Single Cylinder Paso

discussions specific to the 750 Paso

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WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Single Cylinder Paso

Post by WPT Paso »

New to the group. I have a 1988 Paso. Bike has been thoroughly gone over was running great even with the Weber Carb. Yesterday after about 50 miles of riding it stopped firing on the forward cylinder. I have been troubleshooting I have swapped out the BB1105's I have 3 of them. They all seem to be fine. I did notice some chaffed wires and repaired what I saw. The wiring to the coils seems to be ok and wire tied to the frame. When the bike is running on one cylinder i can disconnect the forward BB1105 and it keeps running, if I disconnect the aft one of course it dies. The oddest part is it seems to be intermittent, the forward cylinder will come back to life.

Any insight would be greatly appreciated.

Thank You
Phil
Last edited by WPT Paso on Sun Jun 22, 2014 10:49 pm, edited 1 time in total.
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

One more thing......appears to be no spark on the forward cylinder plug. Do the coils fail intermittently? Thanks for any input gentlemen.....just had the card done, valve clearances are right on and a fresh set of Shinko's on her. Was hoping to get a few more than 50 miles on her before the weather turns cold again........
nickta
Posts: 295
Joined: Tue Jul 24, 2012 8:54 am
model: 907 I.E.
year: 1992
Location: Cairns, Queensland, Australia

Re: Single Cylinder Paso

Post by nickta »

Sounds like a dodgy connection somewhere. Have you swapped the coils so the horizontal is firing the vertical and vice versa? Does the problem move with the coils? Changed the HT cables? Does it drop the front cylinder when it is hot or cold or both?

There was a thread not that long ago with the same issue. Can't remember if it was in the P750 forum or 906?

Cheers.

Nick.
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paso750
paso grand pooh-bah
Posts: 5558
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: Single Cylinder Paso

Post by paso750 »

a 750 running on one cylinder is not uncommon.
The problem could be everything from
pick-ups
pick up wiring
ground connection to CDI units
CDI units
wiring to the coils (kill switch, ignition switch)
coils
spark plug wires
spark plugs
carb synchronization

Pick ups rarely go south and so do the CDI units. Spark plug wires can age and if a coil has cracks in the housing it can be affected by temperature or humidity.
The most common problem though as Nick already said is the wiring with bad connections and old wires with copper rust.
Measure the voltage at the coils (orange wire) and if it isn`t nearly the same as the battery voltage check the FAQs for the wiring mod after having cleaned the kill switch and all electrical connections (specially the main ground connections).
https://app.box.com/s/sy9pui2rbhfs0njfqat0

G.
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

Thank You Guys,

I did find what I thought was "mice damage" on one of the ground wires to the forward BB1105. I did repair that. The harness going forward looks to be intact and in good shape. I guess my next course of action is to measure voltage to the coils then swap them over. The bike seems to drop the cylinder more often when it is warm. I had a feeling I wouldn't get off this easy with a 26 year old bike. I do need to get this sorted out due to the fact that the rest of the bike is nearly mint condition.

Thanks,
Phil
nickta
Posts: 295
Joined: Tue Jul 24, 2012 8:54 am
model: 907 I.E.
year: 1992
Location: Cairns, Queensland, Australia

Re: Single Cylinder Paso

Post by nickta »

The post I refered to above was in the 906 forum. A 900ss started running on one cylinder. Most likely cause was fuel and carburetor. As G says, check everything!

While you are checking the electrics, get a piece of emery paper and give each earth point a rub, both the connector and the point on the frame it mounts. It doesn't take long, and can't hurt.

Out of curiosity, when it drops the cylinder, is there spark getting to the plug?

Cheers.

Nick.
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

Nick,

No spark on the horizontal cylinder when it drops off. As I said I have switched between 3 BB1105's. All work fine on the vertical cylinder so I know they are all good. I followed the wiring from under the seat to the coils, it all looks remarkably good given the age. I had a friend test the coils and according to him they tested fine.

Feel like I'm running out of options.

