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 Post subject: Dellorto blowback
PostPosted: Fri Nov 26, 2004 11:07 pm 
Try this on for size. i get blowback through the horizontall cylinder carburettor, when bike has warmed up. changed the coils, reguiator,battery and spark plugs.


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PostPosted: Sat Nov 27, 2004 9:10 am 
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paso grand pooh-bah
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Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
:confused:

This sounds a bit strange, minimad. If you're having trouble on just one cylinder, why change the regulator and battery? If the trouble is spark, how come it only happens when the motor's warm? How about checking out the front carburetor? Does it blow back under acceleration, or at idle? Maybe the front carb is rich, so it runs OK only when cold.


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PostPosted: Sat Nov 27, 2004 10:15 pm 
Idie or acceleration it dos't change,and ouly when warmed (about 20mins after startup). changed jet size to bigger one, still didn't change.


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PostPosted: Sun Nov 28, 2004 2:22 am 
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paso grand pooh-bah
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Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
How well are your carbs synchronized, are you using reccomended plugs, and does the front plug look rich or lean?


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PostPosted: Sun Nov 28, 2004 3:06 am 
yes and yes. it's carbon fouling both spark plugs, with both bigger jets and small jets. it's like the motor start to run on one cylinder, and starts to fire at uneven times. can't reuse spark plugs again, even after cleanup. (motor won't start)


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PostPosted: Sun Nov 28, 2004 3:50 am 
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paso grand pooh-bah
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Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
So you're having trouble with both cylinders?


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 Post subject: Re: Dellorto blowback
PostPosted: Sun Nov 28, 2004 1:45 pm 
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paso grand pooh-bah
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Location: Hudson Valley, NY
model: 750 Paso
year: 1988
minimad wrote:
Try this on for size. i get blowback through the horizontall cylinder carburettor, when bike has warmed up. changed the coils, reguiator,battery and spark plugs.


It might be time to look at valve clearances to make sure they are not too tight. When the engine warms it might be causing the intake valve to stay open.

Testing the ignition pickups might reveal something that only fails when hot too.

Good Luck,

Jon

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Jon

'88 750 Paso * '87 750F1
'04 Multi 1080s * '88 650 Indy
'65 250 Monza - Moto Giro Project

Click HERE--> 750 Paso Tech FAQ
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PostPosted: Tue Nov 30, 2004 4:59 am 
:thumbup: skin: Can't say, when flames start to come out of back off carb, i hit the kill switch.
jcslocum:had the ignition pickup tested.( ok).haven't checked the valve clearances.
Thanks


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PostPosted: Tue Nov 30, 2004 6:31 am 
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paso grand pooh-bah
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Joined: Tue Oct 26, 2004 12:00 am
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Location: Kapiti, New Zealand
model: 750 Paso
year: 1988
Sounds like ignition timing. My only experience with that was to set it statically when I had the motor out. It wasn't hard to do. You should be able to get the driveside engine cover off without taking the motor out.

Does anyone else have any advice?


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PostPosted: Tue Dec 21, 2004 10:49 am 
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Location: Australia
model: 906 Paso
year: 1989
Just about the backfiring or spitting back through the carb, check the rubber mount from the carb to the manifold. Make sure there are no cracks or splits in the rubber. They run lean as they suck air. It was common with older Dukes.


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PostPosted: Mon Dec 27, 2004 1:29 am 
:cool: Thanks to all your help. happy riding


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PostPosted: Mon Dec 27, 2004 9:31 am 
I would agree with jomo on this one look for airleaks


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