1989 750 Sport idle issue

[deswoodau]

Fuel pump hasn't changed and should be fine.

Famous last words

LOL, sometimes I wonder why I even own this thing.

Can anyone suggest the correct source to buy a new fuel pump that actually works with the Weber? Part number "43040021A" according to the parts book. I purchased one among some other parts last year from a european supplier and it had too much pressure. I reverted to the original\previous fitment as fuel was seeping from the lines, it was probably for an injected bike. The sound of it alone was enough for me to conclude it had a lot more power\psi.

Anyone tried this one with a Weber? https://ducati-gowanloch.com/shop/bodyw ... 43040021a/

[deswoodau]

wouldnt be the 1st weber Ive seen with a crook float . The black plastic float in my Capri ( 32/36 dgav ) took on fuel and was a real bother to sort . Wasnt untill I parked the car facing steep uphill and I couldnt start it at all.....I could see fuel welling up out of the air correctors and straight down the venturi. I bought a brass float ..... which requires a different float level setting

I handed it over to a local technician at https://www.thornburycarburettors.com.au family owned and doing this type of work since the 1960's. I briefed him on the issue\leak and he's going to bench test and find the issue before proceeding with a fix \ service.

They're a good source for parts too. I purchased my jets and 4.5 venturi's there 8 - 9 years ago.

[higgy]

read this thread on vacuum fuel pumps

https://forums.ducatipaso.org/viewtopic.php?t=6800

[deswoodau]

read this thread on vacuum fuel pumps

https://forums.ducatipaso.org/viewtopic.php?t=6800

Hi Higgy,

I like this idea, looks simple and efficient. Any common issues being introduced?

Would this pump be suffice?

https://www.ebay.com.au/itm/23534034205 ... BMzMjd6qRj

[higgy]

Should do nicely. Have a friend recently did this to his 906 and is happy. I have one for my 906 but it is currently in pieces waiting for spring refresh.

[Mc tool]

I handed it over to a local technician at https://www.thornburycarburettors.com.au family owned and doing this type of work since the 1960's. I briefed him on the issue\leak and he's going to bench test and find the issue before proceeding with a fix \ service.

They're a good source for parts too. I purchased my jets and 4.5 venturi's form him 8 - 9 years ago.

Ha , I live in a town called Thornbury (bottom of the south Island NZ )

[yosemite]

To be perfectly honest here, this is just a wild guess, and probably totally irrelevant to your bike but the 906 pasos have a fuel pressure regulator in the fuel feed to the carb where excess fuel is returned to the tank, does your bike have a similar system fitted, if it does does the regulator work, and if not does it need one?

[deswoodau]

To be perfectly honest here, this is just a wild guess, and probably totally irrelevant to your bike but the 906 pasos have a fuel pressure regulator in the fuel feed to the carb where excess fuel is returned to the tank, does your bike have a similar system fitted, if it does does the regulator work, and if not does it need one?

Yes, there's a return line that routes fuel back to the tank once fuel pressure is met. It'll remain in place even with a vacuum fuel pump fitted.

I received an update this morning too. The Weber technician called to advise the float is causing the fuel overflow issue. Testing discovered the float wasn't producing enough buoyancy and causing excess fuel to spill. Weight is over the prescribed weight by 3 grams he mentioned. Awaiting on parts now. Hopefully I'll have the Weber back in a week post service and set up.

It's what I noticed through my own bench testing. The carb remained stable until I started moving it while under fuel pressure.

[higgy]

Just as a passing note of interest; even brass floats will eventually take on fuel. Especially now with so much ethanol in the mix

[deswoodau]

I mentioned brass as a replacement and the Tech recommends the plastic \ original fitment. I'll go with him on this one.

[Mc tool]

The brass float I refer to is a genuine weber part . I dunno if the plastic float supersedes the brass one but both were available .
Good point about the alcohol and brass there Higgy ( I had to think for a bit ) I do have some old brass shit , miners lamps old ammo etc , and a lot of it has split and shrunk the brass sheet, supposedly caused by years of exposure to alcohol based metal polishes .....but most of this stuff is 100+ years old too .
Huh I have 27 petrol motors ( I counted them ) in various applications and thinkin about it ..... Im sure that weber float is the only brass float I have .

[deswoodau]

Update: The Weber has been serviced and checked over with a brand new float, pump diaphragm and needle valve. The technician performed various bench tests and could no longer detect a fault.

The standard fuel pump remains to avoid introducing new problems.

After some minor idle and air adjustments it finally maintains a stable idle without flooding! A quick ride without the airbox and all appears to be running well (as it did before).

I'll finish putting it back together and continue shaking things out. At this stage things are looking good.

No fuel vacuum pump yet.......I want the baseline back before breaking things again

[deswoodau]

Idle issue fixed.......I went on a 70km ride today and it ran perfectly. I'll leave things alone for the moment until trying the vacuum pump solution.

It's actually nice to have it back on the road again.

[Mc tool]

the stock pump is ok . There should be a T in the fuel line at the carb , one line off the T goes to the carb , the other is a return line to the tank ( should be 3-4mm id). The length of the return line determines the restriction of the return line . Basically the longer the return line the higher the fuel pressure will be at the carb. Real simple and works well once you get the length sorted . Cant remember how long mine ended up but Id start at about 700mm and keep trimming it until you have about 3 psi at the carb . The vacuum pump ( there are shitloads on ebay for naff all ) doesnt need a pressure reg , and while I have heard of others fitting a holley ( or similar ) reg to the stock electric pump the 906 didnt come with a reg ..... just the return line.

[deswoodau]

Thanks MC. Yes, there's a return line to the tank (no reg) that diverts via a small t-junction midway to the carburetor. My return line is only about 180mm, again fuel pressure doesn't appear to be an issue. In fact too much pressure brought me issues when I attempted to renew the pump. I suspect I was sold an injected pump that caused the lines to start weeping fuel so I reverted back to the current pump.

It would be interesting to attempt the vacuum pump at some point. I purchased one for $20 AUD so it's a low cost learning exercise regardless and easy to reverse.