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Discussion Starter · #1 ·
I'm trying to figure out what is happening with my fuel supply. My '97 won't run when connected to my tank. When removing the tank the carbs are empty. I hooked up a gravity fed tank to it and after the carbs fill up the bike runs beautifully and easily empty the 200ml tank. It also starts with no choke at all and is just running beautifully. So, with the tank on a bench and with the fuel lid closed and locked, I applied vacuum to the petcock. It had no trouble draining the contents, ~3 gallons. So the petcock is good, the cap is venting properly and there's no large clogs. I'm not sure where to look next. I recently replaced the fuel filter, fuel line and vacuum line. Could the fuel line be too long and possibly kinking or looping over the height of the petcock's outlet preventing a gravity fed feed? The only thing I can think of that I haven't tried is hooking the tank back up to the bike and manually applying vacuum to the petcock. Any additional suggestions would be greatly appreciated!
 

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07 Ducati SS800 '95 Ducati 900SS/SP '19 Honda CBR650R
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Could the fuel line be too long and possibly kinking or looping over the height of the petcock's outlet preventing a gravity fed feed?
you tell us, is it? If so, its a valid explanation for your fueling difficulties. Are you running an inline filter, necessitating such a length/routing?
 

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Discussion Starter · #3 ·
So that's the problem, the line is kinking. I shortened it but it's still restricting flow quite a bit. I think I have the fuel filter sitting up too high forcing the fuel line to make a sharpish turn causing the problem. So I'll try shortening the ~2.5" hose between the filter and the carb fuel inlet. I'm also using general automotive fuel line (not for efi). Is there anything different that would be more resistant to kinking?
 

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i had this problem as well using a general auto line (efi lines are too thick), ended up just cutting it shorter to make sure it couldn't kink. highly recommend a rail filter, way easier and fewer connections to worry about
 

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07 Ducati SS800 '95 Ducati 900SS/SP '19 Honda CBR650R
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strongly suggest this:

 

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I mounted my in-line filter vertically between the carbs, the bottom butting against the fuel rail tube. I padded it as it could vibrate against a metal bit and eventually leak. That gave enough space to use a more gradual, non-kinked loop in the fuel line.

Another trick is to find a spring which will just fit over the line and run the line through it. The spring, encircling the line, will keep the line from kinking. Copper tube benders, as used to make air compressor lines, are basically springs that slide over the copper and allow you to bend it without kinking.
 

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Discussion Starter · #8 ·
Wow, it's been a month but I finally got through a bunch of things with the bike. Still a no go. I first tried ducatiman's suggestion with the filter. However, I also changed out my fuel line at the same time. I made a mistake and bought 5/16" OD instead of ID pipe. While tight, it "worked". However, the bike would hiccup and stall whenever giving it throttle. After that I purchased some actual 5/16" fuel line and hooked it up but was still having the same problem. So instead removed the inline filter and put my clear filter back on but I used the new 5/16" line and made it so there is ~1/4" between the filter and the carb fuel feed. I then hooked up an overhead fuel supply and the bike seemed to run beautifully, minus a slight throttle hang. Great, so I buttoned up the airbox and everything associated before trying it again and it now it refused to accept fuel. I filled the overhead fuel supply, opened the valve but the fuel refused to flow. I confirmed there was nothing wrong with the fuel supply. I cranked it a bit but still nothing. I pulled the airbox back out, double checked everything, tossed it back in and now it was working. So I stopped the bike, reinstalled the airbox and everything associated so the only missing bits at this point are the fuel tank and seat. I refill the over fuel supply one last time and the problem is back. I absolutely can't get the fuel flowing into the carb. I've never seen this before. I let the bike sit and cool a bit, as it was fully up to temp at this point and voila, the fuel starts flowing fine and the bike starts right up. This likely appears to be my original problem as opposed to the hoses I thought were the issue. So it seems like when the bike is up to operating temps it stops accepting fuel. I'm at a complete loss from here.
 

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Heat the motorcycle to the point where it will not accept gasoline. Tap it lightly with the handle of a screwdriver and check the flow. Maybe the float valves are getting stuck at the inlet.
 

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Discussion Starter · #10 ·
Okay, finally got around to getting back out to the bike. I ran the bike, got it somewhat up to temp with what was left in the overhead fuel canister before it ran dry. Filled it back up, it's not accepting the fuel, I tapped it with a screwdriver handle but nothing. Cranked it over a bit, it started and stalled as expected, tapped it again but still nothing.
 

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Are the vacuum lines well routed? Maybe they are kinking or collapsing when hot (warm rubber is more flexible than cold one)
 

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Okay, finally got around to getting back out to the bike. I ran the bike, got it somewhat up to temp with what was left in the overhead fuel canister before it ran dry. Filled it back up, it's not accepting the fuel, I tapped it with a screwdriver handle but nothing. Cranked it over a bit, it started and stalled as expected, tapped it again but still nothing.
it now sounds like some kind of a float/fuel level issue
 
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Discussion Starter · #13 ·
Are the vacuum lines well routed? Maybe they are kinking or collapsing when hot (warm rubber is more flexible than cold one)
As of right now I'm running without the tank so I have both vacuum lines sealed off. I don't have California emissions on the bike so those are all sealed. I believe that covers all the vacuum lines/ports, right?

it now sounds like some kind of a float/fuel level issue
I think my next step is I'll pull the carbs off and check that the floats are moving freely. Is it worth pulling the jets out and cleaning them out again?
 

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concentrate on float valve motion...totally free or impeded in the least?
 

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Discussion Starter · #15 ·
I just pulled it back apart and opened the float bowls up. The floats move absolutely beautifully. There's nothing impeding them at all.
 

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Discussion Starter · #16 ·
I should also note, that while I thought I had ran it out of fuel, it would start, stumble and stall before pulling it apart, when I flipped the carbs over a few ounces of fuel came out the carb vent hose.
 

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so now you're providing evidence of full fuel flow? Then it sounds as if your pilot jets/circuits are clogged to some degree. Also....air correction jets are clear?
 
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well? any further findings/comments @NickD ?
 

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Discussion Starter · #19 ·
Sorry for the delay. I've had family visiting and didn't have much time to get to the bike. So I pulled the jets, cleaned them out with carb cleaner. I re-assembled the carbs and put them back on the bike. I am still having issues with the carbs accepting fuel. I filled my overhead tank with ~100ml of fuel, the carbs accepted it and drained just about all of it. The bike started up and ran. After it started warming it started sputtering and died due to no more fuel as the tank was empty. I filled it to about the 200ml mark but the carbs won't pull it down. I opened the drain on the float bowls and drained about ~1tsp of fuel from each one, but still no fuel coming in. This would indicate, as you mentioned earlier, that the floats are sticking. However, when I opened them earlier they moved seemingly perfectly. I'm tempted to remove the bowls with the carbs on the bike at this point to investigate further. Assuming I can get in there with my allen wrench.
 

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Discussion Starter · #20 ·
So over the weekend I left the overhead tank's valve open and at some point the fuel got pulled in. This morning I started it and it started right up. So I filled the overhead tank again, drained the bowls and opened the valve, no go. So with the carbs on the bike I removed the bowls and both floats were fine with the float valve open. I turned the fuel valve back on and still nothing. I confirmed the valve on my overhead tank is working by removing the line from the carb and it drained no problem. I attached a picture of my setup to make sure I'm not doing something wrong here.
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