ADVrider

Go Back   ADVrider > Bikes > Old's Cool
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 07-08-2013, 09:33 AM   #1
LonerDave OP
Gnarly Adventurer
 
LonerDave's Avatar
 
Joined: Aug 2011
Location: Lisbon, WI
Oddometer: 118
Diagnosing Misfire Guzzi 850-T

Hello group,

Hope everyone had a great 4th.

Here's the back story:

The Guzzi had been running great all year, when on a short (20 mile) trip around the countryside, I noticed it feeling "lumpy" when I came to a stop sign. Revving it up to about 3k rpm smoothed things out, and I could feel that at speeds below that, one cylinder was not firing. Above 3k, both cylinders run fine. Sometimes it runs fine over entire rev range, sometimes clears up at about 2k, sometimes misfire from idle until 3k. Seems to happen when engine is cold or hot.

I'll spare you too much detail, but here are the highlights of my work and troubleshooting: Rebuilt carbs - new floats (the left one had sprung a leak), o-rings, filter screens. I've had them off several times and I really believe they are quite clean. New plugs. Checked valve lash. Both petcocks appear to deliver plenty of fuel.

Attached a induction timing light to each side and found that the light was not flashing on the left cylinder whan it was having its problem. Flashed intermittently at idle, then stops as I give it a bit of throttle, until I reach about 3k, then starts to flash again. So, intermittent no spark to the left cylinder at speeds below 3k.

All ignition wiring double-checked and tightened. Running a Dyna III with new-ish 3 ohm Flamethrower coils. Had been running fine with this set up for about a year. Coil resistance checked out OK (don't recall numbers off-hand) but were similar for both coils and the right cylinder runs fine. Resistance for plug wires is just a bit higher than 5k ohms (primarily from caps, I believe) and doesn't change if I wiggle the wire (not broken?). Use black NGK caps. No signs of arcing.

Found only 9.5 volts going to each coil with ignition on and motor not running. Goes up to about 10.5 with bike running. Should be 12v, no? But both coils are getting same voltage and it's only the left side that showing problems. Ground for battery and DYNA both appear solid. Have 12+ volts as late as the kill switch.

Checked for movement of DYNA sensors, but they're tight.

Suppose I'll start tracking down the voltage loss to the coils, unless someone tells me that 9.5 volts is OK. Will also swap plug wires to see if problem follows. Could also swap coils, but they're a tight fit, and removing the breather is a bit of a pain.

Anyone have any thoughts on where to look? Thanks.

Dave
LonerDave is offline   Reply With Quote
Old 07-08-2013, 10:38 AM   #2
Andy-Gadget
Any bike can go anywere
 
Andy-Gadget's Avatar
 
Joined: Jul 2006
Location: Hobart, Tasmania
Oddometer: 1,316
"Dyna3" is all that needs to be said, the driver for the coils can burn out very easily, due to a design flaw in all dyna ignitions, where the ignition feeds the coil current for as long as the key is on, unlike the better designed ignitions that turn off if no trigger pulses are detected in a relatively short time.
BMW airhead ignitions do this, watch the volt meter to see the ignition turn off.
Was the key left on with the motor not running before the fault presented?

As the unit is sealed, the only test is to fit a know good "black box" and see if the problem is still there, the most likely fault is in the black box, not the triggers in the dizzy, but who knows with Dyna.

You may be able to tell, I don't like Dyna ignition.
__________________
"If a man empties his purse into his head, no man can take it away from him.
An investment in knowledge always pays the best interest"
Benjamin Franklin.
'95 Sport 1100 Guzzi,'84 Cali 2 Guzzi, '95 Guzzi mille, '84 R65LS, '84 R100, '82 R100RS, '05 DL650, '72 Bultaco Sherpa T 350, '78 Montessa 348, "00 XR650R
Andy-Gadget is offline   Reply With Quote
Old 07-08-2013, 11:32 AM   #3
LonerDave OP
Gnarly Adventurer
 
LonerDave's Avatar
 
Joined: Aug 2011
Location: Lisbon, WI
Oddometer: 118
Don't recall leaving key on without motor running, but generally not a big fan of black boxes either.

I did attempt to troubleshoot the DYNA by reversing the wiring from the sensors (as suggested by DynaTek), but problem usually doesn't show up during cranking, so the issue didn't switch sides. Suppose I could re-route coils to have it run with sensors switched. Sounds like the smart thing to do.

Would really like to go to points, if I can source breaker plate at reasonable cost. Saw a whole distributor on FleaBay, but it doesn't have cap, rotor, etc. I realize I can get those easily enough, but $50 for just the plate goes against my cheapskate nature. Would consider making the change if I was more certain that the DYNA was the issue.

Thanks.
LonerDave is offline   Reply With Quote
Old 07-08-2013, 12:43 PM   #4
Nessman
Cluttered Minimalist
 
Nessman's Avatar
 
Joined: Feb 2004
Location: Everett, WA
Oddometer: 1,535
If you want a points plate I'll mail you one (I've got a few) but...

To make the points plate work right you should file the plate to allow proper gaps.

http://wildguzzi.com/forum/index.php?topic=17283.0

A Dyna is far simpler and the pickups can be tweaked a bit to get it perfect, I'm a fan.

