HELP: 1977 900 bevel twin desmo with bosch ignition running on 1 cylinder - Ducati.ms

l_aysan · Jul 7th, 2011, 9:16 am

hello!

my bike is not running on both cylinders ... the front dropped out

I was riding on the highway and all of a sudden one cylinder dropped out! luckly my buddy was following me ... with a truck! and just so happened to have straps!! (gota love friends with trucks! hahaha)

I'm going to start with spark plug wires (one of those might as well replace, the plugs are brand new 2 weeks ago)

then start troubleshooting by switching components between the 2 cylinders to isolated the issue.

But i would love some advice on where to start or if this is a typical problem easy fix problem with the bosch system (Im use to the horrible Italian electronica that was originaly on the bike)

THE BACK STORY - incase its relevent

the full story is i did a swap too the bosch system (used) late in the season last year. JUST before leaving on a 2 week ride from southern ontario to the southern states (as in stayed up all night the day before leaving to sort out the last bits).

the bike ran AMAZING the whole trip. better than any other trip ...

however, there was a small ghost in the machine, about a week into the trip while on the highway (and only on the highway at cruising speed) one cylinder would drop out for just a sec, MAYBE 5 seconds. then the bike would return to normal.

at first i was mortified that i would have to trouble shoot on the trip.

but it never got better or any worse.

and it only happened maybe once a day, not dependent on weather .... how hard i had ridden that day or anything. it just consistently dropped everyday then came back and never got worse or better.

it continued to happen until the day she died.

when i was getting ready for this season i looked everything over and it all seemed good so i decided it wasnt worth dealing with until i could figure out how to replicate it.

thanks guys

l_aysan · Jul 7th, 2011, 9:21 am

ALSO

what kind of spark plug wires should i use for the bosch system?

Typical copper core?

Thanks

Duccout · Jul 7th, 2011, 11:31 am

I would use copper-cored, but your suggestion of swapping components is a good one. It could be a faulty amplifier; wiring broken down inside the engine; faulty ballast resistor, if you have them fitted; coil, or even a spark plug cap, if you are running the originals, with the metal shielding. If you have the original plug caps, then I would change them first.

Desmo46 · Jul 7th, 2011, 7:41 pm

First check connectors on the resistors and coils then the multipin connectors on the Bosch boxes. They have a habit of the lock tabs "relaxing" allowing the individual wires to just but up against the connector on the box rather than get pushed on. they are inside the plastic connector,so not obvious until you really look. All that maintains the connection is wire and insulator tension. This relaxes, wires move, cylinder looses spark. This is usually intermittent to begin with the becomes permanent.

Then check the triggers for about 220 ohms resistance, then start swapping coils, boxes and resistors.

wilson59 · Jul 7th, 2011, 9:58 pm

Quote:

Originally Posted by Desmo46

First check connectors on the resistors and coils then the multipin connectors on the Bosch boxes. They have a habit of the lock tabs "relaxing" allowing the individual wires to just but up against the connector on the box rather than get pushed on. they are inside the plastic connector,so not obvious until you really look. All that maintains the connection is wire and insulator tension. This relaxes, wires move, cylinder looses spark. This is usually intermittent to begin with the becomes permanent.

Then check the triggers for about 220 ohms resistance, then start swapping coils, boxes and resistors.

Agreed mine used to do this as well . From memory it was a orange wire that was loose check these first.

l_aysan · Jul 8th, 2011, 9:16 am

Thanks soo much guys!

I'm running out today to the hotrod shop to get the cables, and i will definitely start with the orange wire, that little bastard could definitely be the culprit!

shanetbird · Jul 10th, 2011, 5:02 am

Had this on the 82 SS

Most likely plugs, then coil , or connections to coils , low and H/T
But yes the 40mm 's dely's played up as well "lack of use"
So l changed coils after market higher 5 amp output and H/T leads rebuild carbies check remove all connections and clean reconnect all .

some other 1 pot drop out poor fuel, filters in taps
also big find was the electrical connections had deteriorated including the connectors them selfs

Drove me insane all with only 9000 miles on the clock .
shanetbird

l_aysan · Jul 11th, 2011, 2:03 pm

so i started workin on her this weekend.

the front cylinder (the one that wasnt running) the plug cap was loose and probably not connecting well ... so evident that i need new caps and wires.

now the strange part ..... take a look at this picture of BOTH plugs ...... the electrodes are GONE! on Bosch plugs 2 weeks old. the color seems decent ... fairly nice brown, not lean (a bit rich ... but i'll chaulk that up to when i was limping off the highway)

What do you guys think it is?

im gonna check the headgasket torque

I checked the resistance of the pickups and the coils and all that an it all checked out within spec.

also how do you get the plug wires off the coils? i tired unscrewing them but stopped b/c they were not budging and i figured i'd ask before fucking the coils up. should i just get an exacto knife and slice them open? .... they are REAL TIGHT.

any suggestions would be much appreciated ... its far to nice not to be riding!

Thanks

Luke

l_aysan · Jul 11th, 2011, 2:09 pm

Quote:

Originally Posted by shanetbird

Had this on the 82 SS

some other 1 pot drop out poor fuel, filters in taps
also big find was the electrical connections had deteriorated including the connectors them selfs

shanetbird

i rebuilt the carbs last season and dropped and cleaned the float bowls this season.

new filters also last season

and the connectors and connections are damn near perfect with LOTS of contact grease. Im religous about that, I have spent waaaayyyy to long chasing bad grounds, loose wires and dirty connections on the bikes and cars i've built/worked on.

It may take a while but I learn eventually! LOL

Desmo46 · Jul 11th, 2011, 4:08 pm

If it is a 1977, why does it have a Bosch system?