Zenith 28 carburettor

[Azazello]

GTL and later TL (956 ones) have both the zenith 28 carburettor; are they the same carb or do they have some differences?
I'd like to know those differences and how turn a TL carb in a GTL one.

 

[Steve Hennessey]

I doubt very much if there is any physical difference apart from the main jet being slightly larger in the 1108cc GTL. I suggest that if your car is running well with it's 28IF carb then leave well alone.

 

[Azazello]

It was just a curiosity, even because I doubt I will find any difference running on lpg...

 

[DavidN]

I know for sure that the F6 - which is running on a 28IF as well - has a different set-up.
Inside the carburettor there is an additional "pipe" to feed more petrol when under full load. (Its intention is to cool the engine with the additional fuel.)
Experts over here are saying that changing the 28IF on a GTL to an F6 one will give you an additional 3hp (which is about 10 percent!).

 

[Steve Hennessey]

That's a new one on me David. I thought there was only one version of the 28IF! It would be interesting to see an exploded diagram to compare the difference.

 

[DavidN]

I have a few spare 28IF's. One is off an F6, another one off a GTL.
I could take some pictures this weekend if you are interested ...

Cheers,

David

 

[Steve Hennessey]

Thanks - yes, I think it would add to the knowledge base on the forum. May also be handy to post it on the Wikki too!

 

[DavidN]

@ Steve

I found 3 different types of Zenith 28IF's.

The rightmost is the one taken off an F6 van.
It has the additional pipe I was talking about.
It is potruding into the inlet / intake port of the carburettor to feed additional fuel under load.
#V.05 083A - 83 06 13

I think the leftmost must be off a TL.
It only has one pipe that goes down into the fuel chamber of the carburettor.
#V.05 078A - 80 10 28

In the middle you see a GTL 28IF which has two of the pipes going down into the fuel chamber but no pipe into the intake port like the F6 version.
#V.05 075B - 80 01 16

Only difference is in the top half of the carbs.
The lower part seems to be the same with all 3 types.

Cheers,

David

 

[Azazello]

I can see the additional pipe in the f6 carb, but not the differences between the tl and gtl ones...

 

[Steve Hennessey]

Thanks David - really interesting. I wonder if the F6 in the UK had a different version of the 28IF than the GTL. I remember the 28IF on my GTL was useless and I could never get it running right - hence fitting the pumped 32IF7 from a R5 which transformed it into a different car.

 

[DavidN]

I can see the additional pipe in the f6 carb, but not the differences between the tl and gtl ones...

See it now?
TL (which is still an assumption of me) on the left, GTL in the middle, F6 on the right

 

[DavidN]

Found this on another forum.
It should help to allocate the various Zenith models.

According to that list the shown GTL carb (the one in the middle) is off a 845ccm engine.
Now I am confused ...

 

[Geoff in the Gully]

This might help. I found this web page a little while ago - it lists the model numbers of the Zenith carbys and which R4s they were fitted to.

http://www.la4ldesylvie.fr/index.php?option=com_content&view=article&id=47

David, it indicates your middle one is off an 854cc engine - does that seem right?

This chart from the workshop manual gives the jet sizes etc for the various carby models. For some of them at least.

Geoff

 

[DavidN]

...
David, it indicates your middle one is off an 854cc engine - does that seem right?

I really can't confirm nor deny it, as I got most of the spares with my F6. And I was told they've come off a GTL.
The only one I am absolutely sure about is that F6 carburettor. That one I bought as a back-up for my van and it is definitely a F6 carb.

Sorry if I caused some confusion here! ops:

 

[Geoff in the Gully]

Ah! Just saw your post David after I did mine. Maybe we found the same site.

 

[Azazello]

See it now?
TL (which is still an assumption of me) on the left, GTL in the middle, F6 on the right

Probably my problem is that I do not know very well how does a carb work... The two yellow long and thin tubes (vertical) are the ones you are talking about? The first carb has only one of them... Do they bring fuel?

 

[jjad]

We had our GTL Zenith 28 IF (V05 078B) serviced recently, but I can't remember if it had one or two air jets.

In the Haynes manual, I can see only one 'air jet' in its exploded diagram for the early engines (680 747cc and 800 845cc). Unfortunately it doesn't say which carb variants were used on which of these engines (just the type and model).

According to the Haynes supplement, the V05 075B was fitted to the 800 845cc engine (as were the Solex 32 and Zenith 32), while the 688-C1E 1108cc engine had various Zenith 28 IF carbs:

V05 073A(C) .... F6
V05 078(A)(P) .. GTL
V05 082 .......... F6 and GTL
V05 83 ............ F6
V05 902 .......... F6 and GTL
V05 080 .......... GPL

Apart from the V05 902 (which isn't mentioned on la4ldesylvie.fr), this agrees with that website, but tells us whether they were used on the F6 or the GTL.