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 Post subject: Re: 1986 F1B intermittent one-cylinder and sometimes both
PostPosted: Fri Jul 13, 2012 4:31 am 
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Joined: Sat Nov 13, 2010 6:40 am
Posts: 28
If you are venting it via the LH clip-on the bar end plug may need a small hole drilled in it also, my original red plastic factory plug has this.

Andrew


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 Post subject: Re: 1986 F1B intermittent one-cylinder and sometimes both
PostPosted: Sat Jul 14, 2012 6:25 am 
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Joined: Sat Nov 13, 2010 6:40 am
Posts: 28
Another couple of things come to mind, having had similar issues with a couple of previous Dellorto carbed Ducs.

I fitted some clear Cavis Benz lines on my recently restored F1 today & took it for another shakedown run. As fitted he line to the front carb had a fairly horizontal section which I didnt pay much attention to, but the front cylinder felt distinctly lean after a little while, & when I pulled over there was several inches of air bubble upstream of the banjo, i,e no real head of fuel at the carb. Cranked the line up so the bubble could find it way up to the tap I it felt a whole lot better.

It reminded me also of a '90 900SS with 40mm Dellortos I used to own which had similar issues to your bike when I bought it. Was certain I had sorted it when I discovered a previous owner had wired the fuel pump in reverse. Fitted new clear fuel lines at the same time, & while that improved things it didnt totally sort it, & there was a fair bit of air visible in the lines after a run. I then pointed the banjos downwards to create a trap so air couldnt find its way from the carb float up the lines, & it worked. Conveniently also creates a low point so you can see any water or crud in the line.

I looked at a lot of Duc's on the web at the time, & while most had banjos raked upwards there were a few with them pointing down, & thought it worth a try. You'd kind of expect the long horizontal line to the rear carb could give trouble but I guess it typically has a little head at the carb even if there is air in the line. I had issues with starvation on a 650 Pantah years back after fitting an inline filter on the flattish section of line to the rear carb, there ended up being air in the line which struggled to find its way back through the wet mesh. Removed the filter and the problem disappeared.

You could try running a new test line down hill from the tap, across the top of the cases & then up to the banjo. Worth a try, could be a combination of a bit of air in the lines combined with poor venting. If you havent fitted fresh banjo filers recently you might want to punch the mesh out of the banjo filter to see if that helps out.


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