I need help with my 1978 G5 regarding a misfire

[oldbike54]

This might be way off base but check compression.  Symptoms sound a LOT like what happened to my G5 when a head bolt stretched.  Are you getting any oil in the fins?

 Already checked , 168 & 172 lbs .

  Dusty

[Chuck in Indiana]

He said compression is good.
As mentioned above try running a wire directly from the points to the coil. I had an old SP one time that needed that cure. Then, I'd start it up and put an inductive timing light on that cylinder to see if no sh!t it *is* ignition causing the problem.
Oh. And don't rule out a bad spark plug. I have an aviation spark plug tester that I've modded to take Guzzi plugs, too. I have seen bad new plugs.

[Kiwi_Roy]

The ignition is so simple, hot wire the coils and see if it still misses
Perhaps just run a wire from the battery through a switch to the coils.
http://www.thisoldtractor.com/guzzi007/schematics/1978_V1000_SP.gif

[Bazil]

Your previous replacement of condensers probably means you've checked this but .....Condensers securely fixed to the body of the dizzy? If not screwed up tight ( Locktite is your friend) they may not be grounded which can cause misfiring, under load if only a bit loose but anytime if a bit more loose.

[FISSELtheMISSILE]

Looks like I had a faulty (new) condenser. I've got a busy week ahead so I probably won't have time to be rummaging around the local Napa looking for a part that'll work so I've ordered the new condensers & will report back when they're installed. I'm off Xmas eve & hope to work on it again then.

[nunzio]

Your previous replacement of condensers probably means you've checked this but .....Condensers securely fixed to the body of the dizzy? If not screwed up tight ( Locktite is your friend) they may not be grounded which can cause misfiring, under load if only a bit loose but anytime if a bit more loose.

Thanks Bazil !

I never knew that..will be storing that for later use ...Alan

[Kiwi_Roy]

Also pull each of the plug caps and measure the resistance from cap to ground, they should both measure the same e.g. 8k.

I don't think you said if it would cut out on both cylinders at the same time in which case it would be the power to coils or just one side.

[FISSELtheMISSILE]

Quote from: Groover on December 19, 2015, 08:20:42 PM

+ 1 on checking the new condensers. I also got a bad new one. Easy way to check them is to look at the points while the bike is running; If there is one sparking out, then that's the circuit with the bad cap.

Thanks all for the help. Bike's all squared away now. One of the brand new condensers from MG Cycle was bad. I did a little more research and found http://www.thisoldtractor.com/moto_guzzi_tonti_condenser_cross-reference.html which states the condenser microfarad rating is 0.25. A little cross referencing found that Denso makes a very similar condenser with the same rating for Toyota industrial equipment (made in Japan & seemingly very good quality) so I sourced & installed a pair of those, mounting them higher and away from the heat. That's what I get for trusting aftermarket Chinese (probably?) condensers.

For those interested the Denso 0.25 microfarad condenser is Toyota part number 90099-52059. They were only like $6 a piece and, again, seem to be very good quality.

[Chuck in Indiana]

All's well that ends well. Thanks for the update..