Pop go the Fuses

[canuck750]

It was a lovely sunny day today, the roads are finally swept of gravel and the afternoon was open. I dusted off the V7 Sport disconnected the battery tender and fired up the bike. An enjoyable half hour riding around town and went in to my local favorite bike shop to order a set of new BT45 tires for my 750 S3. After a visit I went to start the bike and one click and nothing. Checked the fuses, the main fuse burnt out. Replaced with a spare, snap blows again. Now pulling a fuse from the light circuit, probably too weak, pop another dead one. Third time lucky and away it went for the rest of the afternoon.

Bad fuses or something else to look for?

In the evening the 850 Eldorado ran like a top, it was tuned on a dyno this winter and it runs and starts so much better.

[Muzz]

If you are like me you will carry a pocketful of fuses. ::)

Having said that, I have yet to blow one (where is the fingers crossed icon?)

[guzzisteve]

Want to find the problem, up the fuse size and follow the smoke.

[Kiwi_Roy]

Sorry, fuses don't blow for no reason.

Point me to a schematic.

[rodekyll]

Yup, there's a problem.  Dead short to something.  Best get it fixed before the equation reads: smoke + [misc]drama X distance from home = wish you had.  Did you mess with the battery or anything like the tank recently?  

Not knowing anything about the bike, I'll guess bare wire or appliance to ground.  I'd start by disconnecting all the Packard connectors (handlebar, etc) and rear harness from the main harness and try again.  Wiggle stuff.  Dare it to pop a fuse (a resettable fuse/breaker will be your friend).  If you survive the main harness isolation, add a connector and do it again down the length of whatever it serves.  At some point you'll duplicate the problem.  Then you can get serious about abraded, pinched, burned -- whatever -- wire.

[Sasquatch Jim]

  Positively shocking!

[guzzisteve]

I would check the tin boxes on handle bars first, known problem area.

[mgfan]

Save yourself a ton of time and frustration, give the bike to me!   :BEER:

[Kiwi_Roy]

If you replace the fuse with a headlight bulb (soldered across one of your blown fuses) as you wiggle the wires and create a short the bulb will flash, you go through a lot less fuses that way.
The idea is not to run the bike just supply the wiring with a current limited supply.
 
You can use a smaller bulb like a stoplight instead it just wont supply as much current.


Of course you should disconnect any sensitive electronics like an ECU first because the Voltage will likely be too low to power those properly.

[canuck750]

Thanks for the advice Roy, I will go through the electrics again, something simple I am sure.

The fuse that blows is the main fuse between the battery and the fuse box (1973 V7 Sport all stock, all new electrical throughout).

I rode the bike for half an hour, no issues, even after sitting for six months (and old fuel with stabilizer0. When I came to restart the bike after 30 minutes there was nothing. Flipped the seat up, removed the fuse box lid and it was obvious the main fuse had blown ( I really don't like the original Guzzi fuses (VW type). Replaced fuse, turned key, POP.

I did see a wee little piece of old metal fuse material that may have been able to jingle around under the clear CEV fuse box lid and make a connection across two terminals but it seemed unlikely.

After I replaced the fuse a couple times it seemed to be OK, rode another half hour to clear the tank out.

I would rather polish old rims any day that try and fix electoinics ::)

Wire diagram posted here on Greg Benders great site (see 71 V7 Sport)

http://www.thisoldtractor.com/guzzi007/sportissimo.html

[Kiwi_Roy]

So the bottom fuse is blowing then?
From there the wire goes all over the place, ignition switch back to the fuse box, to rectifier, up to the start button.
The way the ignition switch is shown makes me think it also has a start position,

If you suspect it might be blowing when you try to start, if the starter solenoid is unable to pull in and close it's contacts
there's up to 40 Amps flowing there, when the contacts close it drops down to 10.
To eliminate the starter solenoid just pull the spade connector off so it doesn't get energized.

[JoeW]

Jim, You can buy a 12 volt circuit breaker at an auto parts store. I use a 10 amp breaker so it trips with less load and I don't run the risk of damaging the wiring. You may be able to find an older style one with threaded studs but, it'll probably be an ATO type. You can attach wire leads with insulated alligator clips. Put the breaker in place of the fuse that blows. Sport wiring is not the best thought out IMHO, the main fuse, same amperage as the other six, protects the entire bike, this is one of the reasons the fuse boxes melt in the Sports, and Eldorado's for that matter. Power flows through the main fuse, to the key switch then back to the fuse box through the blue/black wire. Then it flows through each of the other fuses. Since the main fuse is blowing, start there. Do what you did when the fuse blew, if it pops right away, start removing the other fuses one by one until it stops popping. The last fuse you pulled is the circuit with the short. If the breaker has been cycling while you're doing this, heat will start building in the shorted wire, you can isolate it by feel. Since you have an intermittent problem, you may have to start moving and pulling on the harness until the breaker pops.
A very vulnerable spot for shorts on the V7 Sport is the junction block under the tank.