Thanks,
Phil
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paso750
paso grand pooh-bah
Posts: 5558
Joined: Sun Jul 18, 2004 12:00 am
model: 750 Paso
year: 1987
Location: southern Germany

Re: Single Cylinder Paso

Post by paso750 »

what did he test, did he measure the voltage ?
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higgy
paso grand pooh-bah
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model: 907 I.E.
year: 1992
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Re: Single Cylinder Paso

Post by higgy »

As G has stated you need to start with the voltage at the coils with the ignition on. This has got to be the single most misunderstood issue on these bikes, well number 2 for sure I guess the Weber is the single most misunderstood issue on the 750 and 906 :beer: :beer:
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
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Fraser
Posts: 334
Joined: Tue Jan 17, 2006 12:00 am
model: 750 Paso
year: 1986
Location: Lower Hutt, New Zealand

Re: Single Cylinder Paso

Post by Fraser »

Phil,
There are 4 wires coming up from the bottom left hand crankcase cover, these are from the pickups. The wires run up to the 2 little "CDI" boxes under the seat. There are 2 wires for each, unplug them and swap them over to see if the problem also moves. If it does, then the pickups are the issue. Happened to me 2 months ago.

Cheers,
Fraser.
750 Paso
1980 Moto Morini 500 Sport
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

Fraser,

Thank you for the information. I am on the road for work all week, I will give it a try as soon as I return home. Do you know if the pick ups are available? if not is there a replacement part that works?

Thanks,
Phil
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ducinthebay
paso grand pooh-bah
Posts: 1323
Joined: Sat Sep 03, 2005 12:00 am
model: 750 Sport
year: 1990
Location: SF Bay Area

Re: Single Cylinder Paso

Post by ducinthebay »

Coils are certainly a wear item. They do die after some time, and after all these years, is certainly suspect. The stock coils do not have a replaceable high tension lead, so its another potential failure point. Simply swap the wires and try the coils on different cylinders to see if the problem follows the coil. '
'
Aftermarket coils are reasonably priced, and have a much higher output than stock. a nice upgrade.

Cheers,
Phil
Duc in the Bay
1990 750 Sport x2-Rosso Blanko (900ss copy) & Nuovo Nudo (Scrambler project)
1991 907 -mostly stock
2002 ST4s - Lots of mods.
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

Phil,

Is there a straight replacement that will fit and provide better performance for the bike? I have no problem spending money on upgrading the bike. Given that the bodywork is nearly perfect and still shines like it did in 1988, I would like to get it in the same shape mechanically. I might be crazy but I loved the Paso when I was a poor college student and think I've found a good one to spend money on.

Thanks,
Phil
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Fraser
Posts: 334
Joined: Tue Jan 17, 2006 12:00 am
model: 750 Paso
year: 1986
Location: Lower Hutt, New Zealand

Re: Single Cylinder Paso

Post by Fraser »

Phil,

The pickups were available from Stein-Dinse, they were about NZD$195.0, will check when we get home. They were in stock and arrived in 10 days, only sold as a pair.

Cheers,
Fraser.
750 Paso
1980 Moto Morini 500 Sport
WPT Paso
Posts: 9
Joined: Thu Jun 05, 2014 2:47 pm
model: 750 Paso
year: 1988
Location: USA

Re: Single Cylinder Paso

Post by WPT Paso »

Thanks to all of you who replied, sorry for the late reply. turns out to have been a bad coil that was causing the problem. I have ridden the bike about 200 miles and both cylinders running fine.........Of course now I have a starting problem, initially the starter button worked intermittently. Stopped working completely a few days ago. I found myself having to jump the starter contacts to start the bike. I pulled the starter solenoid and tried a replacement. Upon rewiring, as soon as I touch the positive contact or touch the ground to the plate the starter engages.......I am sure I wired it exactly as it was before, one terminal to the starter and 3 red leads to the other terminal..........bike seems to spend more time with the body work off than actually being ridden.

Thanks,
Phil
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