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So, I bought my bike with the Ferracci mikuni flatslide conversion on it already. Pump had always been active, and PO reported bike ran poorly when pump would loose it's connection (bad power connection to the pump in the past had provided this experience).

Pump died, and gravity feed was more than adequate (I removed all the fuel pump plumbing inside the tank so the petcock feeds from the bottom of the tank now).

I find that the bike is quite lean now. I tried going to a bigger needle valve to be sure that wasn't a restriction, and went from a 15 to a 20 pilot, but still it wants full choke, and revs up high at idle.

Would the "pressure" provided by the old pump actually effect the jetting of the bike? Seems odd to me, but that seems to be what's happened (unless an unrelated air leak has developed someplace recently).

Thoughts?

most definitely a pump will effect the level of gas in the float bowl as well as the rate at which it fills effectively richening the mixture. Most likely you can raise the float level to bring things back in line as long as gravity fills the chamber fast enough to maintain the level

seems odd that that would effect it at IDLE, though. Oh well. I think I need to wait for these new float valves to show up before I do anything. I switched from the 1.8 to a 3.0 since there's no pump to push the fuel through the valve.

seems odd that that would effect it at IDLE, though. Oh well. I think I need to wait for these new float valves to show up before I do anything. I switched from the 1.8 to a 3.0 since there's no pump to push the fuel through the valve.

any pressurized system is going to give you a higher fuel level in the float bowl than one strictly gravity feed


higher fuel level means richer mixture especially at lower air flows

when the fuel level gets too high you can watch the fuel get pulled out of your needle jet in spurts making it impossible to get your jetting correct


gravity fed system can require as much as 5 mm higher float level depending on what carb as it takes longer to fill the bowl and less floatation of the levels to close off the flow

you can prove it to yourself at your kitchen faucet, when the water flow is low its easy to block it with your palm. when the flow is high it takes more time and effort to block it with your palm

OK - apparently I introduced another variable at some point - Cables.

Setting a little cable adjustment allowed the carbs to close. Bike runs great, starts well, and seems to like the change from a 15 to a 20 pilot. Hopefully that's it.

If you ever feel that its not getting enough fuel, (mostly under throttle on a long climb) you can still put on a vacuum operated fuel pump off of a Monster, or other bike. There's a recent thread on that somewhere here.

Cheers, Phil

always pays to check the basic setup when troubleshooting to avoid putting the cart before the horse

vacuum pump thread is here http://forums.ducatipaso.org/viewtopic. ... ump#p54486

higgy wrote: any pressurized system is going to give you a higher fuel level in the float bowl than one strictly gravity feed

higher fuel level means richer mixture especially at lower air flows

when the fuel level gets too high you can watch the fuel get pulled out of your needle jet in spurts making it impossible to get your jetting correct

gravity fed system can require as much as 5 mm higher float level depending on what carb as it takes longer to fill the bowl and less floatation of the levels to close off the flow

you can prove it to yourself at your kitchen faucet, when the water flow is low its easy to block it with your palm. when the flow is high it takes more time and effort to block it with your palm

I'm going to have to disagree with you about this. Toilets the world over have a cistern controlled by a ball-cock. Basically a valve which is shut off by a float when it reaches a certain level, just like a float bowl. If the level it stopped flowing depended on pressure there would be overflows where there was a high mains pressure and not enough water for a good flush in areas of low pressure.
The pressure affects the rate of flow, i.e. how fast it fills up, not the height at which it stops which will remain constant. Unless the laws of physics are different for carburators

The pressure affects the rate of flow, i.e. how fast it fills up, not the height at which it stops which will remain constant. Unless the laws of physics are different for carburators

we are talking about raising the height of the float to adjust for the rate of flow to keep the fuel level sufficient to feed the jets


raising the float level will give the system more time to fill the chamber