Ball Bearing Blocked Idle Jet Airway

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Dands
Cucciolo - the Lil Pup
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Ball Bearing Blocked Idle Jet Airway

Post by Dands » Thu May 02, 2019 9:15 am

Hi all

I have a few issues which may or may not be related. My USA delivered 1979 900 GTS came factory fitted with a 32 AS PHF carb on the rear and a CD carb on the front. Now the first "issue" I have is there's a ball bearing inserted into the AS's Idle Jet airway at the carb intake side. So the only open gallery is the main jet. I assume this is for emissions but it makes the idle mixture inoperable. FYI, I do have both carbs running long idle screws as per supplied by Bevel Heaven.

I think I'll try and get the ball bearing out but how is still to be decided. Maybe it's too stuck.

Second issue is the rear carb soaks the intake with fuel. I'm not sure at what point whether idling or stopped, however I removed the carb after a ride and the intake was wet with fuel. I mean splashy wet, not just moist. I checked the float level, the needle and seat which when the carb is tilted forward as per when installed has no fuel leaks.

I've pulled the carb apart, the orange rubber needle does have a visible line, however it was sealing. The one way choke valve seems to be working fine and the choke plunger was indented the same as the front CD carb and as a diagnostic step I have swapped these from to rear. No choke cable binding as far as I can see.

I'm feeling I should replace the needle and seats, and choke inserts but anyone have any other ideas or info?

Thanks very much.

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Craig in France
Cagiva Gran Canyon
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Re: Ball Bearing Blocked Idle Jet Airway

Post by Craig in France » Fri May 03, 2019 8:10 am

Hi and welcome to the Forum - I see this is your first post.

1. Flooding.
Change the needle valves - I see 'valves' in the plural 'cos you might just as well do the one in the other carb at the same time. They operate under very light pressure and modern fuels are unkind to the tips. Result: the valves may seem to be sealing, but probably aren't.

(These days, I find I have to replace one or two every year when fuel starts leaking all over the garage floor just as I get ready for the first ride of the season!)

At the same time, reset the float height(s) carefully as per the Dell'Orto book, i.e. with the carb(s) off the bike and on the bench. Steve used to sell a little tool to make this job easier and more accurate, but I can't see it anymore in his shop. But ask him - or you can always make your own. Try a Forum search for more info on how.

And change the choke pistons ("why not?"). And make sure there's some slack in the cables.

2. Your ball in the 'A' carb is most strange - certainly a new one on me! However, late 1979/1980 was when US emission requirements obliged Ducrappi to fit 'C' series carbs; so maybe some genius either at Dell'Orto or at Ducrappi had the idea of modifying the remaining stock of 'A' model carbs.

That said:
I suspect the body of the carb and its drilling haven't been altered. If so, chances are you should be using an 'A' series idle screw, not the longer 'C' series screw. Anyways, that would be the first thing I would try ...

HTH

Craig

wdietz186
Cagiva Alazzura
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Re: Ball Bearing Blocked Idle Jet Airway

Post by wdietz186 » Fri May 03, 2019 7:11 pm

Didn't the late carbs have a jet or restrictor under the pilot jet? My memory is hazy about it but I remember there was something funky about the Late US spec. pilot circuits to limit the extent of adjustment.

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BevHevSteve
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Re: Ball Bearing Blocked Idle Jet Airway

Post by BevHevSteve » Sat May 04, 2019 8:26 am

Yes the "C" series carbs found on US A Darmah models have a little jet thing under the idle jet. Same with the HD series 36s. Certainly not a ball bearing.

I am just out of stock on the float tool but will have more soon... send an email to me with "ISO float tool" in the subject line and once I have them back in stock I'll email you.
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Dands
Cucciolo - the Lil Pup
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Re: Ball Bearing Blocked Idle Jet Airway

Post by Dands » Tue May 07, 2019 12:32 pm

Thanks all for your responses.

So I have drilled a 1mm hole through the threads and behind the ball bearing. And was able to lever it out with a firm effort. Certainly wouldn't have fallen out or blown out. I'm told it was an emissions mod. Which is fair enough. As the bike had a CD carb on the from from the factory.

I wanted to ask. Regarding float height, the needles have a spring to decrease vibrations hammering the needles. I've read the "sit the carb on the side and measure 18mm. But is this without depressing the spring? I assume I will get the needle to seat, then lay the carb horizontal and adjust the level so the sprung end of the needle is just touching.

Seems logical if the spring is strong enough to lift the needle against the seat. Is this correct?

Thank you.

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Craig in France
Cagiva Gran Canyon
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Re: Ball Bearing Blocked Idle Jet Airway

Post by Craig in France » Wed May 08, 2019 12:57 am

Dands wrote:
Tue May 07, 2019 12:32 pm
Regarding float height, the needles have a spring to decrease vibrations hammering the needles. I've read the "sit the carb on the side and measure 18mm. But is this without depressing the spring? I assume I will get the needle to seat, then lay the carb horizontal and adjust the level so the sprung end of the needle is just touching.
Simply follow the instructions in the Dell'Orto manual - see below. The only thing I would add is that it can be difficult to gauge the precise moment that the valve is closed. To do this, attach a piece of tube to the fuel inlet and blow down the tune while gently while closing the floats. The point where the air stops flowing, that's where your float height should be 18mm.

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