[eweltd]

Hi its Eric here

i have fuse problems too , its on a 2003 v10 centauro when it  had low batt i jumped it off a car it drove for a mile and started to mis when i put in new baterie the fuel pump ran and did not cut out like normal when i switch kill switch to run the second fuse blows , is it the E C U.

[blackcat]

Hi its Eric here

i have fuse problems too , its on a 2003 v10 centauro when it  had low batt i jumped it off a car it drove for a mile and started to mis when i put in new baterie the fuel pump ran and did not cut out like normal when i switch kill switch to run the second fuse blows , is it the E C U.

Not a good idea.

[Chuck in Indiana]

Hi its Eric here

i have fuse problems too , its on a 2003 v10 centauro when it  had low batt i jumped it off a car it drove for a mile and started to mis when i put in new baterie the fuel pump ran and did not cut out like normal when i switch kill switch to run the second fuse blows , is it the E C U.

He, Eric, welcome to WG, by the way. To the best of my knowledge there were no 2003 Centauros. Most were 97 amd 98s. But. There was a transil diode that should have been put on the bike to keep that from happening. It *does* sound like the ECU is tits up to me. What happens is if the battery is truly dead, and you jump it, the alternator decides it *really* needs to charge the battery. That high voltage spike kills the ECU..
Don't take my word as gospel, maybe one of the gurus will chime in shortly.

[twhitaker]

I doubt Eric cooked the ECU if he rode it a mile after jumping the bike.

[JoeW]

The last thing you did, before the problem, was replace the battery. I would recheck your connections there first.

[Antietam Classic Cycle]

I doubt Eric cooked the ECU if he rode it a mile after jumping the bike.

I looked at a Centauro in Bunker Hill, WV once that after a jump start from dead had been ridden from the storage unit to a Harley shop. Total distance of 1/10th mile and the ECU was fried. 

[eweltd]

nope bat is in ok  and bike was reg in uk 2003 so if its ecu any one got 16m ecu for sale at e bay price or less.

[eweltd]

hi
YES it was transil diode well spotted re connecting all bits not ready to start just yet but fuse is holding and pump runs as normal cost of diode repair €100.00 will let you know it runs thanks guys and gals

[Chuck in Indiana]

hi
YES it was transil diode well spotted re connecting all bits not ready to start just yet but fuse is holding and pump runs as normal cost of diode repair €100.00 will let you know it runs thanks guys and gals

My pleasure..  ;D Glad to see a previous owner had installed one.  ;-T

[eweltd]

Transil  diode is buillt in to ecu if  you open ecu there are 2  100 omes resistors in corner a t outher end15 mm x 6 mm bllack component  this is transil diode can be got i  raddionics for 6 euro handy to know if there is a next time
Bike nearly ready to start will post if it runs or not.
Eric

[eweltd]

hi
started bike to day all is good except for flat spot at 3800 rpm it has done it for a while now new plugs leads and caps still at it maybe its time for a new forum THANKS FOR YOUR HELP

ERIC

[Chuck in Indiana]

hi
started bike to day all is good except for flat spot at 3800 rpm it has done it for a while now new plugs leads and caps still at it maybe its time for a new forum THANKS FOR YOUR HELP

ERIC

You can cure that with a brass temp sensor holder..  ;D BTDT

[eweltd]

I dont know tell me more

[rodekyll]

The temp sensor on your rh pot lives in a crappy plastic socket that in turn screws into the engine.  The holder is plastic, so it insulates heat instead of transferring it.  It's plastic so it's also impossible to tighten to the point of not backing off without breaking it off in its bore, and it's plastic, so it's prone to cracking and breaking in normal use.  If you pack the plastic part with heat transfer compound (heat sink compound) you can improve heat transfer, but for some reason I've had them* split soon after packing.

An upgrade is this cute brass sensor holder available from the usual suspects.  It looks like the design was lifted from Lt. Uhura's communications earpiece.  If the light sabre was really a Graflex flashbulb battery pack, then the sensor holder is probably really a Star Trek prop.  Anyway, at $52 + shipping you'll have to budget the beer for a month, but the improvement is worth it. 

This is one of those little devices a guy with a lathe could make in a few minutes and sell waaaay cheap compared to oem pricing while still paying for his machine oil.  EVERYONE with a plastic holder needs one . . . .




*Did I mention they're plastic?

[twhitaker]

 :'( Did I mention I sold an extra I had for little more than shipping? And I can use it now.  :'(

[Chuck in Indiana]

:'( Did I mention I sold an extra I had for little more than shipping? And I can use it now.  :'(

What happened, Terry? Did you try to unplug it and it fall into pieces?  ~; ;D BTDT..

[Antietam Classic Cycle]

:'( Did I mention I sold an extra I had for little more than shipping? And I can use it now.  :'(

And it was much appreciated!  ;-T