black smoke wrong carb

[billythefish]

I recently bought a reconditioned Carburetter from Ebay for my 1971 R4 845cc, it was a zenith 281f ( V. 05 078A ) but from a 1984 R4 GTL .

The Carburetter I took off my car was a Zenith 281f ( V05 069 ) a different number from the one that I bought, I was getting black sooty smoke indicating an over rich mixture, although I have set the mixture screw to the correct setting and the smoke has abated quite a bit and the plugs aren't as sooty black as before..

The car is reaching up to 60 MPH but in a rather sluggish fashion, is this because the Carburetter I've put on has a different set up, or could it be the points / coil need replacing or both.
I do understand that the 1984 GTL would have come off an (1108 cc) engine, is this my problem?

 

[malcolm]

There was a GTL carb fitted to Ornella when I bought her. Didn't work too badly, though I swapped it for a proper carb.

The big thing to watch is the big vacuum pipe that comes out of the side. That needs to be blocked else the car runs very badly.

 

[billythefish]

Thanks Malcolm,
The carb I put one was a Zenith 281f and not the Zenith 281fe which has the vacuum pipe on it, as far as I can see and after my night of delicious red wine when my brains went AWOL ,the Zenith 281f air jet is located inside the carb itself, the only screw that is adjustable is the mixture one, please tell me I'm wrong.

 

[angel]

What you adjust with the mixture screw is the idle phase, once you open the throttle fuelling is a matter of jets and float height. As the 28IF has pressed-in air correction jets, the different numbers could mean that (or a different emulsion tube). However it should not run that rich on an 845 engine (have tried it in the past, and didn't notice any difference).
Check the size of the main and idle jets ( I doubt if anyone could find non-standard ones, though), and the float level setting. Do you have any sign that the overly rich mixture is due to flooding? Then you may need to lower the fuel pressure slightly.

 

[billythefish]

Hi angel,
The carb I bought was a refurbished one so there for it should have the correct main and idle jets, I wonder could the ignition side of it be causing the problem, such as the coil, points or dizzy?
As I said before it does reach speeds of over 60MPH but rather sluggish as if it's only running on three pots however, it is running on the four pots as I have checked.

 

[pepper]

billy, who did the refurbishing? I've heard several people on here having "difficult" experiences with "rebuilt" carburetors!

 

[billythefish]

Pepper I haven't a clue, I bought it off Ebay and you pays your money and you takes your chance unfortunately however, the good news is after following some advice from Malcolm I plugged a small air intake pipe near the bottom of the choke cable with a pop rivet ( just slotted in not fixed ) and low and behold I took the car for a run and the sooty smoke has stopped, the plugs are a grey colour and the car seems to be a good bit better, but I am going to put a new coil and leads on just to see if that will improve it, because it's still a bit sluggish, but not as near bad as it was.
Thank you all for the good sound advice