Technical FZD carby set up

[rizzo360]

Hi Guys,
My carby expertise is very limited, I'm looking to initially setting up this carby fzd 30/24 so i can get it to run without to many dramas what jets would i be looking at using. Engine is stock 500 below are the jets from my carby TIA.
my pump jet is 40
emulsifier is 6747-1
main jet 128 wee bit on the big side me thinks
air corrector 150
idle jet is 38

 

[the hobbler]

In most ways, the 30/24 is a better carb for a 500, or low-tuned 595---the 32/28 is a shade big. Having stated that opinion, I am fully aware that some tuners fit big side-draught Weber carbs to tuned 500/126 engines---for road use, I have never seen the point of fitting carbs that are nearly as big as the cylinder head of the engine!
I would say that you are correct, the 128 main jet is probably a shade too big for a standard 500. As a starting point, may I suggest the following:---
Main jet--------------126
Slow running jet------38 (also known, incorrectly, as the 'idle' jet)
Emulsion tube-------6747/6
Pump jet---------------40
Air-correction jet-----190
Sadly, the 6747/6 Emulsion tube is almost unobtainable, but the 6747/1 can be brought to exactly the same specification by plugging (solder?) the top 2 holes. You may find that you also have to go down a size in the 'pump' jet. If you have too big a pump jet, the engine can be quite 'woolly' when down shifting (d-d-clutching) when the engine is hot.
Making the choke on the FZD work will involve a bit of head scratching and/or a longer choke-operating cable. OR, you could totally ignore the choke lever (inside the car) and rely on using the accelerator-pump as a method of enriching the fuel mix for a cold start. I have found that a couple of slow pumps on the accelerator, followed by the count of (about) 6 before cranking the engine works well (I have a 32/28 on my 650 engine). This delay allows the fuel you have just squirted into the engine to start vaporising---petrol vapour ignites much easier than 'wet splodge'.
How are you for technical 'bumph' on the FZD? I have a fair bit, and if you would like a copy of what I have, drop me a line ([email protected]) and I will copy out what I have a post it to you.
The best way to set any carb up is on a 'rolling road', but lacking that convenience, patience is the next best tool and a note-book to log down how the car is running as you change jets. Lastly, ALWAYS make a note of what jet you have changed and the date that you have made the change.

 

[rizzo360]

Thanks for the reply hobbler much appreciated. Also ive only just fired my engine up for the first time and it's kinda bunny hopping at idle have trouble pin pointing the problem my issue may be normal but not knowing how the idle is supposed to be im not sure.


Cheers

 

[rizzo360]

Hobbler,
Do you think Main jet of 90 will work or is it to small.
Thanks for your input.


Cheers

 

[the hobbler]

I think that will be too small.

 

[rizzo360]

Hi Guys,
So finally my carby parts arrived. I fitted all the new jets (as per your recommendations hobbler) but I cant get it to idle, it starts and runs for 1 second then dead. I can get it to run for 10 20 sec using the choke. What should I be looking for ,here are my stats.....
Main jet--------------126
Slow running jet------38 idle jet
Emulsion tube-------6747/6
Pump jet---------------40
Air-correction jet-----190


Cheers

 

[rizzo360]

Ok so I finally got it to run till my fuel pump **** itself. I removed the plugs looks like it's running really rich. I'll get new pump tomorrow and continue the hunt.

 

[the hobbler]

Try going down 1 size for the main and the slow running jet---don't forget to make a note of the change and the date of the change. The amount that the pump operating rod extends out past the pump spacer can be adjusted by the thickness (i.e. number of) of the gaskets--it should extend 1-1.5mm past the spacer and the gaskets at the point of initial outward movement; alter the inner gaskets to obtain the correct amount showing.