Observations and a question (or three)

discussions specific to the 750 Paso

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Commodore
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model: 750 Paso
year: 1988
Location: USA

Observations and a question (or three)

Post by Commodore »

Cleaning and polishing since purchase on July 4, I finally got a ride. So far, about $1k per mile, but that will improve.

My new favorite. What a great ride. Handling, seating position, sound; a work of art. A great dance partner. So what if much of the fairing has to be removed to top up the oil.

My run down the road and back was interesting. No need to go into details, because I know the carb is at fault...but I'll just say that playing with the choke and not accelerating hard to keep her running were frustrating.

Today, aside from trying to start on the first press of the button, it just cranks and cranks. Plugs remain dry. Right now, I can run her without the gas tank (but with a turkey baster on the main gas line, the recycling line pumping into the turkey baster...) Cali tank, all three lines are clear.

My question, to any of you who can help (especially jayh, thanks, for all your carb research): before I rebuild the stock carb (I left it for last, after my proof-of-concept bench run that showed it seemed to work fine...), were all the weber carb experiments done with the K&N oval air filter, or the stock airbox? Will be ordering parts from Pierce, and jets per your experiments, and need to know if I should ditch the airbox.

This is a great community. Thank you.
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higgy
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Re: Observations and a question (or three)

Post by higgy »

you will save significant $$$ with Alfa1750's store on ebay
http://stores.ebay.com/ALFA1750S-CARBUR ... ARTS-STORE
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
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Commodore
Posts: 25
Joined: Thu Jul 09, 2015 12:59 pm
model: 750 Paso
year: 1988
Location: USA

Re: Observations and a question (or three)

Post by Commodore »

Thanks, Higgy, will do.

Any idea why I would be getting no gas to the cylinders? Anything I should check first? There was gas to the carb (filter chamber was full). Carb off and apart now. Starter valve/jet seems clean on disassembly, and moves smoothly in its bore.

Thanks much
jayh
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Re: Observations and a question (or three)

Post by jayh »

Hi comodore,all done with k&n filter pm me cheers
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higgy
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Re: Observations and a question (or three)

Post by higgy »

Any idea why I would be getting no gas to the cylinders? Anything I should check first? There was gas to the carb (filter chamber was full).

could be the filter is full but not flowing any fuel or installed backwards
could be float level needs adjusting

needle valve could be sticking

hoses could be blocked or not fitted properly


fuel tank clogged or vent blocked or pump not working
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
90 906
92 907ie
Commodore
Posts: 25
Joined: Thu Jul 09, 2015 12:59 pm
model: 750 Paso
year: 1988
Location: USA

Re: Observations and a question (or three)

Post by Commodore »

Jayh, do you have stock exhaust or a more free flowing exhaust to go with your K&N oval air filter?
Commodore
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year: 1988
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Re: Observations and a question (or three)

Post by Commodore »

Higgy,

Weird: all new gas lines, filter, gas tank clean, petcock flowing, return line pumping...and no gas to cylinders. With turkey baster (wish I took a picture of that) all ran fine, accelerated (on center stand...) fine, etc. Once there was gas down in the bowels, I did get it running with the tank, enough to go on a 3 mi. ride. But, as I said, rough. New belts (dots aligned), valves adjust to specs.

Carb apart now; accelerator pump diaphragm stiff as a board. O-rings stiff; but all else seems clean.

Thanks
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Brutus
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Re: Observations and a question (or three)

Post by Brutus »

Did you check the little filter in the Weber itself? It's located at the metal tube where the fuel enters the carb.
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Re: Observations and a question (or three)

Post by Commodore »

Brutus,

Yes, I was surprised to see the filter clean and passing fuel.

Thanks
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paso750
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Re: Observations and a question (or three)

Post by paso750 »

Weird: all new gas lines, filter, gas tank clean, petcock flowing, return line pumping...and no gas to cylinders.
Yes, I was surprised to see the filter clean and passing fuel.
I assume you removed the fuel petcock an cleaned its filter, too.
If the fuel hose is removed from the carb does it pump fuel and how much? You say you replaced all gas lines and I`m wondering if you reused the old Y-piece for the return line and installed it correctly. There should be a jet in one exit of it to reduce the amount of gas being pumped back to the tank. If that was installed incorrectly most of the fuel would be pumped back while the carb would only get a restricted amount which might start the bike but let the engine cut out as soon as it revved higher.
You can put clogged jets on the list of possibilities, too.

G.
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Re: Observations and a question (or three)

Post by Commodore »

Gerhard,

There was a tiny amount of flaky corrosion resting on top of the petcock that I cleaned out. After cleaning, petcock ran gas thru no problem, but I do not know how to get to filter in the petcock?

Did not measure fuel flow, but the "Y" replacement I bought from Bevel Heaven (Steve admits to having little first hand knowledge of Paso) has three equal diameter passages. No jet. The original, as far as I could see, having it come apart in my hands, also did not have a jet, but could have had a smaller return passage diameter. Should I rig up a restriction in the return line?

Photo of test setup: turkey baster feeds new fuel filter; fuel filter to "Y"; "Y" to carb, and return line to turkey baster. Gas manually fed into turkey baster as it was used.
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paso750
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Re: Observations and a question (or three)

Post by paso750 »

If you removed the fuel petcock from the tank you should have seen the filter. This is how it looks (it`s not the identical one but similar).

If there was a jet in the old Y piece it might have been stuck inside the old fuel line. I can`t tell how important that is. Might not be bad that there isn`t one as the fuel pressure of the standard pump is too high for the Weber anyway.
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Re: Observations and a question (or three)

Post by higgy »

and the jet was not installed by the factory. It originated here and a few other forums :thumbup:
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
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paso750
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Re: Observations and a question (or three)

Post by paso750 »

wrong
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higgy
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Re: Observations and a question (or three)

Post by higgy »

double Y ? never saw that one before
Ducati,making mechanics out of riders since 1946
There's no problem so bad that a little fixing can't make it worse! : )
If it ain't broke keep fixin it till it is
88 750
90 906
92 907ie
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