1999 M900 - No Fuel Pump Installed

[koko64]

The OEM hex pump has excellent flow rates way above the rectangle pump's, (which you can witness with clear lines). I went back to it to supply pumper FCRs. I didn't measure it, I could see it. I'd use the rectangle pump in a 600 or 750 with CV carbs though.
It's interesting that even the stock electric pump in a carbed SS/SL has a return line. Though it didn't stop my Superlight's 39 FCRs flooding when crap got past the filter.. What PSI are they rated at, 3-4?

[ducpainter]

no pressure will be safe if the needle has junk holding it open.

[J-Speed Inc.]

I wonder what keeps the rectangle-shaped pump from not supplying enough fuel to the carbs.  It must be a difference in the surface area of the diaphragm or maybe it's sensitivity to vacuum pressure. It could also be how it was mounted in the bike that had starvation issues, if it was installed with much longer fuel lines than factory, that could cause a drop in pressure and volume due to restriction.   

Even at 2-3 psi, I can see an electric fuel pump easily overcoming the pressure of the floats holding the needle valve closed which would cause the carbs to flood fuel everywhere.  All the pump has to do is supply enough fuel volume to keep the float bowls full of fuel, nothing else.  Also, I'm sure Ducati had the technology to put an electric fuel pump in the bike if they wanted to, but chose a vacuum pump, I wonder why?

When I get the pump and the rest of the parts I'm waiting for to put the engine back together, I'll let everyone know how it goes. 

[ducpainter]

The SS models had a low pressure electric pump.

I believe that vacuum pump was cheaper so Ducati used it on their entry level bike.

From experience 3 psi is not enough to overcome a float needle in good condition.

[zooom]

  Also, I'm sure Ducati had the technology to put an electric fuel pump in the bike if they wanted to, but chose a vacuum pump, I wonder why?

The SS models had a low pressure electric pump.

I believe that vacuum pump was cheaper so Ducati used it on their entry level bike.

$$$ and the other issue that older Ducati's were overcoming was the electrical system on the bike was not sufficient for itself long term ( ie:regulator/rectifier units) so putting more items of electrical draw on a system that was on the verge of being taxed as it was would have raised that failure rate up a good bit...

[koko64]

On a similar thread, the comparative flow rates at 3 psi were something like, 60+ liters and 15-16 liters an hour (roughly from memory).

The rectangle pump theoretically should handle a stock 900 with CV carbs on a road bike. Thats a tank an hour, really honkin'.

[Cloner]

There's theory, then there's practice.  In practice I've personally worked on one bike, and have heard of several others, that starved for fuel with the rectangular pump, but worked fine with the OE unit.  I don't know the cause, but I suspect upstream conditions didn't allow the pump to flow at an optimal rate....but regardless, it didn't work with the replacement!

[koko64]

Yeah, theory aside, thats also been my experience.The stock pump's flow rate appears much greater, so I went back to it.

[Howie]

Lots of folk ran their bikes with the pump successfully for years.  Mine was fine for about a month.  My guess is once in a while a pump sneaks through that is not ethanol resistant, possibly "new old stock" or for a different market.

[J-Speed Inc.]

UPDATE:  SHE RUNS!

After installing a new float, DynoJet jet kit, new clutch cover, K&N pod filters, new fuel and vent lines, new fuel pump, new plugs, and oil + filter change, she roared to life last night about 10pm (doubt the neighbors were as thrilled as I was/am). 

Some things I noticed when doing a few short test runs around the neighborhood is that there is a slight stumble at low throttle.  This might be due to the bike needing a carb sync or the mixture screws adjusted. 

Also, the combination of the Arrow exhaust, pos filters, and the open clutch cover make this bike LOUD! 

The speedo wasn't working, but I believe that is due to an issue with the speedo cable routing.

Couple more hours of tinkering and she should be mechanically sound.  There's a Ducati meet up in Ft. Lauderdale, gonna check that out with my sweet "new" ride!

[Dellikose]

Also, the combination of the Arrow exhaust, pos filters, and the open clutch cover make this bike LOUD! 

The filters aren't that bad.

I'm glad that you finally got her going again. Rack up the miles!

[J-Speed Inc.]

Haha typo, that should have read POD filters

Gonna spend a few hours doing more tweaking and checking before I take her on another long journey.  I'm very excited to take my first Duc for a ride!

[d3vi@nt]

Ok, posts such as these require pics!   

[J-Speed Inc.]

Took her for a 22 mile ride through Downtown Ft. Lauderdale on Friday with my friend following me in his car (haha, you know exactly why).  She did well, just a few bouts with randomly raised idle speed.  I richened the idle speed mixture screws and dropped the idle down a bit.  Also passed a rain test, which I wasn't planning to do

South FL forecast shows lots of rain this week.  Hoping I can find an hour or two to take her for a ride.  Don't worry d#vi@nt, I'll take pictures 

[ducpainter]

Took her for a 22 mile ride through Downtown Ft. Lauderdale on Friday with my friend following me in his car (haha, you know exactly why).  She did well, just a few bouts with randomly raised idle speed.  I richened the idle speed mixture screws and dropped the idle down a bit.  Also passed a rain test, which I wasn't planning to do

South FL forecast shows lots of rain this week.  Hoping I can find an hour or two to take her for a ride.  Don't worry d#vi@nt, I'll take pictures 

If the idle continues to hang and you have the idle speed down around 1100-1200 rpm check synch again.