To put a stock plate in you'll have to take out the Dyna plate, giving you access to lube the advance weights/springs at the base of the distributor that cause problems like that.

A hot wire from the battery to the coils will eliminate the voltage drop, a good place to start.
__________________
'07 Bandit 1250ABS

Nessman screwed with this post 07-08-2013 at 12:51 PM
Nessman is online now   Reply With Quote
Old 07-08-2013, 09:30 PM   #5
Andy-Gadget
Any bike can go anywere
 
Andy-Gadget's Avatar
 
Joined: Jul 2006
Location: Hobart, Tasmania
Oddometer: 1,316
The coil voltage sounds about right, don't forget the voltage is electrical "pressure", the 1 volt increase with the bike running is the increase in "pressure" as the charging system works. Coils are effectively connected to the battery directly, with only the ignition key and kill switch between.

Coils are not simple resistance devices, inductance comes into it, like hifi speaker systems, and they act as inductors even with the bike not running.

The ignition system, either points or Dyna, is switching the connection to earth.
Make sure your earth connection of your meter is to the battery earth, not across the coil terminals.

My Cali 2 runs better with good coils as well.



I am currently a fan of Saches ignitions, my Mille GT has an alternator mounted example doing spark duty.
__________________
"If a man empties his purse into his head, no man can take it away from him.
An investment in knowledge always pays the best interest"
Benjamin Franklin.
'95 Sport 1100 Guzzi,'84 Cali 2 Guzzi, '95 Guzzi mille, '84 R65LS, '84 R100, '82 R100RS, '05 DL650, '72 Bultaco Sherpa T 350, '78 Montessa 348, "00 XR650R
Andy-Gadget is offline   Reply With Quote
Old 07-12-2013, 08:30 AM   #6
LonerDave OP
Gnarly Adventurer
 
LonerDave's Avatar
 
Joined: Aug 2011
Location: Lisbon, WI
Oddometer: 118
Many thanks to inmate nessman for breaker plate (received it yesterday).

Ordered new points, plug wires and caps from MG Cycle. Will post updates.

Thanks all.

Dave
LonerDave is offline   Reply With Quote
Old 07-30-2013, 08:23 AM   #7
Nessman
Cluttered Minimalist
 
Nessman's Avatar
 
Joined: Feb 2004
Location: Everett, WA
Oddometer: 1,535
__________________
'07 Bandit 1250ABS
Nessman is online now   Reply With Quote
Old 07-30-2013, 10:45 AM   #8
LonerDave OP
Gnarly Adventurer
 
LonerDave's Avatar
 
Joined: Aug 2011
Location: Lisbon, WI
Oddometer: 118
Ummm...sorry. Yet another of my projects delayed by "other stuff".

Have removed all DYNA bits and wiring. Installed new breaker plate (thanks Nessman!) with new points and condensors. Making new plug wires and wires to coils. Then on to timing.

All straightforward stuff, just having difficulty finding garage time. All 3 kids are off visiting my brother in NC for a week, so my schedule might free up a bit. Wifey might see this as an opportunity to spend "quality time" together as a couple. I have different ideas.

Guess the silver lining is that the Guzzi being inoperative has forced me to ride the other bikes. They were feeling a bit neglected.
LonerDave is offline   Reply With Quote
Old 08-04-2013, 03:06 PM   #9
Rathlindri
Guinness fan
 
Rathlindri's Avatar
 
Joined: Oct 2007
Location: Ireland
Oddometer: 339
condensor faulty?
__________________
You meet the wierdest people on a Guzzi/Triumph
Rathlindri is offline   Reply With Quote
Old 11-04-2013, 09:39 AM   #10
LonerDave OP
Gnarly Adventurer
 
LonerDave's Avatar
 
Joined: Aug 2011
Location: Lisbon, WI
Oddometer: 118
Finally Buttoned Up

Finally got around to finishing the Dyna-to-points conversion (downgrade?). Bike fires right up and no intermitent loss of spark on the left cylinder. Fixt!

Sloppy scientific method prevents me from determining for certain whether the Dyna was really at fault (I replaced plugs and wires at same time I switched to points), but that's my best guess.

Pulled the bike off the lift to take it for a quick spin and discovered no pressure on front brake lever. Had worked a week earlier. No juice in the M/C, so will refill/bleed and see if that helps. May have to rebuild the M/C.

But at least it's a runner. Even if it isn't a stopper.
LonerDave is offline   Reply With Quote
Old 11-05-2013, 05:54 AM   #11
Morizzi
Adventurer
 
Joined: Aug 2009
Oddometer: 40
If it doesn´t bleed easily: Give the M/C a whack with a piece of wood or dead blow hammer. I´ve had the piston stick in there with it fully in.

DOT 3 is more slippery than DOT 4 and doesn´t upset any of the rubber.

Should be changed more regularly but I don´t.
Morizzi is offline   Reply With Quote
Old 11-05-2013, 09:20 AM   #12
danedg
Horizontally Opposed
 
Joined: May 2008
Location: U-puku-ipi-sing
Oddometer: 6,188
Did you check the continudity on the old plugs?
I never did either until I found 3 bad ones in a row. One used and two out of the box.
I ignored my mentor when he said to just change the plugs every year.
Now I do, and I check 'em first.
danedg is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 05:48 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014