely blocked following dirty fuel.
I've tried blasting it with everything I've got, EasyStart, GT85, alcohol etc.

Anyone got a spare or is there a better way to clean it?

[royz]

very fine copper wire like what you find in flex type cable. works a treat.

[Leloby]

Worked. Thx. Car goes OK, going to leave it alone now, if it ain't broke...

Just read a 1987 road test and they complained of slight hesitation too so going to put it down to 'character'
Cheers.

[Wallace]

New poster! (less than 10 posts)

This is brilliant!

I've cleaned up and blown through all the jets I can and it's running and ticking over OK now - so thanks very much guys. All I need to sort out it the mixture screw setting and I think that's best left to the local rolling road guys.

Great stuff.
Cheers!

Not worth paying to get it set up for idle, save your money and purchase an afr gauge.....best thing you'll buy for your 5

http://www.efi-parts.co.uk/index.php?productID=204

Also lots of info regarding correct reading etc in the articles area....hope this helps

[Leloby]

Yep, one should be here Monday or Tuesday. Thanks.

[Wallace]

Yep, one should be here Monday or Tuesday. Thanks.