Technical (Another) Fuel Return Question for an FZD ... and other points

[JumpJet]

Having finally gotten mostly settled in the new house and cleaned the cobwebs off Martina, we went for a longer drive yesterday with lots of hills. On the long downhills in gear, she stalled out at the bottom a couple times and I'm thinking the likeliest culprit is overheating fuel in the carb bowl. I have an FZD 28/30 on a mildly-modified 594cc motor with a 35/75 cam. I'm thinking of plumbing a fuel return line, but my FZD only has one inlet on the top cover - on the front (gearbox) side of the carb. I don't imagine it's safe to just drill it out and fit a barb there, is it?

Toshi, Hobbler... you guys have any ideas or a source for a new, dual inlet top plate? If that's the course I take (drill or new top plate), I'd reroute the inlet to the front and return from the back, ideally.

She's also running fairly rich, so I'm curious if any of you guys have a source for various jets? I haven't taken this carb apart to see what it's jetted as currently (I haven't swapped it out from what you originally sent it to me as, Toshi), so I don't quite know the starting point yet.

Otherwise, she ran pretty hard and got up to and maintained 70mph, somewhat squirrely thanks to the steering box slop... Something I really want to rectify soon. Tom, I think you have a rack swap source (parts, info, etc...), right? If so, mind sending it my way?

Thanks fellas.

 

[Toshi 975]

Good to see that you are all up and running there and going strong by the sound of it. As I said I set the carbs at or close to the jets as recommended byTom for Abarth spec. As no two engines are the same it was always likely that tweaking the jets would be necessary to get it right. In your case I would think that small reduction in the main jet would be the way to go. Jets are easy to obtain here and main jets are quite cheap.
Spare carb tops are not so easy to come by. I would think that after careful examination it should be possible to fit another inlet provided that you can do it safely. On the FZD carbs that have the inlet and outlet pipes this is to accommodate twin carbs so the petrol can pump straight through to the other carb unrestricted. On carbs where there is a recirculating pipe the outlet is restricted to almost a pinhole to ensure the carb is not starved. However it is amazing how much flow you can get through that pinhole, I measured it one time when I had an engine running on the bench.

 

[the hobbler]

Good to see that you are all up and running there and going strong by the sound of it. As I said I set the carbs at or close to the jets as recommended byTom for Abarth spec. As no two engines are the same it was always likely that tweaking the jets would be necessary to get it right. In your case I would think that small reduction in the main jet would be the way to go. Jets are easy to obtain here and main jets are quite cheap.
Spare carb tops are not so easy to come by. I would think that after careful examination it should be possible to fit another inlet provided that you can do it safely. On the FZD carbs that have the inlet and outlet pipes this is to accommodate twin carbs so the petrol can pump straight through to the other carb unrestricted. On carbs where there is a recirculating pipe the outlet is restricted to almost a pinhole to ensure the carb is not starved. However it is amazing how much flow you can get through that pinhole, I measured it one time when I had an engine running on the bench.

Hi Matt;
Delighted to hear that you have got the "wee beastie" aroused from her slumber. Drop me a line direct, and I will give you all the details regarding "rack 'n pinion" steering. I have found some jet sizes for a 30/24 FZD on a '595'---this might be of help to you---I have also found a supplier of jets for the FZD in Italy. They are NOT "OE", but I have found them to be a good quality, having used his products on my carbs with no problems. Give my regards to Sally.