Petcock reserve and replacement question

Status
Not open for further replies.
I just got some BAPs for the roadster after the previous (possible knock-off BAP copies?) got nearly too stiff to turn. I now use the "two reserve taps" setup, as I hate trapped fuel in what is a small tank. This will give around 7-11 gentle miles reserve until you are pushing, depending on how much fuel has slopped over the central tank tunnel before it starts running dry on main.
I went for a , ahem, high speed run, as I had just found my ignition timing scale was a few degrees off (retarded) so wanted to explore the new-found power! Got to about 90mph in top and it started losing power, felt very much like fuel starvation. Switched the reserve tap on and it definitely picked up and revved out nicely. I have the same taps (except for the metric thread) on a big Guzzi that makes a fair bit more power, and not had a problem, so will have to investigate. At least the BAPs are easily dismantled! I have Paioli copy taps on my bonnie, they're nice with 3 positions but hard to get hold of, the BAPs are very common in UK.
 
I just got some BAPs for the roadster after the previous (possible knock-off BAP copies?) got nearly too stiff to turn. I now use the "two reserve taps" setup, as I hate trapped fuel in what is a small tank. This will give around 7-11 gentle miles reserve until you are pushing, depending on how much fuel has slopped over the central tank tunnel before it starts running dry on main.
I went for a , ahem, high speed run, as I had just found my ignition timing scale was a few degrees off (retarded) so wanted to explore the new-found power! Got to about 90mph in top and it started losing power, felt very much like fuel starvation. Switched the reserve tap on and it definitely picked up and revved out nicely. I have the same taps (except for the metric thread) on a big Guzzi that makes a fair bit more power, and not had a problem, so will have to investigate. At least the BAPs are easily dismantled! I have Paioli copy taps on my bonnie, they're nice with 3 positions but hard to get hold of, the BAPs are very common in UK.
disconnect the fuel lines from the taps. turn on the tap and see how much fuel flows from each into a graduated measuring cup for 30 sec. You may find that both taps flow the same - my Paolis flowed the same on the Main and Reserve settings. You may find that one tap alone doesnt flow enough at WOT.

You need at least 300ml/10 fl oz per minute from each tap to supply the commando engine at its maximum HP point. (You want 2x the flow rate for the petcock than the carb can utilize - alas, we have no fuel pumps...).

That is why I didnt install my Paoli BAPs - they flowed less than 300ml - 272ml IIRC - and I have a hottish motor.



 
Status
Not open for further replies.
Back
Top