Wildguzzi.com
General Category => General Discussion => Topic started by: wicks on February 12, 2015, 06:52:36 PM
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This is my ongoing problem...8K mile 73 V7 Sport, replaced or rebuilt everything around the engine. Fuel is flowing. Bike rides lovely for 30 minutes, then when nice and warm, begins to fail to fire on any more gas than idle. Motor gets flooded, bike stalls out. Switch ign off and on and fuel explodes in the headers.
Not sure if this is still happening, but last summer when I was working on this, the gas was bubbling out of the carbs into the (then clear) fuel lines. Fuel overheat a real possiblity? Everything is arranged stock on the bike, double gaskets between manifolds and heads, fully restored standard Dellortos, etc. New everything in fuel system and electrical system. Just fitted electronic ignition, no improvement to this problem.
Just checking if anyone has any new ideas... ???
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re torque heads.
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Possibly the enricher circuit not sealing closed or the carb slides not properly set. Other problems could be a misplaced jet or needle, bad float, or slides inserted backwards.
Is this happening on both sides or just one? Are the enrichers cable or flapper operated?
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"reqorque heads" is an interesting comment. Have done this, but will do again.
Re floats/slides, etc. - all new and working perfect. Bike runs perfect. For a half hour. Then the problems start.
Chokes are flapper, and all of that works perfectly. But just until nice and warm (about 30 minutes ride).
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What kind of coils?
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This is my ongoing problem...8K mile 73 V7 Sport, replaced or rebuilt everything around the engine. Fuel is flowing. Bike rides lovely for 30 minutes, then when nice and warm, begins to fail to fire on any more gas than idle. Motor gets flooded, bike stalls out. Switch ign off and on and fuel explodes in the headers.
Not sure if this is still happening, but last summer when I was working on this, the gas was bubbling out of the carbs into the (then clear) fuel lines. Fuel overheat a real possiblity? Everything is arranged stock on the bike, double gaskets between manifolds and heads, fully restored standard Dellortos, etc. New everything in fuel system and electrical system. Just fitted electronic ignition, no improvement to this problem.
Just checking if anyone has any new ideas... ???
I certainly don't know it all but I've never heard of vapor lock being a problem with a Guzzi. It more often occurs with carbs situated over hot engine and after being parked a short time when no fuel is flowing through cooling the carb, and engine heat is radiating upwards to the carb, evaporating the fuel in the bowl and fuel line and engine mounted mechanical pump. (thinking automotive)
What do your spark plugs look like? Are they wet with gasoline? No? Easiest first. Open the gas cap next time and listen for a suction sound or just see if the bike runs. Could be clogged tank vent.
All that said, I think that if you eliminate ignition as the problem it has to be either lack of valve clearance, incorrect timing or carbs. You've torqued the heads again, recheck the valve clearance. Check the ignition timing again. Maybe put the points back until you solve this.
If it still happens, pull the spark plug caps and put a spare plug into one, ground the plug against the head crank it over and see that you have a big fat spark. If you do, move on to the fuel system.
If you have fuel bubbling up through the fuel line to the petcock, it's filling the bowl, but the bowl vents should be checked too. Blow into them to see that they're clear, not kinked or gunked up with grime from hanging low under the chassis somewhere.
Good luck,
Tobit
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Just a thought, have you checked the cam timing? perhaps the chain is loose? DonG
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Sounds like the exact same problem I had with my first bike, 60 years ago, a 1954 Triumph Tiger Cub. I'd failed to use the proper phenolic heat shield between the head and the carb. After 20-30 minutes, the carb would become extremely hot, and the bike would begin to miss and eventually become unrideable. After a brief cooling off, I'd limp back home.
On your Guzzi, I'd check the carb to manifold, and manifold to head insulation.
CIA,
Dick Casey
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I've never heard of vapor lock being a problem with a Guzzi.
*cough* V11 sport *cough*.. ;D but it can happen to a gravity feed system that has a high spot.
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All of the above items have been dealt with / replaced / cured. Unless there is a heat problem even though I have correct double insulation between heads and manifolds (which would be strange to be an only-on-my-bike situation).
Have to think of the bike as working perfectly - but only for a half an hour until it begins to stall out, then will only restart on idle (any throttle will kill the engine) so, as you said, I limp home after with occaisional full restoration of engine function - but very flighty on and off as I limp home. Wait an hour, and then she is ready to tear up mulholland for another half an hour.
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The coils are the replacement units ordered from MG cycle. As noted, all electrical components replaced with new.
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After you recheck the timing and valve clearances this may be of some help with your bike, the symptoms sound similar to a running problem I had after rebuilding my Eldorado.
You note that everything electrical is new, are the spark plug leads copper core? If you are running 'modern' carbon core high tension leads the coils will overheat after a half hour or less and the spark will deteriorate until you get nothing.
Second thing that happened to me was that the old petcock seals were worn out, one side got hardly a dribble of fuel and the other could not shut off, I replaced both sides with new petcocks. In addition to the new petcocks I got rid of the guzzi 'Y' fuel line splitter and installed the Delorto dual fuel line connectors on the carbs and joined the carbs with a short section of fuel line.
(http://i249.photobucket.com/albums/gg217/canuck750/74%20V7%20Sport/DSC02279_zps1d717df7.jpg) (http://s249.photobucket.com/user/canuck750/media/74%20V7%20Sport/DSC02279_zps1d717df7.jpg.html)
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It sounds like it could be a weak spark, leads, coil, condenser
I assume you saved the original parts, change them out one at a time with what you took off.
My guess would be leads, condenser and coil in that order
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I have replaced everything electrical with new. Then changed to electronic ignition. Also new petcocks. Basically anything that could be new is new.
The spark leads are old fashioned type copper core. They are pretty thin on the insulation front though, could there be some heat problem with them? I changed to new coils a while back and there was no difference in the problem.
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Have to think of the bike as working perfectly - but only for a half an hour until it begins to stall out, then will only restart on idle (any throttle will kill the engine)
Man, that's tough. Still sounds like weak ignition to me, for whatever reason.. <shrug>
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I also use the vintage style metal plug caps - could those be causing a problem when warm?
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I don't have anything to add other than I was thinking about what kind of plug wires you have. have you tried other caps than those old style? I've been told those vintage caps are lousy so I always tossed them for new NGK's.
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Just because it's new is no guarantee it's not faulty, check the spark when cold and again after it fails.
Do it outdoors so its in a similar situation light wise.
Measure the Voltage at the coil hot wire in case it's loosing that.
It could also be something you have done like a loose terminal but it seems heat related.
Condensers are known to fail with heat perhaps wire the new one to the terminal with a jumper lead so you can quickly substitute the old one. The new ones probably been sitting on the shelf for 20 years.
Do something similar with the coil
Electrical troubleshooting is often just a process of elimination.
Don't forget to pull a hose off a carb next time it stops to check the fuel flow. If it's just a trickle blow on the hose, that will often clear the filter.
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What was the last thing you changed/upgraded before this 30 minute shut down surfaced??
Lee
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What do your spark plugs look like? Are they wet with gasoline? No? Easiest first. Open the gas cap next time and listen for a suction sound or just see if the bike runs. Could be clogged tank vent.
Good luck,
Tobit
;-T
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Check the gas cap vent. The two metal discs that sandwich the rubber gasket have ribs in them, they both face outward also, there needs to be a small hole in the rubber disc.